As a further limitation, the time periods t1 and t2 are selected to be within a time period after the activation of the protection device and before the time of the return of the whole group;

or a first half-wave time period;

or only transient current time periods;

or only steady state current periods;

or comprises a transient current time period and a steady state current time period;

or a combination of multiple spaced time periods.

As an alternative embodiment, the grounding protection device obtains two-phase currents of a power supply transformer connected with the bus, and when the fault phase is a missing phase, the power frequency removing high-frequency residual current of the fault phase is replaced by the reverse direction of the sum of the known two-phase power frequency removing high-frequency residual currents.

As an alternative embodiment, the grounding protection device obtains a phase current of the power supply transformer connected with the bus, and when the fault phase is a missing phase, the power frequency-removed high-frequency residual current of the fault phase is replaced by a reverse direction of a product of the known power frequency-removed high-frequency residual current of the first phase and the product of the known power frequency-removed high-frequency residual current multiplied by two.

As an alternative embodiment, the earth protection device captures the three-phase current or the two-phase current or the one-phase current of the supply transformer connected to the busbar.

A distributed small-current grounding line selection system comprises a power supply, a transformer and a plurality of power supply lines, wherein the power supply supplies power to the transformer, the transformer supplies power to a bus, the plurality of power supply lines are connected with the same bus, the transformer is grounded in small current, each power supply line is provided with a respective grounding protection device, and the grounding protection devices perform fault line selection according to the line selection method.

As an alternative embodiment, three phases of the transformer respectively supply power to corresponding phases of the bus, each phase of the transformer is respectively provided with a current transformer, and the secondary side current of each current transformer is respectively input into the grounding protection device of each power supply line.

Compared with the prior art, the beneficial effect of this disclosure is:

(1) the distributed low-current grounding line selection system has the advantages that the number of lead-in wires of each grounding protection device is small, the arrangement and the spatial position arrangement of the lead-in wires of the device are convenient, and the device is convenient to maintain and manage.

(2) The method removes the power frequency current in the current and removes all high-frequency currents above the selected frequency SF, so that the aims of accurately removing interference signals and reserving useful information to the maximum extent can be achieved.

(3) The waveform of the power frequency-removing high-frequency residual current constructed from the current is more distinctive, and the fault line is analyzed by utilizing the similarity in the same direction or the similarity in the opposite direction of a pair of distinctive current waveforms, so that the judgment result is more reliable, and the sensitivity is very high.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.

FIG. 1 is a schematic structural diagram of a distributed low current ground line selection system according to an embodiment;

the specific implementation mode is as follows:

the present disclosure is further described with reference to the following drawings and examples.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The first embodiment is as follows:

an exemplary embodiment, a distributed low current ground selection system, as shown in fig. 1. The power supply transmits power to the transformer T, the transformer T transmits power to the bus M, and the neutral point of the transformer T is grounded through the arc suppression coil L. Suppose that N power supply lines are connected to bus M, and N is 6. The six lines are L1, L2, L3, L4, L5, L6, respectively. Each line has its own ground protection device BH1, BH2, BH3, BH4, BH5, BH6, and for convenience of drawing, only BH1 is shown in fig. 1. Zero mode current i of current transformers TA1, TA2, TA3, TA4, TA5 and TA6 of 6 power supply lines_0,i(i-1, 2, 3, 4, 5, 6) are inputted to ground protection devices BH1, BH2, BH3, BH4, BH5, BH6 of the respective lines,zero mode current i_0,iIs in accordance with the convention that the busbars point towards the lines. i.e. i_0,iThe representation is an instantaneous value of the value,

the expression is phasor. As is well known, the power frequency component of the zero-mode current is the zero-sequence current. Three-phase voltage of bus voltage transformer TV

The grounding protection devices BH1, BH2, BH3, BH4, BH5 and BH6 of each line are input respectively; the A, B, C phases of the transformer T supply power to the A, B, C phases of the bus M, and the A, B, C phases of the transformer T have current transformers TAa, TAb, and TAc, respectively. Secondary side currents of the current transformers TAa, TAb and TAc are respectively input into grounding protection devices BH1, BH2, BH3, BH4, BH5 and BH6 of each line. The secondary side currents of the current transformers TAa, TAb and TAC respectively reflect the primary side current i_a,T、i_b,T、i_c,TPrimary side current i_a,T、i_b,T、i_c,TThe reference direction of (2) is that the bus bars point to the transformer.

