IEEE vs NETA

[Donalddc]

All, this is my first post as I am new to Test Guy. Well, not actually new but just getting involved in the forums. I have been researching PI and DAR criteria. The NETA MTS/ATS says that anything greater than 1 is good, but as I have researched I found a posted quote from IEEE and this table attached. Also, a lot of people have said that under 1.5 is a serious condition. What are your thoughts?

The table below shows the minimum IEEE 43-2013 PI ratings.

DAR PI Insulation Condition
<1.25 1.0-2.0 Questionable
1.25-1.6 2.0-4.0 Good
>1.6 >4.0 Excellent

The table is not showing correctly when I post, so the first set of numbers is DAR, the second PI and the third the condition.

[nwilliams]

All, this is my first post as I am new to Test Guy. Well, not actually new but just getting involved in the forums. I have been researching PI and DAR criteria. The NETA MTS/ATS says that anything greater than 1 is good, but as I have researched I found a posted quote from IEEE and this table attached. Also, a lot of people have said that under 1.5 is a serious condition. What are your thoughts?

The table below shows the minimum IEEE 43-2013 PI ratings.

DAR PI Insulation Condition
<1.25 1.0-2.0 Questionable
1.25-1.6 2.0-4.0 Good
>1.6 >4.0 Excellent

The table is not showing correctly when I post, so the first set of numbers is DAR, the second PI and the third the condition.

NETA-ATS says greater than 1.0 is good for Polarization Index for components like transformers. NETA-ATS also says must be greater than 2.0 for components like motors or generators. For DAR, NETA says 1.0 for DAR on transformers and 1.4 on DAR for motors. For motors, it looks like the IEEE table is fairly consistent with NETA standards. Does IEEE 43 state what components the table is for? I'm not seeing that table in my copy of IEEE 43-2013

[Donalddc]

NETA-ATS says greater than 1.0 is good for Polarization Index for components like transformers. NETA-ATS also says must be greater than 2.0 for components like motors or generators. For DAR, NETA says 1.0 for DAR on transformers and 1.4 on DAR for motors. For motors, it looks like the IEEE table is fairly consistent with NETA standards. Does IEEE 43 state what components the table is for? I'm not seeing that table in my copy of IEEE 43-2013

Thank you for the reply. As I looked deeper into it I found that you are correct. There is a difference between the transformers and motors. That cleared it up!

[backpack96]

NETA-ATS says greater than 1.0 is good for Polarization Index for components like transformers. NETA-ATS also says must be greater than 2.0 for components like motors or generators. For DAR, NETA says 1.0 for DAR on transformers and 1.4 on DAR for motors. For motors, it looks like the IEEE table is fairly consistent with NETA standards. Does IEEE 43 state what components the table is for? I'm not seeing that table in my copy of IEEE 43-2013

[backpack96]

A polariation index is valid, and a great test, for solid dielectric insulation. According to Megger/ Biddle who is the expert on DC insulation testing the PI is not valid on oil filled equipment. One NETA testing company failed a 138 kV transfromer due to a low PI. Overall power factor, TTR, exciting current, DGA, leakage reactance and SFRA were all acceptable. All tests compared to past tests.

From the Megger manual:

It is also interesting to note that many people have tried to use the PI test on oil-filled transformers and
cannot understand why a known good transformer gives them results close to 1. The answer is simple. PI
testing is not appropriate for oil-filled transformers. The concept depends on the relatively rigid structures of
solid insulating materials, where absorption energy is required to reconfigure the electronic structure of
comparatively fixed molecules against the applied voltage field. Because this process can go to a
theoretical state of completion (at “infinite time,” which obviously cannot be achieved in the practical
field, but can be reasonably approximated), the result is a steady diminution of current as molecules reach their
“final” alignment. Because the PI test is defined by this phenomenon, it cannot be successfully applied to fluid
materials since the passage of test current through an oil-filled sample creates convection currents that
continually swirl the oil, resulting in a chaotic lack of structure that opposes the basic premise upon which the PI test rests.