Is it possible that motor will be over than kW rating when operated ? 2

[Jed057]

Dear any guru

Is it possible that motor will have power over than kW (From name plate) rating when operated ?

Young Eng

 

[davidbeach]

Apply more than rated load and the motor will draw more than rated power.

 

[rbulsara]

Not for too long though...

Rafiq Bulsara

http://www.srengineersct.com

 

[Skogsgurra]

There are two possibilities to have more than rated kW out of the motor.
One is to run it at a lower temperature than rated ambience, which usually is around 40 C.
The other method is to apply a higher than rated frequency.

Motor ratings are actually torque based and upping frequency and speed makes the motor deliver more HP or kW, if you prefer that, than at nominal speed.
It is being done all the time. Very common is to get 73 % more out of a motor by running the nominal 50 Hz motor at 86.5 Hz. Also, a 50 Hz motor will deliver 20 % more power when run from a 60 Hz grid. Provided, of course, that voltage/Hz is kept at nominalvalue.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Hi Gunnar.
Is there a technical reason to choose 86.5 Hz?
Thanks
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Bill - 240 V, 50 Hz motor run at 415 V (standard supply voltage in 50 Hz world) gives 86.5 Hz ?

Muthu

http://www.edison.co.in

 

[Skogsgurra]

Yes, the reason is that sqrt(3) = 1.732 and 50*1.732 = 86.5 (roughly) and European frequency.

Requires motor to be a six-lead one. Connect a 400 V wye 50 Hz motor in delta (230 V @ 50 Hz) and run it at 400 V @ 86.5 Hz

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Thanks Muthu and Gunnar.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Gunnar - question - Why the motor connection has to be changed at all for running at a different voltage if V/F is maintained ?

A 230 V, 50 Hz (delta or wye connected) can be run at 415 V, 86.5 Hz directly without any winding reconnection, right ?

Muthu

http://www.edison.co.in

 

[waross]

Assume a 415V system before and after.
The way the V/Hz ratio at the motor is maintained is to reconnect a 415V motor for 240V (415V/1.73=240V, wye to delta connection change). Now the motor that is connected for 240v 50Hz may be energized at 415V at 86.5 Hz.
Gunnar just taught me that.
Thanks again Gunnar.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Bill

A 415 Wye/230 V Delta is a dual voltage motor for the same rating.

My question was if a 230 V, 50 Hz motor (delta or wye) can be run at 415 V, 86.5 V without doing anything to the connection. And the answer is, yes.

Muthu

http://www.edison.co.in

 

[waross]

A 230V motor will have the same V/Hz ratio at 400V 86.5 Hz.
A 240V motor will have the same V/Hz ratio at 415V 86.5 Hz.
Therein lies my confusion.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

I was thinking star/delta motors, not dual voltage (230/460V) motors. If we are talking about a 230 V motor at 60 Hz, then you can, of course, run it at 120 Hz and 120 Hz without reconnecting it. There might be issues with balancing and bearing, this is only about magnetics.

Gunnar Englund

http://www.gke.org

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[itsmoked]

run it at 120 Hz and 120 Hz

Whew! I'm glad we cleared this up...

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

You seem to overly correct in your thinking, Keith. 120=120, isn't it? Except for extreme values of 120. It may then be 460 V...

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...