三相電路§11—1三相電源通常由三相同步發(fā)電機(jī)產(chǎn)生，三相繞組在空間互差120°，當(dāng)轉(zhuǎn)子轉(zhuǎn)動(dòng)時(shí)，在三相繞組中產(chǎn)生感應(yīng)電壓，從而形成對(duì)稱(chēng)三相電源。NSooIwAZBXCY三相同步發(fā)電機(jī)示意圖一、對(duì)稱(chēng)三相電源的產(chǎn)生三相對(duì)稱(chēng)電壓–+uAAXA相uA=Ucosωt2–+uBBYB相uB=Ucos(ωt–120o)2–+uACZC相uC=Ucos(ωt+120o)2UA=U0oUC=U120oUB=U–120outuAuBuCUAUBUC特點(diǎn):大小相等,相位彼此相差

120o，稱(chēng)為三相對(duì)稱(chēng)電源。UAUCUB正序逆序二、三相對(duì)稱(chēng)電壓源的連接+–+–+–ABCNUAUBUC端線(xiàn)(火線(xiàn))中線(xiàn)(零線(xiàn))UAUBUC相電壓IpUAUBUC三相對(duì)稱(chēng)電壓UABUBCUCAUAUBUCUB–UAB30o3UAUBCUCAY形連接線(xiàn)電壓IlUAB=UA–UB=3UA30oUBC=UB–UC=3UB30oUCA=UC–UA=3UC30oIl=Ip3線(xiàn)電壓也是三相對(duì)稱(chēng)電壓;φ線(xiàn)=φ相+30o;△連接+–++–AXBYCZABCUAUB–UCUABUBCUCA相電壓電源每一相的電壓線(xiàn)電壓端線(xiàn)之間的電壓電源△連接時(shí)：相電壓=線(xiàn)電壓相電流各相電壓源中的電流線(xiàn)電流端線(xiàn)中的電流電源Y連接時(shí)：相電流=線(xiàn)電流三相四線(xiàn)制三相電路ZN三相三線(xiàn)制–+–+–+UAUBUCABCA

B

C

N

NZlZlZlZAZBZC–+–+–+UAUBUCABCA

B

C

ZZZZlZlZl§11—2負(fù)載為Y形連接的三相電路一、三相負(fù)載對(duì)稱(chēng)ZA=ZB=ZC=ZABC+–+–+–UAUBUCNN

A

B

C

ZlZlZlZNZZZIAINIBIC根據(jù)彌爾曼定理(+)=ZN1UNN

Z+Zl1Z+ZlUA+UB+UC=0UNN

=0N、N

為自然等電位點(diǎn)。一相計(jì)算方法ABC+–+–+–UAUBUCNN

A

B

C

ZlZlZlZZZIAINIBICZNIA=Z+ZlUA負(fù)載端相(線(xiàn))電流IB=Z+ZlUB=IA–120oIC=Z+ZlUC=IA+120o三相對(duì)稱(chēng)電流負(fù)載端相電壓UA

N

=IAZUB

N

=IBZ=UA

N

–120oUC

N

=ICZ=UA

N

+120o三相對(duì)稱(chēng)電壓IAIB++IC=0負(fù)載端線(xiàn)電壓UA

B

=UA

N

–UB

N

=3UA

N

30oUB

C

=3UB

N

30o=UA

B

–120oUC

A

=3UC

N

30o=UA

B

+120o三相對(duì)稱(chēng)電壓ABC+–+–+–UAUBUCNN

A

B

C

ZlZlZlZZZIAIBIC小結(jié):1、相電流=線(xiàn)電流，且三相電流對(duì)稱(chēng)。2、負(fù)載端的相電壓對(duì)稱(chēng)。Y形連接，負(fù)載對(duì)稱(chēng)時(shí)：3、負(fù)載端的線(xiàn)電壓對(duì)稱(chēng)。

Ul=

Up3φu線(xiàn)=φu相+30o;二、三相負(fù)載不對(duì)稱(chēng)1、三相負(fù)載不對(duì)稱(chēng),有中線(xiàn):ABC+–+–+–UAUBUCNN

