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(EOD).Professional engineering topics.pdf
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page 216

9. FORMULAS

9.1 ELECTRICAL RELATIONSHIPS

• Ohm’s Law

 

 

 

E

I = Current (Amperes)

I =

E (or V) = Voltage (Volts)

--

 

R

R = Resistace (Ohms)

• DC Power

 

P = IE

P = Power (Watts)

I = Current (Amperes)

 

 

E = Voltage (Volts)

P = IEt

P = Power (Watt-hours)

I = Current (Amperes)

 

 

E = Voltage (Volts)

 

t = time (hours)

• AC Power

 

VA = IE

one phase

VA = IE 2 two phase

VA = IE3 three phase

• AC Power Factor

VA = total power (volt-amps) I = current (RMS amperes) E = voltage (RMS volts)

W PF = -------

VA

PF = power factor (unitless) W = real power (watts)

VA = total power (volt-amps)

• 3 phase AC motor current

page 217

HP( 746)

I = ------------------------------------------------------

E( efficiency) ( PF) 3

I = current (peak amperes)

HP = rated power (horsepower) efficiency = rated efficiency PF = power factor

E = applied voltage (peak volts)

9.2 MECHANICAL FORMULAS

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