CN105071356A - Method for preventing sampling channel AD over-limit differential misoperation - Google Patents

Abstract

The invention discloses a method for preventing a sampling channel AD over-limit differential misoperation. Through real-time rolling, an integral braking coefficient of a sampling point differential flow in a fixed time before each sampling time after the differential flow is started. Once a fact that a differential flow integration braking coefficient is smaller than a threshold value is detected, differential protection is stopped. When the differential flow integration braking coefficient in a continuous cycle is larger than a threshold value, differential protection is started again; and once a fact that the differential flow integration braking coefficient is smaller than the threshold value, differential protection is stopped, thereby effectively preventing the differential protection misoperation caused by sampling channel AD sampling over-limit wave chopping. The method of the invention is particularly suitable for protecting an intelligent transformer station and has advantages of simple principle, high practicability and relatively high applicability. When the differential flow integration braking coefficient in the continuous cycle is larger than a threshold value, differential protection is started again. After a differential flow rolling integration braking method is used, reliability of differential protection is improved.

Description

A kind of method preventing the out-of-limit differential malfunction of sampling channel AD

Technical field

The present invention relates to the new method being applied to electric system protection device; be specifically related to a kind of method preventing the out-of-limit differential malfunction of sampling channel AD; when preventing big current fault outside district by the method for sampled point difference stream integration restraint coefficient in fixing short-data windows, sampling channel AD cuts the differential malfunction that waveguide causes, and can be applicable to various differential protection simultaneously.

Background technology

Along with the increase of electric power system capacity; short-circuit current is increasing; the CT rated current of maximum 100 times can be born according to IEC60255-27 measuring relay and the protection of protective device standard-required; the current range (20 ~ 40 times) that can detect beyond current protective device far away; cause protective device AD sampling channel scope to transfinite causing waveform to cut ripple and cut top; protective device can not correct faults electric current, the visibly moved easy malfunction of the external area error time difference.Cut waveguide for analog channel AD sampling and cause the method and criterion that differential malfunction carries out processing at present specially.

Summary of the invention

In order to solve prior art problem; the invention provides a kind of method preventing the out-of-limit differential malfunction of sampling channel AD; during by being prevented big current fault outside district by the method for sampled point difference stream integration restraint coefficient in fixing short-data windows, sampling channel AD cuts the differential malfunction that waveguide causes, and can be applicable to various differential protection simultaneously.

For reaching above object, the present invention realizes by the following technical solutions.

The technical solution used in the present invention is:

Prevent a method for the out-of-limit differential malfunction of sampling channel AD, comprise the following steps:

(1), difference stream starts in rear first cycle and carries out restraint coefficient calculating based on sampled point Sudden Changing Rate difference stream anomalous integral sampled point Sudden Changing Rate stalling current integration;

Sampled point Sudden Changing Rate difference stream integration I _dfor:

Sampled point Sudden Changing Rate stalling current integration I _rfor:

Restraint coefficient is: K=I _d/ I _r;

Wherein, △ i _d(n-k) for front pushing away M Sudden Changing Rate sampled point difference flow data, △ i _r(n-k) for front pushing away M Sudden Changing Rate sampled point stalling current data;

Described difference stream integration restraint coefficient meets formula K<K _set, be judged to the AD sampling that external area error causes out-of-limit, Blocking Differential Protection, wherein K _setfor difference stream integration restraint coefficient threshold value;

During external area error, due in non-ad out-of-limit section of ripple region, protection correctly can reflect each side current data, and difference stream is less, and stalling current is large, and the difference stream integration restraint coefficient calculated is less, reliable locking; During troubles inside the sample space, due to the basic homophase of each side electric current, there is not restraint coefficient comparatively zonule, can correctly opening.

(2), after difference stream startup one cycle, sample based on fixed data window, data window width is constant, uses sampled point difference stream anomalous integral sampled point stalling current integration to carry out restraint coefficient calculating, pushes away fixed data window and calculate before each sampling instant.

The difference stream integration restraint coefficient calculated when any instant meets formula K<K _settime, be judged to external area error, Blocking Differential Protection; If K value is greater than threshold value in a continuous cycle, then reopen differential protection;

(3), the front fixed data window that pushes away calculates, and move at 1 after a point data window of often sampling and carry out restraint coefficient calculating, circulating rolling calculates.

The method of the out-of-limit differential malfunction of sampling channel AD is prevented by the present invention; once detect that difference stream integration restraint coefficient is lower than threshold value; Blocking Differential Protection, moves when integration restraint coefficient is greater than threshold when the poor flow roll in a continuous cycle 20ms and reopens differential protection.Ensure that the reliability of differential protection, real-time and rapidity.

More preferably, K _setspan be [0.15,0.2].

More preferably, cycle is 20ms.

Compared with prior art; beneficial effect of the present invention comprises: when detecting that sampled point difference stream integration restraint coefficient is lower than Blocking Differential Protection during threshold value; effectively avoid the differential protection malfunction because sampling channel AD out-of-limit section of ripple causes, there is applicability more widely.When the poor flow roll in a continuous cycle move integration restraint coefficient be greater than threshold time, then reopen differential protection.After adopting difference flow roll to move integration deceleration method, improve the reliability of differential protection action.And the method is simple and practical, amount of calculation is few, is highly susceptible to Microcomputer Protection and realizes.

Accompanying drawing explanation

Fig. 1 is external area error phase current AD oscillogram when cutting ripple;

Fig. 2 is that external area error AD cuts ripple time difference stream oscillogram;

Fig. 3 is that external area error AD cuts ripple time difference stream integration restraint coefficient.

Embodiment

Below in conjunction with accompanying drawing, the present invention is further described.

