ABSTRACT
At the end of this chapter you should be able to:
• appreciate why a.c. is used in preference to d.c.
• describe the principle of operation of an a.c. generator
• distinguish between unidirectional and alternating waveforms
• define cycle, period or periodic time T and frequency f of a waveform
• perform calculations involving T = 1 f
• define instantaneous, peak, mean and r.m.s. values, and form and peak factors for a sine wave
• calculate mean and r.m.s. values and form and peak factors for given waveforms
• understand and perform calculations on the general sinusoidal equation υ=Vm sin(ωt±φ) • understand lagging and leading angles
• combine two sinusoidal waveforms (a) by plotting graphically, (b) by drawing phasors to scale and (c) by calculation
• understand rectification, and describe methods of obtaining half-wave and full-wave rectification
• appreciate methods of smoothing a rectified output waveform
Electricity is produced by generators at power stations and then distributed by a vast network of transmission lines (called the National Grid system) to industry and for domestic use. It is easier and cheaper to generate alternating current (a.c.) than direct current (d.c.) and a.c. is more conveniently distributed than d.c. since its voltage canbe readily altered using transformers.Whenever d.c. is needed in preference to a.c., devices called rectifiers are used for conversion (see Section 16.7).
