JP2969724B2 - Change protection relay - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variation protection relay that detects a digital electrical quantity from an electric power system by sampling and protects the digital electrical quantity from a vector variation.

B. Summary of the Invention The present invention samples a quantity of electricity in a power system, detects a change in the frequency of the power system in a change protection relay that performs a protection operation from the vector change, and responds to the increase or decrease of the frequency. Sampling time interval (sampling cycle)
By correcting the increase / decrease, erroneous detection due to frequency fluctuation is prevented, and the detection sensitivity is also increased.

C. Conventional technology The change protection relay is configured such that the amount of voltage or current to be protected changes from a certain value to another value, and if the change is equal to or greater than a set value, it is responsive. It is applied to voltage drop relays and phase comparison relays by detecting voltage drop and current phase change.

Conventional change amount protection relays include a method of calculating an effective value change amount and a method of calculating a vector change amount to detect the change amount. In the former, the effective value change amount of the electric quantity is obtained from the difference V = | (t−α) | − | (t) | (1) between the voltage effective value before a certain time and the current voltage effective value. .

In the latter, the vector change amount of the electric quantity is obtained from the difference V = | (t−α) − (t) | (2) between the voltage vector before a certain time and the current voltage vector.

Note that the time t and α in the above equations (1) and (2) are constant times.

D. Problems to be Solved by the Invention In the conventional method of detecting the amount of change in the effective value, there is a problem that the responsiveness is poor because the effective value is obtained by rectifying the voltage or the like. On the other hand, in the method of detecting the vector change amount, the response is excellent because of the instantaneous vector comparison.However, in the digital processing of sampling the voltage value at fixed time intervals, a slight frequency change in the power system causes erroneous detection in the voltage value sampling. This may cause a malfunction in the variation protection relay, resulting in a problem that the detection sensitivity of the variation must be reduced.

An object of the present invention is to provide a variation protection relay that prevents erroneous detection while increasing the detection sensitivity in vector variation detection.

E. Means for Solving the Problems In order to achieve the above object, the present invention detects a digital electric quantity by sampling from an electric power system, finds a vector change amount of the digital electric quantity, and sets the vector change amount to a set value. In the variation protection relay performing the protection operation in comparison with, a means for obtaining and storing a frequency timing a predetermined time before the timing synchronized with the frequency of the power system by sampling the voltage waveform of the power system, and The frequency of the power system is determined by comparing the frequency timing with the frequency timing synchronized with the current frequency of the power system, and when the frequency changes to a higher value, the sampling time interval for detecting the digital electricity amount is shortened, and Correction means for lengthening the time interval of the sampling when the frequency changes to a lower value; Detection prevents variation of erroneous detection due to frequency fluctuation by increasing or decreasing the sampling time interval in correspondence with the increase or decrease of the frequency of the power system to also be able to prevent any incorrect detection enhance the detection sensitivity.

F. Embodiment FIG. 1 is a processing flowchart of a digital change amount protection relay showing an embodiment of the present invention, in which a protection operation is performed from a voltage change amount.

In the figure, steps S1 and S2 are parts for correcting the sampling cycle according to the frequency change of the system. Steps S3 to S8 at the subsequent stage are the same as those of the conventional relay that performs the protection operation from the vector change amount (voltage change amount) as in the example of the equation (2). Sampling is performed at the sampling cycle corrected in S2.

First, the frequency (f) timing before a certain time synchronized with the frequency of the power system is obtained and stored by sampling the voltage waveform of the power system to be protected (step S).
1).

This measurement is the same as the voltage measurement described later, removes the harmonic component and the noise component through a filter from the voltage waveform from the auxiliary transformer provided in the conventional digital protection relay, performs sampling and holding with a sample and hold circuit, A /
It is obtained by converting it into a digital value by a D converter, and the frequency timing is, for example, a zero cross point of the voltage.

