Stevenson J. Power system analysis

40 CHAER 1 BASIC CONCES

1.25. Write the two nodal admittance equations, similar to Eqs. (1.57) and

.58)

for the

voltages at nodes  and

of the circuit of Fig. 1.23. Then, arrange the nodal

admittance equations for all four independent nodes of Fig. l.23 into the

Y b

form

of Eq. (1.61).

1.26. The values for the parameters of Fig. 1.23 are given in per unit as follows:

Ya = -jO.8

-j4.0

-)·0 .8



.

= -

j4.0

-j8.0

-j5.0

Substituting these values in the equations determined in Prob. 1.25, compute the

voltages at the nodes of Fig. 1.23. umcrically determine the corresponding

matrix

CHAPTER

TRANSFORMERS

Transformers are t

e link between the generators of the power system and the

transmission lines, and between lines of dierent voltage levels. Transmission

hnes operate at nominal voltages up to 765 kY line to line. Generators are

usually built in the range of 18-24 kV with some at slightly higher rated

voltages. Transformers (llso lower the voltages to distribution levels and  nally

fer residential use at 240/12() V. They are highly (nearly JOO) ecient and

very fcliablc.

In this ch,tprcr we discuss the modeling of transformers and see the great

adv�\nu\gs of per-unit calculations. We also consi d er trnsformers that regulate

vI(at�e gnitudc and phdSC shifting, a nd in this and a later chapter we shall

sec how t

ese regulating transformers a rc Llsed to control the