Electrical Formulas Electrical Formulas. 399 www.emersonct.com 800-893-2321 Symbols & Formulae Electrical Formulae Electrical Quantities …

Electrical Formulae Electrical Quantities Quantity Symbol Unit NameUnit Symbol Electromotive force E, e* Volt V Potential difference V, v* Volt V Current I, i* Ampere A Magnetic fl ux ? Weber Weber Frequency f Hertz Hz Flux linkage ? Weber-turns – Resistance R Ohm ? Inductance L Henry H Capacitance C Farad F Impedance Z Ohm ? Reactance X Ohm ? Power,dc,or active P Watt W Power, reactive Q Volt-ampere reactive VAr, var Power, total or apparent S Volt-ampere VA Power factor angle ? – °, deg. Angular velocity ? Radians per second rads-1 Rotational velocity n Revolutions per second s-1 ,rev s-1 Revolutions per minute min-1, rpm Effi ciency ? – Number of pairs of poles p- * Capital and small letters designate rms and instantaneous value respectively. AC Single-Phase All quantities r.m.s. values: V = I Z Total or apparent power in VA = V l = I 2 Z = V2 Z Active power in watts, W =V l cos ? Reactive power in VAr = V l sin ? AC Three-Phase (Assuming Balanced Symmetrical Waveform) All quantities r.m.s values: V l = Line-to-line voltage V p = Phase voltage (line-to-neutral) I l = line current (wye) I p = Phase current (delta) In a WYE connected circuit, V p = V l 3, V l =3V p , I l = I p In a DELTA connected circuit: I p = I l 3, I l =3 I p V l = V p Total of apparent power in VA = 3 V l I l Active power in watts,W = 3 V l I l cos ? Reactive power in VAr = 3 V l I l sin ? Power factor (pf) = cos ? = Active power / Apparent power = W / VAr

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