Field Testing of Motors, IEEE 43

[SecondGen]

Recommended minimum insulation-resistance values for motors

• According to IEEE Standard 43, motor windings made before 1970 should have a minimum insulation resistance of 1 Megohms per kV + 1 Megohm.
• Form-wound coils made after 1970 should have a minimum insulation resistance of 100 Megohms.
• Random-wound stator coils and form-wound coils rated below 1 kV should have a minimum insulation resistance of 5 Megohms.

Motor Temperature Correction Factor

The temperature correction factors for motor windings are different than for other types of insulation as they use a 40°C base temperature.


Invalid Motor PI Values

IEEE Standard 43 recommends that when the insulation resistance is above 5 Gigaohms that the PI is not valid. This is because the leakage current is in the microampere range and too many factors can influence the measurement.


Recommended PI for Motor Insulation Classes

Class A insulation is the odd-ball of the group. All other insulation classes have a recommended PI of 2.0, but Class A has a recommended PI of 1.5.


Indications of Brittle Motor Insulation

According to IEEE Standard 43, when the PI value exceeds 8 it may indicate insulation that is dried out and brittle to the point that it could fail mechanically as well as electrically.


Reference: NETA World Summer 2004 Tech Quiz #68

[ejbrewer]

Why is 1970 used as a reference for different results?

[SecondGen]

The standard that we generally reference within industry is the IEEE 43, which went through a major revision in May, 2000. It was updated because post 1970 insulation systems went through a series of changes in their chemical makeup.

The insulation systems of newer insulation systems are very different from the older systems, including how they react through testing methodologies. The revised standard drastically changed a number of traditional testing programs for insulation resistance that had been in place for over 50 years, including the Polarization Index (PI), insulation to ground tests and AC vs DC testing of insulation systems.

http://www.motordoc.org/wp-content/u...ng-Article.pdf

[Mathewfex]

Spot on with this write-up, I absolutely feel this amazing site needs much more attention. I?ll probably be returning to read through more, thanks for the information!

[bwillsey88]

Very helpful!

[Gnollio]

Very helpful!

Can someone walk me threw this test?
So far i here is what i have
Remove internal and external connections before the testing begins.
Discharge the windings to the grounded value. Do i have to know the model of the motor to know this or is there a label i can refer to?
Apply a maximum dc voltage between the stator and conductor in the windings.
Use a megohmmeter to measure the resistance.
Obtain a reading at one and 10 minutes so the final value can be determined.
Turn the power supply off after the readings have been received.
Use the PI test formula to calculate the final resistance.
The entire test duration must be performed within 10 minutes.
Take note of the winding temperature at all times. Perform this portion since the test is of single- and three-phase induction motors. This is why the windings should be grounded based on the testing procedure performed.

[zslater]

Recommended minimum insulation-resistance values for motors

• According to IEEE Standard 43, motor windings made before 1970 should have a minimum insulation resistance of 1 Megohms per kV + 1 Megohm.
• Form-wound coils made after 1970 should have a minimum insulation resistance of 100 Megohms.
• Random-wound stator coils and form-wound coils rated below 1 kV should have a minimum insulation resistance of 5 Megohms.

Motor Temperature Correction Factor

The temperature correction factors for motor windings are different than for other types of insulation as they use a 40°C base temperature.


Invalid Motor PI Values

IEEE Standard 43 recommends that when the insulation resistance is above 5 Gigaohms that the PI is not valid. This is because the leakage current is in the microampere range and too many factors can influence the measurement.


Recommended PI for Motor Insulation Classes

Class A insulation is the odd-ball of the group. All other insulation classes have a recommended PI of 2.0, but Class A has a recommended PI of 1.5.


Indications of Brittle Motor Insulation

According to IEEE Standard 43, when the PI value exceeds 8 it may indicate insulation that is dried out and brittle to the point that it could fail mechanically as well as electrically.


Reference: NETA World Summer 2004 Tech Quiz #68

Thank you so much for this. This is the information format that works best for me instead of having to dig up the obscure like Class A is the oddball of the group. Much easier to remember it that way.

[southbury]

I would say with this post,
Understanding this and knowing tables 1-3 of IEEE 43,
You have 99% of the material needed for both the exam and the real world.

Simply-Brilliant in its simplicity

[carl21]

Recommended minimum insulation-resistance values for motors

• According to IEEE Standard 43, motor windings made before 1970 should have a minimum insulation resistance of 1 Megohms per kV + 1 Megohm.
• Form-wound coils made after 1970 should have a minimum insulation resistance of 100 Megohms.
• Random-wound stator coils and form-wound coils rated below 1 kV should have a minimum insulation resistance of 5 Megohms.

Motor Temperature Correction Factor

The temperature correction factors for motor windings are different than for other types of insulation as they use a 40°C base temperature.


Invalid Motor PI Values

IEEE Standard 43 recommends that when the insulation resistance is above 5 Gigaohms that the PI is not valid. This is because the leakage current is in the microampere range and too many factors can influence the measurement.


Recommended PI for Motor Insulation Classes

Class A insulation is the odd-ball of the group. All other insulation classes have a recommended PI of 2.0, but Class A has a recommended PI of 1.5.


Indications of Brittle Motor Insulation

According to IEEE Standard 43, when the PI value exceeds 8 it may indicate insulation that is dried out and brittle to the point that it could fail mechanically as well as electrically.


Reference: NETA World Summer 2004 Tech Quiz #68

the answer is 10 on our test guy exam. can we somehow confirm which answer is right?