JP3645065B2 - Change width relay - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a change width relay (change width detection relay) such as a digital type change width overcurrent relay that responds to the magnitude of a change width of an input current, among protective relays that protect a power system and various devices. .
[0002]
[Prior art]
As is well known, the digital protection relay protects the power system and various devices by taking in the analog amount of the power system and performing digital computation using data obtained by A / D conversion.
Among these digital type protective relays, the variable width overcurrent relay is known to be able to reliably detect a system fault even if the difference in magnitude between the load current and the fault current at the time of a system fault is very small. It is generally used as a fail safe for distance relays.
In general, in the digital type change width overcurrent relay, the calculation principle shown in Formula 1 is used. In Equation 1, k indicates the present time, K indicates a change width set value, and a indicates a constant time period equivalent value (number of cycles).
[0003]
[Expression 1]
Σ | I _k -I _(ka) | ＞ K
[0004]
As described above, in the change width overcurrent relay, the difference between the current input value and the input value before a certain time limit (generally, one cycle or two cycles before) is utilized by using the periodicity of the input fundamental wave. Thus, the current change width is calculated.
Here, FIG. 3 shows a configuration of a variable width overcurrent relay, in which 11 is an analog filter to which current is input, 12 is sample hold means, 13 is A / D conversion means, and 14 is A / D before a certain time limit. A memory 15 for storing the output of the D conversion means 13 and a change width detection calculation means 15 for calculating from the outputs of the A / D conversion means 13 and the memory 14 according to the equation (1).
[0005]
[Problems to be solved by the invention]
Now, it is generally known that the change width overcurrent relay is vulnerable to frequency fluctuations on the basis of the calculation principle as described above, and countermeasures have been conventionally taken by various filters and calculation methods.
However, for systems with flicker loads such as welding machines, various electric motor application equipment, electric furnaces, etc., there is usually no fundamental countermeasures as a single variable overcurrent relay, and flicker appears prominently. When used in a system, the current situation is that a normal overcurrent relay (HOC) is used, or operation setting and sequence processing are used.
In addition, when it is not clear that flicker loads exist in the system, or when the system configuration is changed and flicker loads exist, the countermeasures for these flicker loads are not taken. There is a risk of malfunction.
[0006]
That is, in Formula 1 described above, the constant time-equivalent value a is an x cycle of the fundamental wave (x = 1 or x = 2 is common). When the calculation result on the left side of 1 is 0 and the operation is not reached, and the magnitude of the fundamental wave changes, the relay operation is performed by detecting the change amount.
[0007]
Here, consider a case where a flicker load exists in the system. The flicker load is a load that generates a waveform in which the fundamental wave shows a beat of about 10 [Hz], which is generally perceived as flickering of a fluorescent lamp by human eyes, or is evaluated by so-called ΔV ₁₀ .
This beat waveform can be obtained in a pseudo manner by superimposing a component having a fundamental frequency ± 10 [Hz] on the fundamental wave.
[0008]
Therefore, when the waveform of the fundamental wave frequency ± 10 [Hz] is superimposed on the fundamental wave, as shown in FIG. 4, with respect to the fundamental wave (frequency is assumed to be n [Hz]), the same value is obtained at the present time k and one cycle before. However, in the waveform of n + 10 [Hz] or n-10 [Hz], the value of the current k is different from the value of one cycle before the fundamental wave.
For this reason, even if there is no change in the magnitude of the fundamental wave, the change in magnitude is detected by the component of n ± 10 [Hz] according to the calculation principle of Equation 1.
[0009]
FIG. 1 shows frequency characteristics when a = 1 in Equation 1. In FIG. 1, the horizontal axis represents frequency, and the vertical axis represents current change detection amount (times).
As is clear from FIG. 1, when the fundamental wave (for example, 50 [Hz]) is constantly applied, the change detection amount is 0 times, that is, the calculation result of the change width overcurrent relay is zero, whereas 50 + 10 [Hz] When the waveform is superimposed, the detected amount of change becomes 0.6 times, and this causes the change width overcurrent relay to continue operation (malfunction).
[0010]
Therefore, the present invention pays attention to the fact that the input waveform of the relay due to the flicker load existing in the system is a superimposed waveform of the distorted wave that makes the fundamental wave beat every 10 [Hz]. An object of the present invention is to provide a variable width relay that does not erroneously detect or malfunction with respect to a frequency ± 10 [Hz].
