Increasing motors power rating

[Chpal1984]

Hi,

I have a motor that has a power rating of 45kW. I have a test where I could really use nearer 50kW. On the motor's nameplate, it has a a 53kW power rating at a 440V 60Hz and a 45kW power rating at 400V 50Hz. If I bought a power converter to convert supply to 60Hz, would I be increasing my available power?

Then can anyone suggest a good power converter supplier and how much they might cost?

Thanks
Chris

 

[edison123]

The higher the speed, the higher the power rating. That applies to your driven equipment too. So, think it through.

Muthu

http://www.edison.co.in

 

[waross]

The specialized inverter is called a Variable Frequency Drive.
You can't increase the safe torque but you can increase the speed.
You cannot exceed a safe Volts per Hertz ratio.
But you can increase the voltage in proportion to an increase in frequency.
400 Volts / 50 hz = 8 Volts per Hertz.
440 Volts / 60 Hz = 7.3 Volts per Hertz. Less than base rating. Safe V?Hz ratio.
480 Volts / 60 Hz = 8 Volts per Hz.
With a suitable VFD you can apply double voltage and double frequency for double HP.
The safe current and the safe torque remain the same. The increase in power is derived from an increase in voltage and an increase in speed/frequency.

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

 

[315kVA]

But voltage and frequency can be increased up to a certain point. I suppose the limiting factor for the voltage is insulation, and for the speed the mechanical properties of the motor, maybe the bearings? Can someone explain more?

 

[waross]

The first limit for voltage is the Volts per Hertz ratio.
For most industrial induction motors the magnetic circuit will saturate at 10% to 15% above rated voltage UNLESS the frequency is also increased.
When the magnetic circuit is driven into saturation the current increase is disproportionate to an increase in voltage.
In hard saturation a motor may fail due to excess I[sup]2[/sup]R losses in less than one minute.
If the frequency only is increased the motor speed will increase but the torque will drop off and the motor will be constant HP.
When the voltage is increased in proportion to an increase in the frequency, full rated torque may be developed and the HP will increase as the speed increases.
As a practical example;
A dual voltage NEMA T frame motor is typically rated for 230/460 Volts. The windings are all suitable for use at 460 Volts. If this is an inverter rated motor the safe voltage will be higher yet.
Most such motors may be connected for 230 Volts and be supplied with 460 Volts (Actually 480 Volts) at 120 Hertz.
The speed and as a result the HP will be doubled.
If you need more than 200% speed you may be considering the wrong motor. At higher percentage speeds bearings and centrifugal forces become a limiting concern.

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

 

[jraef]

How have you determined the required power of 50kW? We need to start there. Because of you are looking at a machine that is rotating, the power requirement is based on speed, as the motor power rating is. If however your machine is linear in nature, to use a rotating motor, you need something that will tranit that rotation into linear motion, and that always involves losses, so to get 50kW in LINEAR motion power, the input from your motor will need to be MORE than 50kW to account for those losses.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

I have a test where I could really use nearer 50kW

What are you testing. The solution may be easy or it may be unreasonable depending on the application.

If I bought a power converter to convert supply to 60Hz, would I be increasing my available power?

Rated HP may not be usable HP.
It depends.

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

 

[davidbeach]

Wouldn't the right sized motor be easier and less expensive than futzing with a drive? If you have cube law load that speed increase will result in a load increase to nearly 80kW.

 

[waross]

http://www.driveswarehouse.com/s-82...ct3=&select4=s-82-ac-motors&select5=&select6=

Models:
PSV7D-601-1
SJ700D-450HFUF3-1
or
SJ700D-550HFUF3
or
ODP-2-64075-3HF4N-TN

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

 

[zlatkodo]

Sometimes, when the motor core has a "reserve", there is a possibility for new winding with higher power at same core.
In order to check, the main measures of the stator core and a photo of nameplate should be known.

Winding Repair and Design

 

[iceworm]

I have a motor that has a power rating of 45kW. I have a test where I could really use nearer 50kW.

As others said, do you need the 50KW at the 50HZ speed, or can you use it at the 60HZ speed?

Second: You said "test". So, how long of a test? 30seconds, 1minute, longer?

Also consider you are asking for a 10% overload for a "test":
Even if it is an IEC 1.0 SF, and the Overloads are set to 115%, it likely won't trip for 30 - 60 seconds.
And if it is a 1.15SF, overloads set to 125%, it may not trip.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[waross]

Elvis has left the building.
Unfortunately he seems to have taken Chpal1984 (the Original Poster) with him.

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

 

[315kVA]

Iron losses depend on induction and frequency. If we increase voltage and frequency proportionally the induction remains constant, but frequency is neverheless increased. Even if we keep the current around nominal, thus keeping the copper losses constant, we should have some increase in overall heating of the motor. From your experience, how big a role will this play when we want to "uprate" a motor? Could it be a limiting factor or is this effect marginal?

 

[waross]

I have never had a problem. I suspect that the effect is marginal. I suspect that the end result may be a small percentage shortening of the life of the motor, and that that may be overwhelmed by other effects such as high ambient temperatures, elevated humidity and operating and loading factors.
The effect of going from 50 Hz to 60 Hz will be much less than the effect of going from DOL to VFD.
We are considering a possible 20% increase in a type of loss that is quite small to begin with.

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