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Home > Technical Information > Formulae 
Formulae

 

Index
Quantities and Units (default is SI units system)
Current
Efficiency
Fan load power
Ohm's Law
Power Factor
Power output, Torque and speed
Pump load power
Slip, p.u.
Slip, %
Synchronous Speed (rpm)
Torque, output and speed

 

Quantity Symbol Unit Symbol Example
apparent power  S Voltage x Current VA 120kVA (1000 x V x I )
current I Ampere A  
efficiency Effy per unit   0.95 (i.e. 95%)
frequency f Hertz Hz 50 Hz
poles p  number   2 pole, 4 pole 
pole pairs pp number    4 pole is 2 pp 
active power P Watt W kW = 1000 x W
power, input Pin Watt W  
power, output Pout Watt W  
power factor pf per unit   0.86
reactive power Q Voltage x Current reactive var  
slip s per unit    
speed N revs per minute   Not SI unit
torque   T  Newton . metre Nm   
voltage V Volt V  

 

 

quantity direct current (DC)

alternating current, 1 phase

( AC, 1ph )

alternating current, 3 phase

( AC, 3 ph )
current
Pout
V x Effy
Pout
V x Effy x pf
Pout
√3 x V x Effy x pf
efficiency
Pout
V x I
Pout
V x I x pf
Pout
√3 x V x I x pf
power factor  
pf =   Pin
V x I
pf =   Pin
√3 x V x I

 

Formula  
Fan load power
Hp = ft 3/min x pressure (lbs/ft2)
33000 x Fan efficiency (p.u.)
Fan load power
kW = Flow (m3.s-1)  x pressure (kPa)
 Fan efficiency (p.u.)

Ohm's Law

(Resistive circuits)

V = I x R

I = V / R

R = V / I
Power (kW)
P  =   T (N.m) x rpm
9550
Power (Hp)
P  =   T (lb.ft) x rpm
5250
Power Factor
pf  P in
V x I
Pump load power (Hp)
Hp = Galls/min x Head (ft) x Specific gravity
3960 x Pump efficiency (p.u.)
Pump load power (kW)
kW = 9.81 x Head (m) x Specific gravity
1000 x Pump efficiency (p.u.)
Slip, s,  (p.u.)
s  =   NS - N
NS
Slip,  (%)
s (%)  = NS - N x 100
NS
Synchronous speed, NS,  (rpm)
NS = Hz x 120
p (poles)
Torque (N.m)

T  = kW x 9250
rpm
 
Torque (lb.ft)
T  = Hp x 5250
rpm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                                     

 
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