After upgrading the insulation materials, the insulation resistance must be tested using a 500VDC megohmmeter in a cold state to ensure a resistance value >100MΩ. Long-term stability should be verified by monitoring during high-temperature operation.
1. Test Prerequisites
Power Off and Cooling: The system must be completely powered off and allowed to cool naturally to <80℃ to ensure operational safety.
Cleaning: Wipe electrical interfaces such as terminals and plugs with anhydrous alcohol to remove carbon powder and oxide layers.
Environmental Requirements: The test environment should be dry, with a relative humidity <60%, to avoid surface leakage interference caused by high humidity.
Engineering Recommendation: It is preferable to conduct the test the morning after the equipment has been shut down, when temperature and humidity are more stable.
2. Correct Testing Procedure
Steps and Key Points
① Instrument Selection: Use a 500VDC megohmmeter (do not use a multimeter). A digital meter is recommended for improved accuracy.
② Wiring: Connect the "L" terminal to the heating circuit, and the "E" terminal to the equipment casing or ground wire. If the environment is humid, the "G" shield terminal can be used.
③ Applying Voltage: Start the megohmmeter and maintain the test voltage for 1 minute until the value stabilizes.
④ Reading the Resistance Value: Record the final stable value in MΩ.
⑤ Data Recording: Record the test time, temperature, humidity, operator, and resistance value, and include them in the "Insulation Testing Log".
Pass/Fail Standards:
Cold State (<80℃): >100MΩ (Ideal >200MΩ)
High Temperature Operation (150℃~400℃): >10MΩ (Ideal >50MΩ)
3. Verification and Tracking After Upgrade
Initial Power-On Monitoring: Observe for tripping, abnormal current, and temperature fluctuations; Use an infrared thermal imager to detect localized overheating points and eliminate potential contact problems or leakage.
Retest After 72 Hours of Operation: After shutdown and cooling, retest the insulation resistance to confirm no significant decrease (a sudden drop >20% requires investigation);
Establish Trend Records: Compare data before and after the upgrade to generate an insulation performance improvement report for subsequent maintenance decisions.
