JPH0552467B2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to a ground fault detection method for high voltage equipment,
In particular, it relates to a method for detecting ground fault current and ground fault locations in sealed electrical equipment.

(Technical background of the invention and its problems) Recently, due to the problem of land shortage and safety in cities, high voltage equipment such as substations has been replaced with an air insulation system in which live parts are insulated by air, The so-called reduced-sized gas insulated switchgear (hereinafter referred to as GIS), which has live conductors placed inside a container and insulated between them using SF6 gas, etc., has come to be widely adopted. In this GIS, the conductor of the live part is completely covered by a metal pressure vessel, so in the event of an internal accident, it is difficult for maintenance personnel to visually determine the location of the accident. Also,
The size of GIS, for example for 500KV, can be over 100 meters in length. In order to quickly carry out recovery work such as isolating and replacing the accidental part, it is extremely important to detect the accident and to know the point of the accident within a short time after the accident occurs. Furthermore, if the magnitude of the fault current can be known, the extent of damage can be estimated.

Internal accidents in high-voltage equipment include ground faults and phase-to-phase short circuits, but there are cases in which the ground fault ends alone,
In many cases, ground faults develop into phase-to-phase short circuits, so it is of great significance to promptly detect ground faults.

(Purpose of the Invention) The present invention has been made in view of the above-mentioned needs, and is intended to detect the internal ground fault location and ground fault current value of sealed electrical equipment such as GIS. The purpose of this invention is to provide a fault detection method.

(Summary of the Invention) In the present invention, in a high-voltage device, each of the folded closed cases that are divided and insulated from each other is grounded by a plurality of grounding wires. Currents I1 and I2 flow through any pair of grounding wires among the plurality of grounding wires connected to the closed case of the same insulation class.
|I′2a sinωt + αI′2b sin(ωt+βθ) |>K However, I1=I′2a sinωt I2=I′2b sin(ωt+θ) I′2a and I′2b are the respective maximum current values ω is the angular frequency of the current, t is time, α and β are arbitrary constants, and K is characterized in that it is determined that a ground fault has occurred when the current value is in the dead zone.

(Embodiments of the Invention) [Configuration of the Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a partially cutaway sectional view of a GIS tank 1 in which the ground fault detection method of the present invention is implemented. In FIG. 1, a GIS tank 1 has a central conductor 2 to which a high voltage from a power transmission line (not shown) is applied, and a closed case 4 that is divided and insulated from each other via an insulating plate 3. There is. Two ground wires 5a and 5b are attached to each closed case 4 and grounded. Current detection heads 6a and 6b are connected to the ground lines 5 and 5b, respectively. These detection heads 6a, 6b are connected to the ground wire 5.
The ground fault induced current I due to the ground fault current flowing through a and 5b
1 and I2, respectively, are incorporated. Two optical fibers 7, 8, 7', 8' are connected to each of the detection heads 6a, 6b, and the other ends of these optical fibers are connected to a receiver 9.

FIG. 2 shows one detection head 6 of the above-mentioned detection device.
3 is a wiring diagram from a to a receiver 9. FIG.

A magnetic core 10 is provided in the detection head 6a, which is arranged to face the ground wire and forms a magnetic path for magnetic flux generated by a ground fault current in the ground wire. The above-mentioned coil 11 for inducing ground fault current is wound around this magnetic core 10, and the coil 1 is connected in series with a semi-fixed resistor 12 and a pair of light emitting diodes 13 and 14 connected in parallel with each other with opposite polarities. It is connected. The output lights of the light emitting diodes 13 and 14 are input to optical-to-electrical converters (hereinafter referred to as O/E converters) 15 and 16 of the receiver 9 via optical fibers 7 and 8, respectively. The outputs of the O/E converters 15 and 16 are sequentially connected to a synthesis circuit 17 and a determination circuit 18, which will be described later.

The receiver 9 receives the ground fault induced current I from each optical fiber transmission line 7, 8, 7', 8' as shown in FIG.
1, an O/E converter 15,1 including avalanche photodiodes corresponding to each positive and negative component of I2.
6, 15', 16', and synthesis circuits 17, 17' for synthesizing their outputs, respectively. The determination circuit 18 includes a correction circuit 19 that adjusts the phase and absolute value of the output from the synthesis circuit 17', an adder 20 that adds the outputs of this correction circuit 19 and the synthesis circuit 17, and the output of the adder 20. It has a current output device 21 that displays the current as it is, a determiner 22 that compares the output of the adder 20 with a predetermined value K to determine a ground fault, and a ground fault display section 23.