Prevent a method for the out-of-limit differential malfunction of sampling channel AD, comprise the following steps:

(1), difference stream starts in rear first cycle 20ms and carries out restraint coefficient calculating based on sampled point Sudden Changing Rate difference stream anomalous integral sampled point Sudden Changing Rate stalling current integration;

The analog input of protection carries out current sample with constant sample frequency, and in every cycle, sampling number is N.After protection starts, each sampling instant, chooses the data window that length is fixed as M and carries out differing from stream integration braking coefficient calculations.

Data window time span calculates according to the maximum sample range of AD and system maximum short circuit current, and be sampled as 40 times of rated current for maximum, the actual maximum short circuit current of system is 100 times, then external area error starts more than 40 times of rated current time difference streams.

Then poor stream Startup time is:

T＝arcsin(40/100)/360*20ms＝1.3ms。

Consider that fault current exists positive and negative half-wave, data window is 2*1.3ms=2.6ms.Consider error and reliability, tripping when preventing troubles inside the sample space from draining out electric current, in big current situation, restraint coefficient threshold is set to 0.15 ~ 0.2.

According to the proportional brake coefficient arranged, in time calculating protection reality and use, fixing data window length can be controlled in about 5ms, can ensure that the difference stream integration restraint coefficient calculated in the worst case is less than 0.15.

Such as every cycle 48 point sampling, corresponding M can be chosen for 12 points.

After differential startup in the first cycle 20ms, from the 1st point started, the Sudden Changing Rate sampled point difference stream before each sampling instant is to current time in fixed data window and Sudden Changing Rate sampled point stalling current calculate difference stream integration restraint coefficient.

Sampled point Sudden Changing Rate difference stream integration I _dfor:

Sampled point Sudden Changing Rate stalling current integration I _rfor:

Restraint coefficient is: K=I _d/ I _r;

Wherein, △ i _d(n-k) for front pushing away M Sudden Changing Rate sampled point difference flow data, △ i _r(n-k) for front pushing away M Sudden Changing Rate sampled point stalling current data;

Described difference stream integration restraint coefficient meets formula K<K _set, be judged to the AD sampling that external area error causes out-of-limit, Blocking Differential Protection, wherein K _setfor difference stream integration restraint coefficient threshold value, be set to 0.15 ~ 0.2;

During external area error, due in non-ad out-of-limit section of ripple region, protection correctly can reflect each side current data, and difference stream is less, and stalling current is large, and the difference stream integration restraint coefficient calculated is less, reliable locking; During troubles inside the sample space, due to the basic homophase of each side electric current, there is not restraint coefficient comparatively zonule, can correctly opening.

(2), after difference stream startup one cycle 20ms, sample based on fixed data window, data window width is constant, uses sampled point difference stream anomalous integral sampled point stalling current integration to carry out restraint coefficient calculating, pushes away fixed data window and calculate before each sampling instant;

Now,

Sampled point difference stream integration: $I_d=\underset{k=0}{\overset{M-1}{\&Sigma;}}\left|i_d(n-k)\right|;$

Sampled point stalling current integration:

Restraint coefficient: K=I _d/ I _r;

I _d(n-k) for front pushing away M sampled point difference flow data, i _r(n-k) for front pushing away M sampled point stalling current data.

The difference stream integration restraint coefficient calculated when any instant meets formula K<K _settime, be judged to external area error, Blocking Differential Protection; If K value is greater than threshold value in a continuous cycle, then reopen differential protection;

(3), the front fixed data window that pushes away calculates, and move at 1 after a point data window of often sampling and carry out restraint coefficient calculating, circulating rolling calculates.

Oscillogram when Fig. 1 is external area error phase current AD out-of-limit section of ripple; cause difference miscarriage in Fig. 2 raw; poor stream integration restraint coefficient (as shown in Figure 3) as calculated; there is obvious integration restraint coefficient smaller value; by differential deallock; effectively prevent differential protection malfunction, improve differential protection reliability.Cyclic integral deceleration method is moved in difference flow roll, and simple and practical, only have simple recursion algebraically to sue for peace during calculating, each sampling instant only need add current point, removes in data window the most front, and amount of calculation is few, is highly susceptible to Microcomputer Protection and realizes.

The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (3)

1. prevent a method for the out-of-limit differential malfunction of sampling channel AD, it is characterized in that, comprise the following steps:

(1), difference stream starts in rear first cycle based on the sudden change of sampled point Sudden Changing Rate difference stream anomalous integral sampled point

Wherein, △ i _d(n-k) for front pushing away M Sudden Changing Rate sampled point difference flow data, △ i _r(n-k) for front pushing away M Sudden Changing Rate sampled point stalling current data;

Described difference stream integration restraint coefficient meets formula K<K _set, be judged to the AD sampling that external area error causes out-of-limit, Blocking Differential Protection, wherein K _setfor difference stream integration restraint coefficient threshold value;

(2), after difference stream startup one cycle, sample based on fixed data window, data window width is constant, uses sampled point difference stream anomalous integral sampled point stalling current integration to carry out restraint coefficient calculating, pushes away fixed data window and calculate before each sampling instant;

The difference stream integration restraint coefficient calculated when any instant meets formula K<K _settime, be judged to external area error, Blocking Differential Protection; If K value is greater than threshold value in a continuous cycle, then reopen differential protection;

(3), the front fixed data window that pushes away calculates, and move at 1 after a point data window of often sampling and carry out restraint coefficient calculating, circulating rolling calculates.

2. the method preventing the out-of-limit differential malfunction of sampling channel AD according to claim 1, is characterized in that,

K _setspan be [0.15,0.2].

3. the method preventing the out-of-limit differential malfunction of sampling channel AD according to claim 1, is characterized in that,

Described cycle is 20ms.