0195136047.pdf

466 AC POWER SYSTEMS

η=

9

9. 75

× 100 = 92 .3%

TLVR=

VRNL−VRFL

VRFL

× 100 =

38. 1 − 33

33

× 100 = 15 .45%

Note: If there were no load, the sending-end voltage would appear at the receiving

end.

(ii) 0.9 PF leading:

PR= 10 × 0. 9 =9MW

PS=

√

3 × 33. 2 × 0 .175 cos( 25. 8 − 11. 3 )°= 9 .74 MW

η=

9

9. 74

× 100 = 92 .4%

TLVR=

33. 2 − 33

33

× 100 = 0 .61%

10.4 Learning Objectives

Thelearning objectivesof this chapter are summarized here, so that the student can check whether

he or she has accomplished each of the following.

• Past, present, and future trends of power systems in the United States.


• Three-phase power calculations and power factor improvement.


• Basic notions of power transmission and distribution.


• Working with load-bus data, transmission-line data, and source-bus data.


• Simple transmission-line model and its circuit calculations.

10.5 PRACTICAL APPLICATION: A CASE STUDY

The Great Blackout of 1965

In the United States, electric utilities grew first as isolated systems. Gradually, however, neigh-

boring utilities began to interconnect, which allowed utility companies to draw upon each others’

generation reserves during time of need and to schedule power transfers that take advantage

of energy-cost differences. Although overall system reliability and economy have improved

dramatically through interconnection, there is a remote possibility that an initial disturbance

may lead to instability and a regional blackout.

The worst power failure in history occurred on Tuesday evening, November 9, 1965. At

the height of the rush hour, complete darkness descended, and practically everything came to a

standstill over an area of 83,000 square miles. About 30 million people were affected in eight

states and part of Canada. The system involved was the Canadian–United States eastern power

complex (CANUSE).

Many guesses were offered as to the cause of the blackout, but most were far from correct.

At first, little hope was held out for pinpointing the exact reason for the failure within a short

time. However, on November 15 it was announced that the cause had been found. The failure

was attributed to a faulty relay at Sir Adam Beck Plant no. 2 at Queenston, Ontario (see Figure

R. McCaw, “The Great Blackout,”Power Engineering, Dec. 1965.