CN1182297A - Relay protection method and device to recognize symmetry of transformer exciting surge - Google Patents

Abstract

The said device includes voltage-to-frequency convertor (VFC), sampling and differential circuit, delay circuit absolute value circuit, comparator circuit for symmetry recognition, etc. The output of reactive mutual inductor is connected to VFC, and processed in the serial sampling and differential circuit, delay circuit absolute value circuit, comparator circuit through multiple-point sampling, current conversion, etc. The said device can perform reliable symmetry recognition of exciting surge.

Description

The relay protecting method and the device thereof of the identification of transformer excitation flow symmetry

The present invention relates to relay protecting method and device, refer more particularly to relay protecting method and protective device thereof the identification of transformer excitation flow symmetry to electrical network.

In the existing microcomputer transformer differential relaying protection that puts into operation, promptly be identified as the method and the protective device thereof of criterion: comprise utilization interval angle method and second harmonic method with magnetizing inrush current.The protective device more complicated of utilization interval angle principle realizes difficulty.There is defective in the second harmonic method on principle, three-phase transformer is when magnetizing inrush current, the second harmonic content that may have a certain phase is less, for addressing this problem, all adopt or the door mode of braking, be have in the three-phase current one mutually braking then three-phase is all braked but this deferred action when causing some fault again.For example, single-phase internal fault takes place in the time of inrush current of transformer, differential protection is failure to actuate because of the braking of shoving that perfects phase, and the time constant of high-power transformer is all very big, and main protection waits until that shoving disappearance could export, and it is oversize to delay time.WBZ-1201 type waveform symmetry type magnetizing inrush current transformer relay protecting device also is a kind of utility unit; it is handled with differential pair difference stream waveform; its sampling instrument transformer is a current transformer; adopt instantaneous value to differentiate symmetry; then move above threshold value if satisfy counting of symmetric condition, on the contrary then locking, the symmetrical degree difference of neighbouring sample point; even differ greatly, can not the reliable recognition symmetry.Therefore the reliability and the completeness of protective device are not enough.Referring to " Automation of Electric Systems " fourth phase in 1996.

The objective of the invention is: provide a kind of and can guarantee the circuit of symmetry identification, be failure to actuate when guaranteeing magnetizing inrush current the relay protecting method and the protective device thereof of transformer excitation flow symmetry identification, and protective relaying device that can action message during internal fault.

The object of the present invention is achieved like this: adopt reactance transformer, and electric current is carried out frequency inverted, the half cycle integrated value (S+, S-) of difference between current stream is carried out cylindricizing differentiate, output relaying protection actuating signal.

Apparatus of the present invention comprise instrument transformer, voltage to frequency converter (VFC), sampling and difference current circuit, delay circuit, absolute value circuit and the compositions such as comparator that carry out symmetry identification, reactance transformer output is connected to voltage to frequency converter, and sampling and difference current circuit, delay circuit, absolute value circuit and comparator through connecting, it is characterized in that described instrument transformer adopts reactance transformer, and electric current changed, at the comparator input terminal series connection integrating circuit of symmetry identification.

The multi-point sampling circuit that instrument transformer of the present invention is reactance transformer, to be sampling and difference current circuit order for phase 20-30 weekly carries out the circuit of integration at the homophase of the output of absolute value circuit, comparator and the inverting input a pair of a plurality of neighbouring sample point of all connecting.

Working mechanism of the present invention is as follows:

1. adopt the aperiodic component of each road electric current of reactance transformer filtering, eliminate because that aperiodic component causes is asymmetric.

2. the criterion of symmetry identification: S-＞KS+ K be symmetry coefficient wherein $S-=\underset{m=0}{\overset{N/2-1}{\mathrm{\Σ}}}|i(n-m)-i(n-m-N/2)|$ $S+=\underset{m=0}{\overset{N/2-1}{\mathrm{\Σ}}}|i(n-m)+i(n-m-N/2)|$

(N is phase sampling number weekly, i (n) is current current sampling data) as above the foundation of criterion be the time with idle-loaded switching-on, internal fault, external fault, various theory analysises and result of the test all show, idle-loaded switching-on, during external fault, A, B, C three-phase do not satisfy above-mentioned criterion, (K got 8 o'clock), and internal fault, fault satisfies above-mentioned criterion mutually soon, and the action outlet.

Because S-S+ is the half cycle integrated value, its value is steadily judged clear and definite; Through the simulation analysis to magnetizing inrush current, the K value is got and can be guaranteed also not malfunction under the harshest situation of shoving at 8 o'clock, and the actual situation of shoving is far better.Also can be provided with assistant criteria in addition, for preventing when S-, the erroneous judgement of above-mentioned criterion when S+ is very little.Actual motion also shows: idle-loaded switching-on, during external fault, A, B, C three-phase do not satisfy

S-＞KS+ (K gets 8)

And during internal fault, fault satisfies S-＞KS+ soon mutually and makes the Trip Logic action

Adopt multi-point sampling and difference current circuit; calculate the symmetrical degree of power network current by integrating circuit; utilize the principle that difference stream is asymmetric substantially, internal fault time difference stream is symmetrical substantially of magnetizing inrush current; can guarantee symmetry identification, not malfunction when guaranteeing to shove, and protective relaying device when internal fault is arranged moves immediately.

