电工技术课件第5章三相电路.ppt

1、)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120si

2、n(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 t

3、Uu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120

4、sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu SN+_eeU1U

5、2定子定子转子转子+e1e2e3+铁心铁心（作为导磁路经）（作为导磁路经）三相绕组三相绕组:直流励磁的电磁铁直流励磁的电磁铁定子定子转子转子发电机结构发电机结构Wk 2.3W8.05.102203cos3 l lI UP)120sin(m2 tUu 31iCI)23j21(1202 UUU 1203UUU2U1.120120120U3.)23j21(1203 UUU321UUU、0321 UUU或或1iA5.464.3021111 IIIt Ou1u2u32 120 240 360ZUIll 对称三相电动势的瞬时值之和为对称三相电动势的瞬时值之和为 0NoImagetUu sinm1 三个正弦

6、交流电动势满足以下特征三个正弦交流电动势满足以下特征)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(

7、m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu

8、)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu N L2 L3L1NU1V1W1(1)联接方式联接方式中性点中性点UUU 011u Up Ul1U+12i。三三相相线线电电压压也也是是对对称称的的前前相相应应的的相相电电压压,3031u+V038012 U3223UUU 1331UUU 2U 由相量图可得由相

9、量图可得 30 303331UU12UNoImageNoImage 303223UUPIIl L1NL2L3+2i+1u。三三相相线线电电压压也也是是对对称称的的前前相相应应的的相相电电压压,301U31uV038012 U23u p 相相电电压压线线电电压压 时时结结结结论论：电电源源形形联联UUl BCU且且超超线线电电压压形形联联结结时时结结论论：电电源源,3,Y PUUl 2u+L2L1L331u321III、3iL3三相四线制三相四线制380/220伏伏 额定相电压为额定相电压为220伏的单相负载伏的单相负载 额定线电压为额定线电压为380伏的三相负载伏的三相负载+BAABAZZUI

10、 2u3u1U+Z1Z2Z31i2112UUU N 电源中性点电源中性点N 负载中性点负载中性点23uNi1uP3UUlY 联结时：联结时：23I03 2 1 N I I I I 中中线线电电流流+BAABAZZUI 2u3u1U+Z1Z2Z31i2112UUU 23uNi+BAABAZZUI 2u3u1U+Z1Z2Z31i2112UUU 23uNi负载对称时负载对称时,中性线无电流中性线无电流,可省掉中性线。可省掉中性线。Ni所以负载对称时，所以负载对称时，三相电流也对称。三相电流也对称。2i 负载对称时，负载对称时，只需计算一相电只需计算一相电流，其它两相电流，其它两相电流可根据对称性流可

11、根据对称性直接写出。直接写出。A044A50220111 RUI例例1 1：灯组，若灯组，若R1=R2=R3=5 ，求线电流及中性线电流，求线电流及中性线电流IN;若若R1=5 ,R2=10 ,R3=20 ,求线电流及中性求线电流及中性 一星形联结的三相电路，电源电压对称。设电一星形联结的三相电路，电源电压对称。设电源线电压源线电压 。负载为电。负载为电 A044A50220111 RUI线电流线电流 IN。N+2iN R1R2R3L1L2L33u1U11iV0 2201 UNoImageP3 UUl 负负载载对对称称无无中中性性线线时时中性线电流中性线电流A12022A10120220222

12、 RUI解：解：已知：已知：NoImageA120443 IV380,V380,0,03313212211 UUUUUUUU(1)线电流线电流 三相对称三相对称A15010A9010 A3010321 III可可知知：如如：A12011A12022A044321N IIIIN+2iN R1R2R3L1L2L33u1U11iV0 2201 UNoImageP3 UUl 负负载载对对称称无无中中性性线线时时(2)三相负载不对称三相负载不对称（R1=5 、R2=10 、R3=20 ）分别计算各线电流分别计算各线电流中性线电流中性线电流1u 3u Pu2u 0321N IIII解解:(1)中性线未断中

