USRE48775E1 - Self-testing features of sensing and control electronics for a power grid protection system - Google Patents

Abstract

Systems and method for detecting potentially harmful harmonic and direct current signals at a transformer are disclosed. One system includes a protection circuit electrically connected to a transformer neutral, the transformer electrically connected to a power grid, the protection circuit including a DC blocking component positioned between the transformer neutral and ground and one or more switches selectively actuated to form a path between the transformer neutral and ground in the event of unwanted DC current at the transformer neutral. The system also includes a control circuit electrically connected to the protection circuit and positioned to selectively actuate the switches based on observed conditions within the protection circuit. The system further includes a plurality of test connections disposed within the protection circuit and useable to test electrical properties of the protection circuit.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority as a reissue patent application of U.S. Pat. No. 9,077,172, which was filed as U.S. patent application Ser. No. 13/899,078 on May 21, 2013, which claims priority to U.S. Provisional Patent Application No. 61/649,647, filed on May 21, 2012, the disclosure of which is. U.S. Pat. No. 9,077,172 claims priority as a continuation-in-part application to U.S. patent application Ser. No. 13/159,374, issued as U.S. Pat. No. 8,878,396, filed on Jun. 13, 2011, which claims priority from U.S. Provisional Application No. 61/366,088, filed on Jul. 20, 2010, U.S. Provisional Application No. 61/408,319, filed on Oct. 29, 2010, U.S. Provisional Application No. 61/437,498, filed on Jan. 28, 2011, and U.S. Provisional Application No. 61/486,635, filed on May 16, 2011. The disclosures of U.S. Pat. No. 9,077,172, U.S. Provisional Patent Application No. 61/649,647, and U.S. Pat. No. 8,878,396 are hereby incorporated by reference in its entirety their entireties.

TECHNICAL FIELD

The present disclosure relates generally to a high voltage transformer protection system, in particular, the present disclosure relates to self-testing features of a control system that could be used to protect high voltage transformers, power equipment, electronics, and computing systems.

BACKGROUND

Electrical equipment, and in particular electrical equipment operating using alternating current, is subject to varying input signals and conditions. In typical arrangements, alternating current devices in the United States expect to receive a 60 Hz power line source (or 50 Hz in Europe) having a predetermined magnitude (e.g., 120 Volts in North America or 240 Volts in Europe). Although these power sources may vary somewhat, devices made for use with a particular current can typically handle some slight variation in the power signal received.

In some cases, a power signal can vary widely due to external conditions or harmonics. External conditions that may cause harmonics or quasi-direct currents (DC) on a power signal include geomagnetic storms or effects of electrical equipment. Such events can cause the input voltage and current (and resulting power) of a power signal to vary dramatically, causing a potential for damage to the electrical equipment receiving that power signal. Geomagnetic storms or the E3 pulse associated with a high altitude electromagnetic pulse (HEMP) can induce DC or quasi-DC currents called Geomagnetic Induced Currents (GIC) in high voltage power generation, transmission, and distribution system components, i.e. power transmission lines and power transformers. These DC currents can cause half cycle saturation in power transformer cores which in turn can result in excessive reactive power losses, heating, damage and/or failure of such a transformer, particularly in older or poorly maintained transformers. In addition, the half cycle saturation can cause the generation of harmonics of the primary frequency (50 or 60 Hz). This harmonic content can cause power system relays to trigger, which can decouple required compensation components. This in turn can result in the collapse of local or wide area portions of a power grid.

Over approximately the last two decades, several suggested approaches for reducing GIC or HEMP (E3) induced currents in power systems have been proposed. These solutions generally take one of a few forms. A first class of solutions uses a capacitive circuit to simultaneously provide the AC grounding path and a block for the induced DC currents. These solutions generally include a set of switches that allow switching between a normal grounded transformer connection and grounding through the capacitive circuit. These solutions can allow for unintentionally open grounding connections to the transformer neutral, or require expensive electronics for handling ground fault conditions. These capacitive circuit solutions may require readjustment of power system relay settings, as compared to current operational parameters.

A second class of solutions generally includes the continuous use of active components used to reduce potentially damaging GIC events from DC or quasi DC currents in the transformer neutral to ground connection. These solutions typically require expensive power equipment, and are constantly active, such that any failure would render these systems unreliable. Additionally, when this solution is initially installed in the power system many relays/breakers would require readjustments of their settings.

A third class of solutions generally uses a resistive approach in which fixed value resistors are used to continuously reduce the DC current in the neutral to ground connection of a transformer; however in these approaches, the resistor typically must have a high resistance value and would only reduce, not eliminate the DC or quasi DC neutral current. Additionally, during the installation of these classes of solutions a readjustment of the power system's relay settings may be required. As such, there exists no solution that provides a reliable, low cost protection circuit compatible with current power delivery systems. Furthermore, there exists no reliable, testable system for controlling such a protection system that would not require substantial on-site maintenance.

Several suggested approaches for reducing or blocking GIC or E3 induced currents in power systems have been proposed. However, none of these systems provides a comprehensive arrangement for addressing the various types of potentially harmful decisions that may occur. In particular, there has been no known approach that uses a sensing and control system that first senses the presence of GIC or E3 events then switches a DC blocking device to protect high voltage transformers.

For these and other reasons, improvements are desirable.

SUMMARY

In accordance with the following disclosure, the above and other issues may be addressed by the following:

In a first aspect, a system includes a protection circuit electrically connected to a transformer neutral, the transformer electrically connected to a power grid, the protection circuit including a DC blocking component positioned between the transformer neutral and ground and one or more switches selectively actuated to form a path between the transformer neutral and ground in the event of unwanted DC current at the transformer neutral. The system also includes a control circuit electrically connected to the protection circuit and positioned to selectively actuate the switches based on observed conditions within the protection circuit. The system further includes a plurality of test connections disposed within the protection circuit and useable to test electrical properties of the protection circuit.

In a second aspect, a method includes transmitting one or more electrical signals from a protection circuit to a remote system, the protection circuit electrically connected between a transformer neutral of a transformer in a power grid and ground, wherein the remote system periodically assesses operation of the protection circuit based on the one or more electrical signals. The method further includes receiving at a control circuit electrically connected to the protection circuit one or more commands from the remote system to actuate one or more switches in the protection circuit, thereby testing an alternative configuration of the protection circuit.

In further aspects, a sensing and control system for use with an electrical protection circuit is disclosed. The system includes a plurality of detection components configured to detect damaging harmonics and DC or quasi-DC currents on a transformer power line or EMP and IEMI environmental events. These detection components may include, but are not limited to: a harmonic analyzer, a shunt resistor electrically connected between the transformer neutral and ground, a Hall Effect current sensor electrically connected between the transformer neutral and ground, and an electromagnetic field detector positioned external to the shielded enclosure. The system further includes a plurality of threshold detectors configured to compare a signal from a detection component to an adjustable predetermined signal, wherein the threshold detector outputs a signal indication to a controller when the signal from the detection component exceeds the predetermined signal value. The controller, also positioned within the shielded enclosure, is configured to open a normally closed switch in an external protection circuit upon receiving a signal indication from at least one of the plurality of threshold detectors. The controller further includes a control input wherein the control input is received from a power system operator remote from the shielded enclosure. The controller is further configured to execute one or more self-test procedures configured to simulate potentially damaging signals to determine whether the system is functioning properly.

In some embodiments, the controller is configured to open the normally closed switch in response to receipt of a signal from the power system operator remote from the shielded enclosure (e.g., a control system). The system optionally includes a shielded enclosure configured to protect electrical components from electromagnetic pulse (EMP) and/or Intentional Electromagnetic Interference (IEMI). In such optional arrangements, filters are positioned along the inner periphery of the shielded enclosure, configured to prevent high frequency, high power electromagnetic signals from entering the shielded enclosure and potentially damaging electrical components.

In still further aspects, a sensing and control system for use with an electrical protection circuit is disclosed. The system includes a shielded enclosure configured to protect electrical components from electromagnetic pulse (EMP) and/or Intentional Electromagnetic Interference (IEMI). Filters are positioned along the inner periphery of the shielded enclosure, configured to prevent high frequency, high power electromagnetic signals from entering the shielded enclosure and potentially damaging electrical components. The system further includes at least one harmonic analyzer positioned within the shielded enclosure, configured to detect damaging harmonics on a transformer power line. The system further includes at least one threshold detector configured to compare a signal from a harmonic analyzer to an adjustable predetermined signal, wherein the threshold detector outputs a signal indication to a controller when the signal from the harmonic analyzer exceeds the predetermined signal value. The controller, also positioned within the shielded enclosure, is configured to open a normally closed switch in an external protection circuit upon receiving a signal indication from at least one of the threshold detectors. The controller further includes a control input wherein the control input is received from a power system operator remote from the shielded enclosure.

In a still further aspect, a system for detecting potentially damaging electromagnetic signals including high direct currents in a transformer neutral and harmonics of a primary power frequency is disclosed. The system includes a plurality of detection components electrically connected to one or more electrical signal lines leading from one or more connection points on a power grid. The system also includes a controller positioned within an interior volume of an electromagnetically shielded enclosure. The controller is configured to receive an output from each of the plurality of detection components, the controller including a plurality of remotely-set test thresholds, and configured to drive at least one external component in response to sensing a signal from one of the plurality of detection component of a detected harmonic or direct current signal above a respective one of the plurality of remotely-set test thresholds.

