When we need to evaluate the motor condition,HI-POT tester or High Potential tester is the common equipment are used.As we know,a multimeter or ohm meter reading only can determine if a motor winding is open or shorted but cannot checked winding insulation condition if shorted with ground or phase.
The main purpose of the Hi Pot tester is to verify the quality and integrity of the electric motor insulation materials used on the armature or stator and also safe to using it without any defect.
Sometime we not take a serious attention or not know about it to checked winding insulation.This step is important to ensure motor can running in good condition without any breakdown.
What is HI-POT tester?
Normally electrical motor may have a weakened winding that shorts to ground when it running.It have several caused for the winding breakdown due to the value of system voltage,winding heat build up or overloaded mechanical stress.
For other caused it will come from motor terminal board that has an insulation failure from the terminal to ground (earth) or from other terminal for winding connection.
Basic operation of HI-POT Tester
A HI-POT tester produce power source with a high voltage (Volt) and low current (ampere) and it is used to check for an insulation failure for motor winding that the ohmmeter cannot measure with its low voltage power source may miss.
It measures winding insulation resistance to ground (earthing) and terminal board resistance from terminal to ground and from terminal to terminal ( phase to phase )
To get a best result and for safety reason when perform measurement for winding insulation resistance,all wiring is removed from the motor winding terminals.It also same when perform measurement for terminal board resistance, all wiring is removed from the terminal board.
Below is several rules when using the Hi-Pot tester.It is to avoid any serious damage or injuries during insulation measurement and should never be :
1. Operated alone or by an inexperienced service person.
2. Set at a voltage of more than twice the motor operating voltage plus 1000 volts.
3. Be set for more than 5 milliamps without consulting or refer user manual from motor manufacture
4. Applied for more than the time it takes to obtain a reading (no more than a few seconds).
5. Used as a phase-to-phase winding check.
6. For air condition motor compressor,used when the system is in a vacuum.
* SAFETY NOTE : Please read HI-POT tester user manual before using it and refer to the trained or qualified person for assist during measurement.It the best way to avoid any unexpected issued and for safety reason.
It is useful article about Hi-Pot testing.I have done this test with several motors in our mills with Baker insulation tester instrument about one year ago.