Motor Design Characteristics 3

[mcarruthers]

I need Help? I have a motor 440V,2.2KW, 60Hz, 3460rpm, 3.9A PF=0.74, 3 phase. It requires to be installed into a 415V 50Hz system is it possible and what will the above values change to? Please if possible show all workings out cos I am stuck Cheers!

 

[TurbineGen]

What power is the load going to require? You won't want to push that motor to a full 2.2 kW as you will be drawing too many Amps. You don't want to exceed the nameplate amperage. Your voltage might be a little high at 50 hz and could possibly push it into saturation.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[electricpete]

I think there is a related FAQ.

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[dpc]

faq237-1224

"The perfect is the enemy of the good." -- Voltaire

 

[mcarruthers]

The motor is coneected to a pump 2.2Kw(no Belts) Coupling. This pump 2.2kw is taking place of a 4kw pump so maximum is required. Please could you show all calculations so I can show my boss that it may not be possible or to show that it may have discrepencys Thankyou

 

[waross]

Check the FAQ. HP = 2.2 kW x 50Hz/60Hz = 1.83kW.
Voltage 440V x 50Hz / 60Hz = 367V 416V/367V = 120%
Saturation is a possibility.
How old is the motor? 440V hasn't been a standard voltage for 40 or 50 years.

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

 

[mcarruthers]

Waross thanks so what current will the motor pull Is the calculation 1830Kw/1.732x415VxPF0.86=2.96A PF is 0.86 not .74 as stated Cheers

 

[mcarruthers]

The voltage also cannot be made smaller Thanks

 

[mcarruthers]

so 415/366v = 120% so to get the same characteristics out of the motor I would have to drop the voltage to 366.7V. but if 366V x 120% that gives you 440V. Cofused sorry

 

[edison123]

Thumb rule : V/Hz must not change. As Bill points out, at 50 Hz, your voltage must be 367 V so that you don't oversaturate the iron. Use a step down transformer to get 367 V or rewind the motor to right voltage and frequency or buy a new motor.

If you plan to use the same pump, the pump output will drop drastically at 50 Hz. So you need to use V belts and pulleys to get it up to original speed. In which case, the motor will be undersized.

60 Hz to 50 Hz is a bitch, ain't it ?

 

[waross]

The current normally stays the same. Current is what heats the motor. Depending on the motor there may be cooling issues due to the cooling fan running slower.
My bad on the voltage. You will be 13% over voltage. Very close. Some motors will accept +113%, some will fry.
Are you sure the motor is not 460 Volts? That is the standard voltage.


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

 

[Laurier]

You are tackling this problem from the wrong end, the place to start is the pump not the motor. You need to know the head the pump has to pump to and then from the head/flow (Q-H) curve you will be able to work ot the flow, assuming you have the head/flow curve and know the pump head.
However, there will be a reduction in speed of the new motor from the 50Hz frequency, this must be a 2-pole motor, running with 4% slip, (slip will be slightly higher on the lower frequency) So new running speed will be around 2800 rpm, this will change the flow rate, probably lower it, it may also improve efficiency, this will determine the torque required from the motor. Historically, many motors were over-rated for the duty and so this may still be OK on 2.2KW, also, if the pump is old, then you will find the Q-H curve will be lower due to wear, approx 1% in head per year. The V/f ratio is important, but the consequence of increased v/f ratio (4.8 for new motor, 4.2 for the original) will be lower current. Note the other disadvantage of the lower speed will be lower airflow from the TEFC fan, this could be as much as 36% reduced cooling (1-(S1/S2)^2)
Having said all this, i suspect you wont have the Q/H curve and also required head will also be unknown.
So, my recommendation would be if this is the only available motor, you try it. Measure the current the pump draws and then work out the power drawn, if this is close to 2.0KW, then you are lucky, then all you need to do is check the temperature of the motor over extended running.
BUT.... the final question would be to ask about load factor. if this pump is for occasional use, then energy efficiency wont be important. But, if load factor is above 75%, then the best recommendation you can make to your boss is to buy a new high efficiency pump and motor, you will see payback in less than 12 months from improvement in energy efficiency. The rule of thumb is that for a continuously running pump, it consumes its own capital cost in energy in 1 month, we get far too posessive about our pumps and motors! Pennywise £ foolish!

 

[ScottyUK]

Measure the current the pump draws and then work out the power drawn, if this is close to 2.0KW, then you are lucky, then all you need to do is check the temperature of the motor over extended running.

Measuring the current will tell you how much current the motor draws, but not how much power it is delivering. You need to measure the poower factor too, and that's a little harder without specialist equipment. Power factor is load-dependant so the nameplate value is of limited use.


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