13、性线未断L1 L1L2 L3 L1L1 R1R3R2L1L2NL3N 3+A7.120 2103803223 RRUI12IV127107.1222 IR UL2L3L1 此时负载中性点此时负载中性点L1A12011A20120220333 RUIL1 L2、L3相灯仍承受相灯仍承受220V电压电压,正常工作。正常工作。V254207.1233 IR UCu1iiL2L3+R1R3R2L1L2NL3N 5.3 负载三角形联结的三相电路负载三角形联结的三相电路31uA1929 312312III、321III、)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)

14、120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin

15、(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tU

16、u)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu L1+321III、12u3iL2L3i1i2i3A120442 I12uZ31Z12Z23(2)相电流相电流313131ZUI 12232III ZUIIIIPP312312 (1)负载相电压负载相电压=电源线电压电源线电压即即:UP=Ul即即相电流：相电流：121212ZUI 线电流：线电流：31121III L1+321III、3i232323ZUI i1i2i3Z31Z12Z23L2L31

17、2uA120442 I12u相量图相量图ppp psin3 sin3 l lI UI UQ 23pp p psin3 sin3 l lI UI UQ 12pp p psin3 sin3 l lI UI UQ 30负载对称时负载对称时,A1.6 A8.212922022PP ZUI2A1.6 A8.212922022PP ZUI3(3)线电流线电流 A7.463830226713.18Y111 III由相量图可求得由相量图可求得23313III lIIII 32131I 1IZUIPP RXarctan312312 A03-22Y1Y1 RUIA5.103P IIl23A5.103P IIl12

18、A5.103P IIl31PUUl P3 UUl 负载的额定电压负载的额定电压=电源的线电压电源的线电压应作应作 联结联结负载的额定电压负载的额定电压=电源线电压电源线电压0321 u uu即即：应作应作 Y 联结联结)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m

19、3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)

20、120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin

21、(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu)120sin(m3 tUu 三相电动机绕组可以联结成星形，也可以联结成三三相电动机绕组可以联结成星形，也可以联结成三角形，而照明负载一般都联结成星形角形，而照明负载一般都联结成星形(具有中性线具有中性线)。A6713.180 3-37347.101 I对称负载对称负载 联结时：联结时：12U同理同理1U1I对称负载对称负载Y联结时：联结时：相电压与相相电压与相电流的相位差电流的相位差当负载对称时：当负载对称时：P

22、=3Up Ipcos pZUIlP 所以所以正误判断正误判断)120sin(m2 tEu P3IIl CBAZZZ 因因为为三三相相电电压压对对称称，且且333222111 ZUIZUIZUI UUU 01AIBI NIaIAUBUCU+BAABAZZUI ZBZCZAAAB3ZUIA Wcos23202203803 PWcos53202203803 P+Wcos53202202203 P AABA330ZUI AABA330ZUI 5320V30380ABZU三三相相负负载载对对称称已已知知：正误判断正误判断IUI 有一三相电动机有一三相电动机,每相的等效电阻每相的等效电阻R=29,等效等效

23、 感抗感抗XL=21.8,试求下列两种情况下电动机的相电流、试求下列两种情况下电动机的相电流、线电流以及从电源输入的功率，并比较所得的结果：线电流以及从电源输入的功率，并比较所得的结果：(1)绕组联成星形接于绕组联成星形接于Ul=380 V的三相电源上的三相电源上;(2)绕组联成三角形接于绕组联成三角形接于Ul=220 V的三相电源上。的三相电源上。例例1:解解:(1)NoImageNoImageNoImageNoImageNoImage(2)NoImage 比较比较(1),(2)的结果的结果:有的电动机有两种额定电压有的电动机有两种额定电压,如如220/380 V。当电源电压为当电源电压为3