Characteristics of the present invention are: overcome differential protection and be failure to actuate because of the braking of shoving that perfects phase; the time constant of high-power transformer is all very big; main protection waits until that shoving disappearance could export; the oversize shortcoming of delaying time; also overcome the employing instantaneous value and differentiated symmetry, then moved above threshold value if satisfy counting of symmetric condition, on the contrary then locking; the symmetrical degree difference of neighbouring sample point, even differ greatly.So the deficiency that can not move reliably.The protective relaying device of magnetizing inrush current symmetry identification a kind of symmetry identification that is used to guarantee and the energy action message is provided.

The invention will be further described below in conjunction with accompanying drawing with by embodiment:

Fig. 1 is a circuit diagram of the present invention

Fig. 2 amplifies and freq converting circuit figure for the utility model

Fig. 3 is the electrical block diagram of reactance transformer

Fig. 4 is the circuit diagram that the main element of the utility model circuit diagram constitutes

The flow chart that Fig. 5 adopts microprocessor to compare for the present invention

As shown in the figure, the flow chart that Fig. 5 adopts microprocessor to compare for the present invention carries out according to step in the block diagram the calculating of amount of sampling gained, the writing among the memory ROM shown in Figure 4 or write in the subsidiary memory of CPU of control microprocessor program.Seldom state herein.The flow chart that the present invention adopts microprocessor to compare is concentrated the characteristics that the inventive method has been described.

In the given circuit of Fig. 1; similar with WBZ-1201 type waveform symmetry type magnetizing inrush current transformer relay protecting device; voltage to frequency converter VFC is the NVFC-6 type; only instrument transformer is reactance transformer AC, and LFP971C, the employed built-up circuit of LFP972C type magnetizing inrush current transformer relay protecting device produced with the auspicious relaying protection in south parent company are identical.Sampling and difference current circuit are seen the explanation of Fig. 2 among the figure, time-delay T/2 is the half period delay circuit, ABS (*) is an absolute value circuit, integrator is conventional logical circuit or by microprocessor it is added up, K is the amplitude adjusted factor, comparator can adopt conventional logical circuit hardware, can also realize by microprocessor.Its output is amplified the driving Trip Logic by three-phase respectively, Fig. 2 amplify for the utility model and freq converting circuit figure also identical with custom circuit, MCl741 is an amplifier, plays corrective action, and AD651 realizes the electric voltage frequency conversion, 8254 is counter, frequency signal is converted to digital signal, and in this figure, S10-S12 uses for thumbwheel switch ` does zeroing, IA2 is for being converted into the electric current of voltage signal, and F4 is a frequency signal.Sampling and difference current circuit are weekly the multi-point sampling circuit CPU that phase 20-30 is ordered, and carry out the circuit of integration at the homophase of the output of absolute value circuit, comparator and the inverting input a pair of a plurality of neighbouring sample point of all connecting.Adopt multi-point sampling and difference current circuit, the amount of statistical average neighbouring sample point, guarantee that its symmetrical degree is identical, alternating current is behind reactance transformer, become the correspondent voltage signal,, pass through rolling counters forward again by amplifier and electric voltage frequency conversion, promptly can be exchanged into the digital signal that is suitable for Computer Processing, symmetrical identification can realize by software.In the electrical block diagram of Fig. 3 reactance transformer, i1 is the electric current of desire sampling, through instrument transformer L secondarily the utmost point produced the voltage u that is directly proportional with the primary current variable quantity, this voltage is changed through voltage to frequency converter again.W`C is adjustable resistance and electric capacity.The current i of electrical network obtains voltage u through reactance transformer in Fig. 4, obtain frequency signal f behind the process A/D change-over circuit AD651 again after the amplifier that constitutes through MCl741 amplifies then, thereafter pass through counter 8254 input microprocessor CPU, memory can be ROM and RAM.

Claims (3)

1. transformer excitation flow symmetry identification protecting method; it is characterized in that the instrument transformer of electrical network sampling is adopted reactance transformer; and electric current carried out frequency inverted, and the half cycle integrated value (S+, S-) of difference between current stream is carried out cylindricizing differentiate, output relaying protection actuating signal.

2. transformer excitation flow symmetry identification protecting device; comprise instrument transformer, voltage to frequency converter (VFC), sampling and difference current circuit, delay circuit, absolute value circuit and the compositions such as comparator that carry out symmetry identification; reactance transformer output is connected to voltage to frequency converter; and sampling and difference current circuit, delay circuit, absolute value circuit and comparator through connecting; it is characterized in that described instrument transformer adopts reactance transformer; and electric current changed, at the comparator input terminal series connection integrating circuit of symmetry identification.

3. by the described transformer excitation flow symmetry of claim 1 identification protecting device; it is characterized in that sampling and multi-point sampling circuit that the difference current circuit is ordered for phase 20-30 weekly, carry out the circuit of integration at the homophase of the output of absolute value circuit, comparator and the inverting input a pair of a plurality of neighbouring sample point of all connecting.

Images