The grounding protection device of each line respectively calculates the zero sequence voltage of the bus

If the zero sequence voltage of the bus is larger than the setting value, the power system is indicated to have a ground fault, and the ground protection devices of all lines respectively start a line selection process. The line selection strategy and criterion for low-current grounding line selection are specifically as follows:

(1) judging the fault phase; for example: u shape_a、U_b、U_cThe smallest phase is the failed phase; (2) removing the zero-mode current i of the line_0,iRemoving all high-frequency current above the selected frequency SF to obtain zero-mode power-frequency-removed high-frequency residual current i of the circuit_0,i,α(ii) a Removing power frequency current in the phase current of the T fault of the transformer, removing all high-frequency current above the selected frequency SF, and obtaining power frequency-removing high-frequency residual current i of the T fault phase of the transformer_g,T,α(ii) a For example: phase a isThe fault phase is i_g,T,α＝i_a,T,α(3) Calculating zero-mode power frequency and high-frequency residual current i of the circuit_0,i,αIntegral W of the energy of (1) over the time periods t1 and t2_iIs available

Calculating; calculating power frequency and high frequency removing residual current i of T fault phase of transformer_g,T,αIntegral W of the energy of (1) over the time periods t1 and t2_g,TIs available

Calculating; (4) if W is_i＞I_set,7And is and

and is

Then the present line is a faulty line.

Wherein: t is not less than 0₁，t₁＜t₂＜t_set1；t_set1The time from the start of the low-current grounding protection device to the reset of the whole group is obtained. Suggest to take k₄＝0～0.5，k₄1-2; setting value 7_set,78 th setting value I_set,89 th setting value I_set,9May be determined empirically from operating experience.

Of course, in various embodiments, there are many ways to remove the power frequency and high frequency current, such as:

the method for removing power frequency current by using zero-mode current comprises the following steps: (1) and after the A/D sampling of the zero-mode current, obtaining the zero-mode power frequency-removed residual current through a digital power frequency wave trap. (2) Taking a steady-state current of a power frequency cycle after the transient current of the zero-mode current disappears as a sample, and carrying out power frequency Fourier transformation, wherein the expansion of the power frequency current information obtained by the transformation in the whole time period of the grounding protection is the power frequency current. The zero-mode current is zero-mode de-power-frequency residual current by subtracting the expanded power-frequency current in the whole time period of the grounding protection. (3) Taking a steady-state current of a power frequency cycle after the transient current of the zero-mode current disappears as a sample, wherein the expansion of the sample in the whole working time period of the grounding protection is the power frequency current. The zero-mode current is zero-mode power frequency residual current obtained by subtracting the expanded power frequency current in the whole working time period of the grounding protection. The side effect is that even order higher harmonic component in the zero mode current is removed, and odd order higher harmonic component in the zero mode current is amplified. But does not adversely affect the line selection decision. (4) Other methods.

The method for removing the high-frequency current by the zero-mode current comprises the following steps: (1) the zero-mode current is passed through an analog low-pass filter (e.g., a capacitor) before a/D sampling. (2) The zero mode current is passed through a digital low pass filter after a/D sampling. (3) Other methods.

The operating characteristics of the low current ground selection criterion are analyzed below.

Before or after the ground fault of the power system occurs, unbalanced zero sequence current exists in each line of the power system. Experience has shown that: the unbalanced zero sequence current is basically power frequency current. When the low-current grounding line selection is in a high-resistance grounding fault, the main reason that the line selection cannot be correctly performed is that a fault signal is very weak, and the amplitude of unbalanced current is close to the size of the fault signal. The power frequency current in the zero-mode current is removed, all high-frequency currents above the selected frequency SF are removed, and the remaining zero-mode power frequency removed high-frequency residual current is used as a grounding line selection criterion. Therefore, the interference signals are accurately removed, the useful signals are reserved to the maximum extent, the main interference in the zero-mode current is eliminated, the useful fault signal characteristics of the zero-mode current are highlighted, and the purpose that the fault line can be judged by weak fault signals is achieved.

When a ground fault suddenly occurs, the transient current amplitude of the zero-mode current of each line is several times or more than ten times larger than the power frequency zero-sequence current amplitude of the line; the transient current amplitude of the fault line zero-mode current is the largest. In the first half-wave time, the transient current of the zero-mode current of the non-fault line changes in the same direction, and the transient current of the zero-mode current of the fault line changes in the opposite direction.

A large amount of fault recording data show that: when a line has a ground fault, particularly a high-resistance ground, the arc resistance of a grounding point is mostly changed, and the arc ground generates a large amount of high-frequency attenuation current, and the arc ground may be interrupted. If the grounding is stable, the zero-mode power frequency removing high-frequency residual current also has fifth harmonic and other higher harmonics.

