JPH0452049B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground fault indicator that indicates when a ground fault occurs in a power distribution line.

The purpose of this is to clearly distinguish between cable ground faults where the insulation recovers instantly and metal ground faults where the ground fault continues, and to display a fault indication only in the case of a metal ground fault. Moreover, even if there is a ground fault that may be confused with a metal ground fault, such as a momentary ground fault caused by contact with a tree, erroneous indications due to this can be prevented, and the above-mentioned metal ground fault can be clearly indicated even more reliably. To provide a ground fault indicator.

The drawings showing the embodiments of the present application will be described below. In FIG. 1, reference numeral 1 denotes a high-voltage distribution line, which is composed of distribution lines such as underground cables and overhead distribution lines. 2 is a multi-circuit switch installed on the high-voltage distribution line 1, and is generally installed inside a handhole A or a building B. 3 is a ground fault indicator attached to the distribution line drawn out from the multi-circuit switch 2.

Next, this ground fault indicator 3 will be explained in detail based on FIG. 2. This display 3 is a display circuit 4
and a power supply circuit 16.

First, in the display circuit 4, 5 is a well-known zero-phase current transformer attached to the distribution line, which detects the flow of current due to a ground fault in the distribution line 1 and outputs a detection signal. be. Reference numeral 6 denotes a sensitivity adjuster for adjusting input sensitivity.
7 is a well-known amplifier circuit, and 8 is a first integrating circuit which receives the output signal of the amplifier circuit 7 and outputs a signal obtained by removing the pulse portion of the signal. The time constant of this circuit 8 is such that it absorbs the signal from the amplifier circuit when it is a pulse-like signal in the case of a general cable ground fault, and absorbs the signal in the case of a metal ground fault (power applied to the distribution line). When the signal has the same waveform as the waveform), it is set to a value such that it can be output through the integrating circuit 8, for example, 1.5 milliseconds. Reference numeral 9 denotes a first level discrimination circuit which produces an output when the output signal of the first integration circuit 8 exceeds a predetermined reference level. Reference numeral 10 denotes a well-known differential circuit, which is composed of, for example, a capacitor and a resistor. 11 is a well-known rectifier circuit, and 12 is a waveform shaping circuit, each of which generates an output signal for a certain period of time each time a signal from the rectifier circuit 11 is received. 13 is a second integrating circuit which integrates the output signal from the waveform shaping circuit 12 with a long time constant and outputs the integrated signal. 1
Reference numeral 4 denotes a second level discrimination circuit which produces an output when the output of the second integration circuit 13 reaches a predetermined level. Reference numeral 15 denotes a display section which performs display operations in response to the output of the second level discrimination circuit 14.

Next, the power supply circuit 16 is a circuit for supplying power to the display circuit 4. In this power supply circuit 16, numeral 17 is a well-known current transformer which generates an alternating current output when a load current flows through the distribution line. Reference numeral 18 represents a known transformer, 19 represents a known rectifier circuit, and 20 represents a known smoothing circuit. Reference numeral 21 designates a well-known constant voltage circuit that always produces a constant voltage DC output even if the input voltage from the smoothing circuit 20 fluctuates, and the DC output from this constant voltage circuit 21 is used for the display circuit. 4 is supplied to each circuit.

Next, regarding the operation of the display 3 having the above configuration, the output waveforms of each circuit are shown in FIG. The explanation will be given with reference to When a metal ground fault occurs at a certain point on the high-voltage distribution line 1 and the balance between the three phases of the distribution line is lost, a zero-sequence current flows. Then, the zero-phase current transformer 5 of the ground fault indicator 3 installed on the power supply side of the point of occurrence of the metal ground fault in the distribution line detects this current, and the detection as shown in FIG. 3 5a occurs. Output a signal. This signal passes through the sensitivity adjuster 6, and then passes through the amplifier circuit 7.
The signal is amplified to form a waveform as shown in 7a, and reaches the first integrating circuit 8. Note that the sensitivity adjuster 6 is connected to the display 3.
If a ground fault occurs on the power supply side from the attached point, even if the current transformer 5 detects the charging current (scooping current) at that time, the subsequent circuits are adjusted so that they do not operate. be. The signal is integrated in the first integrating circuit 8 and becomes a waveform as shown in 8a, and reaches the first level discriminating circuit 9. The first level discrimination circuit 9 has a reference level 9b determined in advance, compares the signal 8a with the reference level 9b, and outputs a signal as shown at 9a when the signal 8a exceeds this level 9b. This signal is differentiated by a differentiator circuit 10, and a rectifier circuit 11
The signal is rectified at 11a to become a signal as shown in 11a, and reaches the waveform shaping circuit 12. The waveform shaping circuit 12 outputs a waveform signal 12a that lasts for a certain period of time, regardless of the magnitude of the signal, every time the signal from the rectifier circuit 11 is received. This signal is integrated by the second integration circuit 13 to form a waveform as shown in 13a, and reaches the second level discrimination circuit. Second level discrimination circuit 1
4, a predetermined level 14b is determined in advance,
Comparing the signal 13a and the predetermined level 14b, the signal 1
3a exceeds this level 14b, a signal as shown at 14a is output. This signal reaches the display section 15, and the display section 15 performs a display operation.

