JPH07303328A - Ground-fault detecting device - Google Patents

Abstract

PURPOSE:To minimize the influence of a residual current by providing a digital potentiometer which is connected to a photoelectric conversion section and actuated by a signal from a controller and a variable amplifier which is connected to the potentiometer and composed of an amplifier. CONSTITUTION:A controller calculates the effective value of a residual signal and changes the amplification factor of an R-phase variable amplifier 20 by adjusting the digital potentiometer of the amplifier 20 by transmitting a signal to the potentiometer so that the value of the residual signal can become the minimum. After changing the amplification factor of the amplifier 20, the controller again finds the residual current and calculates the effective value of the zero-phase current. The controller sets the potentiometer so that the residual current can become the minimum by repeating the above-mentioned operation several times. Then the controller minimizes the influence of the residual current by adjusting a variable antplifier 20 connected to an S-phase photocurrent sensor and another variable amplifier connected to a T-phase photocurrent sensor. By repeating this adjustment several times in the order of phase, the residual current is minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault accident detection device for a distribution line, which detects a zero-phase voltage and a zero-phase current having little influence of residuals and detects a ground fault.

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional ground-fault accident detecting apparatus includes photocurrent sensors 1, 2, 3 for detecting a current and light detecting a voltage for each phase R, S and T of a distribution line. Voltage sensors 4, 5, 6 are provided. Reference numeral 7 denotes an electro-optical conversion unit for converting an electric signal into an optical signal, which is connected to each sensor via an optical fiber. Reference numeral 8 denotes an opto-electric conversion unit for converting an optical signal into an electric signal, which is connected to each sensor via an optical fiber. Reference numerals 9 and 10 denote amplifiers for amplifying the signal of the opto-electric converter, and the outputs of the amplifiers are output to the adders 11 and 12 described later. The adder 11 adds the signals detected by the photocurrent sensors provided in each phase of the distribution line to calculate the zero-phase current, and outputs the zero-phase current to the amplifier 13. The adder 12 adds signals detected by optical voltage sensors provided in each phase of the distribution line to calculate a zero-phase voltage, and outputs it to the amplifier 14. The amplifiers 13 and 14 are adders 1
A / D converters 17, 18 amplify the signals corresponding to the zero-phase current or zero-phase voltage from 1 and 12, and extract the fundamental wave component of the output, and the analog of the fundamental wave component The signal is converted into a digital signal and output to the control device 19. The control device 19 calculates the effective value of the input zero-phase current signal and zero-phase voltage signal, or controls the circuit and communicates with the outside. In this conventional ground fault detector, the line voltage and line current of each phase are calibrated by adjusting the amplification factors of the amplifiers 9 and 10, and then the zero-phase current and zero-phase voltage are adjusted to the amplifiers 13 and 14. To calibrate. This calibrated ground fault detection device is installed and used on the actual distribution line.

[0003]

When the ground fault detection device is calibrated and then installed on the power distribution line, each sensor unit is selected depending on the mounting condition of the photocurrent sensor or the photovoltage sensor or the mounting location (near a building, a tree, etc.). Since the voltage detection sensitivity changes due to changes in the current detection sensitivity and the stray capacitance between the phases, a residual component is generated, and there is a problem that the ground fault accident detection device does not operate or the detection accuracy deteriorates. It is an object of the present invention to provide a ground fault accident detection device in which after the ground fault accident detection device is installed on a power distribution line, the amplification factor of the sensor output of each phase is adjusted to reduce the influence of the residual component. And

[0004]

In order to solve the above-mentioned problems, a ground fault detection device according to the present invention uses a photoelectric conversion unit to convert the signals of a photocurrent sensor and a photovoltage sensor provided on a distribution line into electricity. In a ground fault accident detection device that converts into a signal and adds the electrical signals of each phase of the distribution line to detect a ground fault accident by the control device, a digital signal that is connected to the opto-electric converter and operates by the signal from the control device. Potentiometer,
A variable amplifier including an amplifier connected to the digital potentiometer is provided.

