POLARIZATION INDEX ..

[powerjunx]

HI FOLKS.
ANYBODY KNOWS THE MINIMUM POLARIZATION INDEX FOR THE OIL/MINERAL-IMMERSED AND DRY-TYPE TRANSFORMER WHETHER A SINGLE PHASE, 3 PHASE OR EVEN A MULTIPLE-WINDING TRANSFORMER THAT WOULD BE SUITED FOR OPERATION OTHERWISE IT WILL THEN BE RECOMMENDED FOR SERVICING?
THANKS.

 

[busbar]

NETA 2001MTS §7.2.2: “… compared to previously obtained results and not be less than 1.0.”

 

[19gabi50]

A polarization index of 1.0 reveals dirty or wet insulation.
It should be at least 2 or 3.

 

[neps3]

fbjavier

Refer IEEE Std 43-2000 for the appropriate values.

kantor

 

[Saut]

What's the IR after one minute? the standards recommended that if it's more than 10Gohm after a minute, the PI need not hit 2, a 1.5 is good enough. The PI depends on the first minute reads too as short windings saturate faster.

 

[neps3]

The std says that if the one minute IR is greater than 5GOhm then the PI may or may not be an indication of the condition of the insulation, therefore is not an assessment tool.