CN1584614A - Single-phase grounding selection for small-current system - Google Patents

Abstract

A method for selecting out single phase earthing in small current system includes injecting a current signal with specific frequency intermittently to three phase circuit; carrying out voltage preprocessing, synchronous sampling and digital filtering to detect the current signal comparing resistive current size of the current signal in each subcircuit and confirming that subcircuit with the largerst resistive current is earthing subcircuit.

Description

Small current system single-phase grounding selecting method

(1) technical field

The present invention relates to a kind of small current system single-phase grounding selecting method, be applicable to the single-phase grounding selecting and the location of power system transformer substation 6KV, 10KV, 35KV system.

(2) background technology

At present, small current system single-phase grounding selecting method can be divided into first-harmonic method, harmonic wave method, transient signal method and injection method etc. technically.First-harmonic method and harmonic wave method all are to utilize ground connection branch road zero-sequence current to equal the characteristics of other all branch road zero-sequence current sums, carry out route selection by comparing amplitude and phase place size, but the first-harmonic method only are suitable for isolated neutral system.The transient signal method is that the transient signal when catching ground connection carries out route selection." S injection method " is representative injection signal selection method, this method is to inject a set specific frequency signal from line voltage distribution mutual inductor (PT) secondary side mutually to ground connection, receive the signal of this frequency in each branch road outlet by receiver, carry out route selection according to the amplitude of this signal and preset threshold comparative result in advance.By the practical application of above-mentioned each method, advantage is separately all arranged, but all exist the not high shortcoming of route selection accuracy rate.

(3) summary of the invention

The present invention is directed to the deficiencies in the prior art, provide a kind of accuracy rate high small current system single-phase grounding selecting method.

The solution that the present invention adopts is: when small current system generation single-phase earthing, inject a characteristic frequency current signal from line voltage distribution mutual inductor PT zero sequence winding batch (-type) ground, this signal is injected into three-phase line by line voltage distribution mutual inductor PT primary side, detection to this characteristic frequency current signal is the threephase current transformer CT of elder generation to each branch road, one of zero sequence CT and special signal transmitter and zero sequence winding voltage are carried out pre-service, carry out synchronized sampling by the high speed A device then, by digital signal processor DSP data are carried out digital filtering and processing, current in resistance property size by each branch road particular current signal relatively is as the route selection criterion, the corresponding ground connection branch road of current in resistance property the maximum.

Frequency and the mains frequency of the particular current signal of injecting are synchronous, and are and the lowest common multiple of fundamental frequency is harmonic current between minimum.Can improve the precision of digital filtering so greatly.

The frequency of the particular current signal of injecting is away from fundamental frequency.Here get this signal frequency greater than third harmonic frequencies.Can eliminate system's arc suppression coil like this to injecting the absorption of marking current.

The particular current signal of injecting adopts the batch (-type) method for implanting, and the image data after will injecting by data processing links to each other synchronously with preflood image data, then the difference of the two is carried out digital filtering.Doing like this can be before carrying out digital filtering, just can be with most of power frequency and harmonic component filtering thereof.

The present invention passes through the size of each branch road particular current signal of comparison as the route selection criterion, but compares its current in resistance property size as the route selection criterion.Can eliminate the influence of each branch road capacity current like this, improve the route selection accuracy.This method does not need to judge the ground connection phase, and signal intensity is only to inject three times of signal intensity mutually to ground connection.Implement simply, reliably accuracy of detection and accuracy height.

(4) description of drawings

Fig. 1 is a principle of work synoptic diagram of the present invention.

Fig. 2 is a principle of work equivalent circuit diagram of the present invention.

Fig. 3 is a route selection criterion schematic diagram of the present invention.

Fig. 4 is a principle of work block diagram of the present invention.

Wherein: 1, signal generator, 2, particular current signal, 3, single-pole single-throw switch (SPST), 4, line voltage distribution mutual inductor PT, 5, the PT primary side, 6, PT zero sequence winding, 7A, flow through the current signal I that PT primary side A injects mutually _SA, 7B, flow through the current signal I that PT primary side B injects mutually _SB, 7C, flow through the current signal I that PT primary side C injects mutually _SC, 8, ground connection, 9, be injected into the current signal I of PT zero sequence winding _S2, 10, inject the particular current signal summation I of circuit from the PT primary side _S11A, circuit bus A phase, 11B, circuit bus B phase, 11C, circuit bus C phase, 12, main-transformer, 13A, 1# branch road A phase, 13B, 1# branch road B phase, 13C, 1# branch road C phase, 14A, 2# branch road A phase, 14B2# branch road B phase, 14C, 2# branch road C phase, 15A, 3# branch road A phase, 15B, 3# branch road B phase, 15C, 3# branch road C phase, 16, arc suppression coil, 17, zero sequence winding voltage or residual voltage pretreatment unit, 18, particular current signal is converted the equivalent current source of primary side, 19, stake resistance Rg, 20,1# branch road equivalence three-phase ground capacitance sum Cel, 21,2# branch road equivalence three-phase ground capacitance sum Ce2,22,3# branch road equivalence three-phase ground capacitance sum Ce3,23, to the zero sequence current signal I1 ' pretreatment unit of 1# branch road, 24, to the zero sequence current signal I2 ' pretreatment unit of 2# branch road, 25, zero sequence current signal I3 ' pretreatment unit to the 3# branch road, 26, multi-way switch circuit, 27, high speed A device A/D, 28, digital signal processor DSP or single chip circuit, 29, show and keyboard circuit, 30, warning circuit, 31, the teletransmission communicating circuit, 32, the mains frequency lock unit, I ₁, be injected into the particular current signal value of 1# branch road, I ₂, be injected into the particular current signal value of 2# branch road, I ₃, be injected into the particular current signal value of 3# branch road, I _Rg1, the earth point G that flows through the current in resistance property of particular current signal, I _C1, the earth point G that flows through the capacity current of particular current signal, U ₀, the line zero sequence voltage that produces of the particular current signal injected, ₁, the signal specific injected is at the zero-sequence current of each branch road and the phase angle of residual voltage.

