How calculate ampere for electric motor?
Generally for electric motor size,it rated by horsepower (hp) or kilowatts (kW) unit.We can recognize the electric motor size when refer to their kilowatts or horsepower.So from power (kW/hp), how we can know the full load ampere for electric motor?
This time i want share about how to calculated the full load ampere (FLA) of electric motor from their power rated.It not difficult if we know the right formula to get the answer.From this calculation we only can estimate the value of full load ampere.
We cannot get the actual full load ampere because it depend on efficiency of motor.If electric motors have a higher efficiency rating,it will draw fewer amps, for example a 10 HP motor with a 60% efficiency rating will draw about 65 amps at 230 VAC compared to about 45 amps for a motor with a 80% rating.
How to calculate from power ( kW & HP ) to ampere ( I )?
1) Kilo watt (kW) to ampere ( I )
For 3 phase power supply ; kW = I x V x 1.732 x pf
For 1 phase power supply ; kW = I x V x pf
Example : 1 unit compressor size rated 37 kw,415 VAC,3 phase and 80% pf,calculate the full load ampere?
Calculation :
kW = I x V x 1.732 x pf
I = kW / (V x 1.732 x pf )
I = 37 / (415 x 1.732 x 0.8 )
I = (37 / 575) x 1000
I = 64.4 ampere ( full load ampere)
2) Horse power ( hp ) to ampere ( I )
First we must convert from hp to kW using this formula :
1 Hp = 0.746 kW
After that use the formula kW to ampere :
For 3 phase power supply ; kW = I x V x 1.732 x pf
For 1 phase power supply ; kW = I x V x pf
Example :-
1 unit induction motor power rated 25 hp,200 VAC,3 phase,90 % power factor,calculated the full load ampere.
Calculation :-
kW = 25 hp x 0.746
kW = 18.65
kW = I x V x 1.732 x pf
I = kW / V x 1.732 x pf
I = 18.65 / ( 200 x 1.732 x 0.9 )
I = (18.65 / 311.76) x 1000
I = 59.8 ampere ( full load ampere )
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Should we take into consideration the efficiency of the motor?.
For efficiency is not compulsory if we don’t have the value.,we can ignore the value :D
In your formula Efficiency factor is not accounted – is there some reason for this. I thought the formula was kW = I x V x 1.732 x pf x Efficiency?
Yes Steve..it true.You can include with efficiency value if you know but if not you can skip it.
Hi. May I help you to calculate the electrical load list of power plan.
amir.masror@gmail.com