A kind of method of small current grounding system single-phase grounding selectingTechnical field
A kind of method that the present invention relates to small current grounding system single-phase grounding selecting.
Background technology
In China 3kV～66kV supply and distribution net, major part all uses neutral point not direct grounding way, because it connectsDuring earth fault, the electric current flowing through earth point is little, so being commonly referred to as small current neutral grounding system (NUGS), it includes that neutral point does not connectsGround system (NUS), neutral by arc extinction coil grounding system (NES, also referred to as resonant earthed system) and Neutral Grounding through Resistance in ElectricalSystem (NRS).In recent years, along with being widely used from motion tracking arc, for solving what system occurred at instant of failureResonance problems, begins with arc suppression coil and nonlinear resistance string (or also) connection and the method for operation in parallel with spark gap.
The probability of small current neutral grounding system generation singlephase earth fault is the highest.But, when system generation singlephase earth faultTime, owing to not constituting short-circuit loop, earth-fault current is more much smaller than load current, particularly neutral by arc extinction coil groundingSystem earth electric current is the least, and three-phase line voltage remains in that symmetrical relations, does not affect power supply continuous to load, therefore need not jump immediatelyLock, code regulation can continue to run with l～2h.But, due to the appearance of earth point, the now electricity over the ground of healthy phases in systemPressure rises to 1.732 times of primary voltage, and the insulation to electrical network forms threat, it is easy to induces another point in the weak place of electrical network and connectsGround, thus form phase fault.Along with the increase of power system capacity, the increase of total line length, capacitance current is increasing, arc lightThe overvoltage multiple that ground connection causes is the highest.
To this end, scientific worker both domestic and external is in succession at aspects such as the mode of connection, over-voltage measure and ground protectionsStudied, thirsted for reducing to greatest extent the probability that singlephase earth fault occurs, and, once there occurs single-phase connecingEarth fault, it is also desirable to faulty line can be selected as early as possible to fix a breakdown in time.And compensated distribution network occurs single-phaseDuring earth fault, due to faulty line and the zero-sequence current of non-fault line phase and amplitude the most relatively, thus causeThe problem that route selection False Rate is higher.
Summary of the invention
For the problems referred to above, the present invention provides a kind of method of small current grounding system single-phase grounding selecting, solves at presentDue to the phase place of faulty line Yu the zero-sequence current of non-fault line during compensated distribution network generation singlephase earth faultWith amplitude the most relatively, the problem that the route selection False Rate that causes is higher.
For realizing above-mentioned technical purpose, reaching above-mentioned technique effect, the present invention is achieved through the following technical solutions:
A kind of method of small current grounding system single-phase grounding selecting, it is characterised in that comprise the steps:
Step 1, collection bus or the residual voltage of outlet, the zero-sequence current of outlet, calculate residual voltage amplitude in real time；
Step 2, think bus or outlet generation singlephase earth fault when residual voltage amplitude starts voltage more than route selection,Enter step 3；
Step 3, intercept when fault occurs before and after the zero-sequence current of each cycle and the data of residual voltage, and to transient stateResidual voltage and transient zero-sequence current data carry out wavelet package transforms；
Step 4, compare transient zero-sequence current and the phase place of transient zero-sequence voltage after wavelet package transforms, if phase place is identical, beNon-fault line, if opposite in phase, is faulty line, thus completes earthing wire-selecting.
Preferably, wavelet package transforms used strict support orthogonal wavelet base DB10 small echo.
Preferably, small current neutral grounding system is 3kV-66kV small current neutral grounding system.
The invention has the beneficial effects as follows:
(1) transient zero-sequence voltage and transient zero-sequence current only with this circuit judge whether earth fault, it is not necessary toThe zero-sequence current data of All other routes, therefore this method may be used for centralized earth protective device, it is also possible to for separate roomEvery protection device in.
(2) earth fault transient process and electric network composition, parameter, the method for operation are relevant.Transient current is much larger than stable state electricityCapacitance current, transient state maximum current value phase angle initial with false voltage is relevant, and transient current is not affected by arc suppression coil, and arc light connectsGround and intermittent ground connection transient state component are more rich, solve to utilize the inaccurate problem of steady-state current route selection.