When the line has a ground fault, all the zero-mode power-frequency-removed high-frequency residual currents of non-fault lines flow into the earth from the line, flow into the fault line from the earth ground point, flow into the fault phase bus from the fault line, flow into the fault phase coil of the transformer from the fault phase bus, and flow into the neutral point of the transformer from the fault phase coil of the transformer; the arc suppression coil connected to the neutral point of the transformer has very high reactance to the transient current and its high frequency current, and the transformer coil has only leakage reactance to the transient current and its high frequency current, so that the zero-mode power frequency removing high frequency residual current flows from the neutral point of the transformer to the other two non-fault phases of the transformer and then flows into the circuits in proportion to form the zero-mode power frequency removing high frequency residual current of each circuit. If there is DC attenuation current in the zero-mode power-frequency-removing high-frequency residual current, the DC attenuation current flows into the ground from the neutral point arc suppression coil and flows into the fault phase of the fault line from the fault point. It can be seen that the power frequency and high frequency removing residual current i of the fault phase coil of the transformer_g,T,αEqual to zero-mode de-mains frequency de-high frequency residual current of a fault phase flowing into a fault line from a fault point. The zero-mode power-frequency-removing high-frequency residual current of the fault line is equal to the difference of the zero-mode power-frequency-removing high-frequency residual current of the fault phase flowing into the fault line from a fault point and the zero-mode power-frequency-removing high-frequency residual current flowing into the ground from the line. Therefore, if the ith line is a fault line, the power frequency removing and high frequency removing residual current i of the fault phase of the transformer_g,T,αZero-mode power frequency-removing high-frequency residual current i with fault line_0,i,αIn the opposite direction, and W_g,TGreater than W_i. If the ith line is a faulty line, then there is

It can be seen that if the inequality is not equal

If so, the line is a faulty line.

If the ith line is not a faulty line, then there is

Visible inequality

And if not, judging that the line is not a fault line.

In the same way, require W_i＞I_set,7And also to ensure judgment reliability. If the zero mode of the circuit is removed, the power frequency is removed, and the high frequency residual current i is removed_0,i,αToo little energy, large error, and possible wrong line selection. Therefore, zero-mode power frequency-removing high-frequency residual current i of the circuit is required_0,i,αIs greater than the 7 th setting value. Furthermore, the circuit can be used for removing power frequency and high frequency residual current i in a zero mode_0,i,αThe concentrated time periods are compared to define the t1 and t2 time periods. Or, the circuit is used for removing power frequency and high frequency residual current i in a zero mode_0,i,αThe combination of the time periods of the plurality of discontinuities in the energy comparison set defines the t1 and t2 time periods. The time period is selected in a mode of being within a period of time after the protection device is started and before the time of resetting the whole group; or a first half-wave time period; or only transient current time periods; or only steady state current periods; or comprises a transient current time period and a steady state current time period; or a combination of multiple spaced time periods. According to different actual operation power distribution network conditions, different time period combination modes are selected, the method is flexible to apply, and the best effect is achieved.

The existing widely applied transient method grounding line selection compares the initial direction and amplitude of the transient waveform of the zero-mode current of each line only in the first half-wave time of the fault. After the first half-wave time, the criterion is invalid. The effective time period of the criterion is very short. T of the present embodiment₁And t₂A relatively long section may be taken. The criterion algorithm of the embodiment can comprise a fault characteristic section conforming to the transient method grounding line selection, andfault signature sections that do not meet transient ground routing may be included. The reliability and sensitivity of the criterion are superior to those of the line selection method by the transient method.

The main component of the three-phase current of the transformer is load current which is far greater than power frequency removing high-frequency residual current in the three-phase current. However, the transformer fault phase power frequency removing high-frequency residual current as one of the criteria removes the load current when removing the power frequency, so the low-current grounding line selection criterion cannot be interfered by the load current.

The small current grounding line selection criterion can be used for a system with a neutral point not grounded and can also be used for a system with a neutral point grounded through an arc suppression coil.

The distributed grounding protection device has fewer lead-in wires, is convenient for arrangement of the lead-in wires and arrangement of space positions, and is convenient for maintenance and management.

The grounding line selection method of the low-current grounding system provided by the embodiment can be completely realized. Has wide application prospect.

Example two:

as shown in fig. 1, the A, B, C phases of the transformer T have current transformers TAa, TAb, and TAc, respectively. The current transformers TAa, TAb, and TAc reflect the primary side current i, respectively_a,T、i_b,T、i_c,T. However, some distribution networks have current transformers in the A, C phases of the transformer T and no current transformer in the B phase.

The field practical operation experience shows that when a small-current grounding system has a grounding fault, the attenuation direct-current component of the neutral point arc suppression coil of the transformer is very small, and the influence on the small-current grounding route selection criterion is very small when the attenuation direct-current component is ignored. Therefore, when the B phase is a fault phase, the power frequency of the fault phase of the transformer T is removed to remove the high-frequency residual current i_g,T,α＝-(i_a,T,α+i_c,T,α) The disclosed method can still be used to select a faulty line. However, the sensitivity and reliability are slightly worse than those of the first embodiment. The same thing as in the first embodiment is not redundant here.

