← All revision guidesSEMESTER 2 · DI02C00171
6FLASHCARDSAC Fundamental
Sinusoids, phasors, impedance, resonance and three-phase circuits.
Sinusoidal quantities
Q1What is the RMS value of a sine wave?
Vrms = Vm/√2 and Irms = Im/√2.
Q2Define phase difference.
The angular displacement by which one sinusoidal quantity leads or lags another of the same frequency.
Q3What is impedance?
The total opposition to AC, expressed as Z = R + jX in ohms.
Power and resonance
Q1Write the single-phase active-power equation.
P = VI cos φ watts using RMS voltage and current.
Q2What happens at series resonance?
XL equals XC, impedance becomes minimum and current becomes maximum.
Q3Why is power factor improved?
It reduces line current, losses, voltage drop and kVA demand for the same useful power.