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sykimk (Electrical) (OP)
13 Sep 07 10:20

Gents,

Typically, Inverter fed motors should have inverter duty not standard duty. However, motors for inverter service have alrealdy been purchased with NEMA standard duty not inverter duty.

So, I am looking for suppliers of LV VSD suitable for operating non-inverter duty motors.
Could you please recommend some vendors who can provide the solution for this problem?

Thanks in advance.

dpc (Electrical)
13 Sep 07 12:19
All the drives use very similar technology on the inverter side.  Having an adjustable carrier frequency might be helpful, but other than that, I'm not sure there is much that will be different inside the drive.  Use of output reactors may help reduce high-frequency voltage peaks on the motor windings.  

boaterbill (Electrical)
13 Sep 07 15:39
If the motors are new, the winding insulation should be OK.  How long are the motor leads from the VFD?  Anything over 100 feet I would put on an output reactor to reduce the harmonic spikes at the motor.
Skogsgurra (Electrical)
13 Sep 07 16:37
Yaskawa has a three-level inverter, forgot the type. It produces only half the voltage steps compared to a standard PWM drive. It is still tough on the motors, though. But better than a classic PWM.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

rvasant2 (Chemical)
13 Sep 07 16:50
I have an application of pumping water with a 15 HP motor. THe flow is varing and can be between 10% to 100%. To save energy, I intend to pumt this motor on a VFD and control the discharge pressure. How would I calculate the energy consumption as a function of motor speed?
Skogsgurra (Electrical)
13 Sep 07 17:30
Hey! You with the 15 HP pump motor. This is hi-jacking. Start a new thread with that question.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

ozmosis (Electrical)
14 Sep 07 2:38
sykimk
what do you mean by LV? Once you start getting an AC supply >460Vac then the peak-peak seen by the motor becomes harsher.>500Vac supply becomes a real problem.
As already pointed out, most PWM VFDs are similar. Other factors that will impact will be motor cable length too. Longer cables will increase the spikes seen at the motor.
jraef (Electrical)
14 Sep 07 12:36
There are VFDs out there which make claims to being suitable for use on non-inverter duty motors. But when you read the fine print, what they say is basically what you have just been told in here; it's OK under certain circumstances.

If I were you however, I would get the best VFD I can afford from a supplier I trust who has good local support, then add some quality filtering on the output to protect the motors. But it's a lot for one person to know for sure, so I tell people to look to TCI or MTE (in North America anyway) for good after-the-fact filtering products. That industry changes fast so that I would just call their applications engineers and explain what you have. They should help you get the right thing.
ykee (Electrical)
14 Sep 07 13:19
Talk to the motor supplier about the suitability of using your motors with VFD's.  They may have confidence that their motors can be used with VFDs.  In any case, find out what happens to any warranty on the motors if you use any kind of VFD to drive them.  I know in the past I've had the suppliers agree to warranty motors driven by VFD, even though they were not inverter duty (still puts you on the hook for downtime etc. if they fail).

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