JPS6248451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground fault phase selection relay for protecting a power transmission and distribution system, and is particularly suitable for application to a single-end power supply system.

Conventional analog type ground fault phase selection relays have a response time of about 60 to 100 milliseconds to a ground fault in the power distribution system, which is not satisfactory in terms of the degree of spread in the event of an accident. In addition, digital ground fault phase selection relays have been developed, but the phase detection period requires at least 1/2 cycle of the fundamental frequency, and even faster processing is currently required. It is. Therefore, as protective relay systems based on digital arithmetic processing are being realized, there is a need for ground-fault phase relays that can cope with this system.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to provide a ground fault phase selection relay that has a fast response speed and can perform digital calculation processing.

The ground fault phase selection relay of the present invention includes sampling and holding means for sampling and holding an instantaneous value of alternating current from a power transmission and distribution system, and generating a sampling pulse that determines the sampling instant and sampling interval Δt in the sampling and holding means, and generating means for supplying to the sampling and holding means; analog-to-digital conversion means for converting the instantaneous value of the alternating current held in the sampling and holding means into a digital signal and outputting it to the data processing means; From the output digital quantities of the analog-to-digital conversion means corresponding to the alternating current amount and the zero-phase alternating current amount, for each phase α, α = cot ^-1 (B/A-C ₁ /C ₂ ) (where A is the above-mentioned alternating current). The digital quantity at time t from the time the quantity passes the zero point, B is the digital quantity at time t + Δt, C ₁ and C ₂ are constants), and calculate the phase difference between the reference AC amount and the zero-phase AC amount The present invention is characterized by comprising a data processing means for performing ground fault phase selection.

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

FIG. 1 shows an example of the configuration of a ground fault phase selection relay according to the present invention. This ground fault phase selection relay includes a sampling hold device 1, a sampling pulse generator 2, a multiplexer 3, an A/D (analog
It consists of a digital) converter 4, a data processing device 5, and an input/output device 6. Sampling hold device 1
2 simultaneously samples and holds the instantaneous values of current and voltage from the power transmission and distribution system based on the sampling pulses generated by the sampling pulse generator 2. The data is then sequentially supplied to the A/D converter 4 via the multiplexer 3, where it is converted into a digital signal. The data processing device 5 is
It has a processor 11, a RAM 12, a ROM 13, and a divider 14. The ROM 13 holds a microprogram for controlling data processing by the processor 11, the RAM 12 stores data calculated by the processor 11, and the divider 14 is provided to execute calculations described later at high speed. The input/output device 6 processes the input of the setting value of the ground fault phase selection relay and the output of the ground fault phase selection relay.

