JPS6212878A - System for monitoring earth and short-circuit of one-point earthing system - Google Patents

Abstract

PURPOSE:To detect whether earth or short-circuit is generated or not in the non-working status of a system and to discriminate whether a detecting function is normal or not by calculating impedance between branch points of an earthing cable. CONSTITUTION:Respective pairs of exciting transformers CT10-CT1n and current detecting transformers CT20-CT2n are connected between respective branch points of earthing cables 70-7n in an earthing network consisting of an one-point earthing system. The transformers CT10-CT1n in respective paths are successively excited, loop currents of respective paths are detected by the transformers CT20-CT2n forming pairs with the transformers CT10-CT 1n synchronously with the excitation and the loop impedance is calculated on the basis of the loop currents to detect whether earth or short is generated or not. Prior to said detection, the transformers CT10-CT1n are excited with a constant voltage and output signals from the transformers CT10-CT1n are detected to discriminate whether short-circuit or disconnection is generated or not in the transformers, wirings or the like.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to a method for monitoring ground faults and short circuits in a single point grounding system, and more specifically, the present invention relates to a method for monitoring ground faults and short circuits in a single point grounding system. The present invention relates to a novel ground fault/short circuit monitoring method that can detect whether or not a ground fault has occurred, and can also detect whether or not the detection function is normal.

<Prior Art> Conventionally, test systems that use large amounts of power have generally adopted a single-point grounding system in which the system is grounded at one point from the viewpoint of system maintenance and control system malfunction prevention. In order to constantly monitor whether or not a ground fault or short circuit has occurred in the single-point grounding system, for example, the ground current is detected, and if the detected current value deviates from the normal value, it is detected and the ground fault is detected. , to notify that a short circuit has occurred.

In the above test systems that use high power, if the system is operated with a ground fault or short circuit occurring, a large current will flow to the equipment where the ground fault or short circuit has occurred, causing damage to the equipment. Not only that, but also because a large current flows through the grounding cable, the potential of other equipment increases rapidly based on the inductance component of the grounding cable, causing problems such as damage to other equipment or malfunction. do.

Even if the above-mentioned detection method is adopted, it will not be a fundamental solution to such problems. There is a strong need for the development of a monitoring system that can remove ground faults and short circuits without damaging equipment.

Furthermore, such a monitoring system is also required to be capable of determining whether or not it is in a state where it is possible to accurately detect the occurrence of a ground fault or short circuit.

<Purpose> This invention was made in view of the above problems,
Ground faults in single-point grounding systems that can reliably detect whether a ground fault or short circuit has occurred when the system is not in operation, and can also determine whether the above detection function is normal or not. , aims to provide a short circuit monitoring method.

In order to achieve the above object, the ground fault/short circuit monitoring method of the present invention is based on a ground fault/short circuit monitoring system that detects a route from each branch point to an adjacent branch point, and a path from each branch point to an open end of a ground network consisting of a single point grounding system. A pair of excitation transformers and a current detection transformer are installed on the path leading to the path and the path leading to the ground point, and the excitation transformers installed on each path are sequentially excited and synchronized with the excitation of the excitation transformer. Then, the loop current of each path is detected by the current detection transformer paired with the excitation transformer, and by calculating the loop impedance based on the loop current, it is detected whether a short circuit or ground fault has occurred. Since the loop current is inversely proportional to the loop impedance, it is possible to determine which branch is abnormal by detecting the loop current of each branch. Prior to the above detection, the excitation transformer is excited at a constant voltage, the output signal of the current detection transformer is detected, and it is determined whether a short circuit or disconnection has occurred in the transformer, wiring, etc. By determining the state of the output signal of the current detection transformer, it is possible to determine whether a short circuit or disconnection has occurred.

However, it is preferable to excite the excitation transformer using a low-frequency sine wave that is less affected by the capacitance and inductance components of the grounding system, so that it is possible to reliably detect whether or not a ground fault or short circuit has occurred. I can do it.

