  Circuits, Formulas and Tables Electrical Engineering - Basic vocational knowledge (Institut f³r Berufliche Entwicklung, 201 p.)  11. Basic symbols and formulas of electrical engineering  (introduction...) 11.1. General direct current engineering 11.2. Magnetic field 11.3. Law of induction 11.4. Electric field 11.5. Alternating current engineering 11.6. Calculation of power

### 11.5. Alternating current engineering

 frequency T = cycle duration in s gyro-frequency phase angle instantaneous value of a sinusoidal a.c. voltage instantaneous value of a sinusoidal a.c. current maximum value - of a sine-wave voltage U = virtual value - of a sine current I = virtual value inductive resistance (inductive reactance) L in H capacitive resistance (capacitive reactance) C = capacity in F Series connection

 impedance [W] ohmic drop in voltage UR = I · R [V] inductive voltage drop UL = I · XL = I · w L [V] capacitive voltage drop [V] Ohm’s law for alternating current [A]

Powers in case of single-phase alternating current

 apparent power S = U · I [VA] active power P = U · I · cos z [W] reactive power Q = U · I · sin z [Var] power factor Powers in case of three-phase alternating current

 apparent power [VA] active power [W] reactive power [Var] power factor efficiency for motors and generators Pe = effective power Pi = indicated power speed calculation of three-phase motors rotating field speed  p = number of pole pairs slip [%] n = rotor speed