Inverter duty motor insulation
Inverter duty motor insulation
(OP)
The VFD system (USA installation) has PWM Active Front End (AFE) and two motor inverters fed from the common DC bus. Inverter 1 is connected to 575V motor, therefore, the AFE input voltage is 575V (after step-up drive isolation transformer 480V/575V). The DC bus voltage is 900VDC. The Inverter 2 is connected to 460V motor (to be built in EU as US version). The motor 2 supplier states that since the DC bus voltage is 900V, the motor insulation (as per standard) should withstand peak voltage 1800V (2 times DC bus voltage). To achieve that, they plan to enhance the existing insulation, and de-rate the motor (thicker insulation-reduced winding copper cross-section to fit the slot-reduced torque/power). We argue, that Inverter 2 will be set up for 480V, so the motor 2 terminal voltage will be 480V and not 575V. Insulation standards are based on terminal voltage value. In our opinion, motor insulation will see increased DC bus potentials to ground, so only insulation to ground should be enhanced and not phase-to-phase and turn-to-turn insulation. Can anybody comment whether we think correctly?





RE: Inverter duty motor insulation
"Will work for (the memory of) salami"
RE: Inverter duty motor insulation
The fact that motor voltage has been set to 480 V doesn't change the DC link voltage and neither the PWM edges. They will still reach around 2*900 V if your cables are of any length (reflections at the high impedance at the motor end causes this).
Let your supplier have it his way. You will be in a really weak situation if you force him to use standard insulation. Not only will you risk the longevity of the motor - you will also void the guarantee.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Inverter duty motor insulation
RE: Inverter duty motor insulation
RE: Inverter duty motor insulation
But, gosh, the reactor would probably cost same as just buying the right motor and KISS.
www.KilroyWasHere<dot>com
RE: Inverter duty motor insulation
RE: Inverter duty motor insulation
Example how much it cuts output spikes (the issue):
reactor.jpg(72.5 KB)
https://www.box.com/shared/05khulpaza4t8ou1y10t
www.KilroyWasHere<dot>com