C&G Unit 302: Principles of electrical science
This chapter discusses the principles of electrical machines and describes electrical quantities in Star and Delta configurations. It examines the principles of electronic components in electrical systems. An electrical machine may be used as a motor or a generator, although in practice the machine will operate more efficiently when operated in mode for which it was designed. The electrical power in a circuit is the product of the instantaneous values of the voltage and current. An auto-transformer motor starter provides another method of reducing the starting current by reducing the voltage during the initial starting period. The performance of a lamp is quoted as a ratio of the number of lumens of light flux which it emits to electrical energy input which it consumes. Thus efficacy is measured in lumens per watt; the greater the efficacy the better is the lamp’s performance in converting electrical energy into light energy.