4160v Motor Insulation Resistance Testing

[Dmalone]

I have a 4160V squirrel cage motor with Class B insulation. The motor is operated very infrequently (about once every two months) for testing and is only needed as a backup. I have situations where this motor is idled for several months at a time and I would like to know when (after a period of how many weeks/months) I should perform an IR test prior to operating the motor? Also, are there any standards that discuss this type of situation?

 

[petersonra]

I have a 4160V squirrel cage motor with Class B insulation. The motor is operated very infrequently (about once every two months) for testing and is only needed as a backup. I have situations where this motor is idled for several months at a time and I would like to know when (after a period of how many weeks/months) I should perform an IR test prior to operating the motor? Also, are there any standards that discuss this type of situation?

I don't know of any standards on this.

Is it likely to get damp inside the motor? If so, some heaters might be in order.

I don't know that an IR test 6 times a year is necessary

A proper IR test on a 4160V motor is no fun from what I have been told.

 

[zog]

ANSI, NETA, NEMA all cover this.


IR 1 minute = kV+1 for most windings made before 1970, all field windings, and others not lited below.

IR 1min=100 Meg for most DC armature and AC windings built after 1970

IR 1min= 5 Meg for most machines and random wound stator coils and form wound coils rated below 1kV.

All values temp corrected to 40 degrees C (Very important to do this)

DAR and P.I should be > 1.0

 

[petersonra]

ANSI, NETA, NEMA all cover this.


IR 1 minute = kV+1 for most windings made before 1970, all field windings, and others not lited below.

IR 1min=100 Meg for most DC armature and AC windings built after 1970

IR 1min= 5 Meg for most machines and random wound stator coils and form wound coils rated below 1kV.

All values temp corrected to 40 degrees C (Very important to do this)

DAR and P.I should be > 1.0

I thought his question on standards was on how often an IR test should be performed on seldom used equipment. I have not seen anything on that issue.

 

[maxamps]

maxamps

maxamps

I have a 4160V squirrel cage motor with Class B insulation. The motor is operated very infrequently (about once every two months) for testing and is only needed as a backup. I have situations where this motor is idled for several months at a time and I would like to know when (after a period of how many weeks/months) I should perform an IR test prior to operating the motor? Also, are there any standards that discuss this type of situation?

We have a similar situation, that we only operate our 4160 motors every few months. We have our techs meg the motor prior to starting. If we have 5 Meg ohms of better, we start the motor. I would not expect your IR test to reveal anything on the windings from outside of the motor cases.

 

[zog]

I thought his question on standards was on how often an IR test should be performed on seldom used equipment. I have not seen anything on that issue.

Hmm, may have mis read the OP. Anyways I think it is a good idea to Meg before energizing. Blow ups are expensive.

 

[petersonra]

Hmm, may have mis read the OP. Anyways I think it is a good idea to Meg before energizing. Blow ups are expensive.

doing 6 IR tests a year is also expensive. It will take at least an hour of electrician time for the test and may well stretch into 4 hours or more depending on just what has to be done to do the test. You may be looking at a several thousand dollar a year expenditure of electrician time.

 

[zog]

doing 6 IR tests a year is also expensive. It will take at least an hour of electrician time for the test and may well stretch into 4 hours or more depending on just what has to be done to do the test. You may be looking at a several thousand dollar a year expenditure of electrician time.

Should take 15 minutes, 30 max.

 

[petersonra]

Should take 15 minutes, 30 max.

the test itself might.

how about the time to -

go get the megger out of the shop
get your arc flash suit and 10kv gloves
find the helper because you are not allowed to work on 4160 alone
walk out to the motor
lockout, and prove it is deenergized
do the test
undo the lockout
take the arc flash suit and megger back to the shop and put it away

2 people - easily 2 hours each in many places

if it is connected to a soft start or vfd you will also have to disconnect it to do the test and then reconnect it. not a trivial thing with 5kv conductors.

 

[zog]

Union shop?