Volt - unit of electrical potential or motive force - potential is required to send one ampere of current through one ohm of resistance
Ohm - unit of resistance - one ohm is the resistance offered to the passage of one ampere when impelled by one volt
Ampere - units of current - one ampere is the current which one volt can send through a resistance of one ohm
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:
Voltage V = I × R = P / I = √(P × R) in volts V
Current I = V / R = P / V = √(P / R) in amperes A
Resistance R = V / I = P / I2 = V2 / P in ohms Ω
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
Quantity |
Name |
Definition |
frequency f |
hertz (Hz) |
1/s |
force F |
newton (N) |
kg•m/s² |
pressure p |
pascal (Pa) = N/m² |
kg/m•s² |
energy E |
work joule (J) = N•m |
kg•m²/s² |
power P |
watt (W) = J/s |
kg•m²/s³ |
electric charge Q |
coulomb (C) = A•s |
A•s |
voltage V |
volt (V)= W/A |
kg•m²/A•s³ |
current I |
ampere (A) = Q/s |
A |
capacitance C |
farad (F) = C/V = A•s/V = s/Ω |
A²•s4/kg•m² |