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Huynh Hoai Nhat
01-15-2014 08:44 PM

Standard For Winding Isualation Resistance Of Large Motor!

Standard For Winding Isualation Resistance Of Large Motor!!!!We use standard IEEE 43 - 2000 for minimum acceptable value of Winding isualation resistance. But our customer use the manual standard: They apply minimum value for motor is 2.2Mohm with 6kV motor? the manual standard of customers have applied right? please give me some advide! Many thank
01-15-2014 11:27 PM
Top #2
Charles Yung
01-15-2014 11:27 PM
IEEE 43-2010 calls for a minimum IR of 5 meg-ohms for random windings, or 100 meg-ohms for form coil windings. The earlier standard was for "1 plus 1 meg-ohm per kV of rating". In this case, his 2.2 Mohm value is still below that earlier standard of 7.6 meg-ohms.
You might emphasize the safety aspect of the revised Standard, to help convince them of the importance of following the IEEE 43 Standard. Good luck!
01-16-2014 01:56 AM
Top #3
Chris Heron
01-16-2014 01:56 AM
Original equipment (from the manufacturer) will generally have a higher "limit" on insulation resistance than a machine that has been in service for some time.

Most manufacturers use IEEE 43 (the most current edition - 2010 - is the one adhered to by the major international companies like GE, ABB, TECO, Hyundai, etc). These limits are noted above by Chuck - roughly 5 x 10^6 ohms for random wound machines, and 100 x 10^6 ohms for form wound designs. In practice, the acceptable limit may be even higher in a company's internal documentation, to be sure that a machine passes a witnessed test in front of the customer.

Once the machine leaves the factory floor, all kinds of things can happen to reduce the observed insulation resistance. These can range from moisture absorption during transport or storage (the transporter did not adequately protect the equipment during travel, or the user did not do so once at site), to winding damage incurred by handling, to the presence of contaminants affecting the insulation properties evident during operation.

As equipment manufacturers (and service providers), our industry can recommend values that are reasonable because we see a large population of equipment in all kinds of applications and environments. We base our recommendations on the side of safety - both for the equipment and, more importantly, for the operating personnel. However, the ultimate choice on whether to run a machine is in the hands of the equipment owner; if they want to run a machine with a lower-than-recommended measurement, that's their choice. Any consequences of their actions (equipment damage, personal injury, or loss-of-life) resulting from the decision are ultimately theirs to bear as well.

My personal recommendation is that the values in the 2010 edition of the standard are minimums for equipment in a condition that approximates "as new" (clean, dry, no winding damage, etc). For equipment with an extended service life in the presence of contaminants, each one should have a case-by-case evaluation by someone with experience.
01-16-2014 04:39 AM
Top #4
John Schwab
01-16-2014 04:39 AM
I agree with Charles. I called Tom Bishop yesterday on this same question. I asked for what the minimum rule of thumb for the megohm at 15kv would be and he gave me a very educated answer. he guys at EASA really know what they are talking about.

By the way Chuck, I will be in on your Core Repair and Restack Webinar at 1:00 today.
01-16-2014 06:53 AM
Top #5
Randy Keener
01-16-2014 06:53 AM
I use the IEEE 43 std for field testing. These minimum resistance values work well for motors which have recently de-energized. There is little reason to suspect moisture. So low resistance values are a good indication of contamination or other weaknesses which warrant repair. If the motor has been de-energized for some time and there is a likelihood of moisture absorption, the moisture issue may need to be addressed if excessive.
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