CN100367597C

CN100367597C - Maximum differential flow brake device for preventing multiple-branch voltage transformer differential protection unwanted operation

Info

Publication number: CN100367597C
Application number: CNB2004100162873A
Authority: CN
Inventors: 徐习东
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2004-02-13
Filing date: 2004-02-13
Publication date: 2008-02-06
Anticipated expiration: 2024-02-13
Also published as: CN1558493A

Abstract

The present invention relates to a phase-splitting zero-sequence brake method for preventing the unwanted operation of differential protection for multiple-branch transformers; a ratio is composed of a maximum value of a three-phase electric current in the differential protection for transformers and a maximum value of a zero-sequence electric current at each neutral point grounding side (or branch) of a transformer. When a ratio value is smaller than a definite value K, a comparator 4 outputs 0; an external grounding fault is judged, and a three-phase differential protection outlet is locked. The proposal has the advantages that the present invention can thoroughly avoid the unwanted operation of differential protection for transformers caused by the external grounding fault at the neutral point grounding side when the errors of a three-phase electric current transformer are not consistent, and has no influence on the correct action of differential protection for internal faults.

Description

Prevent the maximum difference stream brake apparatus of multiple-limb transformer differential protection malfunction

Technical field

The present invention relates to a kind of protection equipment for transformer, particularly a kind of maximum difference stream brake apparatus that prevents the malfunction of multiple-limb transformer differential protection.

Background technology

Existing power transformer differential protection device by the ratio brake element, promptly by the ratio of differential current and through current, is discerned external area error and troubles inside the sample space; By shoving and the overexcitation braking member, promptly, discern magnetizing inrush current and overexcitation electric current simultaneously, reach the purpose of differentiating internal fault by analyzing the waveform or the harmonic content of differential current.To both sides being arranged or being the power transformer of neutral-point solid ground more than the both sides, when a ground connection side generating region external ground fault, may big earth fault zero-sequence current appear many sides.For preventing that this zero-sequence current from causing differential protection malfunction, extensively adopt the method that ground connection side three-phase current is carried out conversion at present, eliminate the influence of zero-sequence current.But it is inconsistent to work as ground connection side threephase current transformer error; and transformer is only when the neutral ground side that external area error takes place has power supply; can not eliminate the influence of the zero-sequence current that external ground fault in neutral ground lateral areas causes by conventional method; bigger differential unsymmetrical current will be had; the ratio brake element; the braking member that shoves can not reliably be braked this; especially very little even be under zero the situation at the transformer load electric current; the ratio brake element; the braking member that shoves can not be braked this; as long as error current surpasses threshold, transformer differential protection is with malfunction.

Summary of the invention

The purpose of this invention is to provide a kind of maximum difference stream brake apparatus that prevents the malfunction of multiple-limb transformer differential protection; by the maximum component ratio braking member in the zero-sequence current of the maximum in the three-phase differential current in the usefulness transformer differential protection and each neutral ground side (or branch) of transformer; when rate value during less than setting value K; be judged to district's external ground fault, the outlet of locking rate of three phase flow differential protection.Advantage of the present invention is, in the time of can avoiding the threephase current transformer error inconsistent fully, and the transformer differential protection malfunction that external ground fault in neutral ground lateral areas causes.

