JPH0646205B2 - Single point grounding system ground fault and short circuit monitoring method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ground fault and short-circuit monitoring method for a single-point ground system, and more specifically, a ground fault and a short circuit to each branch of a single-point ground system having a plurality of branches. The present invention relates to a new ground fault and short-circuit monitoring method capable of detecting whether or not a fault has occurred.

<Prior Art> Conventionally, in a test system that uses a large amount of power, a system that generates a strong magnetic field, etc., a single-point grounding system that grounds at a single point has been adopted from the viewpoints of system maintenance and control system malfunction prevention. Has been done. Then, in order to constantly monitor whether or not a ground fault or a short circuit has occurred in the one-point ground system, for example, the ground current is detected, and it is detected that the detected current value deviates from the normal value, and the ground fault is detected. , The fact that a short circuit has occurred is notified.

In the above-mentioned test system using large power, when the system is operated in the state where the ground fault and the short circuit occur, a large current flows to the device where the ground fault and the short circuit occur, and the above device is damaged. Not only that, a large current also flows through the ground cable, causing the potential of other equipment to increase sharply based on the inductance component of the ground cable, causing damage to other equipment or causing malfunctions. To do.

Adopting the above-mentioned detection method does not provide any essential solution to such a problem, and it is necessary to detect the location of ground fault or short circuit before operating the system. ,
It has been earnestly desired to develop a monitoring system capable of removing a ground fault or a short circuit before causing damage to equipment.

<Purpose> The present invention has been made in view of the above problems,
An object of the present invention is to provide a ground fault / short circuit monitoring method for a single-point grounding system capable of reliably detecting whether or not a ground fault / short circuit has occurred in a non-operating state of the system.

<Structure> In order to achieve the above object, the present invention provides a ground fault and short-circuit monitoring system in which a path from each branch point to an adjacent branch point, and each branch point to an open end of a grounding network composed of a single-point grounding system. Each set of excitation transformer and current detection transformer is attached to the path leading to and to the grounding point, and the excitation transformers attached to each path are sequentially illustrated and synchronized with the excitation of the excitation transformer. Then, the current detection transformer paired with the excitation transformer detects the loop current of each path, and the loop impedance is calculated based on the loop current to detect whether a short circuit or a 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.

However, it is preferable to excite the excitation transformer with a low-frequency sine wave that is not easily affected by the capacitance and inductance components of the ground system, and be sure to detect whether a ground fault or short circuit has occurred. You can

<Example> Hereinafter, detailed description will be given with reference to the accompanying drawings illustrating an example.

FIG. 3 is a schematic diagram of a test system with a single-point grounding system. Equipment (2) (3) (4), etc. are connected to a power cable (12) for a power source (1).
Connect the casings (22), (23) and (24) of each device (2), (3) and (4) and the power source (1) with the ground cable (3).
There is one point grounding via 1) (32) (33) (30). In addition, accessory devices (4a) (4b) (4c), etc. are connected to the device (4), and casings (24a) (24a) (24a) (24c) of these accessory devices (4a) (4b) (4c)
b) and (24c) are also connected to the above ground cable (33) through the ground cables (33a), (33b) and (33c). Then, the casing (23) of the device (3) and the casing (24) of the auxiliary device (4c) are
c) and are connected via the 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.

FIG. 1 is a diagram showing an electrical configuration for implementing a ground fault and short-circuit monitoring system of a single-point ground system, a ground cable.
(30) (31) ... Between each branch point (used as a concept including the connection point with the casing, the grounding point, etc.) (70) (71)
...... (7n), one pair of excitation transformers (CT10) (CT11) ……
(CT1n) and transformer for current detection (CT20) (CT21) …… (C
T2n) is attached, the output signal of the oscillator (51) is amplified by the amplifier (52), applied to the switching device (53), and the amplified signal is
Exciting transformer (CT10) (CT11) by switching device (53)
It is configured to be applied to (CT1n). Then, the output signal of the current detection transformer (CT20) (CT21) ... (CT2n) is applied to the switching device (61) which operates in synchronization with the switching device (53),
The output signal of the switching device (61) is amplified to a predetermined level by the amplifier (62), converted into a digital signal by the A / D converter (63), and applied to the central processing unit (CPU), and the central processing unit (CP)
The display device (64) is driven by U).