In a further aspect, a method for controlling an electrical protection circuit configured to detect potentially damaging electromagnetic signals in a transformer neutral is disclosed. The method includes receiving a plurality of detector signals at a controller, the controller housed within an electromagnetically-shielded enclosure, and the detector signals including a harmonic detector signal and a direct current detector signal. The method further includes sampling each of the plurality of detector signals to detect a peak value over a predetermined period for each of the plurality of detector signals. The method further includes comparing each of the peak values to a corresponding remotely-set test threshold associated with that signal type, and, based on that comparison, generating one or more alarms if the remotely-set test threshold is exceeded, and communicating at least the one or more alarms to a remote system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic front view of the sensing and control electronics connected to an example embodiment of a high voltage transformer environment.

FIG. 2 illustrates an example embodiment of an electrical protection circuit external to the control system of the present disclosure.

FIG. 3 illustrates an example embodiment of a sensing and control system connected to a continuous grounding system including an example embodiment of an electrical protection circuit.

FIG. 4 is an example embodiment of the sensing and control system contained within a shielded enclosure including an external electromagnetic field detector.

FIG. 5 is an example embodiment of the sensing and control system contained within a shielded enclosure.

FIG. 6 is an example embodiment of the harmonic analyzer contained within the sensing and control system.

FIG. 7 is another example embodiment of the harmonic analyzer contained within the sensing and control system.

FIG. 8 is another example embodiment of the harmonic analyzer contained within the sensing and control system.

FIG. 9 illustrates an example embodiment of a threshold detector circuit contained within the sensing and control system.

FIG. 10 illustrates an example embodiment of the sensing and control electronics including self-test functionality.

FIG. 11 is an example embodiment of the sensing and control electronics including monitoring and alarming functionality.

FIG. 12 illustrates an example implementation of a harmonic sensing arrangement incorporated into a sensing and control system.

FIG. 13 illustrates an example implementation of a neutral direct current sensing and self-test arrangement incorporated into a sensing and control system.

FIG. 14 illustrates an example implementation of a circuit in which a neutral impedance measurement and self-test arrangement can be incorporated, as associated with a sensing and control system.

FIG. 15 illustrates an example embodiment of an electrical protection circuit external to the control system of the present disclosure.

DETAILED DESCRIPTION

In general, the present disclosure describes systems and methods for sensing damaging DC or quasi-DC currents which cause harmonic content on a power line, and controlling a switch assembly in an electrical protection circuit to protect high voltage transformers and other electrical equipment from the damaging DC or quasi-DC currents. Large DC neutral currents and harmonic voltages can be the result of geomagnetic (solar) storms, high altitude electromagnetic E3 pulse (HEMP-E3) or other electrical equipment, such as switching power supplies, arc welding equipment, plasma cutting, electric discharge machining equipment, arc lamps, etc., which are on the same power grid or local power circuit. Overall, the present disclosure describes methods and systems for sensing the harmonic content of a 50 Hz or 60 Hz power line source, and potentially damaging neutral DC currents, and controlling equipment to be switched to a protective mode of operation in case such harmonics or DC currents are detected. In some embodiments, the present disclosure relates to methods and systems for self-testing circuitry used to protect against such DC and quasi-DC currents as well as the control systems used to manage operation of that circuitry.

Protection of high voltage power systems from GIC (solar storms) and EMP E3 pulses are achieved using a system that senses damaging DC currents on a power line signal and external high electromagnetic events. The sensing systems disclosed herein provide electronics used to detect the presence of DC currents in the neutral connection of high and extra high voltage power transformers. The sensing system may additionally include a harmonic, or total harmonic, distortion (HD or THD) sensor that senses harmonics on the power line signal which are caused by a DC current and half wave saturation in the transformer windings. The sensing systems may additionally include an electromagnetic field detector that detects external electromagnetic pulse (EMP) events. The sensing systems may additionally include a detector that computes current through a shunt resistor or a Hall Effect current sensor that is electrically connected to the transformer neutral.

The present disclosure further includes a control system that sends signals to an electrical protection circuit to test and control the operation of a switch assembly in a DC blocking assembly contained in the electrical protection circuit. The control system controls a switch in an electrical protection circuit to protect high voltage transformers from geomagnetic and EMP (E3 pulse) induced currents. A DC blocking component (including one or more capacitors, resistors or combinations thereof) is hard wired in the electrical protection circuit to provide an uninterruptable AC grounding path for the high power systems, for example to the neutral of “Y” configured high transformers or autotransformers. Under normal operation, a second parallel grounding path provides a low impedance, standard grounding path through a closed switch assembly. In some embodiments discussed herein, at least a testing portion of the system can be located either within control circuitry, or within a supervisory control and data acquisition (SCADA) system monitoring the circuitry.

FIG. 1 is a schematic front view of example electrical equipment protected according to the features of the present disclosure, and a physical layout of certain components of the present disclosure. In the embodiment shown, a piece of electrical equipment, shown as a high-voltage transformer100, is electrically connected to an electrical protection circuit102. The electrical protection circuit102 can, for example, include at least a portion of the devices described below, according to the embodiments shown inFIGS. 2-9. Thehigh voltage transformer100 is typically mounted on a concrete pad. An electrical protection circuit102 is electrically connected to thehigh voltage transformer100 as discussed above, encased in a housing, and placed on electrically grounded supports103. In addition to protecting against GIC events, all control electronics (semiconductor devices) are enclosed in an EMP/IEMI shielded and electrically filtered enclosure104 is electrically connected to the electrical protection circuit102 andhigh voltage transformer100, and includes sensing andswitch control circuitry105. It should be noted that without the shielded and filtered enclosure104 the system is capable of protect transformers against GIC and EMP E3 events but not against EMP E1, E2, and IEMI pulse threats.

In some embodiments, the sensing andswitch control circuitry105 is communicatively connected to a remote supervisory control and data acquisition (SCADA) system110, which can monitor operation of the sensing andswitch control circuitry105, and can provide remote controls over certain functionality of that circuitry. For example, and as discussed further below, in some embodiments, the SCADA system110 can monitor operation of the electrical protection circuit102 and sensing andswitch control circuitry105 associated with one ormore transformers100.

In certain embodiments, the electrical protection circuit102 includes the switch assemblies and DC blocking components discussed inFIGS. 2-3, while the control system104 contains sensing and switch actuation circuitry as illustrated inFIGS. 3-10, below. Self test features are discussed in connection withFIGS. 10-15. However, other arrangements of components for an electrical protection device can be provided.

Referring now toFIG. 2, a first generalized embodiment of anelectrical protection circuit200 useable with the sensing and control electronics of the present disclosure is shown. Thecircuit200 generally is connected between a transformer neutral10 of a transformer12 (shown as Y-transformer in the embodiment shown) and aground14. Theelectrical protection circuit200 includes aswitch assembly202 including an electrically controlledswitch204 connected between the transformer neutral10 andground14. Ashunt resistor206 can be connected between theswitch204 andground14, which can be used to sense DC current passing between the transformer neutral10 andground14. In certain embodiments, theshunt resistor206 would typically have a low resistance, on the order of a few milliohms, to allow for a low impedance ground connection through the switches. In another embodiment, theshunt resistor206 could be replaced by a Hall Effect current sensor or other non-contact current sensor. Additionally, an electrically-controlled highvoltage grounding switch208 can be connected between the transformer neutral10 and theswitch204, for example to protect theswitch204 from high voltages during a ground fault event. In some embodiments, theground14 can be connected to a station ground grid, while in other embodiments it can be connected to the transformer housing which is in turn grounded.

Theswitch204 can be any of a variety of fast acting electrically-controlled switches, such as a high voltage circuit breaker switch. In the embodiment shown, theswitch204 is a normally-closed connection which can be opened rapidly via an electrical control input. Example sensing and control circuitry that can be connected to the control input is discussed further in connection withFIG. 3-10, below.

ADC blocking component210 is connected in parallel with theswitch assembly202 between the transformer neutral10 and theground14. As further explained in the examples below, theDC blocking component210 can include one or more direct current blocking devices (e.g., capacitors or resistors) capable of inserting some blocking of a current path betweenground14 and the transformer neutral10, to prevent damaging DC or quasi DC ground currents in the transformer neutral10, which would in turn cause possible damage to thetransformer12. Depending on the specific application, either a capacitive or resistive (or some combination thereof) blockingdevice210 could be employed in theprotection circuit302. Furthermore, in certain embodiments, theDC blocking component210 is hard wired to theground14, therefore providing an AC ground for the transformer (or other power component) even if theswitches204 and208 inadvertently malfunction.

In normal operation, the transformer neutral10 is grounded through theswitch assembly202. That is, theswitch assembly202, includingswitch204 and highvoltage grounding switch208, is normally in a closed position. This corresponds to the standard grounding configuration used by utilities; consequently, a grounding system such as is disclosed herein does not require readjustments to the utility electrical equipment to which it is attached prior to use. In this first mode of operation, theDC blocking component210 is not energized, because the switching assembly creates a short around it. If a ground fault is detected while operating in this normal operational mode (no GIC), the grounding through the switch assembly will handle the ground fault current until the power system relays isolate the faulted equipment. When the presence of either high power harmonics or a quasi DC current in the neutral to ground connection is detected, the switch assembly is opened by the GIC sensing and control electronics. In this second mode of operation theDC blocking component210 provides the AC grounding for the transformer neutral. This mode of operation protects against DC or quasi DC currents associated with either GIC or EMP E3 events. This GIC protective mode remains operational until a power system operator at a remote location declares the event to be over and re-closes theswitch assembly202.

