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Anonymous Poster

Insulation Values for AC Motors

02/25/2010 2:53 PM

Can anyone tell me what is insulation value for a motor? I was told for a 460V motor rated for VFD use, the insulation value is 1600V? I need the spec to size a VFD for the motor. Thanks.

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Power-User

Join Date: Dec 2006
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#1

Re: AC Motor

02/25/2010 3:33 PM

guest; we doubled the rated voltage and added 1000 volts 1,960 volts. perry

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Anonymous Poster
#2
In reply to #1

Re: AC Motor

02/25/2010 3:54 PM

Is that the general rule of thumb?

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Guru

Join Date: Feb 2009
Location: Houston, USA
Posts: 947
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#3
In reply to #2

Re: AC Motor

02/25/2010 4:01 PM

NEMA MG-1, Section IV, Part 31 (31.4.4.2: Voltage Spikes)

Motors with base rating voltages Vrated ≤ 600 volts:

Vpeak = 3.1 x Vrated

Motors with base rating voltage Vrated > 600 volts:

Vpeak = 2.04 x Vrated

Where:

Vpeak is a single amplitude zero-to-peak line-to-line voltage.

Vrated is the rated line-to-line voltage.

So, you are right with insulation rating 1600V (460 x 3.1 = 1426 ~ 1600).

In your spec, do not forget to mention the motor should be 'inverter-rated' including other requirements for the VFD motor.

The following links also may help for other requirements:

http://cr4.globalspec.com/thread/40051

http://www.reliabilityweb.com/excerpts/excerpts/VFD_Motor_Testing.pdf

- MS

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Anonymous Poster
#4
In reply to #3

Re: AC Motor

02/25/2010 4:51 PM

Sorry, I checked out the links you provided but I didn't see any reference to the 3.1 x Voltage formula.

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Guru

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#5
In reply to #4

Re: AC Motor

02/25/2010 5:44 PM

The links are provided to give you the idea about the requirements of VFD motors, not to the NEMA MG 1 standard.

The formula has been provided from NEMA MG-1 standard. You have to buy it from http://www.nema.org/stds/mg1.cfm. However you can see the index of NEMA MG 1 from http://www.nema.org/stds/complimentary-docs/upload/MG%201-2006%20Rev%201_contents.pdf.

I have a copy of it and quoted the NEMA article number and name (31.4.4.2: Voltage Spikes) from there. Hope you understood.

- MS

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Commentator
India - Member - New Member Engineering Fields - Electrical Engineering - New Member Technical Fields - Technical Writing - New Member

Join Date: Feb 2010
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#6

Re: Insulation Values for AC Motors

02/26/2010 4:52 AM

As the voltage rating of motor is less than 1000V, so simply add Vr+1KV=0.46+1=1.46KV. So the insulation resistance value should be atleast 1.5 MΩ.

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Anonymous Poster
#7

Re: Insulation Values for AC Motors

02/26/2010 5:01 PM

I asked the manufacturer what the insulation voltage/value was but they had no idea what i was talking about.. is there another name for this?

The VFD has 4 values of voltages that apply to the motor, it's either 1000, 1200, 1488 or 1600.. I googled this and found nothing... still confused...

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Guru

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#8
In reply to #7

Re: Insulation Values for AC Motors

02/26/2010 6:09 PM

Don't be confused the 'rated voltage' with the 'voltage spike'. The motor rated voltage is still 460V in your case.

The NEMA inverter rated motor insulation should withstand a voltage level of 'Voltage Spikes' of 3.1 times of the rated voltage. The PWM (Pulse Wave Modulation) inverter creates the spike voltage and if the motor is not able to withstand this voltage, its life will be shortened. For standard motors, the insulation is generally capable of withstanding 1.5 times of the rated voltage but the inverter rated motor should have its insulation to withstand 3.1 times of rated voltage. If you buy a NEMA inverter rated motor, its insulation must have this high spike voltage withstand capability.

- MS

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Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

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#9

Re: Insulation Values for AC Motors

01/20/2025 11:28 AM

<...anyone...>

Yes. Motor manufacturers can. Telephone?

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