ABSTRACT
At the end of this chapter you should be able to:
• understand the
• understand the term
• use V1
V2 = N1
N2 = I2
I1 in
• construct a and calculate magnetizing and core loss components of the no-load current
• state the e.m.f. mN and use it in calculations • construct a for an inductive circuit assuming the volt drop in the
windings is
• describe transformer
• derive the equivalent referred to the primary of a transformer
• understand voltage
• describe losses in transformers and calculate efficiency
• appreciate the concept of resistance matching and how it may be achieved
• perform calculations using R1= ( N1
• describe an auto transformer, its advantages/disadvantages and uses
• describe an isolating transformer, stating uses
• describe a three-phase transformer
• describe current and voltage transformers
A transformer is a devicewhich uses the phenomenon of mutual induction (see Chapter 11) to change the values of alternating voltages and currents. In fact, one of the main advantages of a.c. transmission and distribution is the ease with which an alternating voltage can be increased or decreased by transformers. Losses in transformers are generally low and thus
efficiency is high. Being static, they have a long life and are very stable. Transformers range in size from the miniature units
used in electronic applications to the large power transformers used in power stations. The principle of operation is the same for each. A transformer is represented in Figure 23.1(a)
as consisting of two electrical circuits linked by a common ferromagnetic core. One coil is termed the primary winding, which is connected to the supply
of electricity, and the other the secondary winding, which may be connected to a load. A circuit diagram symbol for a transformer is shown in Figure 23.1(b). Some typical practical transformers are shown in Figure 23.2.
