Baker D30R User Manual - Test Sequence, Voltages &

12/3/2009 | 71-022 V6 

D30R 

17 

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Test sequence, voltages & 

applicable standards 

Recommended testing sequence 

In order to test motors adequately and to have effective predictive maintenance programs,  

Baker Instrument Company, an SKF Group Company, suggests using a specific test sequence. 

The general idea is to perform the test sequence as a series of progressively more rigorous 

tests, accepting the idea that if a test fails, troubleshooting and repair should begin at that 

time.

Further, more rigorous testing should only commence after satisfactory diagnosis and/or 

repair

.

The suggested testing sequence is: (1)Resistance test, (2)Meg-ohm, (3)HiPot and finally (4) 

Surge.

1) Coil Resistance test 

A coil resistance test looks for resistance imbalance between phases, discrepancies between 

measured resistance values, previous measurements and nameplate values. If a problem is 

found, the motor should be inspected for the cause of the discrepancies. Typical problems 

that may exist are 1) hard shorts to the motor’s core, 2) hard shorts between coils either 

within the same phase or between phases, 3) coils rewound with the improper gauge wire, 4) 

loose or corroded connections. Further HiPot or Surge testing is not necessary until the 

resistance measurement is acceptable. 

2) Megohm test  

A Megohm test is performed using a test voltage based on the operating voltage of the motor 

and the appropriate standards/company testing guidelines. Look for an unusually low 

Megohm value when compared to previous measurements or industry accepted limits for the 

type of insulation in the motor. If a low Megohm value is measured, the motor should be 

inspected for ground wall insulation damage. Some part of the ground wall insulation has 

failed. Possible problems include: 1) slot liner insulation or enamel wire insulation may be 

burned or damaged, 2) the motor might be full of dirt, carbon dust, water or other 

contaminates, 3) connections to the actual coils may be bad, 4) wrong insulation may have 

been used to connect the coils to the motor’s junction box, etc. No further testing is necessary 

until the reason for low meg-ohm readings

is found and corrected.  

3) Principles of the Dielectric Absorption (DA) test 

The Dielectric Absorption (DA) test is essentially a short-duration PI test and is usually 

intended for smaller motors. Larger motors whose insulation does not easily polarize are also 

good candidates for the DA test. Other than the shorter test time, all other principles are the 

same as the PI test, explained in the next section. 

While the PI test is recommended only for motors 200 horsepower or greater, the DA test is 

useful for motors in approximately the 50 to 200 horsepower range. The DA value is the ratio 

of the ground wall insulation resistance (IR) at 3 minutes to the IR value at 30 seconds. 

4) Principles of the Polarization Index (PI) test 

The 

Polarization Index test (PI test)

 is the most confusing HVDC test in use due to the 

subtleties in the interpretation of the results. The PI test is performed in order to 

quantitatively measure the ability of an insulator to polarize. When an insulator polarizes, the 

electric dipoles distributed throughout the insulator align themselves with an applied electric 

field. As the molecules polarize, a “polarization current”, also called an absorption current, is