JPH0526933A - Zero-phase current detection device - Google Patents

Abstract

PURPOSE:To obtain an accurate zero-phase current for detecting rounding by eliminating an error due to zero-phase current by a tidal flow. CONSTITUTION:A positive-phase voltage 18 is created as a voltage source of reference vector which does not change normally and during a grounding accident. Then, a phase difference between the positive-phase voltage 18 and a zero-phase current 7 due to a tidal flow is authorized by a constant phase authorization element 21 and a compensation current 23 is output by a phase shift element 22. The zero-phase current for detecting grounding is output by subtracting the compensation current 23 from an apparent zero-phase current. In the case of an accident, the compensation current 23 is obtained by using an operation result immediately before the accident and its output continues.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zero-phase current detecting device used for accurately detecting a zero-phase current in a digital bus protection relay device in a power system.

[0002]

2. Description of the Related Art FIG. 4 is a schematic diagram of a system of a conventional digital type bus bar protection relay device of this type. In the figure, 1
Is a current transformer for measuring a large current flowing through the bus to a small current that can be input by the device, and 2 is a transformer for measuring a high voltage of the bus, which is low enough for the device to input Reference numeral 3 is a digital type busbar protective relay device, which is 3a.
Is an input converter for converting the current and voltage data input to the device into a value suitable for a digital relay to convert from an analog amount to a digital amount, and 4 is a digital relay unit, which is input from the input converter 3a. An analog input section 4a for converting the converted current and voltage data from an analog amount to a digital amount, and an accident detection for converting the input voltage data from an analog amount to a digital amount and transmitting an output signal when the voltage value is below a predetermined value Microcomputer unit 4c for calculating the differential amount based on the digital amount of current data obtained from the relay 4b and the analog input unit 4a to judge the operation of the differential relay, and a ground fault relay inside the microcomputer unit 4c. 4d and a digital input / output unit 4e for inputting / outputting a trip signal and the like. A trip output 5 outputs a trip signal to the circuit breaker. With the above device configuration, the busbar protection relay device
When a ground fault occurs on the bus bar, the fault current is taken into the ground fault relay and calculated, and a trip command is output.

By the way, a three-phase circuit in an electric circuit is
Ideally, the phase currents of the A-phase, B-phase, and C-phase are perfectly balanced, and the zero-phase current, which is the sum of the phase currents, is ideally zero. However, an actual three-phase circuit in a power system, etc. has a slight zero phase due to the magnitude of the power supply voltage, the phase imbalance, the fluctuation of the load of each phase, and the imbalance of the charging current due to the ground capacitance of the cable. An electric current is generated. The existence of zero-phase current due to this constant power flow affects the detection of a ground fault in the busbar protective relay device as an error.

FIG. 5 illustrates the above situation.
That is, in the figure, 6 is a ground fault current that newly flows due to a ground fault that has occurred in the system, 7 is a zero-phase current due to the above-mentioned tidal current that constantly flows, and the sum of both currents is apparent ground fault current data 8
Is taken into the arithmetic processing unit 9 of the ground fault relay 4d.

Next, the operation will be described with reference to the waveform chart of FIG. FIG. 6 is a graph showing changes in each voltage and current before and after the occurrence of a ground fault accident (A-phase 1-line ground fault).
Waveform of each phase voltage of phase C and C, 11 is a waveform of zero phase voltage, 1
2 is a waveform of a constant zero-phase current due to a tidal current, 13 is a waveform of a fault current due to a ground fault accident, 14 is a waveform of an apparent ground fault current captured by a ground fault relay 4d, which is waveform 12 and waveform 1.
It is the sum of 3.

First, normally, the ground fault accident current 6 (waveform 13)
Is not flowing and only the zero-phase current 7 (waveform 12) due to the tidal current is input to the ground fault relay as a differential amount. The differential amount of the zero-phase current due to this tidal current is the current when a ground fault accident occurs. Since it is extremely smaller than that of the above, it is determined that the relay is not operating by the arithmetic processing. Then, next, when a ground fault accident occurs on the bus bar, a ground fault fault current 6 (waveform 13) flows, and an apparent ground fault fault current 8 (waveform 14) obtained by adding a zero-phase current 7 (waveform 12) thereto. Taken into the ground fault relay 4d,
The relay operation is determined by the arithmetic processing.

