Common Electrical Unit & Formulas

Watt - unit of electrical energy or power - one watt is the product of one ampere and one volt - one ampere of current flowing under the force of one volt gives one watt of energy

Volt-ampere (VA) - is a measurement of power in a direct current ( DC ) electrical circuit. The VA specification is also used in alternating current ( AC ) circuits, but it is less precise in this application, because it represents apparent power , which often differs from true power .

Kilovolt Ampere - one kilovolt ampere - KVA - is equal to 1000 volt amperes

Power Factor - ratio of watts to volt amperes

Most important Formulas:

Power P = V × I = R × I2 = V2 / R in watts W

Electrical Potential - Ohm's Law

Ohm's law can be expressed as:

V = R I (1a)

V = P / I (1b)

V = (P R)1/2 (1c)

Electric Current - Ohm's Law

I = V / R (2a)

I = P / V (2b)

I = (P / R)1/2 (2c)

Electric Resistance - Ohm's Law

R = V / I (3a)

R = V2/ P (3b)

R = P / I2 (3c)

Electric Power

P = V I (4a)

P = R I2 (4b)

P = V2/ R (4c)

where

P = power (watts, W), V = voltage (volts, V)

I = current (amperes, A), R = resistance (ohms, Ω)

Electric Energy :Electric energy is power multiplied time, or

W = P t (5)

where

W = energy (Ws, J), t = time (s)

Electrical Motors : Electrical Motor Efficiency

μ = 746 Php / Pinput_w (6)

where

μ = efficiency

Php = output horsepower (hp)

Pinput_w = input electrical power (watts)

or alternatively

μ = 746 Php / (1.732 V I PF) (6b)

Electrical Motor - Power

P3-phase = (V I PF 1.732) / 1,000 (7)

where

P3-phase = electrical power 3-phase motor (kW)

PF = power factor electrical motor

Electrical Motor - Amps

I3-phase = (746 Php) / (1.732 V μ PF) (7)

where

I3-phase = electrical current 3-phase motor (amps)

PF = power factor electrical motor

Electrical measurements

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