Example three:

as shown in the power distribution network of fig. 1, A, B, C phases of the transformer T are respectively provided with a current transformerTAa, TAb, and TAC. The current transformers TAa, TAb, and TAc reflect the primary side current i, respectively_a,T、i_b,T、i_c,T. In order to further reduce the number of lead-ins of the earth protection device, the earth protection device may only take one phase current, for example, the a-phase current.

When the phase B is a fault phase, the power frequency of the fault phase of the transformer T is removed to remove the high-frequency residual current i_g,T,α＝-2i_a,T,αAnd calculating, and still selecting the fault line by using the method disclosed by the invention. When the C phase is a fault phase, the power frequency of the fault phase of the transformer T is removed to remove the high-frequency residual current i_g,T,α＝-2i_a,T,αAnd calculating, and still selecting the fault line by using the method disclosed by the invention. However, the sensitivity and reliability are slightly worse than those of the first embodiment. The same thing as in the first embodiment is not redundant here.

As will be appreciated by one skilled in the art, embodiments of the present disclosure may be provided as a method, system, or computer program product. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present disclosure may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and so forth) having computer-usable program code embodied therein.

The present disclosure is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the disclosure. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Although the present disclosure has been described with reference to specific embodiments, it should be understood that the scope of the present disclosure is not limited thereto, and those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.

Claims

1. A distributed small current grounding line selection method is characterized in that: distributing an earthing protection device on each power supply line connected with the same bus in a distributed manner, wherein the earthing protection device acquires each phase voltage of the bus, the current of a power supply transformer connected with the bus and the zero-mode current of a protected power supply line, and if the zero-sequence voltage of the bus is greater than a setting value, executing the following line selection steps:

judging the fault phase;

removing protected confessionZero-mode current i of electric line_0,iRemoving all high-frequency current above the selected frequency to obtain zero-mode power-frequency-removed high-frequency residual current i of the protected power supply line_0,i,α(ii) a Removing power frequency current in the transformer fault phase current, removing all high-frequency current above the selected frequency to obtain power frequency-removed high-frequency residual current i of the transformer fault phase_g,T,α；

W_i> I_set,7；

I_set,7、I_set,8、I_set,9setting values are respectively; k is a radical of₄、k₅Is a proportionality coefficient; i is 1, 2, 3, N; subscript 0 refers to zero sequence; subscript alpha refers to power frequency and high frequency residual current removal; subscript g indicates the faulted phase; subscript T refers to transformer T fault phase; w_iZero-mode power frequency and high-frequency residual current removing i of finger line_0,i,αIntegral of the energy of (a) over the time periods t1 and t 2; w_g,TI for removing power frequency and high frequency residual current from T fault phase of transformer_g,T,αIs integrated over the time periods t1 and t 2.

2. The distributed small-current grounding line selection method as claimed in claim 1, characterized in that: the time periods t1 and t2 are selected within a period of time after the protection device is started and before the time of the whole group returning;

or a first half-wave time period;

or only transient current time periods;

or only steady state current periods;

or a combination of multiple spaced time periods.

3. The distributed small-current grounding line selection method as claimed in claim 1, characterized in that: the grounding protection device obtains three-phase current or two-phase current or one-phase current of a power supply transformer connected with a bus.

4. A distributed small-current ground line selection method according to claim 3, characterized by: and the grounding protection device acquires the two-phase current of the power supply transformer connected with the bus, and when the fault phase is a missing phase, the power frequency-removing high-frequency residual current of the fault phase is replaced by the reverse direction of the sum of the known two-phase power frequency-removing high-frequency residual currents.

5. A distributed small-current ground line selection method according to claim 3, characterized by: and the grounding protection device acquires a phase current of the power supply transformer connected with the bus, and when the fault phase is a missing phase, the power frequency and high frequency removing residual current of the fault phase is replaced by the known reverse direction of multiplying the power frequency and high frequency removing residual current of the fault phase by two.

6. A distributed small current grounding line selection system is characterized in that: the method comprises a power supply, a transformer and a plurality of power supply lines, wherein the power supply supplies power to the transformer, the transformer supplies power to a bus, the plurality of power supply lines are all connected with the same bus, the transformer is grounded with small current, each power supply line is provided with a respective grounding protection device, and the grounding protection devices perform fault line selection according to the line selection method of any one of claims 1 to 5.

7. The distributed small-current grounding line selection system as claimed in claim 6, wherein: the three phases of the transformer respectively supply power to corresponding phases of the bus, each phase of the transformer is respectively provided with a current transformer, and the secondary side current of each current transformer is respectively input into the grounding protection device of each power supply line.