FIG. 2 is a flow chart showing the operation for monitoring the ground fault and the short circuit. In the step, the transmitter (51) is operated,
Switches (53) (6
1) Switch the channel and apply the amplified signal to the excitation transformer (CT1n) selected in the step to excite the ground cable (7n) and in the step, output the signal from the current detection transformer (CT2n). Collect
By applying the signal from the current detecting transformer (CT2n) to the central processing unit (CPU) in the step, for example, the effective value is calculated and converted into the loop impedance in the step. Next, in step, it is compared with a reference loop impedance stored in advance in a memory (not shown). Then, if it is smaller than the reference loop impedance, by driving the display device (64) in the step, an alarm indicating that a ground fault or a short circuit has occurred in the ground cable (7n) is displayed, and the following steps are repeated. Is determined and processed. On the other hand, if the impedance is equal to or higher than the reference loop impedance, the determination and processing are performed as they are in the step or less.

In summary, calculate the loop impedance sequentially from the ground cable (70) to the ground cable (7n), and display that the ground fault or short circuit has occurred only for the ground cable that is smaller than the reference loop impedance. You can

Therefore, for example, as shown in FIG. 3, when a ground fault occurs inside the device (2) (in the case of the history of the previous test, or when it occurs due to an artificial work error, etc.) (Possibly), the impedance of the loop formed by the ground cables (72) (70) is reduced, and the current detection transformer (CT2
2) Since the output signal of (CT20) becomes large, it is possible to drive the display device (64) to display that a ground fault has occurred in the single point grounding test system. It is possible to prevent damage to the device due to activation of the power source (1).

In addition, as shown in Fig. 3, the ground cable (3
2) is designed to carry a circuit return current, and this ground cable (32) is in contact with the accessory (4c), the ground cable (33c) of the accessory (4c). An unexpectedly large current may flow, and as a result, the inductance component of the ground cable (33c) may cause the potential of the accessory device (4c) to jump up significantly, damaging the control device or causing a malfunction. Since the impedance of the loop formed by (74) (75) (77) (78) becomes small and the output signal of the current detection transformer (CT24) (CT25) (CT27) (CT28) becomes large, the display device ( 64) can be driven to indicate that a short-circuit has occurred in the single-point grounded test system.In this case as well, the power source (1)
It is possible to prevent the equipment from being damaged due to the activation of the.

Although only the case where the present invention is applied to the test system has been described above, a system other than the test system may be used, and the point is that the system can be similarly applied as long as it is a single-point grounding system.

<Effect> As described above, according to the present invention, the impedance between the branch points of the ground cable is calculated in the state where the power source is not activated, and the ground fault and the short circuit are detected by the impedance. It is possible to reliably prevent inconveniences such as equipment damage, controller damage, and malfunction by activating the power source in the state where a ground fault or a short circuit occurs.

[Brief description of drawings]

FIG. 1 is a diagram showing an electrical configuration for implementing a ground fault and short-circuit monitoring system of a single-point grounding system, FIG. 2 is a flowchart showing an operation for monitoring a ground fault and a short-circuit, and FIG. 3 is a single-point grounding system. Schematic of the test system of FIG. (1) …… power source, (2) (3) (4) …… equipment, (4a) (4b) (4c) …… auxiliary equipment, (30) (31)… (3n) (70) (71 )… (7n) …… Grounding cable, (CT10) (CT11)… (CT1n) …… Excitation transformer, (CT20) (CT21)… (CT2n) …… Current detection transformer, (53) (61)… … Switch, (CPU) …… Central processing unit

Claims (2)

[Claims] 1. A set of one excitation set for each of a path from a branch point to an adjacent branch point, a path from each branch point to an open end, and a path to a ground point in a grounding network composed of a single-point grounding system. A transformer and a current detection transformer are attached, the excitation transformers attached to each path are sequentially excited, and in synchronization with the excitation of the excitation transformer, a loop for each path is formed by a current detection transformer paired with the excitation transformer. Detect the current,
A ground fault / short circuit monitoring method for a single-point grounding system, which detects whether a short circuit or a ground fault has occurred by calculating the loop impedance based on the loop current. 2. The ground for a one-point grounding system according to claim 1, wherein the exciting transformer is excited by a low frequency sine wave which is less likely to be affected by the capacitance component and the inductance component of the grounding system. Short-circuit and short-circuit monitoring method.