ZAZBZCIAICIBINIA=UAZAIB=UBZBIC=UCZC不對(duì)稱(chēng)負(fù)載端的相電壓對(duì)稱(chēng)。負(fù)載端的線(xiàn)電壓對(duì)稱(chēng)。

Ul=

Up3φ線(xiàn)=φ相+30o;2、三相負(fù)載不對(duì)稱(chēng),無(wú)中線(xiàn):由彌爾曼定理：UN

N=ZA1+ZB1+ZC1ZAUA+ZBUB+ZCUC負(fù)載端相電壓UAN

=UA–UN

NUBN

=UB–UN

NUCN

=UC–UN

N不對(duì)稱(chēng)ABC+–+–+–UAUBUCNN

ZAZBZCIAICIBUAUBUCUN

NUAN

UBN

UCN

相(線(xiàn))電流=ZAUAN

IA=ZBUBN

IB=ZCUCN

IC不對(duì)稱(chēng)§11—3負(fù)載為△形連接的三相電路一、三相負(fù)載對(duì)稱(chēng)ABCZZZUAB相電流

—每一相負(fù)載上的電流。IAB=UABZIBC=UBCZ=IAB–120oICA=UCAZ=IAB+120o三相對(duì)稱(chēng)電流IABIBCICA線(xiàn)電流ABCZZZUABIABIBCICAIAIBICIA=IAB–ICAIABIBCICAICA–IA30o3IABICIB=3IAB–30oIB=IBC–IAB=3IBC–30o–120o=IAIC=ICA–IBC=3ICA–30o+120o=IA小結(jié):1、相電壓=線(xiàn)電壓，且三相電壓對(duì)稱(chēng)。2、負(fù)載端的相電流對(duì)稱(chēng)。△形連接，負(fù)載對(duì)稱(chēng)時(shí)：3、負(fù)載端的線(xiàn)電流對(duì)稱(chēng)。Il=Ip3φi線(xiàn)=φi相–30o;二、三相負(fù)載不對(duì)稱(chēng)ABCZABUABIABIBCICAIAIBICZBCZCA相、線(xiàn)電壓仍相等且對(duì)稱(chēng)。相電流：IAB=UABZABIBC=UBCZBCICA=UCAZCA不對(duì)稱(chēng)線(xiàn)電流IA=IAB–ICAIB=IBC–IABIC=ICA–IBC

線(xiàn)、相電流之間不再有和30o的關(guān)系。3不對(duì)稱(chēng)特殊情況：ABCZZZUABIABIBCICAIAIBICIA=0IB==–

ICUBCZ//(Z+Z)ABCZZZUABIABIBCICAIAIBIC相電流：IAB==–

ICAUBCZ+ZIBC=UBCZ線(xiàn)電流：相電流：IAB=0IBC、ICA不變。線(xiàn)電流：IA=–ICAIB=IBCIC不變。§11—4三相電路的功率PY=UAIAcos

A+UBIBcos

B+UCICcos

CZAZBZCIAICIBABCUABUAY形連接：負(fù)載對(duì)稱(chēng)時(shí)：PY=3UPIPcos

=

UlIlcos

A3△形連接：ABCZABUABIABIBCICAIAIBICZBCZCAP△=UABIABcos

AB+UBCIBCcos

BC+UCAICAcos

CA負(fù)載對(duì)稱(chēng)時(shí)：P△=3UPIPcos

=

UlIlcos

3三相對(duì)稱(chēng)負(fù)載cos

IlUlP=UlIlcos

3Q=UlIlcos

3S=

UlIl3三相電路功率的測(cè)量：三相四線(xiàn)制(三表法):P1=UAIAcos

AP=P1+P2+P3三相三線(xiàn)制(兩表法)：三相負(fù)載IAIBICW1**ABCN三相負(fù)載IAIBICW1**AW2**BCP1=UACIAcos

1

1為與的相位差。UACIAP2=UBCIBcos

2

2為與的相位差。UBCIB則：P=P1+P2注意