JPH0571911B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a zero-phase current transformer that detects a zero-phase current in order to discover a ground fault in a three-phase distribution line.

[Conventional technology]

Figure 2 is a schematic diagram showing the configuration of a conventional zero-phase current transformer described in ``Instrument Transformers'' (Denki Shoin, written by Mihoji Ikeda), in which 1a, 1b, and 1c are the positions. A three-phase distribution line with a phase difference of 120 degrees is shown. Inside of it 3
An annular iron core 2 is provided so that the phase distribution lines 1a, 1b, and 1c pass through it, and a secondary winding 3 is wound around a part of the iron core 2. A current detection section 4 that detects the current flowing through the secondary winding 3 is connected.

The current flowing through the three-phase distribution lines 1a, 1b, 1c is
At steady state, it consists of a positive phase component and a negative phase component, and the magnetic flux induced in the iron core 2 is a composite of the magnetic fields proportional to the positive phase component and negative phase component of each phase. The magnetic flux of core 2 is zero. Therefore, in this case, no current flows through the secondary winding 3. However, when a ground fault occurs in a distribution line, zero-sequence current flows through the distribution line, and even if the three-phase currents are combined, they do not become zero.
Magnetic flux is induced in the iron core 2, a secondary current proportional to the zero-sequence current flows in the secondary winding 3, and the current is detected by the current detection section 4.

[Problem that the invention seeks to solve]

In the event of a ground fault, in order to narrow the power outage area as much as possible and shorten the recovery time,
It is necessary to quickly and accurately find the location of a ground fault, and for this purpose it is better to install zero-phase current transformers not only within the substation premises, but also midway along the distribution line.

However, in the conventional zero-phase current transformer, the three-phase distribution line runs through one iron core, so
When trying to install a zero-phase current transformer on an outdoor distribution pole due to the large iron core, there is a problem that it is difficult to install it, and the distribution line may not pass through the conductor's iron core. Because of this, there was a problem in that accidents could escalate in the event of a lightning strike.

The magnitude of the zero-sequence current that occurs when a ground fault occurs in a distribution line is 1/100 to 1/1000 of the magnitude of the current flowing through each distribution line during normal operation. In the method of detecting a zero-sequence current by converting it into a signal and then synthesizing each phase current, it was necessary to increase the detection accuracy of each phase current.

The present invention has been made in view of the above circumstances, and provides a zero-phase current transformer that is small and lightweight, has no risk of aggravating ground faults, and is suitable for installation on power distribution poles, etc. The purpose is to

[Means for solving problems]

The zero-phase current transformer according to the present invention detects the zero-phase current of a three-phase distribution line, and includes three photocurrent detection elements that detect the current of each phase of the three-phase distribution line; an electrical/optical signal converter that provides an optical output signal to the photocurrent detection element; and an optical output signal that is provided from the electrical/optical signal converter to each photocurrent detection element based on the optical signal output from each of the photocurrent detection elements. an optical signal output controller that controls the electrical/optical signal converter so that the levels of the signals are the same; and an optical multiplexer that individually takes out each optical signal output from each of the three photocurrent detection elements and combines them. and a circuit that detects a zero-sequence current of a three-phase distribution line based on the output of the optical multiplexer.

[Effect]

In the zero-phase current transformer of the present invention, the current of each phase is detected as an optical signal by a photocurrent detection element provided in each of the three-phase distribution lines. The detected optical signals are combined by an optical multiplexer, and then a zero-sequence current is detected based on the output of the optical multiplexer.

〔Example〕

The present invention will be specifically described below based on drawings showing embodiments thereof. FIG. 1 is a schematic diagram showing the configuration of a zero-phase current transformer of the present invention, and in the figure, 1a, 1b, 1
c shows a three-phase distribution line with a phase difference of 120 degrees. Photocurrent detection elements 5a, 5b, and 5c, which can detect the magnitude of the current flowing through the corresponding distribution line based on the rotation of the light deflection plane according to the magnetic field strength, are installed on each distribution line 1a, 1.
It is provided within the magnetic field generated by the currents b and 1c. The photocurrent detection element 5a (5b, 5c) converts an electrical signal into an optical signal via optical fibers 6a (6b, 6c) and 7a (7b, 7c), respectively.
It is connected to an optical distributor 9a (9b, 9c) that distributes optical signals from the optical signal converter 8a (8b, 8c) and the photocurrent detection element 5a (5b, 5c). electricity·
The optical signal output from the optical signal converter 8a (8b, 8c) is transmitted through the optical fiber 6a (6b, 6c), the photocurrent detection element 5a (5b, 5c), and the optical fiber 7a (7c).
b, 7c) to the optical distributor 9a (9b, 9c)
Enter. The magnetic field generated by the current flowing through the power distribution line 1a (1b, 1c) rotates the light deflection plane in the photocurrent detection element 5a (5b, 5c). The optical splitter 9a (9b, 9c) distributes the input optical signal and converts it into an electrical/optical signal converter 8a (8b, 8
c) to connect the electrical/optical signal converter 8a (8b,
The distributed optical signal is outputted to an optical signal output controller 10a (10b, 10c) that controls the optical signal output from 8c) and an optical multiplexer 11 that combines a plurality of optical signals.