In some embodiments, to account for an extremely unlikely event that a GIC and ground fault would occur simultaneously, asurge arrester212, sometimes known as a varistor or a MOV (metal oxide varistor) or other such surge arresting device, would trigger to protect the blockingcomponents210. Theswitch assembly208 would then be reclosed by a signal from a relay detecting fault current through the transformer neutralcurrent transformer214 which in turn will trigger thehigh voltage switch208 to reclose. Therefore thesurge arrester212 provides the initial grounding within one cycle of the ground fault and until theswitch assembly202 can be reclosed. It is noted that the probability of this simultaneous event (GIC and ground fault) is so small that in practice it may never occur in the lifetime of the system.

To reduce the cost of thesurge arrester212, it may be desirable to use a low cost surge arrester that is a sacrificial device, such that it only protects for one event and will then require replacement. After the surge arrester has been sacrificed, it by its design becomes a short circuit to ground. A second option is to incorporate additional surge arresters in the initial installation with switches such that if the first arrester is sacrificed a second can be switched in as a replacement as needed. A third option is to incorporate a very heavy duty surge arrester in the initial installation that will guarantee that the surge arrester will withstand many ground fault events without failing.

By opening the switch assembly, theDC blocking component210 shown inFIG. 2 provides the AC grounding path for the transformer neutral10, while at the same time blocks or reduces the DC or quasi DC induced by a geomagnetic storm or EMP E3 event. Blocking the DC both protects thetransformer12 from entering half cycle saturation which in-turn can cause transformer excessive reactive power losses, overheating, damage or even failure. Additionally, blocking the DC also prevents the generation of harmonics in the power system which in-turn can prevent the tripping of power relays, the disconnection of power compensation components, excessive reactive power burden and potentially the collapse of either small or large portions of the power grid.

Further, to increase the reliability of theDC blocking component210, either a parallel bank of multiple capacitors or resistors could be used such that if one or more of these capacitors or resistors fail the others would still be available as blocking components.

Additionally, and as further disclosed below, to protect against the E1 and E2 portions of an electromagnetic pulse (EMP) and/or Intentional Electromagnetic Interference (IEMI), all the sensitive sensing and control electronics of such a system can be placed in a shielded and electrically filtered enclosure, such as the enclosure containing control system104 ofFIG. 1. All components which are not housed in the shielded enclosure do not contain sensitive semiconductor electronics and hence would survive either an EMP or IEMI event. In an alternative embodiment where the sensing and control electronics are not placed in a shielded and electrically filtered enclosure, the transformer will still be protected against geomagnetic induced GIC. Additional details regarding the contents of such an enclosure are discussed in further detail below.

In various embodiments, different types of electrical protection circuits could be used. In example embodiments, electrical protection circuits could include those described in copending U.S. patent application Ser. No. 13/159,374, entitled “Continuous Uninterruptable AC Grounding System for Power System Protection”, the disclosure of which is hereby incorporated by reference in its entirety.

Referring now toFIG. 3, an example embodiment of asystem300 including anelectrical protection circuit302 electrically connected to the sensing andcontrol system310 of the present disclosure is shown. In this example embodiment, a Hall Effect current sensor could alternatively be used in place of theshunt resistor206 ofFIG. 2 (andcurrent sensing device314, described below) for measuring the DC current in the transformer neutral to ground connection. In such embodiments, the Hall Effect sensor would be sacrificed by either an EMP or IEMI attack. There is also a possibility that a Capacitive Voltage Transformer (CVT) (not shown) connected to a phase of thetransformer10, would likewise be sacrificed by an EMP or IEMI attack.

The sensing andcontrol circuit310 includes control electronics, such as a sensing andcontrol module312, as well as acurrent sensing unit314. Arelay control circuit316 is connected to the sensing andcontrol electronics312, and generates aswitch control output313 used to actuate theswitches204 and208.

The sensing andcontrol module312 senses harmonics which are generated in a half cycle saturated transformer under a GIC event. For example, themodule312 can include a harmonic sensor that will measure the signal from a standard capacitive voltage transformer (CVT) (not shown) which is located on one of the transformer phases. When the signal from either of the neutral DC current or harmonic sensor exceeds a preset value, a signal is sent to open the two switches in the switchingassembly202. The preset values will be selected by the utility or power system engineers according to the protection requirements of each particular installation. The typical ranges for preset values of DC or quasi DC current are expected to be in the range of about 5-50 amps. The typical ranges for preset values of the power harmonic levels are expected to in the range of about 1% to 10% total harmonic distortion (THD). Thecurrent sensing circuit314 measures neutral DC or quasi DC current caused by a geomagnetic storm acrossshunt resistor206, and sends the result of that measurement to the sensing andcontrol module312 to trigger therelay control circuit316 as necessary.

In the embodiment shown, thecontrol circuit310 is enclosed within a shieldedenclosure320, and includes a plurality offilters322 positioned at a periphery of theenclosure320 to prevent high frequency, high power electromagnetic radiation from entering the enclosure, thereby exposing the sensitive control and sensing electronics to potential interference and damage. Thefilters322 can typically be a low pass or band pass filter with surge suppression to suppress any high voltage signals from entering the enclosure. In the embodiment shown, the shieldedenclosure322 is an EMP/IEMI faraday shielded enclosure with conductive gaskets around all door openings to provide radiative protection from electromagnetic frequencies typically from about 14 kHz to 10 GHz. Additionally, in the embodiment shown, afilter322 is positioned on apower input324, as well as on aCVT input326, operator inputs and outputs328, theswitch control output313, andcurrent sensing inputs330 connecting across either side of theshunt resistor206. Additionally, any fiber communications in and out of theenclosure320 will be filtered via an appropriate waveguide-beyond-cutoff frequency penetration, which will inherently provide protection against EMP and IEMI events.

In operation, when a GIC event is detected by thecontrol circuit310, the low DC voltage switch, i.e.switch204, will be opened by therelay control circuit316, viaswitch control output313. Following this action a signal will open the highvoltage grounding switch208. Thegrounding switch208 will then typically remain open for the duration of the geomagnetic storm event, typically on the order of a few hours to a day. During this period theDC blocking component210, in thiscase capacitor304, provides the AC ground for the transformer neutral10 oftransformer12. The reclosing of thegrounding switch208 will typically be controlled by the operator of the power system after the geomagnetic storm has passed. However, some utility installations may prefer to configure their system to reclose the switches automatically, e.g., after a predetermined period of time.

To ensure that the transformer protection would continue its protection function under an EMP or IEMI attack, an Electromagnetic (EM) Field, adetector352 could be added to this protection system as shown, connecting to the sensing andcontrol electronics312 via afilter322. Thedetector352 resides outside of theenclosure320, and would allow the detection of either the EMP E1 or E2 pulse or an IEMI pulse which in turn would be used to open theswitch assembly202, includingswitches204,208 and hence switch in the necessary transformer protection. TheEM detector352 could be mounted on the top or side of the control house and be connected by a shielded conduit to the protectedcontrol electronics310.

In various embodiments, different types of electromagnetic field detectors could be used asdetector352. In example embodiments, electromagnetic field detectors could include those described in copending U.S. patent application Ser. No. 12/906,902, entitled “Electromagnetic Field Detection Systems and Methods”, the disclosure of which is hereby incorporated by reference in its entirety.

In operation, even if a Hall Effect sensor and/or the CVT (not shown) were damaged or destroyed by an electromagnetic event, theEM detector352 would open theswitch assembly202 which in turn would protect theHV transformer10.

The sensing andcontrol system310 of the present disclosure is contained within a shieldedenclosure320. The periphery of the shielded enclosure is lined by a plurality offilters322 that are electrically connected to sensing andcontrol electronics312. In some embodiments, the sensing and control electronics include aharmonic analyzer406, a plurality of threshold detectors408, and acontroller410 as shown and further described inFIG. 4. The sensing andcontrol electronics312 sense potentially harmful harmonics and/or DC currents in a power line and operate theDC switch204 and highvoltage grounding switch208 in theelectrical protection circuit302.

Referring now toFIG. 4, a first generalized embodiment of the sensing andcontrol system400 of the present disclosure is shown.FIG. 4 illustrates a system for detecting a variety of different types of potentially harmful signals to thetransformer12 or other electrical equipment that is the subject of the present disclosure. In particular, the system includes a sensing andcontrol system400 that detects power harmonics, direct currents (as well as quasi-direct current signals), and EMP/IEMI events according to the present disclosure.

The sensing andcontrol system400 of the present embodiment includes a shieldedenclosure402 that contains a plurality offilters404 lined along the periphery of the shieldedenclosure402. The sensing andcontrol system400 additionally contains an EM field detector412 (e.g., analogous todetector352 ofFIG. 3) positioned outside the shieldedenclosure402 and is electrically connected to afilter404. Eachfilter404 is electrically connected to athreshold detector408a-c (collectively referred to as threshold detectors408), aharmonic analyzer406, or directly to acontroller410. The output of theharmonic analyzer406 is electrically connected to athreshold detector408b. Eachthreshold detector408a-c outputs a signal to acontroller410. Thecontroller410 sends signals remote from the shieldedenclosure402 through a plurality offilters404.

