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POLYPHASE CIRCUITS

[CHAP. 11

Fig. 11-33   14:16 pffiffiffi ð10Þ ¼ 1002:5 W 2   8:01 2 PB ¼ IB eff RB ¼ pffiffiffi ð15 cos 308Þ ¼ 417:0 W 2  2 10:21 PC ¼ IC2 eff RC ¼ pffiffiffi ð10 cos 308Þ ¼ 451:4 W 2 PA ¼ IA2 eff RA ¼

and so the total average power is 1870.9 W. From the results of Problem 11.13, the wattmeter readings are:    208 8:01 pffiffiffi 48:938 ¼ 817:1 W WB ¼ Re ðVBA eff IB eff Þ ¼ Re pffiffiffi 608 2 2    208 10:21  pffiffiffi 127:598 ¼ 1052:8 W WC ¼ Re ðVCA eff IC eff ¼ Re pffiffiffi 24008 2 2 The total power read by the two wattmeters is 1869.9 W.

11.15 A three-phase, three-wire, balanced, -connected load yields wattmeter readings of 1154 W and 557 W. Obtain the load impedance, if the line voltage is 141.4 V.  tan  ¼ and, using PT ¼

    pffiffiffi W2  W1 pffiffiffi 577 3 ¼ 0:577 ¼ 3 1731 W2 þ W1

 ¼ 30:08

pffiffiffi 3VL eff IL eff cos , pffiffiffi 3VL eff 3VL2 eff cos  3ð100Þ2 cos 30:08 VLeff ¼ ¼ ¼  ¼ 15:0  Z ¼ IPh eff IL eff PT 1154 þ 577

Thus, Z ¼ 15:0 30:08 .

11.16 A balanced -connected load, with Z ¼ 30 308 , is connected to a three-phase, three-wire, 250-V system by conductors having impedances Zc ¼ 0:4 þ j0:3 . Obtain the line-to-line voltage at the load. The single-line equivalent circuit is shown in Fig. 11-34. By voltage division, the voltage across the substitute Y-load is    10 308 250 pffiffiffi 08 ¼ 137:4 0:338 V VAN ¼ 0:4 þ j0:3 þ 10 308 3 pffiffiffi whence VL ¼ ð137:4Þð 3Þ ¼ 238:0 V.

Mahmood_Nahvi_eBook_Schaum_s_Outlines_Theory_An  
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