This ground-fault phase selection relay detects the peak value of the voltage or current currently being taken in from the power transmission and distribution system.
The sampling and holding device 1 samples the instantaneous value of the fundamental frequency Ep at every time Δt using a pulse from the sampling pulse generator 2, and holds the value. The respective voltage and current values held here are sequentially sent to the A/D converter 4 by the multiplexer 3 based on clock pulses (not shown).
Then, the A/D converter 4 converts the instantaneous values of voltage and current into digital data, and supplies the digital data to the data processing device 5. The data processing device 5 calculates the phase of each voltage and current value based on the data at each time Δt. Therefore, let the instantaneous value at time t from the time of passing the zero point be A, and the phase be α,
Assuming that the instantaneous value at time t+Δt is B and the phase is α+Δα, the phase α can be determined as follows. First, the instantaneous values A and B are A=Ep sinα...(1) B=Ep sin(α+Δα)...(2), so from equations (1) and (2), B/A=Ep sin(α+Δα)/ Ep sinα=sinαcosΔα+cosαsinΔα/sin
α…(3) is found. Here, Δα is known from the time Δt and frequency and is constant, so Then, equation (3) is B/A=C ₁ +cosα/sinαC ₂ =C ₁ +C ₂ cotα…(
5) becomes. Therefore, from this equation (5), the phase α can be determined as α=cot ⁻¹ (B/A−C ₁ /C ₂ ) (6). However, cotα is α
and α+180° take the same value, so when the instantaneous value A has negative polarity (sin α<0), processing is performed such as adding 180° to α. In this way, the phase of one input quantity (alternating current quantity) can be detected, but the present invention applies the above-mentioned method to two input quantities, calculates the phase of each, and calculates the difference between them. This is to determine the phase difference and perform ground fault phase selection. That is, if the reference voltage is, for example, the a-phase voltage,
As shown in Figure 2, if the phase of the zero-phase voltage V〓o lags within the range of 0° to 90° with respect to the a-phase voltage V〓a, there is an a-phase ground fault, 30° to 120°. If the advance is in the range of 150° to 240°, it is determined to be a B-phase ground fault, and furthermore, if it is in the range of 150° to 240°, it is determined to be a C-phase ground fault. However, the phase within the above range depends on the magnitude of the fault point resistance Rg. In reality, taking into account errors in the detection end and equipment, the a-phase voltage V〓a
, the phase is divided into three leading phases of 15°, 135°, and 255°, and ground fault phase selection is performed depending on the range of the zero-sequence voltage Vo. In addition, the reference voltage may be not only the a-phase voltage but also the b-phase and c-phase voltages or each line voltage, but the boundary between the three phase divisions determined as described above may be different. Become. The reference voltage is the voltage when the power transmission and distribution system is healthy, and can be detected at all times even before an accident occurs.
By storing this in the RAM 12 and detecting the phase of only the zero-sequence voltage V〓o after an accident, it is possible to select the ground fault phase, but the phase is not an exact value, and if the range is known, the desired phase can be detected. Able to achieve purpose. Now, if an a-phase ground fault occurs between times t _o-1 and t _o , as shown in Fig. 3A and B, the phase of the a-phase voltage V 〓 a changes, and the zero-sequence voltage Vo occurs. As mentioned above, since the data of the instantaneous value of the a-phase voltage V〓a is stored in the RAM 12 at every sampling time interval Δt, the data corresponding to times t _o and t _o+1 , for example, one cycle before, is stored in the RAM 12 at every sampling time interval Δt. Since V _ao-12 and V _ao-11 are obtained from the RAM 12, their phase α _va is obtained from equation (6), α _va = cot ^-1 (V _ao-11 /V _ao-12 )-C ₁ /
C ₂ ...(7). Also, the phase α of the zero-phase voltage V〓o at that time
_vp is calculated by substituting the instantaneous values V _po and V _po+1 into equation (6), α _vp = cot ^-1 (V _po+1 /V _po )-C ₂ /C ₂ ...(
8) becomes. Then, the phase difference = α _vp − α _va is
It is in the range from 225° to 15° counterclockwise, and cot>cot15° and sin>0...(9) or cot<cot225° and sin<0...(10). This calculation is performed by the data processing device 5 (first
Figure) is executed as follows. First, based on the microinstructions of ROM13,
The CPU 11 reads data V _ao-12 and V _ao-11 of the instantaneous value of the a-phase voltage from the RAM 12, and reads {(V _ao-1
1 /V _ao-12 )-C ₁ }/C ₂ is caused to be executed by the divider 14. Next, the CPU 11 calculates the phase α of the a-phase voltage at times t _o and t _o+1 from the calculation result.
Find _ao and store it in RAM12. Similarly,
After obtaining the phase α _vp of the zero-sequence voltage, the CPU 11 calculates the phase difference and outputs a ground fault phase selection signal to the input/output device 6. Here, among the above calculation processes _, {(V _po+1 /V _p
An example of the arithmetic processing of ₀ )-C ₁ }/C ₂ will be explained with reference to FIG. Now, the output data of the divider 14 {(V _p
o+1 /V _po )-C ₁ }/C ₂ is M, as shown in FIG. The address of the RAM 12 is set based on the value obtained by multiplying the data M by 20, such as when 1, . . . (However, the fourth
The address of RAM 12 in the figure is expressed in hexadecimal. ) and RAM1 specified in this way
2, the phase α _vp corresponding to data M,
That is, by storing the data of cot ^-1 M, phase data can be obtained from the output data of the divider 14. For example, if the output data M of the divider 14 based on the data at times t _o and t _o+1 is M
= 1.25, the address of the RAM 12 is ××14 (in hexadecimal notation), and it can be seen from the phase data of the RAM 12 that the phase α _vp is 45°.
The phase data shown in Figure 4 is sin α _vp > 0
However, if sin α _vp < 0, then sin
It is sufficient to add 180° to the phase data of α _vp >0. Note that if the AB line voltage is used as the reference voltage, its phase will not change even if a ground fault occurs, so the phase data is obtained using the sampling data at the time of the fault and compared with the phase data of the zero-sequence voltage. Then, the phase difference can be determined.

As described above, according to the present invention, digital arithmetic processing is performed, and the response speed to a ground fault in a power distribution system, etc., is only 2Δt when the sampling time interval is Δt, so it is extremely fast. Sorting relays can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the ground fault phase selector according to the present invention, Fig. 2 is a vector diagram showing the 1-line ground fault phase selection characteristics, and Figs. 3 A and B are waveforms of the a-phase ground fault. 4 are diagrams for explaining arithmetic processing of phase data. 1... Sampling hold device, 2... Sampling pulse generator, 3... Multiplexer, 4
...analog-digital converter, 5...data processing device, 6...input/output device.

Claims (1)

[Scope of Claims] 1. A sampling and holding means for sampling and holding an instantaneous value of an alternating current amount from a power transmission and distribution system, and a sampling and holding means for generating a sampling pulse that determines a sampling instant and a sampling interval Δt in the sampling and holding means; generating means for converting the instantaneous value of the alternating current held in the sampling and holding means into a digital signal and outputting it to the data processing means; From the output digital quantity of the analog-to-digital conversion means corresponding to the zero-phase alternating current, for each phase α, α=cot ^-1 (B/A−C ₁ /C ₂ ) (where A is the zero point of the alternating current). A digital quantity at time t from the time of passage, B is a digital quantity at time t + Δt, C ₁ and C ₂ are constants), and the phase difference between the reference AC amount and the zero-sequence AC amount is calculated and the ground fault phase is calculated. What is claimed is: 1. A ground fault phase selection relay comprising: data processing means for performing selection.