A kind of maximum difference stream brake apparatus that prevents the malfunction of multiple-limb transformer differential protection, this device circuit structure is characterized in that as shown in Figure 1: this device by first group of filter 01,02 ... 0n, second group of filter 11～13, the first maximizing circuit 21, the second maximizing circuit 22, multiplier 3, comparator 4 constitute; Wherein first group of filter 01,02 ... input difference each the neutral ground side of input transformer of 0n or the zero-sequence current instantaneous value signal 3i of ground connection branch ₁₀, 3i ₂₀... 3i _N0Its output is connected with the input of the second maximizing circuit 22 respectively; An input of the output termination multiplier 3 of the second maximizing circuit 22; Another input input setting value K of multiplier 3, the negative input end of its output termination comparator 4; The input of second group of filter 11～13 is imported the three-phase differential current instantaneous value signal i that obtains respectively from transformer differential protection _Da, i _Db, i _Dc, its output connects the input of the first maximizing circuit 21 respectively; The positive input terminal of the output of the first maximizing circuit 21 and comparator 4 joins; Comparator 4 output three-phase brake signals.Arrive under the same side, the same no-load voltage ratio situation in differential current and zero-sequence current reduction, the K value is 0＜K＜1/3, and n is transformer neutral point ground connection side number or ground connection branches.When comparator 4 positive input terminal signals less than the negative input end signal, comparator output 0 is judged to district's external ground fault, the outlet of locking biased differential protection; Otherwise comparator output 1 allows the differential protection action.

With prior art relatively; advantage of the present invention is to have proposed first to add in traditional multiple-limb transformer differential protection to pass through with the maximum component ratio braking member in the zero-sequence current of the maximum in the three-phase differential current in the transformer differential protection and each neutral ground side (or branch) of transformer; when rate value during less than setting value K; be judged to district's external ground fault, the outlet of locking rate of three phase flow differential protection.Use this programme; in the time of can avoiding the threephase current transformer error inconsistent fully; the transformer differential protection malfunction that external ground fault in neutral ground lateral areas causes; also can prevent under other non-internal fault situation; the transformer differential protection misoperation that the differential unsymmetrical current that zero-sequence current causes causes, and the correct operation of differential protection under the zone of influence internal fault situation not.

Description of drawings

Fig. 1 is the circuit block diagram that prevents the maximum difference stream brake apparatus of multiple-limb transformer differential protection malfunction.

Embodiment

Embodiment 1

A kind of maximum difference stream brake apparatus that prevents the malfunction of multiple-limb transformer differential protection, its circuit structure as shown in Figure 1, transformer neutral point ground connection side is counted n=3.When comparator 4 positive input terminal signals less than the negative input end signal, comparator 4 output 0 is judged to district's external ground fault, the differential outlet of locking rate of three phase flow; Otherwise comparator 4 outputs 1 allow the action of three-phase differential protection.Arrive under the same side, the same no-load voltage ratio situation in differential current and zero-sequence current reduction, K gets 0.1.The advantage of using this programme is, in the time of can avoiding the threephase current transformer error inconsistent fully, and the transformer differential protection malfunction that external ground fault in neutral ground lateral areas causes.

Claims

1. maximum difference stream brake apparatus that prevents the malfunction of multiple-limb transformer differential protection; it is characterized in that: this device by first group of filter (01,02 ... 0n), second group of filter (11～13), the first maximizing circuit (21), the second maximizing circuit (22), multiplier (3), comparator (4) constitute, wherein first group of filter (01,02 ... input difference each the neutral ground side of input transformer 0n) or the zero-sequence current instantaneous value signal (3i of ground connection branch ₁₀, 3i ₂₀3i _N0), its output is connected with the input of the second maximizing circuit (22) respectively, an input of the output termination multiplier (3) of the second maximizing circuit (22); Another input input setting value K of multiplier (3), the negative input end of its output termination comparator (4); The input of second group of filter (11～13) is imported the three-phase differential current instantaneous value signal (i that obtains respectively from transformer differential protection _Da, i _Db, i _Dc), its output connects the input of the first maximizing circuit (21) respectively, the positive input terminal of the output of the first maximizing circuit (21) and comparator (4) joins, comparator (4) output three-phase brake signal, and n is transformer neutral point ground connection side number or ground connection branches; When comparator (4) positive input terminal signal less than the negative input end signal, comparator output 0 is judged to district's external ground fault, the outlet of locking biased differential protection; Otherwise comparator output 1 allows the differential protection action.

2. brake apparatus according to claim 1 is characterized in that: under the same side, same no-load voltage ratio situation, setting value K is 0＜K＜1/3 in differential current and zero-sequence current reduction.