JPS6212874A - Method for measuring earth resistance in one-point earthing system - Google Patents

Abstract

PURPOSE:To measure earth resistance always precisely by applying a signal with a prescribed frequency level to an exciting transformer and calculating the earth resistance of a one-point earthing system on the basis of an output signal obtained from a current detecting transformer. CONSTITUTION:The exciting transformer 2 and the current detecting transformer 3 are connected to a reference loop, a signal with the prescribed frequency is applied to the transformer 2 and an output signal is obtained from the transformer 3 to execute initial calibration on the basis of the output signal of the transformer 3. The transformers 2, 3 are fitted to the one-point earthing system, the signal with the prescribed frequency is applied to the transformer 2 and the earth resistance of the system is calculated by an arithmetic unit 8' on the basis of the output signal obtained from the transformer 3 and displayed on a display unit 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for measuring ground fault resistance in a single point grounding system, and more particularly to a method for measuring ground fault resistance that can accurately measure ground fault resistance.

<Prior Art> Conventionally, so-called single-point grounding systems, in which grounding is performed at one point, have been widely used, particularly in systems that apply large amounts of power, systems that generate strong magnetic fields, and the like.

In such a single-point grounding system, when a ground fault occurs, a large current flows to the device that caused the ground fault, potentially damaging the device, and due to the influence of the cable inductance with respect to other devices, the mti However, it is necessary to take some countermeasures to avoid inconveniences such as damage to the equipment or malfunction, but it is possible to identify the occurrence of a ground fault by detecting abnormal current during system operation. The reality is that only countermeasures have been considered.

Therefore, when a ground fault occurs, especially in systems that apply large amounts of power, the equipment has already been damaged by the time the occurrence of a ground fault is identified, so it is important to prevent damage to the equipment. This is insufficient.

In addition, ground fault phenomena do not only occur instantaneously, but may also cause the ground fault resistance to gradually decrease, eventually resulting in a fatal ground fault condition for the system. This is also an insufficient countermeasure.

Purpose> This invention was made in view of the above problems,
It is an object of the present invention to provide a method for measuring ground fault resistance of a single point grounding system that can always accurately measure the ground fault resistance of the single point grounding system.

<Configuration> In order to achieve the above object, the ground fault resistance measuring method of the present invention measures ground fault resistance using an excitation transformer and a current detection transformer. Attach the excitation transformer and current detection transformer, apply a signal of a predetermined frequency to the excitation transformer, obtain the output signal of the current detection transformer, and perform initial calibration based on the output signal of the current detection transformer. Then, install the above excitation transformer and current detection transformer to the single point grounding system, and
A signal of the predetermined frequency is applied to the excitation transformer, and the ground fault resistance of the −° point grounding system is calculated based on the output signal from the current detection transformer.

That is, as shown in Fig. 1, an excitation transformer (2) and a current detection transformer (3) are attached to a reference loop (1) whose resistance value is known in advance, and the excitation transformer (2) is On the other hand, a signal Ei of a predetermined frequency from the oscillator (4) is applied via the amplifier (5), an output signal from the current detection transformer (3) is applied to the shunt resistor (6), and the shunt The voltage between both terminals of the resistor (6) is input to the input device (
The measured voltage E can be obtained by converting the level using a sword and applying it to the voltage measuring device (8). Since the loop resistance is known, by using reference loops with different resistance values and obtaining the measured voltage in each case, EO=a/RO+b and El=a/R
A relational expression 1+b can be obtained, and constants a and b can be calculated from these two expressions.

For a single-point grounding system in which ground fault resistance is to be measured, for example, as shown in Figure 2, an excitation transformer (211) and a current detection transformer are installed, and a transmitter (
4) is applied via the amplifier (5), the output signal from the current detection transformer (3) is applied to the shunt resistor (6), and the shunt resistor (6)
The voltage between both terminals of is converted to level by input "R117), and the constants a, b and R=a/(E
-b) arithmetic unit (8) that stores the arithmetic program;
By applying the calculation results of the arithmetic unit (8) to the display (9), it is possible to easily and accurately calculate the ground fault resistance of the single point grounding system.

With the above configuration, it is possible to measure the degree of ground fault in a single-point grounding system, and even in systems that are surrounded by concrete and have a relatively low ground resistance, it is possible to measure It is possible to accurately detect a state in which the ground resistance has further decreased due to leakage, etc., and furthermore, it is possible to predict to a certain extent the time until a ground fault condition ultimately occurs, based on the value of the ground resistance. In terms of maintenance of the single-point grounding system, it also has unique effects, such as being able to set the optimal maintenance execution timing.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the initial calibration state; FIG. 2 is a diagram showing the operational status.

Claims (1)

[Claims] 1. Connect the excitation transformer and the reference loop to the reference loop. and current detection transformer and excitation. A signal of a predetermined frequency to the transformer is applied, and the current detection transformer is output signal from the current detection transformer. Perform initial calibration based on the output signal of Next, for single-point grounding systems, excitation transformer and current detection transformer. Attach the lance and follow the instructions above. Apply a frequency signal to the excitation transformer, Based on the output signal from the current detection transformer. Calculate the ground fault resistance of a single point grounding system. A single point grounding system that is characterized by Method for measuring ground fault resistance in systems.