In operation, the components in the sensing andcontrol system400 are contained within an EMP/IEMI shieldedenclosure402 that is configured to protect the sensing and control electronics from electromagnetic interference. The periphery of the shieldedenclosure402 is lined with a plurality of low pass or band pass filters404 to prevent high frequency, high power electromagnetic signals from entering the enclosure that would expose the sensitive control and sensing electronics to potential interference and damage. Thefilters402 are generally analogous tofilters322 ofFIG. 3, described above.

In certain embodiments, the present disclosure includes aharmonic analyzer406 located within the shieldedenclosure402 as discussed in more detail below. Theharmonic analyzer406 is another example of a detection component used to detect the total harmonic distortion (THD) on an incoming power line signal from thetransformer12. Theharmonic analyzer406 is electrically connected to thecontroller410, described in further detail below.

In the embodiment shown, the plurality ofthreshold detectors408a-c are each configured to compare an incoming signal indication from a detection component, such as an external electromagnetic (EM)field detector412, to an adjustable predetermined threshold value. If the predetermined threshold value is exceeded, the corresponding threshold detector408 will send a signal to acontroller410 also positioned within the shieldedenclosure402. Thecontroller410 is configured to drive at least one of the external components of theelectrical protection circuit200 such as aswitch204, as shown inFIG. 3. For example, if the DC or quasi-DC current through ashunt resistor206 positioned between transformer neutral and ground exceeds the predetermined threshold value of the threshold detector408, the threshold detector408 will send an indication to thecontroller410. Thecontroller410 will in turn send a signal through afilter404 to open the normally closedswitch204 that is located between transformer neutral and ground in order to protect thehigh voltage transformer12 from damage.

In the embodiment shown, each of thethreshold detectors408a-c can be configured to detect a different type of signal, or a signal received having a different triggering threshold. For example,threshold detector408a, which is configured to detect a predetermined direct current above a predetermined threshold, can be configured to triggercontroller410 when above a first threshold, butdetector408b, which receives signals fromharmonic analyzer406, can be configured to triggercontroller410 upon detection of a different type of signal, or at a different signal threshold level. The same is true ofthreshold detector408c, which receives signals from theEM field detector412. In alternative embodiments, additional types of potentially harmful signals can be monitored and fed to a threshold detector for triggeringcontroller410.

Thecontroller410 can be any of a number of types of programmable circuits, and configured to generate a switching output signal in response to receipt of a signal from one or more of thethreshold detectors408a-c. In some embodiments, thecontroller410 is a microprocessor configured for managing switching outputs based on programmable logic based on detection of a signal from either a threshold detector or acontrol input414. In the embodiment shown, thecontrol input414 is electrically connected to thecontroller410, and leads to a system controller remote from the shieldedenclosure402. Thecontrol input414 may exchange data between the system controller and thecontroller410, for example to communicate a history of switching events triggered by the sensing and control electronics, as well as to provide remote triggering and reset functionality. Thecontrol input414 can also trigger execution of one or more self-test procedures configured to simulate potentially damaging signals for monitoring purposes. Thecontroller410 can, for example, test switch actuation based on switch indication and high voltage grounding switch indication inputs, as depicted. These self-test procedures are described more fully below.FIG. 5 illustrates an example embodiment of the present disclosure for detecting power harmonics in a transformer. Theelectronics500 can be used, for example as a portion of the sensing andcontrol electronics400 ofFIG. 4, or alternatively as a stand-alone element in situations where harmonic signals are of primary concern (rather than in combination with sensing of DC signals. This example embodiment includes a series of sensing and control components contained in a shieldedenclosure502 that is lined with a plurality offilters504. These filters are analogous to the filters described inFIG. 4. Thesensing components501 include afilter504, aharmonic analyzer506, and athreshold detector508. Afilter504, to reject conducted high energy electromagnetic pulses and intentional electromagnetic interference (IEMI), is electrically connected to a signal line extending into the shieldedenclosure502. Thefilter504 is electrically connected to aharmonic analyzer506 that outputs a signal to athreshold detector508. Thethreshold detector508 is electrically connected to acontroller510 also contained within the shieldedenclosure502.

In another example embodiment example, only a DC signal would be sensed in a transformer neutral to ground connection, for example in a situation where DC currents are of primary concern.

The present disclosure also includes acommunications bus514 that is electrically connected to thecontroller510. Thecommunications bus514 leads to a system operator remote from the shieldedenclosure502. Thecommunications bus514 may also execute one or more self-test procedures configured to simulate potentially damaging signals for monitoring purposes. These self-test procedures are described more fully below.

In operation, theharmonic analyzer506 receives a voltage signal from a CVT (not shown in the figures) located on one of the phases of thepower transformer12 through afilter504. Theharmonic analyzer506 detects power harmonics in atransformer12. The harmonics detected by theharmonic analyzer506 are compared to an adjustable predetermined threshold value of athreshold detector508. If the harmonics exceed the predetermined threshold value of thethreshold detector508, the threshold detector sends a signal indicating the threshold value has been exceeded to thecontroller510 located within the shieldedenclosure502. In some embodiments the harmonic analyzer, threshold detector and controller are all implemented within a microprocessor. Thecontroller510 sends a switch indication signal through afilter504 to open a DC switch, such asswitch204 ofFIGS. 2-3, followed by a signal to open a highvoltage grounding switch208 to protect thetransformer12 and/or to provide electric power grid stability from potentially harmful DC currents in the transformer neutral and to reduce harmonics on the power line signal.

Referring now toFIGS. 6-8, various embodiments of sensing and control electronics including a harmonic analyzer useable in the systems ofFIGS. 3-5 (e.g., as harmonic analyzer406).FIG. 6 illustrates a first possible embodiment of aharmonic analyzer600, useable asharmonic analyzer406 as shown inFIG. 4 orharmonic analyzer506 as shown inFIG. 5 for detecting power harmonics in atransformer12. This embodiment uses amicroprocessor600 to compute a Fast Fourier Transform (FFT) to detect power harmonics in thepower signal603. This embodiment includes amicroprocessor800 that contains anFFT calculator602, and a totalharmonic distortion calculator606. TheFFT calculator602 in themicroprocessor600 transforms thepower line signal603 into a plurality of frequency signals, acting as a bank of bandpass filters. The sample rate of the system and number of points in the FFT are set so that each of the harmonics of the harmonics of the input signal falls into a different filter bin, corresponding to a unique output index in the FFT. These signals605 are separated intofrequency bands607 corresponding to a range of harmonics of the 60 Hz (or 50 Hz) power frequency using bandpass filters within the Fast FourierTransform Filter Band602. These harmonics are then used to calculate the total harmonic distortion (THD)609 using a totalharmonic distortion calculator606 in themicroprocessor600.

This totalharmonic distortion signal609 is then compared to a preset threshold level in the microprocessor (e.g., illustrated as threshold detector608) and if THD signal exceeds the present level a signal is sent to open the switch assembly, includingswitches204 and208.

FIG. 7 illustrates a further possible embodiment of aharmonic analyzer700. Theharmonic analyzer700 can be used in place ofharmonic analyzer406 as shown inFIG. 4 orharmonic analyzer506 as shown inFIG. 5, for detecting power harmonics in atransformer12. Theharmonic analyzer700 is electrically connected between afilter701 and athreshold detector716. Collectively, these components comprisesensing components501. This example embodiment of aharmonic analyzer700 includes alow pass filter702 electrically connected to anamplifier704 and aphase correction module706. The output of thephase correction module706 is electrically connected to a summingamplifier708. The output of the summingamplifier708 is connected to arectifier circuit709, which adjusts the amplitude of the signal, resulting in asignal714 proportional to total harmonic distortion.

In operation, this example embodiment of aharmonic analyzer700 subtracts an unfilteredpower line signal710 from a filtered and phase shiftedsignal712, which is then amplitude adjusted to output the totalharmonic distortion signal714. This example embodiment includes alow pass filter702 configured to filter the noise of an unfilteredpower line signal710. From the low pass filter, the filtered power line signal passes through anamplifier704 for amplitude adjustment. The signal then passes through aphase correction module706 configured to synchronize the phase of the amplitude adjusted and filtered signal. The filtered, amplitude adjusted and phase shiftedsignal712 is then compared to the unfilteredpower line signal710 at a summingamplifier708. The summingamplifier608 subtracts the two signals to output thepower line harmonics714 of the power line signal. The power line harmonics signal is then rectified at therectifier circuit709 to produce a voltage proportional to the THD on the power line. The totalharmonic distortion signal714 is then sent to athreshold detector716, for comparison to the total harmonic distortion as explained above in connection withFIG. 5.

FIG. 8 illustrates another possible embodiment of aharmonic analyzer800, useable asharmonic analyzer406 as shown inFIG. 4 orharmonic analyzer506 as shown inFIG. 5 for detecting power harmonics in atransformer12. Theharmonic analyzer800 includes a power line signal electrically connected to a low-pass filter801 and athreshold detector812. This example embodiment of aharmonic analyzer800 includes alow pass filter802 electrically connected to a phase-lockedsinusoidal oscillator804. Theoscillator804 is used to produce a clean signal lacking harmonic content, that replicates the 60 Hz (or alternatively 50 Hz) power line signal. Anamplitude adjustment circuit808 adjusts the output of theoscillator804 to match the expected power line signal frequency. The output of the amplitude adjusted, phase-locked sinusoidal oscillator804 (from the amplitude correction circuit808) is electrically connected to a summingamplifier810. Finally, the output of the summingamplifier810 is connected to arectifier811 to produce asignal818 which is proportional to the total harmonic distortion (THD) on the power line. Collectively, these components comprisesensing components801.

