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.
How do you test an electric motor with a megger?
How to Test a Motor using Megger?
- One megger lead should be placed on the ground terminal or wire, and the other lead should be placed on a phase wire or terminal.
- To test the megger, press test.
- If the resistance reading is extremely high (greater than 10 megohms), the motor insulation is likely to be good.
Can a megger damage a motor?
A high voltage for an extended period of time may cause motor windings to weaken or fail, and the testing procedure itself may cause damage to the winding insulation. Any megger with a higher voltage output than 500 volts DC should be used by an experienced technician.
What do megger readings mean?
After the initial 60 seconds, if the megger reads a resistance of less than 1 (1,000 ohms) on your meter, the cable has failed and needs to be removed. if the megger reads a resistance of between 1 and 1.25 on your meter, the cable passes. any reading above 1.25 is considered excellent.
As shown below, a DC voltage of 500V or 1000V is applied between the motors windings and the ground to measure insulation resistance. During the measurement and right after, avoid touching any motor terminals as some of them carry lethal voltages.
What is the minimum acceptable value of insulation resistance?
According to the rule, insulation resistance should be at least one megohm and should be roughly one megohm for every 1000 volts of operating voltage (for example, a motor rated at 2400 volts should have a minimum insulation resistance of 2.4 megohms).
What is a good insulation resistance reading?
RCDs may also have an impact on insulation resistance test results. The test voltage applied may be reduced to 250 V d.c., but the minimum acceptable value of insulation resistance remains 1 M (see Regulation 612.3.2).
What should be the insulation resistance of motor?
It is advised that the motors insulation resistance be at least 1 M 1 and that I0r be 200 A or less for voltages of 200 V to ground.
What should be megger value?
1. IR Values For Electrical Apparatus & Systems
| Max.Voltage Rating Of Equipment | Megger Size | Min.IR Value |
|---|---|---|
| 600 Volts | 1,000 Volts | 100 MΩ |
| 5 KV | 2,500 Volts | 1,000 MΩ |
| 8 KV | 2,500 Volts | 2,000 MΩ |
| 15 KV | 2,500 Volts | 5,000 MΩ |
How many ohms should a motor read?
A good motor should register less than 0.5 ohms in resistance when measured between the motor frame (body) and earth. Any value higher than 0.5 ohms indicates a problem with the motor.
What is an acceptable insulation resistance reading?
According to the rule, insulation resistance should be at least one megohm and should be roughly one megohm for every 1000 volts of operating voltage (for example, a motor rated at 2400 volts should have a minimum insulation resistance of 2.4 megohms).
How do you check a megger on a 3 phase motor?
How to Test a Motor using Megger?
- One megger lead should be placed on the ground terminal or wire, and the other lead should be placed on a phase wire or terminal.
- To test the megger, press test.
- If the resistance reading is extremely high (greater than 10 megohms), the motor insulation is likely to be good.
What does Megging a motor mean?
We are testing the insulation of the motor, more specifically between the motor windings and the motor casing, and if a fraction of current flows, it can be measured by these highly sensitive meters. This insulation test of motor windings is also known as megging, to megger, or to meg a motor.
What is the resistance of a motor winding?
You can try drying the connector and retesting to see if you get more accurate results. The reading should be between 0.3 and 2 ohms. If it is zero, there is a short; if it is over 2 ohms or infinite, there is an open.
What is the voltage of a megger motor?
Use a megger with a test voltage that is appropriate for the particular motor, as follows: Low Voltage Motors (208-600 VAC) should only be tested with a 500 Volt megger; Medium Voltage Motors (2300-6600 VAC) should be tested with a 1000 Volt megger.
How do you ohm out a motor?
Ohming a Single Phase Motor To determine whether a motor is single phase or three phase, first turn off all power to the apparatus, lock out the disconnect switch, and tag it. If no voltage is being read in any of the power leads inside the apparatus, then set your meter to a low ohms scale.
How do you use a multimeter to megger a motor?
Start by completely cutting off the power to the spindle motor, then check each wire, including T1, T2, T3, and the ground wire. If the reading is infinite, your motor should be in good shape.
What is the purpose of a megger test on an electric motor?
Megger testing determines the motors health by measuring the resistance between the phase windings of the test motor and ground. If there is insulation breakdown, the resistance is negatively impacted, there is a difference between phases, or between one measurement and the previous one, the resistance changes, and the resistance is negatively impacted.