第三章 三相正弦交流電路【精品-】

第三章三相正弦交流電路

3.3.1負(fù)載星形接法及計(jì)算3.3.2負(fù)載三角形接法及計(jì)算3.4不對(duì)稱(chēng)三相電路的分析計(jì)算3.5三相電路的功率3.1三相正弦交流電動(dòng)勢(shì)3.2三相發(fā)電機(jī)繞組的連接3.3三相負(fù)載3.1.1三相正弦交流電動(dòng)勢(shì)的產(chǎn)生NSAXe在兩磁極中間，放一個(gè)線圈。根據(jù)右手定則可知，線圈中產(chǎn)生感應(yīng)電動(dòng)勢(shì)，其方向由AX。讓線圈以的速度順時(shí)針旋轉(zhuǎn)。合理設(shè)計(jì)磁極形狀，使磁通按正弦規(guī)律分布，線圈兩端便可得到單相交流電動(dòng)勢(shì)。3.1三相正弦交流電動(dòng)勢(shì)???AXYCBZSN定子轉(zhuǎn)子定子中放三個(gè)線圈：AXBYCZ首端末端三線圈空間位置各差120o轉(zhuǎn)子裝有磁極并以的速度旋轉(zhuǎn)。三個(gè)線圈中便產(chǎn)生三個(gè)單相電動(dòng)勢(shì)。3.1.1三相正弦交流動(dòng)勢(shì)的產(chǎn)生大小相等，頻率相同，相位互差120o3.1.2三相電動(dòng)勢(shì)的特征：Em

3.1.3三相電動(dòng)勢(shì)的瞬時(shí)關(guān)系eA+eB+eC=03.1.4三相電動(dòng)勢(shì)的相量關(guān)系3.2三相交流電源的連接3.2.1星形接法AXYCBZN（中線）（火線）（火線）（火線）AXYCBZN三相四線制供電火線（相線）:ABC中線（零線）：N3.2.1星形接法

三相繞組星形連接的兩組電壓相電壓：火線對(duì)零線間的電壓ACBN120120120線電壓：火線間的電壓CABN注意規(guī)定的正方向線電壓和相電壓的關(guān)系30線電壓和相電壓的關(guān)系線電壓與相電壓的關(guān)系---為相電壓---為線電壓在日常生活與工農(nóng)業(yè)生產(chǎn)中，多數(shù)用戶(hù)的電壓等級(jí)為3.2.2三角形接法A?AXYCBZBC??特點(diǎn)：線電壓=相電壓短路+–EA?XYZBC??問(wèn)題討論???+++---EEE直流電源串接不行，三相交流電源可以，為什么？A?XYZBC??

三相交流電源中三個(gè)電源可以串接的原因：三相電源的電壓在任何瞬間相加均為零。Em星形接法ACB

NZZZ3.3三相負(fù)載三角形接法ACBZZZ???負(fù)載也有兩種接法:ACBNZZZ相電流(負(fù)載上的電流)：3.3.1負(fù)載星形接法線電流(火線上的電流)：

ACBNZZZ星形接法特點(diǎn)相電流=線電流*:零線電流*線電壓=相電壓,ACBNZZZ線電壓領(lǐng)先于相電壓30°。ACBNZAZBZC負(fù)載星形接法時(shí)的一般計(jì)算方法一般線電壓為已知，然后根據(jù)電壓和負(fù)載求電流。（1）負(fù)載不對(duì)稱(chēng)時(shí)各相單獨(dú)計(jì)算三相負(fù)載R、L、C以及三相線電壓：求：各相、各線及中線電流CRABNLC已知：解：1.