The optical signal output controller 10a (10b, 10c) is
A control signal is output to the electrical/optical signal converter 8a (8b, 8c) so that the level of the optical output signal from each electrical/optical signal converter 8a (8b, 8c) is the same. The optical multiplexer 11 includes optical splitters 9a, 9b, 9c.
The combined optical signal is passed through a filter to separate it into a DC component and an AC component.
The component optical signals are output to the optical/electrical signal converter 12. The optical/electrical signal converter 12 converts these two component optical signals into electrical signals, and outputs the electrical signals to the signal processing circuit 13 . The signal processing circuit 13 calculates the quotient (AC component/DC component) of the input two-component electric signal, and converts this calculated value into a zero-sequence current.

Next, the operation will be explained. The optical signals of the same level converted from electrical signals by the electrical/optical signal converters 8a, 8b, and 8c are converted into electrical/optical signal converters 8a, 8b, and 8c.
8b, 8c via optical fibers 6a, 6b, 6c, photocurrent detection elements 5a, 5b, 5c
In this case, the light deflection plane rotates depending on the strength of the magnetic field generated by the current flowing through the power distribution lines 1a, 1b, and 1c. The optical signal whose polarization plane has been rotated passes through optical fibers 7a, 7b, 7c and is sent to optical splitters 9a, 9b,
9c and input to the optical multiplexer 11, where the three-phase optical signals are combined. Optical distributor 9
The optical signals distributed at the terminals a, 9b, and 9c are input to the optical signal controllers 10a, 10b, and 10c, and based on the input signals, the respective electrical/optical signal converters 8a, 8
The control signals are transmitted from the optical signal output controllers 10a, 10b, 10c to the electrical/optical signal converters 8a, 8b, 8c so that the levels of the optical output signals of the optical signals 8a, 8c are the same.
is output to.

The combined optical signal passes through a filter in the optical waveguide 1 and is divided into AC and DC components, and the optical signal of each component is converted into an electrical signal by the optical/electrical signal converter 12. is converted by the signal processing circuit 13 and the zero-sequence current is detected.

During steady state, the vector sum of alternating current flowing through three-phase distribution lines 1a, 1b, and 1c is zero, and the levels of the optical output signals from electrical/optical signal converters 8a, 8b, and 8c are the same, so the light during steady state The AC component of the signal is zero. Therefore, the quotient of both components in the signal processing circuit 13 becomes zero, and no zero-sequence current is detected.

On the other hand, if a ground fault occurs, the three-phase distribution line 1a,
The vector sum of AC flowing through 1b and 1c is not zero, and there is an AC component of the optical signal. In this case, the signal processing circuit 13 calculates the quotient (a non-zero value) of both components, and multiplies this calculated value by an appropriate proportionality constant to detect the zero-sequence current.

In this embodiment, since the signal processed by the signal processing circuit 13 is only the zero-sequence current component, the zero-sequence current can be accurately detected without increasing the processing accuracy of the signal processing circuit 13 too much.

〔Effect of the invention〕

As described above, the zero-phase current transformer according to the present invention individually extracts the optical signal output from each photocurrent detection element,
An optical signal output controller is provided to control the electrical/optical signal converter so that the level of the optical output signal given from the electrical/optical signal converter to each photocurrent detection element is the same based on each of these optical signal outputs. Therefore, there are variations in the characteristics such as modulation degree and loss of each photocurrent detection element, the characteristics of the electric/optical signal converter, and the loss of other optical transmission media, and other variations in characteristic deterioration over time. However, the same level of optical signal output can be given to each photocurrent detection element without being influenced by these factors, and excellent effects such as stable detection accuracy and high reliability can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a zero-phase current transformer of the present invention, and FIG. 2 is a schematic diagram showing the configuration of a conventional zero-phase current transformer. 1a, 1b, 1c...3-phase distribution line, 5a, 5
b, 5c...photocurrent detection element, 11...optical multiplexer. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A zero-phase current transformer that detects a zero-sequence current in a three-phase distribution line, comprising three photocurrent detection elements that detect the current in each phase of the three-phase distribution line, and each of the photocurrent detection elements. an electrical/optical signal converter that provides an optical output signal to each photocurrent detection element, and an optical output signal that is provided from the electrical/optical signal converter to each photocurrent detection element at the same level based on the optical signal output from each of the photocurrent detection elements. an optical signal output controller that controls the electric/optical signal converter so that A zero-phase current transformer comprising: a circuit for detecting a zero-phase current of a three-phase distribution line based on the output of the wave transformer.