Megger testing measures resistance between the phase windings of the motor under test and ground. If there is an insulation breakdown, the resistance is negatively impacted and there is a departure between phases or between one measurement and a previous one and a determination of motor health is made.
Why do we Megger a motor?
To measure the resistance in a three-phase motor, you will need a megohmmeter, otherwise known as a megger. Unlike an ohmmeter, a megger can measure high-voltage resistance values, which are generally the kinds of values you will encounter with three-phase motors.
Why do we need to check the insulation resistance of a motor?
To prolong the life of electrical systems and motors, regular insulation resistance testing is required. Over the years, after many cycles of operation, electric motors are exposed to environmental factors such as dirt, grease, temperature, stress, and vibration.
What does Megging a motor tell you?
It specifically tests the motor windings insulation. Depending on the insulation class of the motor, a good motor could measure well into Tera Ohms or 1,000,000,000,000 ohms! This is an insulation test of motor windings, commonly referred to as megging, to megger, or to meg a motor.
What voltage should you Megger a motor?
The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. For example, a motor rated at 2,400 volts should have a minimum insulation resistance of 2.4 megohms.
Can a megger damage a motor?
Never use a megger if the motor windings are under a vacuum. … A high voltage for too long of a time may further weaken or fail motor windings and the winding insulation could be damaged by the testing procedure.
What is the insulation resistance of a motor?
A general rule-of-thumb is 10 Megohm or more.
|Insulation resistance value||Insulation level|
|2 Megohm or less||Bad|
What is the minimum insulation resistance of a motor?
It is recommended that the insulation resistance of the motor should at least be 1 MΩ1）, and for the voltage to ground of 200 V, I0r should be 200 μA or below.
What is a bad insulation resistance reading?
The purpose of the IR test is to check for damaged insulation, this can be mechanical damage or damage by heat, (overloaded cables), readings less than 2 Mohm indicate damaged insulation, readings of 2-50 Mohm are indicative of long circuit lengths, moisture and contamination and do not indicate the insulation quality, …
How do you Megger a 3 phase motor?
Connect one probe of the megger to the earth connection in the motor. So insulation resistance to earth can be checked then connect the second probe to the first winding and check the value, then do it for the second and third, and if all the values are almost the same then its ok.
What could cause the insulation of a motor to fail?
Around 55% of insulating failures in motors occur due to overheating. Overheating can be caused by poor power quality, or a high temperature operating environment. For every 10oc that the temperature of a motor rises, the insulation life reduced by 50%.
How Megger test is done?
Megger testing is an electrical test of insulation performance in an electrical apparatus. A mega-ohm meter is applied to each phase connection for the motor leads and ground, and a voltage applied.
How do you test an insulation resistance on a motor?
Perform an insulation resistance test on each conductor in the cable. Apply 1000 VDC for 1 min (one- minute insulation resistance test) to low voltage cables (1 kV or less) and use a megohmmeter, or insulation multimeter (IMM) to measure the insulation resistance.