电机学习题与解答 下载本文

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rk?高压侧短路电阻

PkIk2129?103??5.2?157.5

2222x?z?r?58.67?5.2?58.44? kkk 高压侧短路电抗

o 折算到75C时短路电阻

rk75oC?235?75235?75rk??5.2?6.448?235?15235?15

2 折算到75C时短路阻抗

ozk75oC?rk275oC?xk?6.4482?58.442?58.8?

\型等效电路原副边的电阻

r1?r2?''rk75oC2?6.448?3.224?2

\型等效电路原副边的电抗

x1?x2?xk58.44??29.22?22

3 基准阻抗

z1N?'*mU1NU??I1NSN21N(220?10320000?103)2?2420?3

r 励磁电阻标幺值

'rm3040???3.772420z1N3 'xm32161.3???39.872420z1N3

x 励磁电抗标幺值

'*mr 短路电阻标幺值

*k75oC?rk75oCz1N?6.448?0.00824203

*xk? 短路电抗标幺值

xk58.44??0.0724z1N24203

\型等效电路原副边电阻的标幺值

r?r?*1*2rk*75oC2?0.008?0.0042

*xk0.0724x?x???0.036222 \型等效电路原副边电抗的标幺值

*1*2(2) 短路电压的标幺值

*uk?I1Nzk75oCU1N?zk75oCz1N*?zk?75oC

58.8?0.072924203

短路电压有功分量的标幺值

*uka?I1Nrk75oCU1N?rk75oCz1N?rk*75oC?0.008

*ukr? 短路电压无功分量的标幺值

短路电压的百分值

I1Nxkx*?k?xK?0.0724U1Nz1N

uk(%)?I1Nzk75oCU1NI1Nrk75oCU1N*?100(%)?zK?100(%)?7.29(%)75oC

短路电压有功分量的百分值

uka(%)?*?100(%)?rK?100(%)?0.8(%)75oC

短路电压无功分量的百分值

ukr(%)?I1Nxk*?100(%)?xK?100(%)?7.24(%)U1N

(3) 额定负载时,负载系数??1

sin?2?0 ①cos?2?1时,电压变化率和二次端电压分别为:

*?u??(rk*cos?2?xksin?2)?1?0.008?1?0.008

U2?(1??u)U2N?(1?0.008)?11?10.912kV

sin?2?0.6 ②cos?2?0.8(?2?0)时,电压变化率和二次端电压分别为

*?u??(rk*cos?2?xksin?2)?1?(0.008?0.8?0.0724?0.6)?0.04984

U2?(1??u)U2N?(1?0.04984)?11?10.452kV

sin?2??0.6 ③cos?2?0.8(?2?0)时,电压变化率和二次端电压分别为

*?u??(rk*cos?2?xksin?2)?1?(0.008?0.8?0.0724?0.6)??0.03704

U2?(1??u)U2N?(1?0.03704)?11?11.407kV

I1N(4) 一次侧额定电流

SN20000?103???157.5A3U1N220?103

22P?Ir?157.5?6.448?159.9507kW oKN1NK75C于是满载时的铜损耗

效率

P0??2PKN??(1?)?100(%)2?SNcos?2?P0??PKN47?12?159.9507?(1?)?100(%)?98.7(%)1?20000?0.8?47?12?159.9507

?m?(5)最大效率时,负载系数为 最大效率为

P047??0.542PKN159.9507

?max?(1??(1?

2P0)?100(%)?mSNcos?2?2P02?47)?100(%)?99(%)0.542?20000?0.8?2?4.7

2-26 一台单相变压器,SN=20000kVA ,

U1N/U2N?2203/11kV,fN=50赫,线圈为铜线。

空载试验(低压侧):U0=11kV、I0=45.4A、P0=47W;

短路试验(高压侧):Uk=9.24kV、Ik=157.5A、Pk=129W;试求(试验时温度为150C): (1)折算到高压侧的“T”形等效电路各参数的欧姆值及标么值(假定

r1?r2'?rkx',x1?x2?k22);

(2)短路电压及各分量的百分值和标么值;

(3)在额定负载,cos?2?1、cos?2?0.8(?2?0)和cos?2?0.8(?2?0)时的电压变化率和二次端电压,并对结果进行讨论。

(4)在额定负载, cos?2?0.8(?2?0)时的效率; (5)当cos?2?0.8(?2?0)时的最大效率。

U011?103zm???242.29?I45.40解:(1)低压侧励磁阻抗

rm? 低压侧励磁电阻

p0I0247?103??22.8?245.4

22x?z?r?242.29?22.8?241.21? mmm 低压侧励磁电抗

22K? 变比

U1N?U2N220113?11.547

'22r?Kr?11.547?22.8?3040? mm 折算到高压侧的励磁电阻

22 折算到高压侧的励磁电抗xm?Kxm?11.547?241.21?32161.3?

'UK9.24?103zk???58.67?IK157.5 高压侧短路阻抗

rk?高压侧短路电阻

PkIk2129?103??5.2?157.5

2222x?z?r?58.67?5.2?58.44? kkk 高压侧短路电抗

o 折算到75C时短路电阻

rk75oC?235?75235?75rk??5.2?6.448?235?15235?15

2 折算到75C时短路阻抗

ozk75oC?rk275oC?xk?6.4482?58.442?58.8?

\型等效电路原副边的电阻

r1?r2?''rk75oC2?6.448?3.224?2

\型等效电路原副边的电抗

x1?x2?xk58.44??29.22?22

3 基准阻抗

z1N?'*mU1NU??I1NSN21N(220?10320000?103)2?2420?3

r 励磁电阻标幺值

'rm3040???3.77z1N24203 'xm32161.3???39.872420z1N3

x 励磁电抗标幺值

'*mr 短路电阻标幺值

*k75oC?rk75oCz1N?6.448?0.00824203