This example embodiment is similar to theharmonic analyzer706 ofFIG. 7, but uses a phase-lockedsinusoidal oscillator808 to generate a clean 120V, 60 Hz (or clean 240 V, 50 Hz) reference signal that is subtracted from the unfilteredpower line signal814. This alternative embodiment includes alow pass filter802 configured to filter out the noise and harmonics of an unfilteredpower line signal814. The filtered signal is then used as a reference signal input to a phase-lockedsinusoidal oscillator804. The phase-lockedsinusoidal oscillator804 generates a clean 120V, 60 Hz signal816 that is compared to the unfilteredpower line signal814 at a summingamplifier810. The summingamplifier810 andrectifier811 output thesignal818 that is proportional to total harmonic distortion on thepower line signal814, and that is sent to athreshold detector812.

FIG. 9 illustrates a possible embodiment of athreshold detector900, useable as the threshold detector408 as shown inFIG. 4 orthreshold detector508 as shown inFIG. 5 for comparing power harmonics and DC currents in atransformer12. This example embodiment of a threshold detector receives harmonics or quasi-DC currents from a rectifier (e.g.,rectifier709 ofFIG. 7 or 811 ofFIG. 8) that is electrically connected to acomparator904. Thecomparator904 is electrically connected to areference generator906 and a hold and resetcircuit908. The hold and resetcircuit908 outputs a signal to an electrically connectedcontroller910 that is located external to thethreshold detector900.

In operation, the threshold detector receives harmonics or quasi-DC currents from an incoming power line signal or aharmonic analyzer406. Thecomparator904 compares the rectifiedsignal903 to areference signal907. Thecomparator904 receives thereference signal907 from anadjustable reference generator906 that defines a harmonic distortion acceptable to thetransformer12. Upon a comparison between thereference signal907 and theinput signal903, thecomparator904 generates a signal that can be captured at a hold and resetcircuit908. The captured signal is then sent to acontroller910 that can be used to trigger aswitch204 as shown inFIGS. 2-3.

FIG. 10 represents an example embodiment of the present disclosure ofFIG. 4, but additionally includes self-test features to ensure proper system operation. This embodiment of the present disclosure includes a self-testDC voltage source1012, a self-testharmonic source1014, a self-testEM detector source1016, and a self-testAC voltage source1018 located within the shieldedenclosure402. In some embodiments, these self-test features are triggered automatically on a periodic basis by thecontroller410. These self-test features can also be triggered by a user operating a control system located at a remote site from the shieldedenclosure402, or performed at a remote system, as illustrated inFIG. 12.

In the embodiment shown inFIG. 10, a self-testAC voltage source1018 generates an AC signal with a frequency different from that received at thetransformer12. The AC voltage exits the shieldedenclosure402 through afilter1004 and is applied to the transformer neutral10. Theelectrical protection circuit200 as shown inFIG. 2, in its normal operation mode, measures the magnitude of the current across aDC blocking device210 based on a known amplitude of the AC signal generated by theAC voltage source1018. Thecontroller410 compares the magnitude of theDC blocking device210 with an expected value to determine whether theDC blocking component210 is operating accurately.

Another self-test function within the present disclosure is a self-testDC voltage source1012 that generates a direct current intended to simulate a direct current in the transformer neutral10 to ground14 connection. The generated direct current is outside the range of normal operation of the direct current in the transformer neutral10 to ground14 connection. The direct current generated by the self-testDC voltage source1012 exits the shieldedenclosure402 through afilter1004 and re-enters the shieldedenclosure402 through the direct current signal input. The generated signal is then passed through a threshold detector408 for comparison to a known value that is acceptable to thetransformer10. If sensing andcontrol system1000 is operating properly, thecontroller410 will trigger an indication signal that will exit the shieldedenclosure402 through afilter404 to open aswitch204 in theelectrical protection circuit200. If thecontroller410 does not open theswitch204, thecontroller410 will send an error message to a remote control system external to the shieldedenclosure402.

Another self-test function within the present disclosure is a self-testharmonic source1014 that generates a harmonic signal intended to simulate undesired harmonics on a power line signal. The generated harmonic signal exits the shieldedenclosure402 through a filter1005 and re-enters the shieldedenclosure402 through the power line signal input. The signal is passed through aharmonic analyzer406 that compares the generated harmonic signal to a known, acceptable frequency. If the sensing andcontrol system1000 is operating properly, thecontroller410 will trigger an indication signal that will exit the shieldedenclosure402 through afilter404 to open aswitch204 in theelectrical protection circuit200 as shown inFIG. 2. If thecontroller410 does not open theswitch204, thecontroller410 will send an error message to a remote control system external to the shieldedenclosure402.

In addition to the tests described above, various other self-tests can be performed using the circuitry ofFIG. 10. For example,controller410 can detect defects or variances in operation of circuitry ofFIGS. 1-9, such as by detecting a rate of discharge of capacitors (e.g., capacitor304), or other electrical characteristic of a DC blocking device210 (a capacitor or other DC blocking element). In some example embodiments, the self-tests can include testing ofsurge arrester212, for example to determine if thesurge arrester212 has previously experienced a pressure relief mode. For example, the self-test can detect whether the surge arrester has a particular voltage range; before a pressure relief mode has occurred, the voltage range can be from 0 to 15 kV and current range can be 0-60 kA, with a duration of about ¼ cycle; after the pressure relief mode occurs, the voltage range would be about 0 to 1 kV and current of about 0 to 1 kA for about 6 cycles.

In still further embodiments, other types of tests and monitoring could be performed. For example, as discussed further below in connection withFIG. 15, the monitoring of a spark gap conduction duration could be monitored and recorded. In such cases, a spark gap state can be tested, for example by determining whether voltages of 0-7 kV have been detected, and for less than ¼ of a cycle; in such cases, no spark is formed. However, if a voltage of 0-2.4 kV (asymmetric) and 0 to 1 kV rms (symmetric) with 0 to 60 kA (asymmetric) or 0 to 25 kA rms (symmetric) have been found, a spark gap has formed.

Referring now toFIG. 11, analternative arrangement1100 of self-test functionality is illustrated, in conjunction with the sensing and control electronics. In general, thealternative arrangement1100 generally corresponds to thecircuitry400 ofFIG. 4, but has incorporated into acontroller1110, also referred to as sensing and control electronics, a number of the self-test functions described in connection withFIG. 10, above, as well as other self-test and monitoring functions. In particular, the sensing and control electronics contain a number of additional functions/features; namely, monitoring, alarming, and automatic controls. In one example system, thecontroller1110 is used to monitor various voltage or current parameters, as well as switch positions in a high voltage transformer protection system, such as the one described in copending U.S. patent application Ser. No. 13/159,374, entitled “Continuous Uninterruptable AC Grounding System for Power System Protection”, the disclosure of which was incorporated by reference in its entirety above. In the embodiment shown, thearrangement1100 additionally contemplates a remote parameter settings capability by the operator, as further discussed below.

In general, thearrangement1100, rather than includingthreshold detectors408a-c as illustrated inFIGS. 4 and 10, implements monitoring, alarming, and self-test systems into thecontroller1110. In particular, signals1112a-e are directed to thecontroller1110 to be measured with sample and hold firmware, software or hardware within the switch controller/driver (or digital signal processor) for a set time duration. In example implementations, the sample and hold firmware within thecontroller1110 samples the parameter to be monitored at a sufficiently high rate, for example 1 kHz or higher, and detects peak signal values over a preset duration (e.g., one second, or some other duration). These peak values can then be transmitted over a fiber or other bus onto the utility SCADA or other control system remote from thearrangement1100 at an analogous (e.g., one Hertz) rate. Some of the parameters that can be monitored include, for example: a peak quasi-DC current in the transformer neutral; peak total harmonic distortion (THD); peak value of a detector such as an EMP or IEMI detector; power source, typically 120 volts DC, from the batteries in the sub-station house; peak value of the current in the transformer neutral current transformer (CT) signal; position of the DC disconnect switch; position of the high voltage AC switch (also referred to as an AC Grounding Switch); and the peak signal from any other parameter in the system or the position of any other switches or equipment in the overall system described herein or in copending U.S. patent application Ser. No. 13/159,374.

In example embodiments, thecontroller1110 also incorporates alarm functions capable of being communicated to a system operator. For example, if one of the above monitoring parameters exceeds a preset threshold value, an alarm is either sounded or transmitted to a remote system, so that an operator can take action to ensure the system is operating as intended and as designed. Thecontroller1110 may also trigger an alarm if one of the switches is not in a correct position according to the desired mode of operation.

In some embodiments, thecontroller1110 also includes built-in automatic controls to command the system to sequence through the various modes of self-testing. Such automatic control will reside in a digital signal processor or other type of micro-controller incorporated into thecontroller1110.

