JPH03245715A - Digital-type protective relay - Google Patents

Abstract

PURPOSE:To reduce a detection error in an effective value in the vicinity of a fundamental frequency of the quantity of input electricity by a method wherein a change in the gain of an analog filter caused by fluctuation of the frequency of the quantity of the input electricity is corrected by an operation of a digital filter in a microprocessor. CONSTITUTION:A change in the gain of an analog filter is large in a low frequency band, and therefore it is seen that a digital filter needs to be given a high-pass characteristic. Herein an output of the analog filter 20 is transmitted through the digital filter operating on the basis of the formula.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a digital protective relay for protecting a power system.

(Prior Art) FIG. 2 shows a schematic configuration of a digital protective relay. In the figure, 10 is an input converter such as a voltage transformer or current transformer to which voltage input or current input from the power system is applied, 20 is an analog filter, 30 is a sample and hold circuit, 40 is a multiplexer, and 50 is an A/D converter, 6
0 is a microprocessor that performs protection calculations based on the effective value of the input electrical quantity, etc., and issues instructions such as tripping of the circuit breaker.

As mentioned above, the input circuit of a digital protective relay is equipped with an analog filter (band-pass filter, low-pass filter, or These combinations) 20 are added.

(Problem to be Solved by the Invention) Here, when the frequency of the system input varies within a range of about a numerical ratio, the gain changes due to the characteristics of the analog filter 2o, and an error occurs when calculating the effective value. This error is small (about 1 to 2%) and can be ignored for overcurrent relays that operate instantaneously, but for relatively long-term overcurrent relays and overload protection relays that operate instantaneously. In relays that integrate the input effective value over a period of time, instantaneous errors accumulate and eventually become large errors.
There was a problem in that the operating accuracy of the relay deteriorated.

The present invention has been made to solve the above problems,
The purpose is to provide a digital protective relay that reduces detection errors in effective values due to fluctuations in input frequency when highly accurate detection of input quantities is required as described above. be.

(Means for Solving the Problems) In order to achieve the above object, the present invention samples data that has passed through an analog filter of an input circuit, and
In a digital protective relay that calculates the effective value of the input electrical quantity using a microprocessor based on the converted digital data and operates based on the result, the gain change of the analog filter caused by the frequency fluctuation of the input electrical quantity is This is corrected by a digital filter using a predetermined arithmetic expression in the microprocessor to reduce the error in detecting the effective value near the fundamental frequency of the input electrical quantity.

(Operation) According to the present invention, by correcting the gain change of the analog filter caused by fluctuations in the input frequency using a digital filter with appropriate characteristics realized by a microprocessor, the analog filter becomes flat in the vicinity of the system fundamental frequency. Gain characteristics are obtained to reduce errors in effective value detection during frequency fluctuations.

(Example) The present invention will be described in detail below with reference to the drawings.

Figure 1 shows that the frequency is ±2.5 earths (4
7.5 Hz to 52.5 Hz) is a diagram showing a change in gain when the frequency is varied.

In FIG. 1, (1) is the gain change of the analog filter 20, and since the analog filter 2o has a higher gain in the low frequency range, the digital filter should have high-pass characteristics. I understand. Also, (2
), (3), (4), and (5) each show the gain change when the output of the analog filter 20 having the characteristic of (1) is passed through a digital filter with the following calculation formula. .

A, +A,, -A,, -Ayu-,
...(2
)A, +2A, -e+A, -e+A, -, -2A, -5
-A, ~6...(3) A, +2A, -t
+2AQ-z+A, -5-A, -4-2A knee 5-2A
--6-A--7...(4) A, +2A, -t"2A
,, -z+ZA, -1-2A Woo 5-2A, -6-2A
, -'y-A--a ... (5) (sample interval 1
．． 66 m 5.50 Hz, electrical angle 30 degrees) Here, 80 indicates the current data when the fundamental wave is sampled at intervals of 30 electrical degrees, A,, -L rAゎ-2,...
Subscript n in etc. 1. n 2t... are one sample period ago and two sample periods ago, respectively.

It shows the data of...

In this example, the gain change of the analog filter 20 is -1°4~
It can be seen that the gain change is improved to -0.8 to 0.1% by passing the signal through a digital filter of formula (5), for example, for 1.1%.

Furthermore, according to the present invention, by appropriately selecting the number of terms and coefficients of the digital filter so as to compensate for changes in gain with respect to the characteristics of any analog filter, it is possible to bring the characteristic of the -layer closer to ideal characteristics. .

(Effects of the Invention) As described above, according to the present invention, since the gain change of the analog filter due to the fluctuation of the input frequency is compensated by the digital filter, Even when highly accurate effective values are required for protection calculations, it is possible to realize a digital protective relay that can operate stably against frequency fluctuations. Furthermore, since the digital filter can be implemented using microprocessor software, there is no risk of complicating the configuration.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between fluctuations in system frequency and changes in gain of an analog filter in an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of a digital protective relay. IO...Input converter 2o...Analog filter 30...Sample hold circuit 40...Multiplexer 5o...A/D converter 60...Microprocessor

Claims (1)

[Claims] A digital device that samples data that has passed through an analog filter in an input circuit, and calculates an effective value of an input amount of electricity using a microprocessor based on the digital data obtained by A/D conversion, and operates based on the result. In the type protective relay, a change in the gain of the analog filter caused by a frequency fluctuation of the input electrical quantity is corrected by calculation of a digital filter in the microprocessor, and an error in detecting an effective value near the fundamental frequency of the input electrical quantity is reduced. A digital protective relay characterized by: