The methods for Testing Insulation Grade of Generator

by Generator D. Diesel Generator

With the rapid development of modern life, people can not live without electricity for a moment. One of the normal operation of electrical appliances is the degree of insulation of insulating materials, that is, the value of insulation resistance. When heated and damped, insulating materials will age and their insulation resistance will decrease, which will lead to electricity leakage or short-circuit accidents of electrical equipment.

To avoid accidents, we need to test the insulation resistance of various electricity equipment, so that can ensure the whether insulation grade meet our requirements. Testing of ordinary resistance commonly by under low voltage and high voltage. While insulation resistance value is higher in generally, the testing value under low voltage can not reflect the real value of  insulation resistance under high voltage.

Diesel generators are equipped with insulation registration. Insulation material is the weakest link in electrical equipment, such as generators. It is vulnerable to high temperature and accelerates aging and damage. We recommend that you learn to test the insulation level to ensure diesel generator have a good insulation performance. So how to test it?

There are two methods to test: electrometric method and non-electric method.


1. Electrometric method

Electrometric method is divided into two kinds: pulse current method and radio interference method. Pulse current method is an on-line detection of the parameters of partial discharge in the operation of generating units, that is, partial discharge is the generated pulse current. Radio interference voltage method is used to detect electromagnetic radiation waves generated by generator partial discharge. Because the pulse current method can calibrate the discharge core according to the equivalent circuit of partial discharge, the detection sensitivity is high, so it is a commonly used method at present.


2. Non-electric method

Non-electric method. Non-electric measurement is a method to detect the partial discharge of generating units by acoustic and special gas instead of measuring the electric parameters. 

There are two commonly used non-electric detection methods. One is ultrasonic detection, which produces pulses when generator partial discharge occurs. Its spectrum is about 1HM, but its acoustic signal is very soft.

3. When testing, state of generator.

When measuring the insulation resistance of the motor winding of diesel generator set, it should be carried out in the actual cold state and hot state respectively. When checking the test, it can only be carried out in the actual cold state.


About different windings for generators, such as stator winding, excitation winding of synchronous generator, reactor and current transformer in excitation system of some self-excitation generator, etc. If both ends of their wires have been drawn out of the generator housing. The insulation resistance of each winding to the housing and the insulation resistance of each winding to each other shall be measured separately. When testing, the winding that not tested should connect to generator housing. Connected windings inside the generator, can only test their insulation resistance value of generator housing. 

When testing, megger of hand-operated power generation, its speed should keep at about 120r/min; The reading should be read after the instrument pointer reaches stability. After measurement, the measured winding should be discharged to the ground before the measurement line is removed.

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About Generator D. Senior   Diesel Generator

110 connections, 1 recommendations, 670 honor points.
Joined APSense since, September 11th, 2017, From Jiangsu, China.

Created on Jul 10th 2019 04:34. Viewed 166 times.


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