CRABNLC相電壓2.相電流：CRABNLC令：3.中線電流4.各電流相量關(guān)系（2）負(fù)載對(duì)稱(chēng)時(shí)，只需計(jì)算一相

如則據(jù)此可直接得出另兩相電流：（中線電流為0）（3）負(fù)載對(duì)稱(chēng)，只要求電流、電壓大小時(shí)，僅算一相有效值即可。負(fù)載對(duì)稱(chēng)時(shí)問(wèn)題及討論零線是否可以取消？三相完全對(duì)稱(chēng)時(shí)，零線可以取消。稱(chēng)為三相三線制。ACBZZZ三相三線制供電時(shí)各相電流的計(jì)算AN'NCB求：各相電流已知：每盞燈的額定值為:220V、100W用結(jié)點(diǎn)電壓法AN'NCBRRRRNN'ABC

每盞燈為220V、

100WRRRRNN'ABC、、代入R值得應(yīng)用實(shí)例--照明電路ACB.........一層樓二層樓三層樓N正確接法:每層樓的燈相互并聯(lián),然后分別接至各相電壓上。設(shè)電源電壓為：則每盞燈上都可得到額定的工作電壓220V。照明電路的一般畫(huà)法零線上不能加刀閘和保險(xiǎn)ABCN.........一層二層三層討論討論照明電路能否采用三相三線制供電方式？ACB.........一層樓二層樓三層樓N不加零線會(huì)不會(huì)出現(xiàn)問(wèn)題?設(shè)線電壓為380V。A相斷開(kāi)后，B、C兩相串連，電壓UBC

（380V）加在B、C負(fù)載上。如果兩相負(fù)載對(duì)稱(chēng)，則每相負(fù)載上的電壓為190V。問(wèn)題1：若一樓全部斷開(kāi)，二、三樓仍然接通,情況如何?ACB.........一層樓二層樓三層樓分析：結(jié)果：二、三樓電燈全部變暗，不能正常工作。問(wèn)題2：

若一樓斷開(kāi)，二、三樓接通。但兩層樓燈的數(shù)量不等（設(shè)二樓燈的數(shù)量為三層的1/4）結(jié)果如何？結(jié)果：二樓燈泡上的電壓超過(guò)額定電壓，燈泡被燒毀；三樓的燈不亮。ACBR2R3分析關(guān)于零線的結(jié)論

負(fù)載不對(duì)稱(chēng)而又沒(méi)有中線時(shí)，負(fù)載上可能得到大小不等的電壓，有的超過(guò)用電設(shè)備的額定電壓，有的達(dá)不到額定電壓，都不能正常工作。比如，照明電路中各相負(fù)載不能保證完全對(duì)稱(chēng)，所以絕對(duì)不能采用三相三相制供電，而且必須保證零線可靠。

中線的作用在于，使星形連接的不對(duì)稱(chēng)負(fù)載得到相等的相電壓。為了確保零線在運(yùn)行中不斷開(kāi)，其上不允許接保險(xiǎn)絲也不允許接刀閘。

3.3.2三角形接法及計(jì)算ACB特點(diǎn)：線電壓=相電壓各電流的計(jì)算ACBZABZBCZCA相電流線電流（2）負(fù)載對(duì)稱(chēng)時(shí)（ZAB=ZBC=ZCA=Z），各相電流有效值相等，相位互差120。ACBZABZBCZCA（1）負(fù)載不對(duì)稱(chēng)時(shí)，先算出各相電流，然后計(jì)算線電流。各電流的計(jì)算同理：設(shè)：負(fù)載為阻性的，阻抗角為0

。負(fù)載對(duì)稱(chēng)時(shí)，三角形接法線、相電流的相位關(guān)系A(chǔ)CB負(fù)載對(duì)稱(chēng)時(shí)三角形接法的特點(diǎn)ACB注意電路中規(guī)定的正方向負(fù)載對(duì)稱(chēng)時(shí)：3.5三相電路的功率三相總有功功率：由負(fù)載性質(zhì)決定星形接法時(shí)：三角形接法時(shí)：有功功率：無(wú)功功率：視在功率：在三相負(fù)載對(duì)稱(chēng)的條件下：?jiǎn)蜗喙β实臏y(cè)量-電動(dòng)式瓦特計(jì)i1i2u在交流電路中其中，為間的夾角。指針偏轉(zhuǎn)角度電流線圈電壓線圈i2和u成正比，且近似同相負(fù)載三相功率的測(cè)量

