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Useful Formulas
Formulas for Electrical
Motors
| To Find |
Direct
Current |
Single
Phase |
Three
Phase |
| Horsepower |
E x I x
EFF
746 |
E x I
x EFF x PF
746 |
1.732
x E x I x EFF x PF
746 |
| Current |
746 x
HP
E x EFF |
746 x
HP
E x EFF x PF |
746 x
HP
1.732 x E x EFF x PF |
| Efficiency |
746 x
HP
E x I |
746 x
HP
E x I x PF |
746 x
HP
1.732 x E x I x PF |
| Power
Factor |
- - - - - |
Input
Watts
E x I |
Input
Watts
1.732 x E x I |
| E = Volts |
I = Amperes |
| EFF = Efficiency
(decimal) |
PF = Power Factor
(decimal) |
| HP = Horsepower |
R = Ohms |
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Useful Formulas
Formulas for Electrical Circuits
| To Find |
Direct
Current |
Single Phase |
Three Phase |
| Amperes |
Watts
E |
Watts
E x PF |
Watts
1.732 x E x PF |
| Volt-Amperes |
- - - - |
E x I |
1.732 x E x I |
| Watts |
E x I |
E x I x PF |
1.732 x E x I x PF |
| E = Volts |
I = Amperes |
| EFF = Efficiency (decimal) |
PF = Power Factor (decimal) |
| HP = Horsepower |
R = Ohms |
| Ohms Law |
Capacitance in Microfarads at 60 Hz |
Ohms = Volts/Amperes (R = E/I)
Amperes = Volts/Ohms (I = E/R)
Volts = Amperes x Ohms (E = IR)
|
| Capacitance = |
26500 x Amperes
Volts |
| Capacitance = |
2.65 x kVAR
(Volts)2 |
|
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to table of contents
Useful Formulas
Temperature Correction of Winding Resistance
| Rc = Rh x |
(K + Tc)
(K + Th)
|
| Value of K |
| Material |
K |
| Aluminum |
225 |
| Copper |
234.5 |
|
Rc = Resistance at temperature
Tc (Ohms)
Rh = Resistance at temperature
Th (Ohms)
Tc = Temperature of cold winding (șC)
Th = Temperature of hot winding (șC) |
| Rh = Rc x |
(K + Th)
(K + Tc)
|
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|
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