Why do we need to conduct insulation resistance testing?

Insulation resistance (IR) testing was developed in the early 20th century and is the oldest and most widely used test for evaluating insulation quality. The insulation resistance test is the second test required by the electrical safety testing standards.

Insulation resistance testing includes measuring the insulation resistance of the tested equipment, with the phase and neutral lines shorted together. The measured resistance must be higher than the limit value specified in international standards. A megohmmeter is used to measure the ohmic value of insulators under DC voltage and has high stability.

Insulation cannot be perfect, just like some things cannot be frictionless. This means that there is always a little current passing through. This is called 'leakage current'.

Good insulation is acceptable, but if the insulation deteriorates, leakage will begin to cause faults. So, what is a "good" insulation material? Well, it needs to have high resistance to current and be able to maintain high resistance for a long time

Why do we need to conduct insulation resistance testing?

The Insulation begins to age. With the increase of service life, its insulation performance will decline. Any harsh installation environment, especially extreme temperatures and/or chemical contamination, will speed up the process. Stress caused by different factors, such as:

1. Electrical stress: mainly related to overpressure and underpressure.

2. Mechanical stress: Frequent start and close sequence can cause mechanical stress.

3. Balance of rotating machinery and any direct stress on cables and general equipment.

4. Chemical stress: The proximity of chemicals, oils, corrosive vapors and dust usually affects the insulating properties of materials.

5. Stress related to temperature change: when the expansion and contraction stress is combined with the mechanical stress caused by the start-stop sequence, it will affect the performance of the insulation material. Operating at extreme temperatures can also cause the material to age.

6. Environmental pollution leads to accelerated aging of insulation.

This wear will reduce the resistivity of the insulation and increase the leakage current, resulting in incidents that can have a serious impact on safety (people and property) and downtime costs.

This deterioration must therefore be identified quickly in order to take corrective action. In addition to measuring new equipment and refurbished equipment during commissioning, regular insulation testing of units and equipment can help avoid such accidents through preventive maintenance. These tests detect aging and premature deterioration of insulation properties before reaching levels that could lead to the events described above.

This test is usually used as a customer acceptance test, and the minimum insulation resistance per unit length is usually specified by the customer. The results of infrared testing are not helpful in finding local defects in insulation like real hipot tests, but can provide information about the quality of the bulk material used as insulation.

Wire and cable manufacturers use insulation resistance testing to track their insulation manufacturing processes and identify problems before process variables deviate from permissible limits.
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