Testing FVD with Smaller Motor

Yes. Or no. Without knowing the details of the VFD, no-one can say. It'll have to remain as one of life's great mysteries.

Are you familiar with the acroymn RTFM?

siemens s120 12kW-1200kW

Test for what?

Test to see if the VFD can make a motor turn? Yes. The VFD does not know or particularly care what size motor it is connected to. It will not protect that motor, but the motor will not harm the VFD.

Test the VFD for how it will perform with the motor it is intended for? Not really, unless all you want is for that larger motor to turn, in which case you spent WAY too much money.

yes to turn that small motor with all parameter, except for the motor data (FLA,kW,etc). and to see all :

DCS control start/stop command,

1.running feedback

2.incresed /decreased speed from remote

3.Analog output for current indication in DCS

4.Analog output for RPM to DCS

as per Siemens vendor if we give smaller motor it will damaged or burn the motor ,he Vfd will pumping torque to the motor.And i have doubt with what he told that's why i ask to all expert and guru in this forum to help me.

"as per Siemens vendor if we give smaller motor it will damaged or burn the motor ,he Vfd will pumping torque to the motor.And i have doubt with what he told that's why i ask to all expert and guru in this forum to help me."

Wow... you have bought a very expensive and powerful VFD, and your vendor hasn't any clue what it is or how it works. Amazing...

You cannot "pump" torque into a motor. You can FACILITATE a motor producing it's MAXIMUM torque, but as long as the voltage and base line frequency are the same as the motor nameplate, you cannot "force" the VFD to do damage to the motor.

If however you have a Medium Voltage VFD and you want to test it with a LOW voltage motor, yes, that is a problem. The voltage output of the VFD must match the voltage on the nameplate of the motor. That's the only important criteria.

As I said, the VFD will not likely be able to PROTECT that small motor from an overload condition. If memory serves me correctly, the Sinamics drives can be programmed for motor currents as low as 50% of the VFD rating. Any lower and the sensing devices lose their accuracy by virtue of the scale. In other words if you have a VFD capable of 1200kW, the current sensing devices that are designed to read current in the 1500-5000A range are not going to be able to accurately sense a motor current of only 5A.

For the same reason, you may not be able to accurately depict the running condition of the motor because inside the VFD, it may ignore a 5A value on a 5000A scale as noise and consider it irrelevant. Typically a "Run" status confirmation comes when the motor is pulling 20% of the VFD programmed FLC. So if the VFD can be "fooled" into thinking the motor is small enough, it might work, but if for example you have a VFD capable of 3000A and the smallest motor FLC you can program is 1500A, the motor current will need to be at least 300A for the VFD to accept that the motor is actually running.

Nor may you be able to depict the motor current communications back to the DCS, but you should be able to see if there is SOMETHING getting back there. It's all about the scaling.

Frequency command and response, should be no problem.

Thank's a lot Mr Jraef...for your explanation, that's why i doubt with what the vendor has told "about pumping torque to the small motor" .

yes you are correct for current feedback it will be problem due to very less than range so VFD doesn't recognise the small current producing by this small motor..so we can ignore this current feedback..by disable this input in DCS Logic

but for testing start and stop motor,Tripping motor for abnormal process in plant , speed variation , speed feedback to DCS still posibble. it's more than enough for us

just correct me if my above statement is wrong

thanks's guru ..

hopefully other expert can give comment or idea