KR950009124B1 - Digital relaying method of electronic switch-board for protecting load-grounding - Google Patents

Abstract

The method comprises the steps of producing image current and image voltage; obtaining the phase difference between the image current and the image voltage; producing image overcurrent ratio in the above result; checking occurrence caused by difference between the reference phase difference and the reference image overcurrent ratio; and stopping the power of load.

Description

Digital relay method for load ground protection of electronic switchgear

1 is a circuit diagram showing the configuration of an electronic switchgear to which the digital relay method of the present invention is applied.

2 is a view showing a digital relay method of the present invention,

(a) is a signal flow diagram showing the main routine.

(b) is a signal flow diagram showing an interrupt routine.

* Explanation of symbols for main parts of the drawings

1: central processing unit 2: sensor signal output unit

3: multiplexer 4: analog filter

5: analog / digital converter 6: keyboard portion

7: display unit 8: ROM

9: ram 10: load driver

CB: Circuit Breaker CT1-CT3: Current Transformer

PT1-PT3: Voltage transformer

The present invention provides an electronic switchgear for supplying power to various loads such as a transformer and a feeder, and the values of phase difference and image current of image voltage and image current of three-phase power of R, S, and T phases supplied to the load. The present invention relates to a relay method for load ground protection of an electronic switchgear which protects a load from damage from ground fault.

Conventionally, in order to protect the load from ground faults, a relay suitable for characteristics is selected according to the grounding method of the power system. Therefore, there are many difficulties in installation operation, and in the case of selecting the relay incorrectly, the relay performance decreases and the ground fault occurs. There was a problem such that the relay function can not be exhibited during the occurrence of.

Accordingly, it is an object of the present invention to provide a digital relay method that effectively protects a load from damage from a ground fault without deteriorating relay performance.

It is another object of the present invention to provide a digital relay method that can be easily applied to any load by simply changing the set value of the operation variable according to the type, capacity and characteristics of the load.

Another object of the present invention is to add and subtract the time according to whether a ground fault occurs, and to cut off the power supply when the counted time is equal to or greater than the set value. To provide a digital relay method to avoid.

The digital relay method of the present invention having such a purpose uses the image current value of the power supplied to the load, the phase difference between the image current and the image voltage, and sets the image overcurrent ratio when the ground fault occurs according to the type, capacity, and characteristics of the load. The power off delay time according to the phase difference between the image current and the image voltage above the value is stored in the preset and lookup table through experiments within the range that does not damage the load.

After sampling and storing the image current and the image voltage of the power supplied to the load at regular intervals, the phase difference between the sampled image current and the image voltage is calculated and compared with the reference phase difference, and the value of the image current and the reference image current. The occurrence of a ground fault is determined by comparing the image overcurrent ratio with the calculated value and the set value, and when the ground fault is detected, if the ground fault occurs after the lead time is Shut off the power so that it is not supplied to the load.

Therefore, according to the digital relay method of the present invention, the ground fault is determined by simply setting the reference phase current value and the reference phase difference between the image current and the image voltage according to the type, capacity, and characteristics of the load, and the load is damaged when the ground fault occurs. Within the cutoff delay time, which is not within the range, power is supplied continuously and the drive continues without stopping due to a momentary ground fault.

Hereinafter, the digital relay method of the present invention will be described in detail with reference to the accompanying drawings.

1 is a circuit diagram showing the configuration of an electronic switchgear to which the digital relay method of the present invention is applied. As shown therein, a central processing unit 1 for controlling the overall operation of an electronic switchgear and R, S and T phases as loads are shown. Circuit breaker (CB) for supplying three-phase power, voltage transformer (PT1-PT3) for detecting the voltage between the RS, ST, and RT phases supplied to the load, and current transformer (CT1) for detecting the current of each phase supplied to the load. CT3), a sensor signal output unit 2 for outputting the detected voltage of the voltage transformers PT1-PT3 and the detected current of the current transformers CT1-CT3, and an output signal of the sensor signal output unit 2; The multiplexer (3) for sequentially selecting and outputting each one, an analog filter (4) for removing a noise signal from the output signal of the multiplexer (3), and converts the output signal of the analog filter (4) to a digital signal to the Analog / D input to central processing unit (1) The de-transducer 5, the keyboard unit 6 for inputting operation commands and various setting values to the central processing unit 1, and the operation state and abnormal state of the electronic switchboard under the control of the central processing unit 1; And a display unit 7 for displaying and a ROM 8 for storing and outputting the operation program of the central processing unit 1 and a look-up table of the cutoff delay time for loss of phase, and the like. The RAM 9 to output and the load driver 10 for controlling the power supply of the load by controlling the circuit breaker (CB) under the control of the central processing unit (1).