<Example> Hereinafter, embodiments will be described in detail with reference to the accompanying drawings showing examples.

Figure 4 is a schematic diagram of a single-point grounding system test system, in which equipment (2) (41, etc.) is connected to the power source (1) via power cables (12), (13), and (14). death,
Casings (22) (2) of each equipment (21 (3) (4) etc.
3) (24) and power source (1) to the ground cable (3)
1) (32) (33>(30)).In addition, attached devices (4a), (4b), (4c), etc. are connected to the device), and these attached devices ( 4a)
(4b) (4C) Casing (24a) (24b) (
24c) also ground cables (33a) (33b)
(33c) is connected to the ground cable (33). Then, the casing (2) of the above equipment (3)
3) and the casing (24C) of the accessory device (4C) are connected via a control cable (44c). A start signal from a control device (not shown) is applied to the power source (1), and the power source (1) is activated by intermittently applying a start signal from the outside.

Figure 1 is a diagram showing the electrical configuration for implementing the ground fault and short circuit monitoring method of a single-point grounding system. This is used as a concept that also includes the connection point, grounding point, etc.・
-...- (CTln), and current detection transformer (C
T20)(CT21)...-(CT2n) are installed, the output signal of the oscillator (51) is amplified by the amplifier (52), and applied to the switch (53), and the amplified signal is
The switching device (53) sequentially switches the excitation transformer (CT10
)(CTII)...-(CTln). And a current detection transformer (CT20
) (CT21) ...... (CT2n) to a switch (61) that operates in synchronization with the switch (53).
), and the output signal of the switch (61) is applied to the amplifier (62
) to a predetermined level, and the A/D converter (63)
It is converted into a digital signal by central processing bag @ (cp
u), and the display device 1 (64) is driven by the central processing unit (CPU).

FIG. 2 is a flowchart showing the operation of monitoring ground faults and short circuits, in which the transmitter (51) is activated in step (2), and the switch (51) is activated in synchronization with each other in step (2).
53) By switching the channel by (61) and applying the amplified signal to the excitation transformer (CTln) selected in step (■), the grounding cable (7n)
is excited, and in step ■, the current detection transformer (C
By collecting the signal from T2n) and applying the signal from the current detection transformer (CT2n) to the central processing unit (CPU) in step (2), for example, an effective value is calculated, and in step (2) it is converted to loop impedance. . Next, in step (2), the loop impedance is compared with a reference loop impedance stored in advance in a memory (not shown).

If the loop impedance is smaller than the reference loop impedance, the display device (64) is driven in step (2) to display a daily report indicating that a ground fault or short circuit has occurred in the grounding cable (7n), and the step is repeated. ■Perform the following judgments and processing. On the other hand, if the loop impedance is equal to or higher than the reference loop impedance, the determination and processing from step (2) onwards are performed as is.

In summary, from the ground cable (70) to the ground cable (
7n), the loop impedance is calculated sequentially and the ground cape is smaller than the reference loop impedance.

It is possible to display that a ground fault or short circuit has occurred only for the

Therefore, for example, as shown in Figure 4, if a ground fault has occurred inside the equipment (2) (this may have occurred in the history of the previous test, or may have occurred due to human work error, etc.) ), the impedance of the loop formed by the grounding cables (70) and (72) becomes smaller, and the output signal of the current detection transformer (CT20) (CT22) becomes larger, so the display device (64) is driven. It is possible to display that a ground fault has occurred in a single-point grounding system test system, and prevent damage to equipment caused by starting the power source (1) when a ground fault has occurred. be able to.

In addition, as shown in Fig. 4, there is a case where the circuit return current is designed to flow through the grounding cable (32) of the equipment (3), and this grounding cable (32) is connected to the attached equipment (3).
4C), a large current unexpectedly flows through the grounding cable (33c) of the attached device (4C), and as a result, the potential of the attached device (4c) increases due to the inductance component of the grounding cable (33c). Although it is conceivable that it will jump up significantly and damage the control device or cause it to malfunction, the impedance of the loop formed by the grounding cable (74H75) (77) (78) will become smaller and the current detection transformer (CT24) ( CT25) (CT27) (CT28
), the display device (64) can be driven to indicate that a short circuit has occurred in a single-point grounded test system; Damage to equipment caused by starting the power source (1) can be prevented.