24、80 V时时,电动机的绕组应联结成星形；电动机的绕组应联结成星形；当电源电压为当电源电压为220 V时时,电动机的绕组应联结成三角形。电动机的绕组应联结成三角形。在三角形和星形两种联结法中在三角形和星形两种联结法中,相电压、相电流相电压、相电流以及功率都未改变以及功率都未改变，仅，仅三角形联结情况下的线电流三角形联结情况下的线电流比星形联结情况下的线电流增大比星形联结情况下的线电流增大 倍倍。NoImage例例2:L1L2L3NoImageNoImage 线电压线电压Ul为为380 V的三相电源上，接有两组对称的三相电源上，接有两组对称三相电源：一组是三角形联结的电感性负载，每相三相电源：一组

25、是三角形联结的电感性负载，每相阻抗阻抗 ;另一组是星形联结的电阻性另一组是星形联结的电阻性负载，每相电阻负载，每相电阻R=10,如图所示。试求：如图所示。试求：(1)各组负载的相电流；各组负载的相电流；(2)(2)电路线电流；电路线电流；(3)(3)三相有功功率。三相有功功率。NoImage设设解：解：V302201 U则则llIUIUQPS3 3 PP22 一相电压与电流的相量图如图所示一相电压与电流的相量图如图所示NoImageNoImageNoImageNoImageNoImageNoImageNoImageBAABAZZUI -30o-67o-46.7oNoImageNoImage 三

26、相对称负载作三角形联结，三相对称负载作三角形联结，Ul=220V，当，当S1、S2 均闭合时，各电流表读数均为均闭合时，各电流表读数均为17.3A，三相功率，三相功率 P=4.5 kW，试求，试求:1)每相负载的电阻和感抗；每相负载的电阻和感抗；2)S1合、合、S2断开时断开时,各电流表读数和有功功率各电流表读数和有功功率P；3)S 1断、断、S 2闭合时闭合时,各电流表读数和有功功率各电流表读数和有功功率P。例例3：AAAS2Z12Z23或：或：P=I 2R P=UIcos tg =XL/RNoImage)120sin(m3 tEu NoImageNoImageNoImage 解：解：(1)

27、由已知条件可求得由已知条件可求得AAAS2Z12Z23(2)S1闭合、闭合、S2断开时断开时 I1=I3=10A I2=17.32 A 流过电流表流过电流表 、的电流变为相电流的电流变为相电流 IP，流过电流表流过电流表 的电流仍的电流仍为线电流为线电流Il。因为开关因为开关S均闭合时均闭合时 每相有功功率每相有功功率 P=1.5 kW 当当 S1合、合、S2断时，断时，Z12、Z23 的相电压和相电流不的相电压和相电流不变，则变，则P12、P23不变。不变。P=P12+P23=3 kWAAAS2Z12Z23I2=0A I1I2 P=1/4 P12+1/4 P23+P31 =0.375 W+0

28、.375 W+1.5 W =2.25 kWAAASS2Z12Z23NoImagel lI UP3cos A605.0220407021 I12i+321NIIII NoImage31I 1202UUNoImageVU .设设 =220 0NoImagel lI UP3cos A605.0220407021 I12i+三层三层二层二层一层一层A01220603011 I+某大楼电灯发生故障，第二层楼和第三层楼某大楼电灯发生故障，第二层楼和第三层楼所有电灯都突然暗下来，而第一层楼电灯亮度不变，所有电灯都突然暗下来，而第一层楼电灯亮度不变，试问这是什么原因？这楼的电灯是如何联接的？同试问这是什么原因？这楼的电灯是如何联接的？同时发现，第三层楼的电灯比第二层楼的电灯还暗些，时发现，第三层楼的电灯比第二层楼的电灯还暗些，这又是什么原因这又是什么原因？P (2)当当P处断开时，二、三层楼的灯串联接处断开时，二、三层楼的灯串联接380V 电压，电压，所所以以亮度变暗，但一层楼的灯仍承受亮度变暗，但一层楼的灯仍承受220V电压亮度不电压亮度不变。变。(3)因为因为三楼灯多于二楼灯即三楼灯多于二楼灯即 ,所以三楼灯比所以三楼灯比二楼灯暗。二楼灯暗。P 三层三层二层二层一层一层A01220603011 I+