Thecontroller1110 can, in some embodiments, also have a function which automatically returns the system back to its normal operation after a GIC event is experienced. With this feature, thecontroller1110 can return one or more of the switches in a circuit to a normally-closed mode after being in the GIC protective mode. In various implementations, this can occur after a preset time delay for example one, three, six or twelve hours, and is adjustable in time by a remote operator. Should the GIC event still be present, thecontroller1110 will receive an indication of that event onlines1112a-e, and will once again automatically go into the GIC protective mode, opening the switches to which it is connected (e.g., switches204,208).

In some embodiments, thecontroller1110 can communicate with and can also be controlled by a utility system operator sending commands through thecontroller1110, for example to either open or close the DC disconnect switch or the high voltage AC switch, or to trigger operation of one or more of the self-test operations, such as are described below in connection withFIGS. 12-14, or above regardingFIG. 10.

The various settings in theoverall arrangement1100 can also be set or readjusted remotely by a system operator. These settings may include trigger thresholds for the various sensing inputs, for example the quasi-DC current, the total harmonic distortion (THD), the EMP/IEMI detector signal, neutral AC rms (root mean squared) voltage trigger level, the signal processing delay for the GIC command generation (0.5 or 1, or 3 or 5 seconds), the neutral rms current trigger levels (50, 100, 200, 400 amperes), or the harmonic detection bandwidth settings (for example 300, 600 or 1,200 Hz).

The system operator, either locally to or remote from thearrangement1100, can also put the controller1110 (and therefore theelectrical protection circuit200 ofFIG. 2) into the GIC protective mode when a geomagnetic storm is anticipated or forecasted by an agency such as NOAA that a solar storm is expected.

The utility operator can also initiate a self-test sequence as needed. However, this function will automatically be deactivated should theelectrical protection circuit200 and associatedcontroller1110 be in the GIC protective mode.

In some embodiments of the self-test arrangements ofFIGS. 10-11, some or all of the self-test features may be excluded or modified. For example, inFIG. 11, thecontroller1110 can be configured to perform only a subset of the tests discussed above, including DC and AC signal tests, or tests of various switches incorporated into circuit interfaced to arrangement1100 (e.g., circuits illustrated inFIGS. 1-9, orFIG. 15, below). Furthermore, as discussed above with respect toFIG. 10, additional tests of discrete circuit components, rather than sensing subsystems, could be performed as well.

Referring now toFIGS. 12-14, specific implementations of a self-test arrangement incorporated into a sensing and control system, such as thearrangement1100 ofFIG. 11 or within a remote SCADA system, are described. In various embodiments, one or more of the self-test procedures described herein can be performed on a selectable, regular basis, such as weekly, semi-weekly, monthly, or some other period. In such testing sequences an internal real-time clock with long life battery can be used as a timer for thearrangement1100.

When performing the one or more self-test operations, thecontroller1110 is configured to disable all monitoring and alarm functions, disable switch control functions (i.e. not sending signals to open the GIC power switches when in the self-test mode), and initiate a series of tests. In one example embodiment, thecontroller1110 will initiate a harmonic self-test mode, starting at a preset time (e.g., about 2 seconds) after the monitoring and switch control disabling operations. In general, the harmonic self-testing is used to determine an overall, total harmonic distortion measurement by way of firmware and/or control electronics. Thecontroller1110 will test harmonic signals, for example using the harmonic self-test mode1200, as illustrated inFIG. 12. As seen in that figure, normally thecontroller1110 receives an input from a capacitive voltage transformer (CVT) (or CVTs located on each arm of a three-phase transformer) is passed toconditioning electronics1202, and to aharmonic detector1204. In a self-test mode, aswitch1206 is used to connect a test signal from aharmonic generator1208, which is triggered within thecontroller1110 or from a remote operator, based on a periodic schedule. The signal amplitude from theharmonic generator1208 is adjustable to a variety of levels of a fundamental amplitude, for example to about 2%, 4%, 7%, and 14% that respectively correspond to the adjustable trigger level settings of theharmonic detector1204, which in this example are 1.5%, 3%, 5%, and 10% of the fundamental amplitude. Note the harmonic generator amplitude selections (for example 2%, 4%, 7% and 14%) could be automatically ganged with the appropriate harmonic detector trigger levels (for example 1.5%, 3%, 5% and 10%) to ensure that the corresponding test amplitude is consistent with the corresponding detector trigger level setting.

In example embodiments, a detected harmonic signal is in the frequency range 0-1,200 Hz. As such, thecontroller1110, or analogous SCADA system, could use a fast fourier transform to measure the total harmonic distortion, and can use adjustable bandwidths of about 300, 600, and 1,200 Hz. In such cases, the above threshold trigger levels could be used; alternatively, continuously adjustable trigger levels of 0.3% to 10% could also be used. The triggers can occur if the total harmonic distortion level for any of the three phases of thetransformer12 is exceeded for a predetermined amount of time. In some cases, the amount of time is continuously adjustable, and can be between about 0.05 and about 5 seconds.

The response of theharmonic detector1204 is observed in response to the generated signal for a period of time (e.g., 3 seconds), and a confirmation message is then returned to a remote system indicating that the harmonic signal is in fact detected (e.g., via DNP3 and web protocols). It is noted that the harmonic signal is not passed onto the switch control outputs, so that the self-test does not trigger some different operation of the switching functionality (i.e., switches208,210) of the system. Output from monitoring electronics will cause a DC breaker, such asbreaker1506 ofFIG. 15, below, to be opened, either bycontroller1110 or by a remote SCADA system.

After the harmonic test is complete, and after some additional delay (e.g., an additional two seconds), a neutral direct current self-test mode is entered, for example using one or more programmed modes such as are illustrated in thearrangement1300 depicted inFIG. 13. As illustrated in that figure, thecontroller1110 will initiate a direct current self-test mode. In the self-test, rather than receiving a signal from a shunt resistor (e.g., resistor206) viaconditioning electronics1302 at a directcurrent detector1304, aswitch1306 selects to receive a direct current voltage from aDC voltage generator1308, which outputs positive or negative voltages of a variety of magnitudes. For example, the DC voltage signal generated by theDC voltage generator1308 can be adjustable to 8 mV, 12 mV, 24 mV & 48 mV. These voltage levels would be ganged with the associated DC detector trigger levels of +/−5 mV, +/−10 mV, +/−20 mV and +/−40 mV. Thedetector1304 receives and detects the various voltage levels, and a confirmation message is then returned to a remote system indicating that a DC voltage is in fact detected (e.g., via DNP3 and web protocols). In various embodiments, the DC voltage applied is a quasi-DC voltage of about 0-10 Hz, and is measured in the presence of a 60 Hz AC voltage having a magnitude of about 0-200 mV. Trigger levels indicating that a direct current signal is present can be set to continuously adjust, to detect DC voltages of +/−1 to +/−50 mV, and would trigger in the event the set voltage is exceeded for about 0.05 to about 5 seconds (also in a continuously adjustable setting. It is noted that a direct current disconnect signal is not passed onto the switch control outputs, so that the self-test does not trigger some different operation of the switching functionality (i.e., switches208,204) of the system, as with the harmonic self-test above. Output from monitoring electronics will cause a DC breaker, such asbreaker1506 ofFIG. 15, below, to be opened, either bycontroller1110 or by a remote SCADA system. After the direct current self-test mode is completed, various monitoring functions can be employed, for example through use of a neutral impedance self test mode depicted in anarrangement1400 illustrated inFIG. 14. Thearrangement1400 generally represents a schematic of particular test signals determined based on thecircuit200 ofFIG. 2, above. In particular, the neutral impedance self-test mode is intended to validate the monitoring circuit for the neutral AC (60 Hz) rms voltage and current. In a normal mode, thearrangement1400 will detect a current range of about 0.2 to 200 amps (rms AC at 60 Hz) at acurrent transformer1402, and a voltage range of about 0.2 to 200 mVolts (rms AC at 60 Hz) at apotential transformer1404. Generally, an alarm should be signaled when the neutral impedance (i.e., voltage/current) is about 20% higher or lower than a preset, adjustable value. This allows the system to determine positions of breakers within the system, such as whether those breakers are open or closed, as well as the positions of auxiliary breaker contacts. Additionally, voltages can be monitored, for example the quasi-DC current value across theshunt resistor206, a DC current at the transformer neutral10, or AC currents as discussed above in connection withFIG. 12. Additionally, an alarm is signaled if the 60 Hz rms neutral current signal drops below a preset level (e.g., adjustable 0.05, 0.1, 0.2, 0.4 ampere settings) for a preset period (e.g., adjustable 10, 20, 40, 80 second periods). In connection with the present disclosure, thecontroller1110 or SCADA system can periodically poll the above parameters via, for example, a DNP or Web protocol.

During normal operation the circuit monitors a 120 volt DC signal provided by station batteries. If this direct current signal drops below 100 volts for more than a minute, one or more alarms are generated. Auxiliary switch contacts are monitored, and, along with the harmonic measurements (THD), and the DC voltage measurement are sent to a remote system approximately every five seconds.

Also during normal operation, the current and voltage signals are passed to thecontroller1100, represented by the functional blocks of theharmonic sensor1406, breaker control circuit1408, andcurrent sensor1410 within theenclosure1412. In a GIC protection mode, a current range is about 0.2 to 200 amps (rms AC at 60 Hz), peak rms at the current transformer1402 (with a switch in a 30 db attenuation position to handle higher voltages), and a voltage range of about 0.4 to 400 Volts (rms AC at 60 Hz) at thepotential transformer1404. To test the capacitor and resistor impedance of thecomponents304,206, respectively, any switches included in the circuit (includingswitch204 as depicted inFIG. 14) are opened. As above, any alarms for a nonfunctioning component are generated and optionally transmitted to a remote system.