[0005]

When the ground fault detection device is calibrated by the above means before being installed on the power distribution line and actually installed on the power distribution line and the ground fault detector is powered on, the residual current and Since the residual voltage is A / D converted, the control device calculates the effective values of the residual current and the residual voltage, and the amplification factor of the variable amplifier of each phase is adjusted in order to minimize the values.
The influence of the residue can be minimized.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention,
FIG. 2 is a circuit diagram of an essential part, and the same parts as those in FIG. Variable resistors 20, 21 are connected to a variable resistor 23 in series with the digital potentiometer 22 as shown in FIG. A fixed resistor 25 is connected in parallel to the amplifier, and one input side of the amplifier is grounded. The digital potentiometer is configured so that a signal from the control device 19 can be input. The ground fault detection device configured as described above calibrates the line voltage and line current of each phase by adjusting the variable resistor 23 of the variable amplifiers 20 and 21. In this case, the digital potentiometer 22 is set to a predetermined size by the control device 19.
Next, the amplifier 1 uses the zero-phase current or zero-phase voltage obtained by adding the line voltage or line current in the adders 11 and 12.
Calibrate by adjusting the amplification factors of 7 and 18. If the photocurrent sensor or photovoltage sensor of the ground fault accident detection device calibrated in this way is installed on the actual distribution line and power is applied to each phase of the distribution line, and a ground fault has not occurred, The current sensor or the voltage sensor detects the line current or the line voltage, the adder detects the residual current or the residual voltage, the amplifier amplifies, and the A / D converter converts the residual current or the residual voltage analog signal into a digital signal. It is converted and output to the control device 19. The control device calculates the effective value of the residual signal, and transmits a signal from the control device to the digital potentiometer 22 of the R-phase variable amplifier 20 so that the value of the residual signal becomes the minimum, and adjusts the digital potentiometer to adjust the amplification factor. Change. After changing the amplification factor of the R-phase variable amplifier, the residual current is obtained again, and the zero-phase current is calculated by the controller as the effective value. This is repeated several times and the digital potentiometer 22 is set so that the residual content is minimized. Next, by adjusting the variable amplifier 20 connected to the S-phase photocurrent sensor and the variable amplifier 20 connected to the T-phase photocurrent sensor, the influence of the residual component is minimized. The above adjustment is repeated several times for each phase to minimize the residual content. R, S, T in the same way
Adjust the variable amplifier 21 connected to the phase photovoltage sensor. After the adjustment, normal measurement is performed to detect the ground fault. In the embodiment, the variable amplifiers 20 and 21 and the adders 11 and 12 are separated, but they may be combined to perform the same function, and the variable resistor 23 is inserted in the variable amplifiers 20 and 21. It may be connected before or after the amplifier.

[0007]

According to the present invention, the amplification factor of each phase is automatically fine-tuned so that the influence of the residual component is minimized when the power of the ground fault detector is turned on. The ground fault accident detection device does not operate and the detection accuracy does not deteriorate, and an effect of being able to detect a ground fault accident accurately and with high accuracy is obtained.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a ground fault accident detection device showing an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram showing the ground fault accident detection device of FIG.

FIG. 3 is a circuit configuration diagram of a conventional ground fault detection device.

[Explanation of symbols]

1, 2, 3 Photocurrent sensor 4, 5, 6 Photovoltage sensor 7 Electric-optical conversion unit 8 Optical-electric conversion unit 11,
12 adder 13 and 14 amplifier 17 and 18 A / D converter
19 Control device 20, 21 Variable amplifier 22 Digital potentiometer 23 Variable resistor 24 Amplifier 25 Fixed resistor

Claims (1)

[Claims] 1. A control device for converting signals of a photocurrent sensor and a photovoltage sensor provided in each phase of a distribution line into an electric signal by an opto-electric conversion unit and adding the electric signals of each phase of the distribution line. In a ground fault accident detection device that detects a ground fault accident by using a digital potentiometer that is connected to the opto-electric converter and is activated by a signal from the control device, and a variable amplifier that is composed of an amplifier connected to this digital potentiometer is provided. Characteristic ground fault accident detection device