CN2687916Y

CN2687916Y - Maximum different-current brake device for preventing transformer differential protection from being malfunction

Info

Publication number: CN2687916Y
Application number: CN 200420020111
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: 2005-03-23
Anticipated expiration: 2014-02-13

Abstract

The utility model relates to a maximum different-current braking device for preventing transformer differential protection. The device comprises a ratio braking element through using the maximum value of three-phase difference motion current in a transformer differential protection device and the zero sequence current of a Y < 0 > side. The outer area earthing fault of the Y < 0 > side is distinguished. When the ratio value of the difference motion current and the zero sequence current is smaller than a setting value K, a comparator exports 0. The situation is judged as an outer region earthing fault, and a three phase difference motion protecting outlet is closed. Otherwise, the comparator exports 1 and permits the three phase difference motion to do protection action. The advantages of the project are : the utility model can completely avoid the false action of the transformer difference motion protection device which the outer region earthing fault of the Y < 0 > side induces when the error of three-phase current transformers is inconsistent. The utility model doesn't influence the correct action of the difference motion protection device under the situation of the inner area fault.

Description

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

Technical field

The utility model relates to a kind of protection equipment for transformer, particularly a kind of maximum difference stream brake apparatus that prevents the transformer differential protection malfunction.

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 Y ₀The power transformer of/Δ wiring is for preventing Y ₀Lateral areas external ground fault zero-sequence current causes differential protection malfunction, extensively adopts Y at present ₀The side three-phase current carries out the method for conversion, eliminates the influence of zero-sequence current.But work as Y ₀Side threephase current transformer error is inconsistent, and transformer is only at the Y that external area error takes place ₀When side has power supply, can not eliminate Y by conventional method ₀The influence of the zero-sequence current that lateral areas external ground fault causes; bigger differential unsymmetrical current will be had; ratio brake element, the braking member that shoves can not reliably be braked this; especially very little even be under zero the situation at transformer opposite side load current; 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 utility model provides a kind of maximum difference stream brake apparatus that prevents the transformer differential protection malfunction, by maximum and the Y with the three-phase differential current in the transformer differential protection ₀The zero-sequence current component ratio braking member of side when the rate value of differential current maximum and zero-sequence current during less than setting value K, is judged to Y ₀Lateral areas external ground fault, the outlet of locking three-phase differential protection.The utility model has the advantages that, in the time of can avoiding the threephase current transformer error inconsistent fully, Y ₀The transformer differential protection malfunction that lateral areas external ground fault causes, and the correct operation of differential protection under the zone of influence internal fault situation not.

A kind of maximum difference stream brake apparatus that prevents the transformer differential protection malfunction; this device circuit structure as shown in Figure 1; it is characterized in that: this device is made of filter 11～14, maximizing circuit 2, multiplier 3, comparator 4, and the input of its median filter 11～13 is A, B, the C three-phase differential current instantaneous value signal i of the formation of input transformer differential protection respectively _Da, i _Db, i _Dc, the input input transformer Y of filter 14 ₀Side zero-sequence current instantaneous value signal 3i ₀An input of its output termination multiplier 3, another input input setting value K of multiplier 3, the negative input end of its output termination comparator 4, three inputs of maximizing circuit 2 connect the output of filter 11～13 respectively, the positive input terminal of its output termination comparator 4, the output output three-phase brake signal of comparator 4.When the positive input terminal signal of comparator 4 less than the negative input end signal, comparator 4 outputs 0 are judged to district's external ground fault, locking three-phase differential protection outlet, 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 the equal reduction of zero-sequence current, setting value K is 0＜K＜1/3; The characteristic of filter 11～14 should be consistent.

With prior art relatively, the utility model has the advantages that maximum and the Y that has proposed first in traditional transformer differential protection, to set up with the three-phase differential current in the transformer differential protection ₀The zero-sequence current component ratio braking member of side, when the rate value of differential current maximum and zero-sequence current during less than setting value K, comparator output 0; be judged to district's external ground fault; the outlet of locking three-phase differential protection, otherwise comparator output 1 then allow the action of three-phase differential protection.The advantage of using this programme is, in the time of can avoiding the threephase current transformer error inconsistent fully, and Y ₀The transformer differential protection malfunction that lateral areas external ground fault causes; also can prevent under other non-internal fault situations; 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 transformer differential protection malfunction.

Embodiment

Embodiment 1:

A kind of maximum difference stream brake apparatus that prevents the transformer differential protection malfunction; its circuit constitutes as shown in Figure 1; when the positive input terminal signal of comparator 4 less than the negative input end signal; comparator 4 outputs 0; be judged to district's external ground fault; the outlet of locking three-phase differential protection, 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 the equal reduction of zero-sequence current, setting value K gets 0.1.The advantage of this device is, in the time of can avoiding the threephase current transformer error inconsistent fully, and Y ₀The transformer differential protection malfunction that lateral areas external ground fault causes, and the correct operation of differential protection under the zone of influence internal fault situation not.

Claims

1. maximum difference stream brake apparatus that prevents the transformer differential protection malfunction; it is characterized in that: this device is made of filter (11～14), maximizing circuit (2), multiplier (3), comparator (4), and the input of its median filter (11～13) is (A, B, C) three-phase differential current instantaneous value signal (i of input transformer differential protection formation respectively _Da, i _Db, i _Dc), the input input transformer Y of filter (14) _oSide zero-sequence current instantaneous value signal (3i _o), an input of its output termination multiplier (3), another input input setting value K of multiplier (3), the negative input end of comparator (4) is connected with the output of multiplier (3), three inputs of maximizing circuit (2) connect the output of filter (11～13) respectively, the positive input terminal of its output termination comparator (4), the output output three-phase brake signal of comparator (4).

2. device 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 the equal reduction of zero-sequence current.

3. device according to claim 1 is characterized in that: the characteristic of filter (11～14) should be consistent.