In addition to the above remote setting operations, it is noted that each of the self-test trigger levels for the various self-test operations described above can be remotely set by the operator. For example, a remote user can set four harmonic detection levels and test levels, with optional detection levels of 1.5%, 3%, 5%, or 10%, and optional testing levels of 2%, 4%, 7%, or 14%. Additionally, a remote user can set any of three harmonic detection bandwidth options, for example 300 Hz, 600 Hz or 1200 Hz. In still further remote operation embodiments, a remote user can set the four DC voltage detection levels and test levels, with detection levels of +/−5, +/−10, +/−20, +/−40 or +/−80 millivolts, and testing levels of 8, 13, 24, 48 or 96 millivolts. In still other examples, a remote user can set the initial time delay for initiating the GIC protection mode, for example from among time delays of 0.5, 1, 2, and 5 seconds. The remote user can also set the neural rms voltage (60 Hz) alarm levels, for example at 70, 140, 280, and 560 Hz. The remote user can also set the neutral rms current (60 Hz) alarm levels, for example at levels of 50, 100, 200, and 400 Hz.

Referring toFIG. 15, afurther arrangement1500 is shown in which anelectrical protection circuit1501 is interfaced to a neutral10 of a transformer, to provide grounding of the neutral10 in the event of harmful signals derived from GIC (solar storms) and EMP E3 pulses. Thecircuit1501 includes akey interlock1502 used to selectively provide a locking connection of the transformer neutral10 toground14. Additionally, and similar to the arrangement ofFIGS. 2-3, anAC breaker1504 is positioned in series with aDC breaker1506 andshunt resistor206. TheAC breaker1504 is, in a default embodiment, in an open position, preventing AC grounding of the neutral10. TheDC breaker1506 is by default in a closed position, and configured to switch open in the event of a large DC current between the transformer neutral10 to ground14, as previously described, and explained in U.S. patent application Ser. No. 13/159,374, entitled “Continuous Uninterruptable AC Grounding System for Power System Protection”, the disclosure of which was incorporated by reference in its entirety above. Theshunt resistor206 provides an interface across which sensing electronics can be connected (e.g., sensing electronics such as are shown inFIGS. 10-11, or electrically connected to or integrated with a SCADA system as discussed above in connection withFIG. 1).

In the embodiment shown, a parallel path between the transformer neutral10 andground14 includes apower resistor1508 in series with acapacitor bank1510, and further in parallel with acurrent transformer1512, which has acontrol monitor1514. Thepower resistor1508, in some embodiments, corresponds to an approximately 1 ohm power resistor configured for large current applications, and useable to limit current occurring based on discharging from thecapacitor bank1510. Thecapacitor bank1510 has, in the embodiment shown, a 2.4 kVolt charging capacity, and a one ohm reactance, thereby allowing thecapacitor bank1510 to provide quick reactivity to changes occurring in the circuit.Current transformer1512 can be used to control current passing through thecapacitor bank1510, withmonitor1514 controlling a step-up/down of thecurrent transformer1512.

Similar to the arrangement ofFIG. 2, asurge arrester212, such as a metal oxide varistor, can be used to manage surge events between the transformer neutral and ground, and can be connected in series with a furthercurrent transformer1516, managed bymonitor1524. Additionally, aspark gap1520 can be connected between the transformer neutral andground14, also separated from ground by a current transformer1526 (which is also controlled by monitor1526). In an example embodiment, the spark gap will fire at about 8 to 9 kVolts, although other thresholds could be used as well. Example operation and design of such a spark gap is described in U.S. Provisional Patent Application No. 61/817,762, the disclosure of which is hereby incorporated by reference in its entirety. It is noted that typical GIC protection events will pass through thesurge arrester212, while high voltage events may trigger operation of thespark gap1520. Athyristor1528 can be used to trigger operation of the current transformers, while alockout1529 prevents protective operation of the overall unity by deactivating the current transformers, thereby disconnecting the transformer neutral10 and ground14 (in a default case).

In addition to the above, in the embodiment shown, avoltage probe1530 can be connected between the transformer neutral10 andground14 as well, to monitor an instantaneous voltage level at the transformer neutral.

It is noted that, in connection with the arrangement recited inFIG. 15, particular test operations could be performed based on use of one or more test inputs that can lead to either sensing and control circuitry (e.g., as inFIGS. 10-11) or to SCADA systems used for remote monitoring and control (e.g., as in SCADA system110 ofFIG. 1). For example in one embodiment, a plurality of current transformer inputs could be tested at each of three phases to detect harmonics that occur. A further current transformer input allows for monitoring current through the breaker assembly includingcircuit breakers1504,1506. A still furthercurrent transformer input1516 can be used to monitor current through thesurge arrester212, and a furthercurrent transformer input1526 can obtain current through thespark gap1520. Additional current transformer inputs could be added for use with different circuit configurations.

In addition to the current transformers, voltage inputs could be used to detect voltages across thecircuit1501. For example, current inputs across theshunt resistor206 could be used to sense and set DC current and harmonic set points. An additional voltage input could be located at the transformer neutral for direct monitoring. Additional voltage inputs could be added for use with different circuit configurations.

In addition to the voltage inputs, various power and breaker inputs could be provided and tested as well. For example, a voltage input from a power station at which the transformer is located could be monitored (e.g., a 120 V DC signal). Additionally, contact positions, such as auxiliary contact positions of both the AC andDC breakers1504,1506, respectively, could be tested.

In connection with the present disclosure, a number of self-test signals can be transmitted to thecircuitry1501 from associated circuitry or SCADA systems to detect and verify correct operation of the circuitry discussed herein. For example, the self-testing system (not shown, but discussed above as integrated into a control electronics system or SCADA system) can transmit the following signals to the circuit1501:

(1) a signal to open theDC breaker1506, which in turn causes theAC breaker1504 to open. In this case, the control system, whether fromarrangements1000, or1100, or from an analogous SCADA system, can send a signal to close theAC breaker1504, and output monitoring signals from system electronics to a remote SCADA System (e.g., system110);

(2) a harmonic signal detected from current transformers located on the phases of thetransformer12;

(3) a position of the AC andDC breakers1504,1506 (i.e., open or closed status);

(4) a current voltage level (AC or DC) acrossshunt resistor206;

(5) a voltage (AC or DC) derived from thevoltage probe1530, directed to a voltage at transformer neutral10;

(6) an AC current through thecapacitor bank1510;

(7) an AC current through thesurge arrester212, as defined bycurrent transformer1516; and

(8) an AC current through thespark gap1520, based oncurrent transformer1522.

The various tests occurring in thecircuit1501 ofFIG. 15 can be, for example, those discussed above in connection withFIGS. 10-14. In addition to the above tests, further testing can be performed on thearrangement1500 using a SCADA system (e.g., system110 ofFIG. 1) to determine other types of faults occurring in the system. For example, an AC current through theshunt resistor206 can be monitored to determine if there is a neutral current over 180 amps for over a minute. This amount of current would cause damage to thepower resistor1508. In such embodiments, the SCADA system connected to thearrangement1500 could send an alarm to a user or local system to deactivate the overall system. Additionally, the SCADA system can determine if impedance across thepower resistor1508 andcapacitive network1510 is within a tolerance range when the breaker assembly (AC breaker1504 and DC breaker1506) are in a normal operating position, as well as when the breaker assembly is in a GIC protective mode. In such cases, the SCADA system and/or control electronics can return thebreakers1504,1506 to a normal mode after a preset time delay. This preset time delay can be variable between about 10 and 720 minutes, and is remotely adjustable.

In addition to the self-test operations discussed in connection withFIGS. 10-15, it is noted that a number of operator controls can be included as well, for use either locally at a control system or via a SCADA system located remotely from thecurrent transformer12 being monitored. In some embodiments, a system operator can selectively switch an overall system into or out from a GIC protective mode by opening theDC breaker1506 and closing theAC breaker1504. Additionally, the operator can remotely set harmonic detection levels explained above, remotely set harmonic detection bandwidths (for example, among the 300 Hz, 600 Hz, and 1,200 Hz levels), remotely set a DC voltage detection level or time delays for triggering the GIC protection mode. It is further noted that, in some embodiments, fewer than all of the self-test operations can be performed at any given time, and that in some embodiments the self-test operations are not performed in direct succession. Various timings can be set for each of the self-test operations as well, consistent with their descriptions above in connection withFIGS. 11-15. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

Claims (38)

The invention claimed is:

1. A system comprising:

a protection circuit electrically connected to a transformer neutral, the transformer electrically connected to a power grid, the protection circuit including a DC blocking component positioned between the transformer neutral and ground and one or more switches selectively actuated to form a path between the transformer neutral and ground in the event of unwanted DC current at the transformer neutral;

a control circuit electrically connected to the protection circuit and positioned to selectively actuate the switches based on observed conditions within the protection circuit;

a plurality of test connections disposed within the protection circuit and useable to test electrical properties of the protection circuit; and

a plurality of detection components electrically connected to one or more electrical signal lines leading from one or more connection points on a power grid;

wherein the control circuit comprises a controller positioned within an interior volume of an electromagnetically shielded enclosure and receiving an output from each of the plurality of detection components, the controller including a plurality of test thresholds, and configured to drive at least one circuit component electrically connected to the transformer neutral in response to sensing a signal from one of the plurality of detection component of a detected harmonic or direct current signal above a respective one of the plurality of test thresholds.