[Operation of the embodiment] The above detection device operates as follows. A current corresponding to the current flowing through the ground wire 5a is induced in the coil 11 of the detection head 6a. Since this current is alternating current, the light emitting diode 13 emits light due to its positive polarity component, and the light emitting diode 14 emits light due to its negative polarity component. Then, the optical fibers 7 and 8 are separately operated.
It is sent to the E converters 15 and 16, and the synthesis circuit 17
The original current waveform is restored.

In this way, the combining circuits 17 and 17' shown in FIG.
and the adder 20 adds it. The output current is determined by a comparison/determination device 22.

Here, the relationship between currents during normal times and during ground faults will be explained with reference to FIGS. 4 and 5. FIG. 4 shows the normal operating condition, where the load current I1 causes the grounding wire 5a,
Induced currents I2a and I2b flow through 5b, respectively. The currents I2a and I2b are equal in magnitude,
The phases are opposite. That is, as shown in the following equation, the two directions cancel each other out, and the vector sum becomes zero.

I〓2a+I〓2b=0 ...(1) On the other hand, if a ground fault occurs between the conductor 2 and the closed case 4 between the grounding wires 5a and 5b, the ground fault will occur as shown in Figure 5. Current If and current I2a, I2
As is clear from Kirchhock's law, the relationship with b can be expressed by the following equation.

I〓2a＋I〓2b＝I〓f ...(2) As mentioned above, find the vector sum of the current flowing through the grounding wires 5a and 5b, and if it is zero, there is no internal ground fault and it is zero. If not, it is clear that a ground fault has occurred. Further, this sum current I〓f represents a ground fault current.

The receiver of FIG. 3 utilizes the above phenomenon to detect ground faults. That is, the adder 20 combines the alternating currents obtained by the two detection heads to obtain a vector sum. Under normal operating conditions, currents as shown by the solid lines are obtained. That is, the output currents of the combining circuits 17 and 17' have opposite phases to each other, and their sum becomes zero. If there is a ground fault,
A current as shown by the broken line is obtained. However, in reality, there are errors in the receiving circuit and the combining circuit, so even under normal operating conditions, the measured value of I〓2a and the value shown in equation (1) differ.
The vector sum with the measured value of I〓2b is not zero.
Therefore, there is a possibility of erroneous determination. In order to prevent this misjudgment, the correction circuit is provided with an adjustment function as shown in the following equation.

I'2a sinωt+αI'2b sin(ωt+βθ)>K...(3) where, I'2a: Peak value of the measured value of the current flowing through the grounding wire 5a I'2b: Peak value of the measured value of the current flowing through the grounding wire 5b Peak value θ: Phase difference between I′2a and I′2b α: Coefficient β that adjusts the magnitude of the second term in equation (3): Coefficient K that adjusts the phase difference: Dead zone α and β are normal operation Adjust so that the value on the left side of equation (3) becomes almost zero. Even so, it cannot be made completely zero, so a dead zone K is provided.
If the determination device 22 exceeds K, it is determined that an internal ground fault has occurred, and the ground fault indicator 23 displays this. The current output from the terminal 21 may be displayed using a cathode ray tube or the like to display the absolute value as a numerical value, or may be output as a waveform. From the above, it is possible to know whether there is a ground fault and the magnitude of the ground fault current.

(Effects of the Invention) According to the present invention, in a high-voltage device having a closed case that is divided and insulated from each other and to which a plurality of ground wires are connected, Since the configuration detects ground faults by focusing on the vector sum of the currents flowing through any pair of ground wires among multiple ground wires, it is possible to clearly distinguish between the induced current during normal operation and the ground fault current during a ground fault. ground faults can be distinguished, allowing highly reliable ground fault detection.
Moreover, if each closed case is grounded at two points, it becomes possible to detect not only ground faults but also the magnitude of ground fault current.

[Brief explanation of the drawing]

Fig. 1 is an equipment configuration diagram related to the method of the present invention, Fig. 2 is a wiring diagram of a part of the detection device, Fig. 3 is a circuit block diagram of the receiver, and Figs. 4 and 5 are diagrams explaining the principle of detection. It is. 1... High voltage switchgear, 2... Center conductor, 4...
...Closed case, 5a, 5b...Ground wire, 6a,
6b...Detection head, 7, 8, 7', 8'...Optical fiber transmission line, 9...Receiver, 15, 15', 1
6, 16'... O/E converter, 17, 17'... Synthesizing circuit, 19... Correction circuit, 20... Adder, 2
2... Comparison judge.

Claims (1)

[Scope of Claims] 1. A plurality of ground wires are connected to each of the closed cases that are divided and insulated from each other, and any pair of ground wires among the ground wires connected to the closed cases of the same insulation category is connected to each other. Detect the currents I1 and I2 flowing in the A ground fault detection method for high voltage equipment, characterized in that a ground fault is determined when K is a current value in a dead zone. ω is the angular frequency of the current. t is time.