Next, when a cable ground fault occurs at a certain point on the high-voltage distribution line 1, the zero-phase current transformer 5 outputs a detection signal 5a in the same way as a metal ground fault. This signal passes through the sensitivity adjuster 6 and the amplifier circuit 7, has a waveform as shown in 7a, and reaches the first integrating circuit 8, as in the case of a metal ground fault. When this signal is integrated by the first integrating circuit 8, the pulse portion of the signal is removed, resulting in a signal waveform as shown in 8a, which reaches the first level discriminating circuit 9. The first level discrimination circuit 9 compares the reference level 9b and the signal 8a.
does not exceed the reference level 9b, so no output is generated. Therefore, the display unit 15 does not perform any display operation.

Next, if a signal similar to a metal ground fault is detected by the zero-phase current transformer due to contact with a tree, etc., the signal waveforms 5a, 7a, 8a, 9a,
11a and 12a are obtained, respectively. However, the time required for ground faults caused by contact with trees, etc., is generally very short. Therefore, the signal waveform 13a of the second integrating circuit 13
is the predetermined level 14b of the second level discrimination circuit 14
does not reach. Therefore, the second level discrimination circuit 14 does not output a signal, and the display section 15 does not perform a display operation.

Here, the value of the constant time T ₁₂ of the signal output from the waveform shaping circuit 12, the value of the time constant of the second integrating circuit 13, the predetermined level 14 of the second level discriminating circuit 14,
The value of b is determined by the fact that the second level discriminator circuit 14 does not produce an output during the duration of an instantaneous ground fault caused by contact with a tree, and the duration of the ground fault is longer than that (ground fault relay in a substation). The second level discrimination circuit 14 is set in relation to each other so that the second level discrimination circuit 14 generates an output when the second level discrimination circuit 14 continues for a period shorter than the time required for the operation of the second level determination circuit 14 to operate. Note that the time it takes for the circuit 14 to produce an output is set to, for example, 0.5 seconds.

Next, FIG. 4 shows an example of the structure of the display section 15, in which 22 is a well-known transistor, 23 is a well-known relay, 24 is a solenoid coil, and 25 is a plunger made of a magnetic material such as iron. A retaining claw 25a is provided at the tip of the cage. 26 is the target.

In this configuration, when the signal 14a from the second level discrimination circuit is applied to the transistor 22, the transistor 22 becomes conductive and operates the relay 23, which closes the contact 23a. Therefore, current flows through the solenoid coil 24, and the solenoid coil 24 is energized. Due to this magnetic force, the plunger 25 moves in the direction of arrow C, and the retaining claw 25a
is removed from the target 26, and the target 26 protrudes downward into a display state.

As described above, in the present invention, the pulse-like signal caused by the cable ground fault among the detection signals is removed by the first integrating circuit 8, so that if a ground fault occurs and the signal is detected. , a cable ground fault that is generally not considered a fault or does not require replacement of the distribution line will not be indicated as a fault, but a fault may be indicated only in the case of a metal ground fault, making it clear that countermeasures are required. Has perceptible usefulness.

Moreover, in the above case, even if a signal similar to a metal ground fault is generated when a tree comes in contact with a power distribution line, the waveform shaping circuit 12, second integration circuit 13, and level discrimination circuit 14 This is because the display is made only when the signal due to the interference comes in beyond the time due to the reasons mentioned above.
This has the effect of preventing erroneous indications due to the above reasons and improving the accuracy of clearly indicating the metal ground fault.

[Brief explanation of the drawing]

The drawings show an embodiment of the present application. Fig. 1 is a system diagram of a high-voltage distribution line, Fig. 2 is a block circuit diagram of a ground fault indicator, Fig. 3 is a waveform diagram, and Fig. 4 is a diagram of a display section. The figure which shows an example of a structure. 1...High voltage distribution line, 3...Ground fault indicator,
8...First integration circuit, 9...First level discrimination circuit, 12...Waveform shaping circuit, 13...Second integration circuit, 14...Second level discrimination circuit.

Claims (1)

[Claims] 1. In a ground fault indicator that is attached to a distribution line drawn out from a multi-circuit switch to detect and display a ground fault when a ground fault occurs in the attached distribution line, The fault indicator consists of a zero-phase current transformer that detects when current flows through the distribution line due to a ground fault and outputs a detection signal, and a zero-phase current transformer that receives the output signal of the zero-phase current transformer. a first integrating circuit configured to output a signal obtained by removing the pulse component from the signal; and a first integrating circuit configured to receive the output signal of the first integrating circuit and generate an output when the signal exceeds a predetermined reference level. a first level discriminating circuit, a waveform shaping circuit that generates an output signal for a certain period of time each time a signal from the level discriminating circuit comes in, and a signal obtained by integrating the output signal from the waveform shaping circuit. a second integrator circuit configured to output
and a display section that performs a display operation in response to the output of the second level discriminating circuit, and the time constant of the second integrating circuit is such that the output signal of the waveform shaping circuit is Necessary to cause the second level discrimination circuit to generate an output in a state that continues for a period longer than the instantaneous contact time of a tree with the distribution line, but for a time shorter than the operating setting time of the ground fault relay at the substation. A ground fault fault indicator characterized in that it is set to reach a certain level value.