Contractors Unlimited

Electric Motor Formula

Electric motors are the most common drives for pumps, fans etc in the refining, oil and gas and petrochem industries. The power supply available determines their characteristics e.g. power, current consumption etc. The following table provides common formula for motor characteristics relative to the power supply.
 
TO FINDDIRECT
CURRENT
SINGLE
PHASE
THREE
PHASE
POWERV x I x EFFV x I x EFF x PF1.732 x V x I x EFF x PF
HORSE
POWER
V x I x EFF
746
V x I x EFF x PF
746
1.732 x V x I x EFF x PF
746
CURRENT       P      
V x EFF
           P        
V x EFF x PF
                 P                
1.732 x V x EFF x PF
EFFICIENCY746 x HP
V x I
746 x HP
V x I x PF
        746 x HP     
1.732 x V x I x PF
POWER
FACTOR
------Input Watts
V x I
Input Watts
1.732 x V x I
SHAFT
SPEED
------------    120 x F   
no. of poles
Where
V= Voltage (volts)I= Current (amps)P= Power (watts)
EFF= EfficiencyHP= HorsepowerF= Frequency (Hz)
PF= Power Factor. A measurement of the time phase difference between the voltage and current in an AC circuit. It is represented by the cosine of the angle of this phase difference. For an angle of 0 degrees, the power factor is 100% and the volt/amperes of the circuit are equal to the watts. (This is the ideal and an unrealistic situation.) Power factor is the ratio of Real Power-KW to total KVA or the ratio of actual power (watts) to apparent power (volt-amperes). For further information on power factor, see our Power Factor toolbox page.


Electric Motors and Drives:
Fundamentals, Types and Applications

 




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