Guide to Insulation Resistance Testing
A manufacturing line that goes down, even for a few seconds, could have a serious impact on production and to the bottom line. A Preventive Maintenance Program (PMP) reduces the risk that a manufacturing plant will experience an unscheduled shutdown.
Every good PMP should include insulation measurement to ensure the thousands of motors used in manufacturing plants and facilities stay up and running. Even better, with data collection and historical analysis you can keep track of equipment status over time to potentially predict a failure in advance. Consider these equipment types and what they mean to your daily operations:
Pumps
Conveyors
Compressors
Fans
Mixers
Grinders
HVAC
Refrigeration
The wire insulation coating inside motors deteriorates over time with typical wear and tear. Other factors that can cause a motor to fail prematurely include moisture or contamination of the insulation. Failure to find degraded insulation in electromechanical equipment can lead to motor failure and lost production. The best method is to integrate regular insulation checks into your preventive maintenance schedule.
Going one step further to incorporate the benefits of data collection can mean the difference between up-and-running and unexpected shutdown.
What is insulation resistance testing?
Insulation resistance testing with an instrument can detect leaks that appear as insulation resistance slowly tapers over time — a sign of normal and expected deterioration. In other cases, tests will detect a more serious issue in the moment when current suddenly drops and returns.
"Leaking" is a term associated with a bad event. In the case of wire insulation in motors, leaks are not only bad but potentially dangerous and costly. When insulation deteriorates or has been damaged, current will leak into parts of the motor it shouldn’t, causing undue wear. The insulation keeps the current flowing along the wire exactly as intended.
While motors play a significant role in industrial operations, insulated wire can be found in other critical electrical equipment as well, such as airport runway lighting or alert monitoring system cables.
Fluke insulation testers are ideal for testing capacitance and leakage current of switchgears, motors, generators, and cables, among other high voltage equipment. Timed ratio tests are used to detect insulation resistance and include the polarization index (PI) and dielectric absorption rate (DAR).
These tests will identify changes in current over the specified periods of time, then produce a comparison in terms of a ratio. For example, if the current flow after 10 minutes is the same after 1 minute, that ratio would be 1:1. This ratio would be highly uncommon, however, because many other factors play a role in how current flows, including voltage and temperature. Since both voltage and temperature are not steady, they must be compensated for in determining actual insulation resistance performance.