負(fù)載ACBN三相總功率為三個(gè)功率表測(cè)得數(shù)據(jù)的總和。三相四線制接法，用三個(gè)功率表測(cè)量：三相總功率等于兩表測(cè)得數(shù)據(jù)之和。ACB三相三線制的電路中，用二表法測(cè)功率：兩表法測(cè)量功率的原理：結(jié)論：三相總功率等于兩表測(cè)得數(shù)據(jù)之和。每單個(gè)功率表的讀數(shù)沒(méi)有意義，實(shí)驗(yàn)用的三相瓦特計(jì)實(shí)際上就是根據(jù)“二表法”的原理設(shè)計(jì)的。求：功率表W1、W2的讀數(shù)。例電機(jī)ACB電機(jī)的功率為2.5kW,（設(shè)電機(jī)為星形接法，

N為其中點(diǎn)。）電源線電壓為380V，各相對(duì)稱(chēng)。電機(jī)ACB（1）求電流大小ACBZBZAZCN設(shè)：（2）求電流、電壓的相位關(guān)系則：ACBZBZAZCN間的相位差已知電機(jī)的同理，由相量圖可得間的相位差W1的讀數(shù)為833.3瓦W2的讀數(shù)為1666.7瓦相序指示器

三相交流電動(dòng)勢(shì)出現(xiàn)最大值的先后順序稱(chēng)為三相電源的相序。

A-B-C稱(chēng)為順相序

A-C-B稱(chēng)為逆相序

將相序指示器接至三相電源上，便可測(cè)出相序：假設(shè)電容C接的是A相，則L1、L2較亮者為B相，另一相為C相。證明，請(qǐng)見(jiàn)教材C

