JPH03230722A - Variation protective relay - Google Patents

Abstract

PURPOSE:To avoid an error in detecting a variation caused by a frequency fluctuation and improve a detection sensitivity by a method wherein the present frequency of a power system is obtained and a sampling period is corrected in accordance with the obtained frequency. CONSTITUTION:In order to compare sampled voltages, a sampling period (t) is determined in accordance with the present frequency of a power system. That is, voltages are sampled with the sampling period (t) corresponding to a frequency fluctuation and a vector variation between a sampled value V(t) and a value V(t-alpha) sampled a certain time ago is detected. By correcting the sampling period (t) like this, a detection error caused by the fluctuation of the system frequency can be avoided and, further, malfunction can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a change protection relay that detects a change in electrical quantity and performs a protective operation.

B. Summary of the Invention The present invention provides a change protection relay that samples the amount of electricity in a power system and performs a protective operation based on the amount of vector change. This prevents erroneous detection caused by the detection and also increases detection sensitivity.

C0 Conventional technology change protection relays are configured to respond when the electrical quantity of the voltage or current to be protected changes from a certain value to another value, and the amount of change is greater than a set value. It detects drops and current phase changes and is applied to voltage drop relays and phase comparison relays.

Conventional change amount protection relays detect the amount of change using two methods: one method is to determine the effective value change amount, and the other method is to determine the vector change amount. The previous sound is the difference between the effective voltage value a certain period of time ago and the current effective voltage value, V = l V(-α) l -'V
(t)l... Find the amount of change in the effective value of the quantity of electricity using (1), etc.

In the latter case, the amount of vector change in the amount of electricity is determined by the difference between the voltage vector a certain period of time ago and the current voltage vector, V=lV(t-α)-V(t): -(2).

D1 Problems to be Solved by the Invention In the conventional method for detecting the amount of change in effective value, since the effective value is obtained by rectifying the voltage, etc., there is a problem in that the response is poor. on the other hand,
The method of detecting the amount of vector change has excellent responsiveness because it uses instantaneous vector comparison, but digital processing that samples voltage values at regular cycles can cause erroneous detection or malfunction due to slight changes in the frequency of the power system. There was a problem that detection sensitivity had to be lowered.

SUMMARY OF THE INVENTION An object of the present invention is to provide a variation protection relay that increases detection sensitivity in vector variation detection and prevents erroneous detection.

E5 Means and operation for solving the problem In order to achieve the above-mentioned object, the present invention obtains the amount of vector change in the dinotal electricity quantity detected by sampling from the power system, and compares this amount of vector change with a set value to protect the object. The variation protection relay that operates includes means for determining the current frequency of the power system and correcting the sampling period according to the frequency, and the sampling corrected from the frequency fluctuation of the power system for detection by sampling the electrical quantity. By setting the period, it is possible to prevent erroneous detection of the amount of change due to frequency fluctuation, and also to increase detection sensitivity and prevent erroneous detection.

F. Embodiment FIG. 1 is a processing flowchart of a digital variation protection relay showing an embodiment of the present invention, in which a protection operation is performed from a voltage change l. First, the timing of the frequency (f) of the power system to be protected is determined and stored (step Sl).

In this measurement, in the same way as the voltage measurement described later, the voltage waveform from the auxiliary transformer provided in the conventional digital protective relay is filtered to remove harmonic components and noise components, and the sample and hold circuit performs sampling and holding. It is determined by converting it into a digital value using a D converter, and the frequency timing is set to, for example, the zero cross point of the voltage.

Next, in step S2, the frequency timing memory value from a certain period of time ago is read out, the current frequency of the power system is determined by comparison with the current frequency (f) timing stored in step S1, and the sampling period t is determined according to this frequency. Determine. Step S3
), the vector change (formula (2) above) between this and the voltage sampling value V(t-α) a certain fixed time ago is calculated (step S4), and this change V and the relay setting value are calculated. Compare (step S5). This comparison is similar to the conventional protection calculation, and as shown in Figure 2, V(t-α) and V(
A relay operation region is determined from the amount of vector change with respect to t), and depending on whether or not relay operation is to be performed (step S6), processing for turning on the operation output (step S7) and turning off the operation output (step S8) is executed.

Therefore, to compare voltage sampling values, a constant sampling period t is determined according to the current frequency of the power system, that is, voltage sampling is performed at a sampling period t according to frequency fluctuation, and this sampling value V (t) The amount of vector change between the sampled value V(t~α) and the sampled value V(t~α) a certain period of time ago is detected. This correction of the sampling period t prevents erroneous detection due to fluctuations in the system frequency and also prevents malfunctions. Accordingly, it is possible to increase the sensitivity in comparing the amount of change in the voltage vector and prevent false detection.

In the embodiment, a case is shown in which the amount of change in voltage vector is detected, but it goes without saying that this can be applied to current or phase comparison relays.

Effects of the G8 Invention As described above, according to the present invention, frequency fluctuations in the power grid are detected when sampling electrical quantities, and the sampling period is corrected accordingly, thereby preventing erroneous detection of electrical quantities due to frequency fluctuations in the power grid. This has the effect of preventing malfunctions and improving detection sensitivity.

[Brief explanation of drawings]

FIG. 1 is a processing flowchart showing an embodiment of the present invention;
FIG. 2 is a diagram of relay operation characteristics. Outside 2 people Figure 1 Actual party is lined up. Figure 2 is relay movement.

Claims (1)

[Claims] (1) Find the amount of vector change in the digital electricity quantity detected by sampling from the power system, and compare this vector change with a set value to determine the current frequency of the power system in the change protection relay that performs a protective operation. A variation protection relay comprising means for correcting the sampling period according to the frequency.