Figure 3 shows a current detection transformer for monitoring ground faults and short circuits.
It is a diagram showing an electrical configuration for determining whether or not the wiring is normal.
2) to the current detection transformer (CT), and the voltage across the resistor (82) is converted to the full-wave rectifier circuit (83).
), and after smoothing by a smoothing circuit (84), the smoothed signal is applied to comparison terminals of two comparators (85) and (86). Different reference signals are applied to the reference terminals of each comparator (85) (86), and the output signal of each comparator (85N8G) is applied to the flip 70 knob (87) (88), respectively. are doing. A reset signal is applied to the flip-flop (87088) for resetting the flip-flop (87088) for each operation.

With the above configuration, the potential difference between both ends of the resistor (82) is
This means that the primary current of the transformer is being measured, and the maximum value is when the wiring is short-circuited in the middle, and the minimum value is when the wiring or the current detection transformer is disconnected. Under normal conditions, it is the intermediate value between the two. becomes.

Since the smoothed signal is also proportional to the above potential difference, by setting the reference signal appropriately, during normal operation,
The output signal of flip 70 tube (81) is “1” level,
The output signal of the flip-flop 70 (88) becomes the "O11 level", and in the event of a short circuit, the flip-flop (87) (8
Both the output signals of the flip-flops (87) and (88) are at the "1" level, and in the event of a disconnection, the output signals of the flip-flops (87) and (88) are both at the "0" level. By detecting the output signal level of the current detection transformer, it can be determined whether the current detection transformer is in a normal operating state.

Although the above description is only for the case where it is applied to a test system, it may also be applied to a system other than a test system.
In short, any single-point grounding system can be similarly applied. Further, although only the case of determining whether the current detection transformer is in a normal operating state has been described, the present invention can be similarly applied to the excitation transformer.

Effect> As described above, the present invention calculates the impedance between the branch points of the ground cable when the power source is not activated, and detects a ground fault or short circuit based on this impedance. Therefore, starting the power source while a ground fault or short circuit is occurring may damage equipment or
It is possible to reliably prevent inconveniences such as damage to the control equipment and malfunctions, and also to ensure that there are no abnormalities in the transformer, wiring, etc. prior to detecting the above-mentioned ground conditions and short circuits, and that the above-mentioned detection can be carried out reliably. Since the above-described method is used for discrimination, it has the unique effect of increasing the reliability of the above-mentioned detection.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the electrical configuration for implementing the ground fault/short circuit monitoring method of a single point grounding system, Fig. 2 is a flow chart showing the operation for monitoring ground faults/short circuits, and Fig. 3 is a ground fault/short circuit monitoring method. Current detection transformer for short circuit monitoring,
Figure 4 is a schematic diagram of a single-point grounding system test system.

Claims (1)

[Scope of Claims] 1. One set each for a path from each branch point to an adjacent branch point, a path from each branch point to the lower end, and a path to the ground point of a grounding network consisting of a single point grounding system. An excitation transformer and a current detection transformer are installed, and the excitation transformers attached to each path are sequentially excited, and in synchronization with the excitation of the excitation transformer, each current detection transformer paired with the excitation transformer is used to By detecting the loop current in the path and calculating the loop impedance based on the loop current, it is possible to detect whether a short circuit or ground fault has occurred. A method for monitoring ground faults and short circuits in a single point grounding system, which detects the output signal of the transformer and determines whether a short circuit or disconnection has occurred in a transformer, wiring, etc. 2. Ground faults and short circuits in the single-point grounding system described in claim 1, wherein the excitation transformer is excited by a low-frequency sine wave that is not easily affected by the capacitance and inductance components of the grounding system. Monitoring method.