R相序指示器L1L2RR=1/(ωC)對(duì)稱(chēng)嗎？三相交流電路小結(jié)（1）--三相電源三相三線制三相四線制ACBNACBACB三相電源一般都是對(duì)稱(chēng)的，而且多用三相四線制接法。三相交流電路小結(jié)(2)--三相負(fù)載星形負(fù)載三角形負(fù)載ACBNZZZACBZZZ三相交流電路小結(jié)(3)--三相電路計(jì)算負(fù)載形接法對(duì)稱(chēng)負(fù)載下：各相電壓、電流單獨(dú)計(jì)算。負(fù)載不對(duì)稱(chēng)時(shí)：負(fù)載對(duì)稱(chēng)時(shí)：電壓對(duì)稱(chēng)、電流對(duì)稱(chēng)，只需計(jì)算一相。求電表讀數(shù)時(shí)，可只算有效值，不算相位。負(fù)載Y形接法電源對(duì)稱(chēng)時(shí)：三相電路的計(jì)算要特別注意相位問(wèn)題。三相交流電路小結(jié)(4)--三相功率計(jì)算三相總功率：負(fù)載對(duì)稱(chēng)時(shí)：和接法無(wú)關(guān)8oFV1iyO&brHX4kAQ)dtJ#6mCT+fwM$8pFV1iyO&brHX4kAR)dtK#6mDT+fwM$8pFV1iyO*brHY4kAR)dtK#6mDT+gwM$9pFV2iyO*brHY4kBR)duK#6nDT+gwM$9pFV2iyP*brIY4kBR)duK#6nDT0gwM%9pFW2iyP*brIY4lBR)euK#7nDT0gwM%9pFW2izP*bsIY4lBR)euK#7nDU0gwN%9pGW2izP*bsIY5lBR-euK!7nDU0gwN%9pGW2jzP*csIY5lBR-euK!7nEU0gxN%9qGW2jzP*csIZ5lBS-euL!7nEU0gxN%9qGW3jzP(csIZ5lBS-euL!7oEU0hxN%aqGW3jzP(csJZ5lCS-evL!7oEU0hxN%aqGX3jzQ(csJZ5lCS-evL!8oEU1hxN&aqGX3jzQ(ctJZ5mCS-fvL!8oEU1hxN&aqHX3jAQ(ctJZ5mCS-fvL$8oEV1hxO&aqHX3jAQ(dtJZ6mCS+fvL$8oEV1hxO&arHX3kAQ(dtJZ6mCS+fvM$8oFV1hyO&arHX3kAQ)dtJ#6mCT+fvM$8oFV1hyO&brHX4kAQ)dtJ#6mCT+fwM$8pFV1iyO&brHX4kAR)dtK#6mDT+fwM$8pFV1iyO*brHY4kAR)dtK#6mDT+gwM$9pFV2iyO*brHY4kBR)duK#6nDT+gwM$9pFV2iyP*brIY4kBR)duK#6nDT0gwM%9pFW2iyP*brIY4lBR)euK#7nDT0gwM%9pFW2izP*bsIY4lBR)euK#7nDU0gwN%9pGW2izP*bsIY5lBR-euK!7nDU0gwN%9pGW2jzP*csIY5lBR-euK!7nEU0gxN%9qGW2jzP*csIZ5lBS-euL!7nEU0gxN%9qGW3jzP(csIZ5lBS-euL!7oEU0hxN%aqGW3jzP(csJZ5lCS-evL!7oEU0hxN%aqGX3jzQ(csJZ5lCS-evL!8oEU1hxN&aqGX3jzQ(ctJZ5mCS-fvL!8oEU1hxN&aqHX3jAQ(ctJZ5mCS-fvL$8oEV1hxO&aqHX3jAQ(dtJZ6mCS+fvL$8oEV1hxO&arHX3kAQ(dtJZ6mCS+fvM$8oFV1hyO&arHX3kAQ(dtJ#6mCT+fvM$8oFV1hyO&brHX4kAQ)dtJ#6mCT+fwM$8pFV1iyO&brHX4kAQ)dtK#6mDT+fwM$8pFV1iyO*brHY4kAR)dtK#6mDT+gwM$9pFV2iyO*brHY4kAR)duK#6nDT+gwM$9pFV2iyP*brIY4kBR)duK#6nDT0gwM%9pFW2iyP*brIY4kBR)euK#7nDT0gwM%9pFW2izP*bsIY4lBR)euK#7nDU0gwN%9pGW2izP*bsIY4lBR-euK!7nDU0gwN%9pGW2jzP*csIY5lBR-euK!7nEU0gxN%9qGW2jzP*csIY5lBS-euL!7nEU0kAQ(dtJZ6mCT+fvM$8oFV1hyO&arHX4kAQ)dtJ#6mCT+fvM$8oFV1iyO&brHX4kAQ)dtJ#6mDT+fwM$8pFV1iyO&brHY4kAR)dtK#6mDT+fwM$8pFV2iyO*brHY4kAR)dtK#6nDT+gwM$9pFV2iyO*brIY4kBR)duK#6nDT+gwM$9pFW2iyP*brIY4kBR)duK#7nDT0gwM%9pFW2iyP*bsIY4lBR)euK#7nDT0gwM%9pGW2izP*bsIY4lBR)euK!7nDU0gwN%9pGW2izP*csIY5lBR-euK!7nDU0gwN%9qGW2jzP*csIY5lBR-euL!7nEU0gxN%9qGW2jzP(csIZ5lBS-euL!7nEU0gxN%aqGW3jzP(csIZ5lBS-evL!7oEU0hxN%aqGW3jzQ(csJZ5lCS-evL!7oEU0hxN&aqGX3jzQ(csJZ5lCS-fvL!8oEU1hxN&aqGX3jAQ(ctJZ5mCS-fvL!8oEU1hxO&aqHX3jAQ(ctJZ5mCS+fvL$8oEV1hxO&aqHX3kAQ(dtJZ6mCS+fvL$8oEV1hyO&arHX3kAQ(dtJZ6mCT+fvM$8oFV1hyO&arHX4kAQ)dtJ#6mCT+fvM$8oFV1iyO&brHX4kAQ)dtJ#6mDT+fwM$8pFV1iyO&brHY4kAR)dtK#6mDT+fwM$8pFV2iyO*brHY4kAR)dtK#6nDT+gwM$9pFV2iyO*brIY4kBR)duK#6nDT+gwM$9pFW2iyP*brIY4kBR)duK#7nDT0gwM%9pFW2iyP*bsIY4lBR)euK#7nDT0gwM%9pGW2izP*bsIY4lBR)euK!7nDU0gwN%9pGW2izP*bsIY5lBR-euK!7nDU0gwN%9qGW2jzP*csIY5lBR-euL!7nEU0gxN%9qGW2jzP*csIZ5lBS-euL!7nEU0gxN%aqGW3jzP(csIZ5lBS-evL!7oEU0hxN%aqGW3jzP(csJZ5lCS-evL!7rHX4kAQ)dtK#6mDT+fwM$8pFV1iyO*brHY4kAR)dtK#6mDT+fwM$9pFV2iyO*brHY4kAR)duK#6nDT+gwM$9pFV2iyP*brIY4kBR)duK#6nDT+gwM%9pFW2iyP*brIY4kBR)euK#7nDT0gwM%9pFW2izP*bsIY4lBR)euK#7nDT0gwN%9pGW2izP*bsIY4lBR-euK!7nDU0gwN%9pGW2jzP*csIY5lBR-euK!7nDU0gxN%9qGW2jzP*csIY5lBS-euL!7nEU0gxN%9qGW3jzP(csIZ5lBS-euL!7nEU0hxN%aqGW3jzP(csIZ5lCS-evL!7oEU0hxN%aqGX3jzQ(csJZ5lCS-evL!7oEU1hxN&aqGX3jzQ(csJZ5mCS-fvL!8oEU1hxN&aqHX3jAQ(ctJZ5mCS-fvL!8oEV1hxO&aqHX3jAQ(ctJZ6mCS+fvL$8oEV1hxO&arHX3kAQ(dtJZ6mCS+fvL$8oFV1hyO&arHX3kAQ(dtJ#6mCT+fvM$8oFV1hyO&brHX4kAQ)dtJ#6mCT+fvM$8pFV1iyO&brHX4kAQ)dtK#6mDT+fwM$8pFV1iyO*brHY4kAR)dtK#6mDT+fwM$9pFV2iyO*brHY4kAR)duK#6nDT+gwM$9pFV2iyP*brIY4kBR)duK#6nDT+gwM%9pFW2iyP*brIY4kBR)euK#7nDT0gwM%9pFW2izP*bsIY4lBR)euK#7nDT0gwN%9pGW2izP*bsIY4lBR-euK!7nDU0gwN%9pGW2jzP*csIY8oEV1hxO&aqHX3jAQ(dtJZ6mCS+fvL$8oEV1hyO&arHX3kAQ(dtJZ6mCT+fvM$8oFV1hyO&arHX3kAQ)dtJ#6mCT+fvM$8oFV1iyO&brHX4kAQ)dtJ#6mDT+fwM$8pFV1iyO&brHX4kAR)dtK#6mDT+fwM$8pFV2iyO*brHY4kAR)dtK#6nDT+gwM$9pFV2iyO*brHY4kBR)duK#6nDT+gwM$9pFW2iyP*brIY4kBR)duK#7nDT0gwM%9pFW2iyP*brIY4lBR)euK#7nDT0gwM%9pGW2izP*bsIY4lBR)euK!7nDU0gwN%9pGW2izP*bsIY5lBR-euK!7nDU0gwN%9qGW2jzP*csIY5lBR-euL!7nEU0gxN%9qGW2jzP*csIZ5lBS-euL!7nEU0gxN%aqGW3jzP(csIZ5lBS-euL!7oEU0hxN%aqGW3jzP(csJZ5lCS-evL!7oEU0hxN&aqGX3jzQ(csJZ5lCS-evL!8oEU1hxN&aqGX3jzQ(ctJZ5mCS-fvL!8oEU1hxO&aqHX3jAQ(ctJZ5mCS-fvL$8oEV1hxO&aqHX3jAQ(dtJZ6mCS+fvL$8oEY4kBR)euK#7nDT0gwM%9pFW2iyP*bsIY4lBR)euK#7nDT0gwN%9pGW2izP*bsIY4lBR-euK!7nDU0gwN%9pGW2izP*csIY5lBR-euK!7nDU0gxN%9qGW2jzP*csIY5lBS-euL!7nEU0gxN%9qGW2jzP(csIZ5lBS-euL!7nEU0hxN%aqGW3jzP(csIZ5lCS-evL!7oEU0hxN%aqGW3jzQ(csJZ5lCS-evL!7oEU1hxN&aqGX3jzQ(csJZ5mCS-fvL!8oEU1hxN&aqGX3jAQ(ctJZ5mCS-fvL!8oEV1hxO&aqHX3jAQ(ctJZ6mCS+fvL$8oEV1hxO&aqHX3kAQ(dtJZ6mCS+fvL$8oFV1hyO&arHX3kAQ(dtJ#6mCT+fvM$8oF