[0007]

The conventional bus-barrier relay device is constructed as described above, and in the ground-fault relay detection portion thereof, there is a true ground-fault current and a zero-phase current due to the constantly occurring tidal current. Since the sum data of is taken in, the zero-phase current due to the tidal current becomes an error in terms of ground fault detection. As a result, in particular, when the ground fault current is set to be low by the grounding resistance, the above error becomes relatively large, and sometimes the ground fault relay may malfunction or malfunction. The present invention has been made to solve the above problems, and is capable of detecting an accurate zero-phase current for ground fault protection by removing an error based on the zero-phase current due to a power flow. The purpose is to obtain a detection device.

[0008]

A zero-phase current detecting device according to the present invention is a zero-phase current detecting means for detecting each phase current of a system and obtaining an apparent zero-phase current from the sum of the calculated currents. Positive phase voltage calculating means for detecting a phase voltage and calculating and outputting a positive phase voltage, zero phase voltage detecting means for detecting a zero phase voltage from each phase voltage, the positive phase voltage when the zero phase voltage is a predetermined value or less The phase of is converted into the phase of the apparent zero-phase current, the magnitude thereof is converted into the magnitude of the apparent zero-phase current, which is output as a compensation current, and the zero-phase voltage exceeds the predetermined value. In some cases, the output of the compensating current calculating means for maintaining the conversion condition immediately before exceeding and continuing the output, and the output of the compensating current calculating means from the apparent zero-phase current is output as a zero-phase current for ground fault detection. It is provided with a subtraction means for performing.

[0009]

Function: A positive phase voltage is created as a voltage source of a reference vector that does not change at all times and during a ground fault. And
At all times, that is, when the zero-phase voltage is below a predetermined value, the compensating current calculating means creates a compensating current from the positive-phase voltage, and the subtracting means cancels the compensating current, that is, the component due to the tidal current from the apparent zero-phase current. Output as zero-phase current for detecting the fault. At the time of an accident, that is, when the zero-phase voltage exceeds a predetermined value, the compensating current calculating means creates a compensating current from the existing positive-phase voltage based on the immediately preceding calculation condition and continuously outputs it. Therefore, even during an accident, the correction process using the compensation current is executed, and an accurate zero-phase current for ground fault detection can be obtained.

[0010]

1 and 2 are system configuration diagrams showing a zero-phase current detecting device according to an embodiment of the present invention. FIG. 1 is a configuration diagram of a portion for producing a compensation current, which will be described later, and FIG. The block diagram of the part which synthesize | combines the said compensation current and outputs to the ground fault relay 4d is shown. In the figure, 15a, 15b, 15c
Are the phase voltages of the A, B, and C phases of the system, and 16 and 1, respectively.
6a is for multiplying a phase correction coefficient by a so-called symmetric coordinate method in order to obtain a positive phase voltage based on the A phase, and 16 is 1
20 ° and 16a perform phase correction of 240 °. Reference numeral 17 denotes an adder as a positive phase voltage calculating means for adding the corrected phase voltages to obtain a positive phase voltage 18 based on the A phase. The positive phase voltage 18 is always used in a series of algorithms for obtaining a compensation current described below. And used as a voltage source for a reference vector that does not change throughout the accident.

Reference numeral 19 is an adder as a zero-phase voltage detecting means for detecting the zero-phase voltage by adding each phase voltage, and 20 is an "H" level signal when the zero-phase voltage exceeds a predetermined value. The zero-phase voltage detecting element 21 is a phase detecting element for detecting the phase difference between the positive-phase voltage 18 and the zero-phase current 7 due to the power flow. When an accident occurs, that is, when the output of the zero-phase voltage detecting element 20 becomes "H" level. The output locks the input of the zero-phase current 7 due to the tidal current, and the phase difference immediately before the accident is continuously output during this period. Two
2 converts the positive-phase voltage 18 into the phase of the zero-phase current 7 due to the tidal current based on the coordinate formula rotation formula based on the phase difference data obtained by the phase verification element 21, and further divides the voltage component to obtain the compensation current 23. This is the phase shift element to be sought. Further, 24 is a subtraction in which the compensation current 23 is subtracted from the apparent zero-phase current (apparent ground fault current data) 8 and output as a zero-phase current (ground fault fault current data after compensation) 25 for ground fault detection. It is a subtractor as a means.