(5) embodiment

In principle of work synoptic diagram shown in Figure 1, line voltage distribution mutual inductor PT 4 zero sequence winding voltages by zero sequence winding voltage or 17 pre-service of residual voltage pretreatment unit after, after A/D converter 27 conversion, deliver to DSP or single-chip microcomputer 28 has judged whether ground connection generation.When ground connection is taken place, DSP or single-chip microcomputer 28 are given an order and are started particular current signal generator 2 and Closing Switch 3, particular current signal is injected into PT along L point, PT zero sequence winding and N point, forms identical electric current 7A, 7B and the 7C of size and Orientation at PT primary side 5, and its size is respectively I _SA, I _SBAnd I _SC, this electric current through bus A phase 11A, B phase 11B and C mutually 11C be injected into each branch road, and flow back to the earth by the form of earth point G or leakage current, form loops with the ground connection 8 of PT primary side.For non-ground connection branch road, leakage current mainly is a capacity current.

The zero sequence current signal I1 ' that records by the three-phase CT of each branch road or zero sequence CT or special signal transmitter, I2 ' and I3 ' include the particular current signal of first-harmonic and higher hamonic wave and injection, this signal is through Signal Pretreatment unit 23,24 and 25 handle after multi-way switch 26 carries out high-speed transitions to A/D converter 27, deliver to DSP or single-chip microcomputer 28 then and carry out the digital filtering processing (referring to Fig. 4, can be by showing and keyboard circuit 29 demonstration result of calculations, and report to the police by warning circuit 30, simultaneously data can be uploaded to host computer by communicating circuit 31), therefrom leach the particular current signal I that obtains injecting after first-harmonic and the higher hamonic wave ₁, I ₂And I ₃Simultaneously the zero sequence winding voltage is also carried out digital filtering and handle, obtain the residual voltage U0 under the particular current signal effect, and obtain and electric current I ₁, I ₂And I ₃Phase angle ₁, ₂And ₃

If PT primary side and zero sequence winding no-load voltage ratio are M: 1, have

I _SA＝I _SB＝I _SC＝I _S/3 (1)

I _S＝3I _S2/M (2)

After this particular current signal was injected into circuit, its equivalent electrical circuit as shown in Figure 2.Because this signal frequency is away from harmonic wave between fundamental frequency, so do not consider first-harmonic and harmonic effects, the influence of arc suppression coil simultaneously also can be ignored.According to the phasor graph of Fig. 3, current in resistance property I is arranged _Rg1For

I _Rg1＝I ₁*COS ₁ (3)

In like manner, to 2# and 3# branch road, residual voltage U ₀With I ₂And I ₃Phase angle ₂And ₃, be ₂= ₃=pi/2 has

I _Rg2＝I ₂*COS ₂＝0 (4)

I _Rg3＝I ₃*COS ₃＝0

I in the formula _Rg2And I _Rg3Therefore represent the current in resistance property of the signal specific of 2# and 3# branch road respectively, the criterion that can obtain earthing wire-selecting according to formula (3) and formula (4) is:

$I_{\mathrm{Rg}\max }=\underset{i=1}{\overset{n}{\max }}(I_{\mathrm{Rg}1},I_{\mathrm{<figure-callout\; id="2"\; label="Rg"\; filenames="A20041002423800061.png"\; state="\{\{state\}\}">Rg</figure-callout>}2},I_{\mathrm{Rg}3},...,I_{\mathrm{Rgi}},...,I_{\mathrm{Rgn}})=I_{\mathrm{Rgk}}..\left(5\right)$

That is, in all branch roads, the branch road of current in resistance property the maximum correspondence of signal specific is the ground connection branch road.Following formula is represented, K# branch road specific signal corresponding current in resistance property maximum is so can think that this branch road is the ground connection branch road.

Above-mentioned criterion has been eliminated the influence of branch road direct earth capacitance, has therefore improved the route selection accuracy greatly.

Claims (3)

1. small current system single-phase grounding selecting method, it is characterized in that: when small current system generation single-phase earthing, inject a characteristic frequency current signal from line voltage distribution mutual inductor PT zero sequence winding batch (-type) ground, this signal is injected into three-phase line by line voltage distribution mutual inductor PT primary side, detection to this characteristic frequency current signal is the threephase current transformer CT of elder generation to each branch road, one of zero sequence CT and special signal transmitter and zero sequence winding voltage are carried out pre-service, carry out synchronized sampling by the high speed A device then, by digital signal processor DSP data are carried out digital filtering and processing, current in resistance property size by each branch road particular current signal relatively is as the route selection criterion, the corresponding ground connection branch road of current in resistance property the maximum.

2. small current system single-phase grounding selecting method according to claim 1 is characterized in that: described characteristic frequency current signal and the mains frequency that injects to three-phase line is synchronous, and is and the lowest common multiple of fundamental frequency is harmonic current between minimum.

3. small current system single-phase grounding selecting method according to claim 1 and 2 is characterized in that: the frequency of the described characteristic frequency current signal that injects to three-phase line is away from fundamental frequency, and this signal frequency is greater than third harmonic frequencies.

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