发布时间 : 星期日 文章《电工与电子技术》习题册习题解答更新完毕开始阅读509373ec102de2bd960588a3
??45?
XC?UC50??25? I2X?Zsin?=50×0.707=35.35?
XL?X?XC=35.35+25=60.35? R?Z?X2?502?35.352?35.35?
XL2 或: R?Zcos?=50×0.707=35.35?
60.35?192.2mH
?31411C???127.3?F
?XC314?25(2)P?UIcos?=100×2×0.707=141.4W
Q?UIsin?=100×2×0.707=141.4Var S?UI=100×2=200VA
L??#*2.一盏日光灯接于220V工频交流电源上,工作时的等效电路如题2图所示。测得灯管两端的电压为60V,镇流器两端的电压为200V,镇流器消耗的功率为4W,电路中的电流为0.4A,工作时的等效电路如题37图所示,求灯管的等效电阻R、镇流器的等效电阻r与等效电感L、灯管及整个电路消耗的功率P。
2解:ZrL?UL200??500? I0.4P4r?r??25? 22I0.4XL?L?ZrL?r2?499.4?
XL?2499.4?1.59H
?314U60R?R??150?
I0.4PR?URI?60?0.4?24W
P?PR?Pr?24?4?28W
3.电路如图所示,已知u=1002sin(100πt+30°)V, i=22sin(100πt+83.1°)A。
?、U?、有功功率P和功率因数cos?,求:R、C、URC并画出电流及各电压的相量图。
3解:u、i的相量表达式为:
???10030?V I??283.UA1
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???u??i?30??83.1???53.1?
R?U100cos??cos(?53.1?)?50?0.6?30? I2U100X?sin??sin(?53.1?)?50?(?0.8)??40???XC
I2XC?40?
106106C???79.6?F
?XC100??40??RI??30?283.1?V?6083.1?V UR???jXI???90??40?283.1? UCC?80?6.9?V
cos??cos(?53.1)?0.6
P?UIcos??100?2?0.6?120W
画出电流及各电压的相量图如右图所示:
#*4.在题4图示电路中,R=1Ω,C=0.001F,
?us=3sin(1000t-)V。求:
2(1)电压uc,uR;
(2)电路的有功功率P;
?,I?,U?,U?的相量图。 (3)作USRC4解:(1)R?1?,
11???1? Z?R?jXC?1?j1??2?? ?C1000?0.0014?U3?3???US??V I?S??A Z2422XC???RI??3??V u?3sin(1000t??)V URR2224???jXI??3?3?V UCC2433?sin(1000t?)V 243232)?1?W (2)P?IR?(24?,I?,U?,U?的相量图如右(3)作USRC uC?图所示:
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5.在题5图示电路中,已知:R=30Ω,L=127mH,C=40μF, u=2202sin(314t+30°)V。求:
(1)电流i
(2)有功功率P及功率因数
(3)画出相量图(含U,I)。 5解:R?30?,
·
·
XL??L?314?127?10?3?40?
题5图 11XC???80?
?C314?40?10?6Z?R?j(XL?XC)?30?j(40?80)?30?j40?50?53.1??
???53.1?,cos??cos(?53.1?)?0.6
??22030?V (1)U?U22030?? I???4.483.1?A ?Z50?53.1i?4.42sin(314t?83.1?)A
(2)P?UIcos??220?4.4cos(?53.1?)?220?4.4?0.6?581W
??RI??30?4.483.1??13283.1?V (3)UR??jXI??j40?4.483.1??176173.1?V ULL?????jXI?UCC??j80?4.483.1?352?6.9V
画出相量图如下图所示:
6.在题6图电路中,已知R=2Ω,L=1H,i(t)=14.14sin(2t)A,求u(t)、iL(t)、电路的有功功率和无功功率及功率因数。
6解:已知??2rad/s,L?1H
XL??L?2?1?2?
由i(t)=14.14sin(2t)A
??得I14.14?0?100?A 22?j2Z?R//jXL??1?j1?245??
2?j235
题6图
??ZI??245??100??10245?V U∴ u(t)?1022sint?(2?V4?5)20t?si?n( 2V45)?IR?IL?10245??U???5245A R2??U10245????52?45A jXL290?∴ iL(t)?522sint?(2?4?5) A10t?si?n(245)P?IR2R?(52)2?2?100W QL?IL2XL?(52)2?2?100Var
S?P2?QL2?1002?1002?1002VA
cos??P1002???0.707 S100227.某供电线路及负载的等效电路如题7图所示。已知负载等效电阻RZ=10
Ω、等效感抗XZ=l0.2Ω,线路的电阻RL=0.5Ω、感抗XL=1Ω,求:
(1)保证电压UZ=220V时的电源电压U和线路压降UZL;
(2)负载有功功率PZ和线路的功率损耗PL;
(3)电路的总功率因数cosφ.
7解:(1)保证电压UZ=220V时的电源电 压U和线路压降UZL
题7图
ZZ?RZ2?XZ2?102?10.22?14.28? ZL?RL2?XL2?0.52?12?1.12?
I?UZZ220??15.4A ZZ14.28线路压降:UZL?IZZL?15.4?1.12?17.25V
URL?IRL?15.4?0.5?7.7V URZ?IRZ?15.4?10?154V
UXL?IXL?15.4?1?15.4V UXZ?IXZ?15.4?10.2?157.1V UR?URL?URZ?7.7?154?161.7V UL?UXL?UXZ?15.4?157.1?172.5V
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