Megger Value of motor

Is it giving several types of earth fault - a clockwise earth fault and an anticlockwise earth fault, for example?

it is giving slack fault indeed

Would that be the directional fault that answers the earlier question?

Dear PW Slack,

We are using 7sj602 relay for HT Incoming and Out Goings at 11 KV. This relay gives us i> , i>> and i>>> Also IE>, IE>> and IE>>>. For IE, it represents the earth fault current. When we consult the manual of this relay, there are two distinguished types of fault currents. These are Directional and non-directional earth fault. My previous question was about this matter. Now this question is about Megger Value calculation. We are using the pet formula of 2 M Ohms for insulation at 400 V. While for 11 KV, we take the insulation level of 12 M Ohms and greater. I have to verify and discuss with the experts here.

Regards,

What is the earth fault protective device set to trip at?

As a rule from practice: minimum acceptable insulation value is 1 kOhm per volt, example - 440 v supply voltage - 440 kOhm minimum insulation resistance (if higher, better).

Regards

For motors rated more than 600v minimum acceptable insulation resistance is 30 M ohm at 40 degree C (cold), when stopped after running (hot) 10 mega ohm is the minimum.

You have to apply temperature correction if temperature is other than 40 deg C.

Dear AA in your previous post I think you have created confusion by using term "directional" but rather I try to clear the matter right there.

IR result must be in unit of MEGA OHM..Not depend rating of motor

The minimum insulation required depends on voltage, not the KW (or HP) of the motor.

Minimum insulation (Mega-ohm) required is KV + 1.

See these links:

http://cr4.globalspec.com/thread/56906/Insulation-of-a-Motor

http://www.megger.com/common/documents/Above1kV_UG_en_V04.pdf (page 25)

- MS

AC Motors, 75°C 120-volt - 1.12 megaohms

208-volt - 1.20 megaohms

240-volt - 1.25 megaohms

480-volt - 1.50 megaohms

DC Motors, 75°C All voltages - 1.00 megaohms

High-Voltage Circuit Breakers, 20°C 10,000 megaohms

High-Voltage Bushings, 20°C 10,000 megaohms

Insulated Cable - Varies as a function of type and thickness of insulation; see ICEA Standards

Transformers, Oil-Filled, 20°C

Where:

E = Voltage rating of winding under test

kVA = Rated capacity of the winding under test

Transformers, Dry type, 20°C, where E and kVA are as defined above

Other Equipment - Refer to Manufacturer's Data

sorry for missing the formula

1.5E/SQRT(KVA) for oil filled

30E/SQRT(KVA) for dry type

above1000 Mohm, it doesn't depend rating of motor only depend warnishing and enamal coating of wire.

Refer to IE Rule No. 48 ans IS 732 if you are from India.