In the digital relay method of the present invention applied to the electronic switchboard configured as described above, as shown in FIG. 2 (a), an initializing operation is first performed, various parameters are set according to the power supply of the load, and the reference image current is also applied. After setting various operating variables such as the reference phase difference of the video current and the video voltage, sampling the currents of the R, S, and T phases and the voltages between the RS, ST, and TS phases at regular intervals, for example, the current data at a period of 1.3 msec. And voltage data is sampled.

That is, after the breaker CB detects the voltage between the RS, ST, and TS phases and the currents of the R, S, and T phases supplied to the load from the voltage transformers PT1-PT3 and current transformers CT1-CT3, respectively. The sensor signal output unit 2 is input to the sensor signal output unit 2, and the sensor signal output unit 2 processes and outputs the voltages between the RS, ST, and RT phases, and the currents of the R, S, and T phases, and outputs the output voltages and currents to the multiplexer 3. Are sequentially selected and output one by one, and filtering and noise are removed from the analog filter (4), and converted into a digital signal from the analog / digital converter (5) and output, and the analog, digital converter (5) outputs RS, ST and The central processing unit 1 samples voltage data on RT and current data on R, S, and T at regular intervals.

The CPU 1 digitally filters the voltage data between the RS, ST, and RT phases sampled and the current data of the R, S, and T phases, and removes the DC and harmonic components. And calculating and storing the phase difference between the image current and the image voltage, and determining whether or not the key signal of the keyboard unit 6 is input, and in case of input, displaying an operation value corresponding to the input key signal. If the key signal is not input, the operation value corresponding to the key signal input immediately before is displayed on the display unit 3 and the function thereof is performed.

In this way, when the video current value and the video voltage value of the power supplied to the load and the phase difference between the video current and the video voltage are calculated and stored, as shown in (b) of FIG. After each 50msec cycle, the stored image current value and the phase difference between the image current and the image voltage are read, and the read image current value is divided by the set reference image current value to calculate the image overcurrent ratio and then the phase difference between the image current and the image voltage. The occurrence of a ground fault is determined by comparing the calculated image overcurrent ratio with the reference phase difference and the reference image overcurrent ratio, respectively.

At this time, if the calculated phase difference is larger than the set reference phase difference, and the calculated image overcurrent ratio is larger than the set image overcurrent ratio, the ground fault occurs. If the cycle time is added and the calculated phase difference is less than the reference phase difference set or the calculated image over current ratio is smaller than the set image over current ratio, the ground fault does not occur. While the count is counted down, it is determined whether the accumulated ground fault occurrence time has elapsed above the set interruption delay time, and when the accumulated ground fault occurrence time exceeds the interruption delay time, the breaker CB is cut off so that power is not supplied to the load.

As described in detail above, in the present invention, when a ground fault occurs when power is supplied to a load, the power is cut off after a set shutdown delay time to prevent damage to the load due to the ground fault. It is easy to install and operate by simply changing the operation variable according to the characteristics and characteristics, and the time required for work is shortened. In case of an instantaneous ground fault in the range that does not damage the load, the power is continuously supplied to the load. There is an effect that can continue to operate without stopping.

Claims (3)

An image current / voltage calculation process for calculating an image current and an image voltage by sampling current and voltages between each phase supplied to a load, and calculating a phase difference between the image current and image voltage calculated in the image current / voltage calculation process. A phase difference calculation step of calculating a phase difference and an image over current ratio by comparing the image current calculated in the image current / voltage calculation step with a reference image current, and the phase difference and image over current ratios calculated in the phase difference calculation step. A judgment step of judging the occurrence of a ground fault by comparing the image overcurrent ratio calculated in the calculation process with the reference phase difference and the reference image overcurrent ratio, respectively, and in the case of determining the occurrence of a ground fault, Digital relay method for protecting the load ground of the electronic switchgear characterized in that the power control step to cut off. The method of claim 1, wherein the determining step comprises determining that a ground fault occurs when the calculated phase difference and the image overcurrent ratio are equal to or greater than the set reference phase difference and the reference image overcurrent ratio. Digital relay method. The method of claim 1, wherein the power supply control step includes: a delayed time for which a ground fault occurrence accumulated time is set while increasing a ground fault occurrence cumulative time in the case of a ground fault; A digital relay method for protecting the load ground of the electronic switchgear, characterized in that the power supply is cut off in case of abnormality.