Next, the operation will be described. In FIG. 1, assuming that the A-phase, B-phase, and C-phase voltages are V _A , V _B , and V _C , the adder 17 sets V _A + aV _B + a ² V _C = V ₁ as a positive reference of the A phase. The phase voltage V ₁ is obtained. Next, the phase verification is performed by the phase verification element 21. This algorithm is shown below. At a certain time t and 90 ° before this (t-9
The positive phase voltage at 0 °) and the zero phase current due to the power flow are V ₁ (t), I _od (t), V ₁ (t-90 °) and I, respectively.
_{If od} (t-90 °) and the phase difference is ψ, the following holds. V ₁ I _od cos ψ = V ₁ (t) · I _od (t) + V ₁ (t−90 °) · I _od (t−90 °) V ₁ I _od sin ψ = V ₁ (t) · I _od ( t-90 °) -V ₁ (t-90 °) · I _od (t) The above equation is calculated every 30 °, an average of about 3 cycles is calculated, and the calculation result is output to the phase shift element 22.

In the phase shift element 22, the phase detection element 21
The positive-phase voltage 18 is converted into the phase of the zero-phase current 7 due to the tidal current based on the output result of (1) by the coordinate axis rotation method, and the voltage component is further divided to obtain the compensation current 23. The algorithm is as follows. I _od ^* = (V ₁ (t) · V ₁ I _od cos ψ + V ₁ (t−90 °) · V ₁ I _od sin ψ) / | V ₁ | ² However, I _od ^* is the compensation current to be obtained, and V ₁ I _od co
The average values described above are used for s ψ and V ₁ I _od sin ψ .
Furthermore, since the positive-phase voltages V ₁ in always positive phase voltage V ₁ and accident somewhat different in size, in practice, always of a value | V
₁₁ |, and the value during an accident is | V ₁₂ |, for example, | V ₁ | ² = | V ₁₁ | · | V ₁₂ |

When the compensation current 23 is obtained in this way,
As shown in FIG. 2, from the apparent zero-phase current 8 to the compensation current 2
3 is subtracted to remove the zero-phase current 7 due to the power flow, and the compensated current is output to the ground fault relay 4d as a zero-phase current for ground fault detection.

When a ground fault occurs, the zero-phase voltage detecting element 20 operates to lock the input of the zero-phase current 7 due to the tidal current to the phase detecting element 21. As a result, the phase verification element 21 outputs the calculation result immediately before the accident to the phase shift element 22, and accordingly, the phase shift element 22 also uses the zero phase current data immediately before the accident to compensate from the positive phase voltage V _1. The current 23 is obtained and the output is continued.

FIG. 3 shows each waveform in the above case.
25 is a fault current after compensation, 23 is a compensation current, and 26 is a current error. It can be seen that the error due to the zero-phase current 7 due to the tidal current is sufficiently compensated at all times and throughout the fault.

In the above embodiment, the case where the invention is applied to the busbar protection relay device is explained. However, the present invention is a device for detecting another ground fault accident in the power system, for example, a transformer protection relay device, a transmission line protection. It can be similarly applied to a relay device and the like, and has the same effect.

[0018]

Since the present invention is configured as described above, an error due to a zero-phase current due to a tidal current is always removed regardless of an accident, and an accurate zero-phase current for ground fault detection is obtained. Reliable protection operation is ensured.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a portion for particularly obtaining a compensation current of a zero-phase current detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a portion for synthesizing a compensation current in the zero-phase current detecting device according to the embodiment of the present invention.

FIG. 3 is a waveform diagram for explaining the operation of the zero-phase current detection device according to the embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional zero-phase current detection device.

FIG. 5 is a diagram showing how current data is taken into a ground fault relay in a conventional device.

FIG. 6 is a waveform diagram for explaining the operation of the conventional device.

[Explanation of symbols]

 15 Each phase voltage 17 Adder as positive phase voltage calculation means 18 Positive phase voltage 19 Adder as zero phase voltage detection means 20 Zero phase voltage detection element 21 Phase verification element 22 Phase shift element 23 as compensation current calculation means 23 Compensation Current 24 Subtractor as subtraction means 25 Zero-phase current for ground fault detection

Claims (1)

Claim: What is claimed is: 1. A zero-phase current detecting means for detecting each phase current of a system and obtaining an apparent zero-phase current from the calculated sum thereof. Positive phase voltage calculating means for calculating and outputting, zero phase voltage detecting means for detecting zero phase voltage from each phase voltage, phase of the positive phase voltage when the zero phase voltage is a predetermined value or less, the apparent zero phase current When the zero-phase voltage exceeds the predetermined value, the conversion condition immediately before the conversion is performed. Zero-phase current having compensation current calculation means for holding and continuing output, and subtraction means for subtracting the output of the compensation current calculation means from the apparent zero-phase current and outputting it as a zero-phase current for ground fault detection Detection device.