2. The system ofclaim 1, wherein the protection circuit is electrically connected to a SCADA system remote from the protection circuit and control circuit, and wherein the SCADA system is electrically connected to the plurality of test connections for remote testing of electrical properties of the protection circuit.

3. The system ofclaim 1, wherein the plurality of detection components are selected from a group of detectors consisting of:

a harmonic analyzer;

a shunt resistor electrically connected between the transformer neutral and a ground;

a Hall effect current sensor connected across a grounding line, the grounding line connected between the transformer neutral and a ground; and

an electromagnetic field detector.

4. The system ofclaim 3, further comprising:

a shielded enclosure having an interior volume, the shielded enclosure configured to shield the interior volume from electromagnetic interference;

a plurality of filters positioned along a periphery of the shielded enclosure and connected to the electrical signal lines, the electrical signal lines extending into the interior volume from external to the shielded enclosure, the filters configured to prevent high frequency, high power electromagnetic signals from entering the shielded enclosure.

5. The system ofclaim 4, wherein the harmonic analyzer is positioned within the shielded enclosure.

6. The system ofclaim 5, wherein the shunt resistor is positioned external to the shielded enclosure.

7. The system ofclaim 6, wherein the Hall Effect current sensor is positioned external to the shielded enclosure.

8. The system ofclaim 7, wherein the electromagnetic field detector is positioned external to the shielded enclosure.

9. The system ofclaim 1, wherein the controller is configured to open a normally-closed switch connected between the transformer neutral and a ground connection.

10. The system ofclaim 1, wherein the controller is configured to open the normally-closed switch upon detection of a harmonic or direct current signal above a threshold on the transformer neutral.

11. The system ofclaim 1, wherein the indication received from at least one of the plurality of threshold detectors represents a detected harmonic, a direct current signal, or an electromagnetic pulse above a threshold associated with that threshold detector.

12. The system ofclaim 11, wherein the controller is configured to, during normal operation of the system, communicate status information regarding signals received from each of the detection components to the remote system.

13. The system ofclaim 12, wherein the system is located at a power substation, and wherein the remote system is located at a central control station and includes the SCADA system.

14. The system ofclaim 1, wherein the controller is configured to execute one or more self-test procedures, the self-test procedures configured to confirm that the system operates as expected in the event of damaging of degrading events.

15. The system ofclaim 14, wherein the one or more self-test procedures are selected from a group of procedures consisting of:

applying an alternating current signal at the transformer, the alternating current signal having a frequency different from that of the power system frequency;

applying a harmonic signal at a harmonic analyzer, the harmonic signal having an amplitude above the preset threshold defined by a threshold detector associated with the harmonic analyzer, the threshold defining a range of amplitudes;

applying a direct current (DC) voltage signal at the transformer neutral to simulate direct current received at the transformer neutral and

applying an electromagnetic (EM) detector signal, the EM signal having an amplitude above the preset threshold defined by a threshold detector, the threshold defining a range of amplitudes.

16. A method comprising:

transmitting one or more electrical signals from a protection circuit to a remote system, the protection circuit electrically connected between a transformer neutral of a transformer in a power grid and ground, wherein the remote system periodically assesses operation of the protection circuit based on the one or more electrical signals; and

receiving at a control circuit electrically connected to the protection circuit one or more commands from the remote system to actuate one or more switches in the protection circuit, thereby testing an alternative configuration of the protection circuit;

receiving a plurality of detector signals at a controller forming a portion of the control circuit, the controller housed within an electromagnetically-shielded enclosure, and the detector signals including a harmonic detector signal and a direct current detector signal;

sampling each of the plurality of detector signals to detect a peak value over a predetermined period;

comparing each of the peak values to a corresponding remotely-set test threshold associated with that signal type, and, based on that comparison, generating one or more alarms if the remotely-set test threshold is exceeded; and

communicating at least the one or more alarms to the remote system.

17. The method ofclaim 16, further comprising communicating each of the peak values to the remote system.

18. The method ofclaim 16, further comprising periodically performing one or more self-test procedures, the self-test procedures configured to confirm that the controller and electrical protection circuit operate as expected in the event of damaging of degrading events.

19. A continuous grounding system for use in an alternating current system including a transformer, the system comprising:

(a) a switch assembly connected between a transformer neutral of a transformer and a ground, the switch assembly having an open position and a closed position, the open position disrupting a path through the switch assembly between the transformer neutral and the ground, and the closed position establishing the path connecting the transformer neutral to the ground through the switch assembly, wherein in normal operation of the alternating current system the switch remains in a closed position; and

(b) a DC blocking component electrically connected in parallel with the switch assembly between the transformer neutral and the ground; and

(c) a control circuit configured to control the switch assembly, the control circuit configured to actuate the switch assembly to an open position in response to receipt of a signal indicative of an electromagnetic signal detected in proximity to the transformer that is indicative of an electromagnetic event capable of damaging the transformer.

20. A protection system comprising:

(a) a switch assembly connected between a transformer neutral of a transformer and a ground, the switch assembly having an open position and a closed position, the open position disrupting a path through the switch assembly between the transformer neutral and the ground connection, and the closed position establishing the path connecting the electrical connection to the ground connection through the switch assembly, wherein in normal operation of the alternating current system including the transformer, the switch remains in a closed position; and

(b) a surge arrester electrically connected between the transformer neutral and the ground; and

(c) a control circuit configured to control the switch assembly, the control circuit configured to actuate the switch assembly to an open position in response to receipt of a signal indicative of an event potentially harmful to the alternating current system including the transformer.

21. A protection circuit for an alternating current system including a transformer, the protection circuit comprising:

a DC blocking component electrically connected between a neutral of the transformer and a ground;

a switching assembly electrically connected in parallel with the DC blocking component, the switching assembly being designed to break or interrupt DC current;

an overvoltage protection device electrically connected in parallel with the DC blocking component and the switching assembly between the neutral and the ground;

a controller, including a processing device, configured to:

(i) detect the presence of a fault current between the neutral of the transformer and the ground that is above a predetermined threshold; and

(ii) upon determining that the fault current is above the predetermined threshold, close the switch assembly, forming an electrical path between a neutral of the transformer and a ground.

22. The protection circuit of claim 21, wherein the controller is further configured to generate an alarm.

23. A protection circuit for an alternating current system including a transformer, the protection circuit comprising:

a DC blocking component electrically connected between a neutral of the transformer and a ground;

a switching assembly electrically connected in parallel with the DC blocking component, the switching assembly being capable of breaking or interrupting DC current;

an overvoltage protection device electrically connected in parallel with the DC blocking component and the switching assembly between the neutral and the ground;

a current measuring device configured to measure a current through the overvoltage protection device; and

a controller, including a processing device, configured to:

(i) monitor a measurement from the current measuring device to detect a current through the overvoltage protection device; and

(ii) upon detecting current through the overvoltage protection device, close the switch assembly, thereby forming an electrical path between a neutral of the transformer and a ground.

24. The protection device of claim 23, wherein the controller is further configured to deactivate the protection mode based upon determining that the overvoltage protection device has triggered.

25. The protection circuit of claim 23, wherein the switching assembly includes a switch operated using a default open position.

26. The protection circuit of claim 25, wherein the switch comprises an AC switch.

27. The protection circuit of claim 26, wherein the switching assembly further includes a DC switch operated using a default closed position.

28. A protection circuit for an alternating current system including a transformer, the protection circuit comprising:

a DC blocking component electrically connected between a neutral of the transformer and a ground;

a switching assembly electrically connected in parallel with the DC blocking component, the switching assembly being capable of breaking or interrupting DC current, the switching assembly including an AC switch and a DC switch, the AC switch being in a default open position;

an overvoltage protection device electrically connected in parallel with the DC blocking component and the switching assembly between the neutral and the ground;

a controller, including a processing device, configured to actuate the switching assembly in response to detecting an electrical condition at the transformer neutral.

29. The protection circuit of claim 28, further comprising a voltage probe connected between the transformer neutral and ground and configured to monitor a voltage level at the transformer neutral.

30. The protection circuit of claim 28, wherein the DC blocking component comprises a capacitor.

31. The protection circuit of claim 28, wherein the DC blocking component comprises a resistor.

32. The protection circuit of claim 28, further comprising a surge arrester electrically connected in parallel with the DC blocking component, the switching assembly, and the overvoltage protection device between the neutral and the ground.

33. The protection circuit of claim 32, wherein the surge arrester comprises a metal oxide varistor.

34. The protection system of claim 20, further comprising a DC blocking component electrically connected in parallel with the surge arrester and the switch assembly between the transformer neutral and the ground.

35. The continuous grounding system of claim 19, further comprising a control input communicatively connected to the control circuit from a remote system, wherein the control circuit is configured to drive the at least one external component in response to receipt of a remote triggering signal.

36. The system of claim 20, further comprising a control input electrically connected to the control circuit to provide remote control of actuation of the switch assembly.

37. The protection circuit of claim 21, further comprising a control input electrically connected to the controller to provide remote control of actuation of the switch assembly.

38. The protection circuit of claim 23, further comprising a control input electrically connected to the controller to provide remote control of actuation of the switching assembly.

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