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that the amount of change over a certain time period of the electric quantity whose fundamental wave frequency is n (n = 10 × m, m is an integer) exceeds a set value. In the change width relay that performs the protection operation by detecting this, for example, the change width between the current value of the electric quantity such as current and the value of the electric quantity before m cycles of the fundamental wave is compared with the set value.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings . In this embodiment , consideration is given to a waveform of n ± 10 [Hz] constantly applied to the fundamental wave (frequency is assumed to be n [Hz]).
That is, as a basic idea, the constant time equivalent value a is set to a value that can ensure periodicity even at fundamental wave frequencies n [Hz] and n ± 10 [Hz] in the above-described formula 1. do it. That is, it is only necessary to calculate with a cycle of the least common multiple of n, n-10, n + 10 [Hz].
[0014]
In the case of a power system, the fundamental frequency n can generally be expressed as 10 × m [Hz] (m = 5 or 6).
1 / n [s] = 1/10 · m [s],
1 / (n-10) [s] = 1 / {10 · (m−1)} [s],
1 / (n + 10) [s] = 1 / {10 · (m + 1)} [s]
Is the least common multiple of 1/10 [s].
Therefore, if data having a period of 1/10 [s] is used as the constant time equivalent value a in Equation 1, it is possible to cope with n ± 10 [Hz].
[0015]
That is, for the input of the fundamental frequency n = 10 × m [Hz], the data before m cycles is (m−1) for the frequency of n−10 = 10 (m−1) [Hz]. This is the data before the cycle, and for the frequency of n + 10 = 10 (m + 1) [Hz], it is the data before (m + 1) cycle, and for each frequency component, the difference from the data before the integer multiple cycle is obtained. Therefore, even when the component of n ± 10 [Hz] is constantly superimposed, this is not erroneously detected as a change.
The period of 1/10 [s] is
(1/10) / (1 / n) = (1/10) / (1 / 10m) = m
Therefore, m = 5 in the system of the fundamental frequency n = 50 [Hz], m = 6 in the system of n = 60 [Hz], and the change width detection using the data before 5 cycles and 6 cycles before, respectively. The principle should be taken.
[0016]
The frequency characteristic of Equation 1 when using the constant time equivalent value a thus obtained is shown as a = m in FIG.
From FIG. 1, the present invention is not limited to the n ± 10 [Hz] component, but also effective for the n × p (integer) ± 10 [Hz] (integer multiple harmonic of the fundamental wave ± 10 [Hz]) component. Thus, it is possible to prevent erroneous detection of the change width with any component that causes the fundamental frequency n to vibrate in increments of 10 [Hz] due to the flicker load.
[0022]
FIG. 2 shows the input current waveform of the relay when a flicker load is present (FIG. 2A), the detection change amount when FIG. 2 is a = 1 (FIG. 2B), and the detection according to the present embodiment. The amount of change (FIG. 2 (c)) is shown.
The input current waveform in FIG. 2A is a waveform having a frequency of n ± 10 [Hz] in the same phase with a fundamental wave (size 1) having a frequency n = 50 [Hz] (size 0.2). ) Are combined distortion waves.
[0023]
In these figures, when the synthetic distortion wave suddenly changes from 0 to 100 [ms], the conventional technique shown in FIG. Although detected, in this embodiment of FIG. 2 (c), it is understood that no change is detected after 100 [ms] corresponding to five cycles of the fundamental wave, and erroneous detection is avoided. .
[0024]
Although above you facilities embodiment was explained in the variation width over-current relay, the present invention is also applicable to the voltage change width relay.
[0025]
【The invention's effect】
As described above, according to the first aspect of the present invention, it is possible to realize a variable width relay that is free from the possibility of erroneous detection, as in a system having no flicker load, even for a system having a large ΔV ₁₀ such as a flicker load. Can do.
Further, even when the flicker load includes a component other than the fundamental frequency ± 10 [Hz], the present invention can reduce the amount erroneously detected by the conventional change width relay. As a result, even when the configuration of the system using the change width relay is changed, it can be used without any problem, and the occurrence of problems can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a detected amount of change with respect to a frequency of current in the embodiment of the invention described in claim 1 and the prior art.
FIG. 2 is a waveform diagram for explaining the effect of the embodiment of the invention described in claim 1 ;
FIG. 3 is a diagram showing a configuration of a change width overcurrent relay.
FIG. 4 is a waveform diagram for explaining a problem of the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Analog filter 12 Sample hold means 13 A / D conversion means 14 Memory 15 Change width detection calculating means

Claims (1)

In a change width relay that performs a protection operation by detecting that a change width of a quantity of electricity having a fundamental frequency of n (n = 10 × m, where m is an integer) exceeds a set value,
A change width relay characterized by comparing a change width between a current value of an electric quantity and a value of an electric quantity before m cycles of a fundamental wave with a set value.

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