Accompanying drawing explanation
Fig. 1 is the flow chart of the method for a kind of small current grounding system single-phase grounding selecting of the present invention；
Fig. 2 is the wiring schematic diagram that the present invention realizes in line-selected earthing device；
Fig. 3 is the wiring schematic diagram that the present invention realizes in feeder protection equipment.
Detailed description of the invention
With specific embodiment, technical solution of the present invention is described in further detail below in conjunction with the accompanying drawings, so that abilityThe technical staff in territory can be better understood from the present invention and can be practiced, but illustrated embodiment is not as the limit to the present inventionFixed.
A kind of method of small current grounding system single-phase grounding selecting, as it is shown in figure 1, comprise the steps:
Step 1, collection bus or the residual voltage of outlet, the zero-sequence current of outlet, calculate residual voltage amplitude in real time.
Step 2, think bus or outlet generation singlephase earth fault when residual voltage amplitude starts voltage more than route selection,Enter step 3.
Step 3, intercept when fault occurs before and after the zero-sequence current of each cycle and the data of residual voltage, and to transient stateResidual voltage and transient zero-sequence current data carry out wavelet package transforms.
In order to match with signal characteristic, the resolution of wavelet transformation on time-frequency plane, be not to immobilize but withFrequency change, i.e. frequency resolution reduces with the rising of frequency, and this adaptivity of wavelet transformation causes little justDuring wave conversion-new problem of frequency analysis, that is, so-called " high-frequency and low-resolution rate " problem.And developed by wavelet transformation andWavelet packet (wavelet packet) technology come, compensate for this deficiency, such that it is able to according to characteristics of signals and analysis requirementResolution is arbitrarily selected in certain frequency domain.
Quick and precisely select fault branch it is critical that utilize Wavelet Packet Technique collect exactly zero-sequence current, zeroThe jump signal that the transient state of sequence voltage is faint, analyzes its feature being clearly distinguishable from non-faulting branch road.Wavelet packet in the present inventionConvert used strict support orthogonal wavelet base DB10 small echo, namely DB small echo during L=10, i.e. 10 rank DB small echos.
Step 4, compare transient zero-sequence current and the phase place of transient zero-sequence voltage after wavelet package transforms, if phase place is identical, beNon-fault line, if opposite in phase, is faulty line, thus completes earthing wire-selecting.
Wherein, small current neutral grounding system is 3kV-66kV small current neutral grounding system, can be applicable to isolated neutral and warpIn the system of grounding through arc.As a example by Fig. 2, using a line-selected earthing device to realize route selection function, line selection apparatus passes throughCable completes the collection of bus residual voltage, the collection of each feeder line branch road zero-sequence current, and then completes earthing wire-selecting.With Fig. 3 it isExample, use by route selection function embed feeder protection equipment method, protection device by cable complete to bus residual voltage withThe collection of feeder line zero-sequence current, completes earthing wire-selecting.
The invention has the beneficial effects as follows:
(1) transient zero-sequence voltage and transient zero-sequence current only with this circuit judge whether earth fault, it is not necessary toThe zero-sequence current data of All other routes, therefore this method may be used for centralized earth protective device, it is also possible to for separate roomEvery protection device in.
(2) earth fault transient process and electric network composition, parameter, the method for operation are relevant.Transient current is much larger than stable state electricityCapacitance current, transient state maximum current value phase angle initial with false voltage is relevant, and transient current is not affected by arc suppression coil, and arc light connectsGround and intermittent ground connection transient state component are more rich, solve to utilize the inaccurate problem of steady-state current route selection.
These are only the preferred embodiments of the present invention, not thereby limit the scope of the claims of the present invention, every utilize thisEquivalent structure or equivalence flow process that bright description and accompanying drawing content are made convert, or it is relevant to be directly or indirectly used in otherTechnical field, be the most in like manner included in the scope of patent protection of the present invention.