Next, in step S2, the frequency (f) timing storage value before a certain time stored in step S1 is read, and the current frequency of the power system is obtained by comparison with the current frequency (f) timing. Correspondingly, the sampling period (time interval) T is increased or decreased.

That is, as described above, the change amount protection relay detects the vector change amount of the electric amount as shown in the above equation (2) by sampling the electric amount such as the voltage or current of the power system, and detects the vector change amount. Thus, the power system is protected by obtaining a response as to whether or not to perform the protection operation. At this time, if the frequency of the power system in which the amount of electricity is to be sampled changes, if the amount of electricity is sampled at a certain time interval, the amount of electricity is erroneously detected. In order to prevent this erroneous detection, in steps S1 and S2, the sampling period T is corrected according to the change in the frequency of the power system, and the system frequency is changed to the subsequent sampling of the electric quantity in step S3 and the like. Enable sampling at the same electrical angle as before.

For example, a digital relay normally samples analog data every 30 electrical degrees (12 samples per cycle), and when the system frequency is 50 Hz, 30 degrees is 1.666666.
... The sampling time interval is set to ms. Here, when the current frequency is obtained from the frequency (f) timing,
For example, when the frequency is changed to 50.20 Hz, the sampling cycle (time interval) T is shortened to 1.660026... Ms, so that the sampling can be performed at the same electrical angle of 30 degrees as before the change in the system frequency. . Conversely, when the frequency changes to a lower value, the sampling can be performed at the same electrical angle of 30 degrees by correcting the sampling period to be longer.

Next, the system voltage (t) is sampled and stored according to the corrected sampling period T (step S).
3). On the other hand, the vector change from the voltage sampling value (t−α) before a certain time (see (2) above)
Expression) is obtained (step S4), and the variation V is compared with the relay set value (step S5). In this comparison, as in the conventional protection operation, as shown in FIG. 2, the relay operation area is determined from the vector change amount between (t−α) and (t), and it is determined whether or not the relay operation is performed (step Operation output on (step S7) and operation output off (step S6)
Step 8) is executed.

Therefore, for the comparison of the voltage sampling value, the sampling period T is corrected in accordance with the increase or decrease of the current frequency of the power system, that is, the voltage sampling is performed by increasing or decreasing the sampling period T in accordance with the frequency fluctuation. ) And a vector change amount between the sampling value (t−α) before a predetermined time is detected. The correction for increasing or decreasing the sampling period T in accordance with the current increase or decrease of the system frequency prevents erroneous detection due to the change in system frequency and prevents malfunction. Along with this, it is possible to increase the sensitivity in comparing the amount of change in the voltage vector, thereby preventing erroneous detection.

In the embodiment, the case where the amount of change in the voltage vector is detected is shown. However, it is needless to say that this can be applied to a current and a phase comparison relay.

G. Effects of the Invention As described above, according to the present invention, frequency fluctuations of the system are detected during sampling of the electric quantity, and the sampling time interval is corrected to increase or decrease in accordance with the increase or decrease of the frequency. This has the effect of preventing erroneous detection of the quantity of electricity due to frequency fluctuation, and thus preventing malfunction and improving detection sensitivity.

[Brief description of the drawings]

FIG. 1 is a processing flowchart showing one embodiment of the present invention,
FIG. 2 is a diagram showing a relay operation characteristic.

Claims (1)

(57) [Claims] 1. A change amount protection relay for detecting a digital electric amount by sampling from a power system, obtaining a vector change amount of the digital electric amount, and comparing the vector change amount with a set value to perform a protection operation. Means for obtaining and storing a frequency timing before a fixed time synchronized with the frequency of the power system by sampling the voltage waveform of the system, and storing the frequency timing of the fixed time and the frequency timing synchronized with the current frequency of the power system. The frequency of the power system is obtained by comparison, and when the frequency changes higher, the sampling time interval for detecting the digital electric quantity is shortened, and when the frequency changes lower, the sampling time interval is increased. A change protection relay comprising: a correction unit.