Do not start the motor when the insulation resistance Fails to meet the requirements

We talked about in the previous article, insulation resistance is to evaluate the overall level of the insulation structure of the motor product is an important performance parameters; insulation resistance with the changes in external conditions and change, such as temperature, humidity and so on.

In the insulation resistance detection, we must pay attention to the problem that the insulation resistance meter used must match the rated voltage of the motor. The standard specifies the lower limit value of cold insulation resistance for different voltage levels. For example, when the rated AC voltage does not exceed 1000V or the rated DC voltage does not exceed 1500V, the lower limit value of insulation resistance of the motor is 5 megohm. When the rated voltage exceeds the corresponding value, the lower limit value of insulation resistance is 50 megohm. The premise of this regulation is to use the megger according to the requirements.

The selection of tramegger shall be based on the voltage not exceeding 500V, 500-3300V and more than 3300V. The corresponding tramegger specification voltages are 500V, 1000V and 2500V respectively. This matching relationship must be well controlled, otherwise it is easy to misjudge the quality compliance.

In order to ensure the quality of motor operation, before starting the motor, especially when placed for a longer period of time, or changes in environmental conditions should be preceded by the insulation resistance of the motor to test, if the insulation resistance does not meet the requirements of the situation, should be necessary to check and analyze, remove the problem and then start the motor, in order to prevent the occurrence of unnecessary failures.

Analyzing the Causes of Low Insulation Resistance of Motors

In the motor manufacturing plant engaged in the test work of comrades may have an intuitive feeling, in general, we detect the cold insulation resistance is shown as infinity, which indicates that the test motor insulation structure and environmental conditions in line with the better, but, in addition to the impact of humidity, when for some reason lead to the motor winding moisture, insulation resistance value will be a significant drop. For motor users and repairers, especially motor storage environment is not very good, or part of the improper handling of the case, the insulation resistance value of the motor will not meet the requirements of the fact.

1.Motor wiring system space distance does not meet or short circuit problem. This problem occurs mostly in the repair of motors or motors in the use of the process, if not in accordance with the provisions of the use of the junction box, resulting in motor terminals with each other or terminals and junction box distance is very close, resulting in the electric components of the electrical gap or creepage distance is not enough, of course, does not rule out the quality of the insulating material, the quality of the problem.

2.The windings are too close to the case. This type of problem may occur in the manufacturing process may also occur in the repair process of the motor. For a lot of motor products, in order to consider the cost of materials, installation space and other factors, it is very likely to cause the fact that the internal space is tight, if coupled with the winding processing quality is not high, it is very easy to windings and chassis, windings and the end cover is very close to the fact that, in particular, the lead and the position of the line welding, the problem is more serious. Similar problems in the repair process of the motor has also appeared.

3.Poor quality of insulating materials in the terminal board, collector ring and other electrically charged components. Terminal block and collector ring insulator because of the process of improper disposal leads to conductive impurities, moisture absorption and other quality problems, the operation of the motor, if the operating environment is poor, the accumulation of dust, will also lead to abnormal insulation resistance.