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| ## Provide manual checks of pertinent results (e.g. service size, main feeder voltage drop) for computer generated output. | | ## Provide manual checks of pertinent results (e.g. service size, main feeder voltage drop) for computer generated output. |
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| === Basic Electrical Engineering Formulas ===
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| ==== List of Symbols ====
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| ''V'' - Voltage (volts)
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| ''I'' - Current (amps)
| | {{SUBPAGES:{{FULLPAGENAME}} |depth=1|linked=true|sep=<br>}} |
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| ''R'' - Resistance (ohms)
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| ''X'' - Reactance (ohms)
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| ''Z'' - Impedance (ohms)
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| ''W'' Real Power (watts)
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| ''θ'' - Phase angle whose cosine is the power factor
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| ''eff'' - Efficiency
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| ==== Direct Current (DC) Formulas ====
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| '''Basic Formulas'''
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| ===== Resistance =====
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| : <math>R={V \over I}</math>
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| : <math>R={V^2 \over P}</math>
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| : <math>R={P \over I^2}</math>
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| ===== Volts =====
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| : <math>V=I \times R</math>
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| : <math>V={P \over I}</math>
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| : <math>V=\sqrt{P \times R}</math>
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| ===== Power =====
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| : <math>P=V \times I</math>
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| : <math>P=I^2 \times R</math>
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| : <math>P={V^2 \over R}</math>
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| ===== Current =====
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| : <math>I={P \over V}</math>
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| : <math>I={V \over R}</math>
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| : <math>I=\sqrt{P \over R }</math>
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| ==== Alternating Current (AC) - Single Phase ====
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| ''Note: V denotes line to neutral voltage.''
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| '''Basic Formulas'''
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| Impedance '''''Z''''' (''ohms'')
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| : <math>Z={V \over I }= \sqrt{R^2+X^2}</math>
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| Volts '''''V''''' (''volts'')
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| : <math>V={I \times Z }</math>
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| Real Power '''''P''''' (''watts'')
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| : <math>P=V \times I \times cos \phi</math>
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| Power Factor
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| : <math>pf=cos \phi</math>
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| : <math>pf={P \over S}</math>
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| Apparent Power '''''S''''' (''volt-ampere'')
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| : <math>S=V \times I</math>
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| Reactive Power '''''Q''''' (''volt-ampere-reactive'')
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| : <math>Q=V \times I \times sin \phi</math>
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| Real Power '''''P''''' (''watts'')
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| : <math>P=V \times I \times cos \phi</math>
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| Voltage Drop
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| : <math>V_d=2 \times (I \times R \times cos \phi + I \times X \times sin \phi)</math>
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| where:
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| :: <math>V_d</math> = voltage drop
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| :: <math>cos \phi</math> = load power factor
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| :: <math>sin \phi</math> = load reactive factor
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| :: <math>X</math> = reactance
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| :: <math>R</math> = resistance
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| ==== Alternating Current (AC) - Three Phase ====
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| ''Note: V denotes line to neutral voltage.''
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| '''Basic Formulas'''
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| Apparent Power '''''S'''''
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| : <math>S=\sqrt {3} \times V \times I</math>
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| : <math>S=\sqrt { P^2 + Q^2}</math>
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| Real Power '''''P'''''
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| : <math>P=\sqrt{3} \times V \times I \times cos \phi</math>
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| Reactive Power '''''Q'''''
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| : <math>Q=\sqrt{3}\times V \times I \times sin \phi</math> | |
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| Power Factor '''''pf'''''
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| : <math>pf={P \over S} = cos \phi</math>
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| Voltage Drop
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| : <math>V_d=\sqrt{3} \times (I \times R \times cos \phi + I \times X \times sin \phi)</math>
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| where:
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| :: <math>V_d</math> = voltage drop
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| :: <math>cos \phi</math> = load power factor
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| :: <math>sin \phi</math> = load reactive factor
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| :: <math>X</math> = reactance
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| :: <math>R</math> = resistance
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| ==== Motors ====
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| 1 horsepower (hp) = 746 watts.
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| '''''Note''': Motor hp rating relates to motor mechanical output. To determine motor input kVA requirements, the motor efficiency and power factor must be accounted for. In general, for preliminary or rough load calculations, assume:''
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| 1 kVA of electrical input power for 1 hp of motor.
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| '''''Example'''''
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| '''''Condition''': A motor control center with a total connected horsepower of 337 hp can be assumed to require 337 kVA of input power. This is a conservative value, particularly for larger motors.''
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| : <math>Torque = {{hp \times 5250} \over {RPM} }</math>
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| ===== Fans and Blower Horsepower Equation =====
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| The following equation determines the required horsepower to drive the fan or blower element. This equation does not compensate for temperature, density or airflow characteristics of any particular fan or blower.
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| : <math>P = { {(Q \times p)} \over {(229 \times \mu )} }</math>
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| or
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| : <math>P = { {(Q \times Pf) } \over {(33000 \times \mu )} }</math>
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| or
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| : <math>P = { {(Q \times Pw)} \over {(6356 \times \mu )} }</math>
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| Where:
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| : P = Power, hp
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| : Q = Flow Rate, cfm
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| : p = Pressure, lb/in<sup>2</sup>
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| : Pf = Pressure, lb/ft<sup>2</sup>
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| : Pw = Water Gauge, Inches
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| : μ= Efficiency coefficient
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| ===== Pump Horsepower Equation =====
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| : <math>hp ={ {GPM \times head \times specific-gravity} \over {3960 \times eff} }</math>
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| '''Motors (Single Phase): '''
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| : <math>hp = {{(V \times I \times eff \times pf)} \over 746}</math>
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| '''Motors (3 phase): '''
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| '''Synchronous Speed:'''
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| : <math>N_s = {{120 \times frequency} \over {No.-of-Poles}}</math>
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| : <math>hp = {{\sqrt{3} \times (V \times I \times eff \times pf)} \over {746}}</math>
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| ==== Power Factor Correction ====
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| The size of the capacitor needed to increase the power factor from pf1 to pf2 with the initial kVA given is:
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| <math>kVAR = kVA \times { { ( \sqrt{1-{pf_1}^2}-1 ) } \over { ( X) } }</math> | |
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| === Sample Calculations- ===
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| '''Under Construction'''
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