課程設(shè)計(jì)短路計(jì)算實(shí)例

1、短路電流計(jì)算實(shí)例【例】計(jì)算BY110kV降壓變電所各電壓級(jí)母線短路時(shí)的短路電流，兩臺(tái)主變壓器為雙 繞組變壓器，變比 110kV/10.5kV，額定容量25000kVA，U%=10.5, S1=1250MVA,Xs1=0.6; S2=350MVA,Xs2=0.8。電網(wǎng)各元件參數(shù)標(biāo)于圖中。試分別計(jì)算k1點(diǎn)和k2點(diǎn)三相短路時(shí)0.2s 和1s時(shí)的短路電流。BY變110kVL1I T1BY變110kVL1I T1110kV圖5.16電力系統(tǒng)接線圖解：（一）參數(shù)計(jì)算及網(wǎng)絡(luò)化簡(jiǎn)（1）選基準(zhǔn)值Sb=100MVA，UB=Uav，求取各元件電抗標(biāo)幺值并繪制等值電路如圖5.17（a） 所示。系統(tǒng) S1、S2： x

2、= 0.6x 100 = 0.048，x = 0.8 x 100 = 0.229S1*1250，S2*350線路L1L5：工頃=0.4x 35 x 1 = 0.106，Xl2* = 0.4x 16x 1 = 0.0484Xl3* = 0.4 x 20 x； = 0.0605， Xl4* = 0.4x 12x ；00 = 0.0362x = 0.4 x 26 x = 0.0786L5*1152主變壓器T1、T2：10.5 10010.5 100 x =x=0.42，x = x = 0.42T1*10025T2*10025（2）利用/Y變換進(jìn)行網(wǎng)絡(luò)化簡(jiǎn)，等效網(wǎng)絡(luò)如圖5.17（b）所示，圖中產(chǎn)生變化

3、的各等 效電抗計(jì)算如下：S1S2(a)等值電路S1S1S2(a)等值電路S1S2(b) A/Y變換后圖5.17 A/Y變換前電力系統(tǒng)的等值電路及其化簡(jiǎn)X = 0.229 X = 0.229 + 0.0786 = 0.3076，x = 0.0484 + 0.0362 = 0.08461*2*x3*X4*x6*=0.048 x3*X4*x6*=0.048 + 0.0357 = 0.0837，x = 0.3076 + 0.0204 = 0.328，* = 0.42/2 = 0.217*X8*=0.0837 + 0.0255 + 0.0837 * 0.0255 = 0.11570.3280.106 x

4、 0.0846 =0.035 7 0.106 + 0.0846 + 0.06050.0605 x 0.0846=0.02040.106 + 0.0846 + 0.06050.106 x 0.0605x = 0.02555* 0.106 + 0.0846 + 0.0605利用Y/變換進(jìn)行網(wǎng)絡(luò)化簡(jiǎn)，求出電源1和電源2對(duì)110kV母線的轉(zhuǎn)移電抗，等 效網(wǎng)絡(luò)如圖5.18(b)所示，圖中產(chǎn)生變化的各等效電抗計(jì)算如下：XX9*0.328 x 0.0255=0.328 + 0.0255 += 0.45340.0837(b) Y/變換后(b) Y/變換后圖5.18 Y/變換前電力系統(tǒng)及其等值電路及其化簡(jiǎn)利用Y

5、/變換，由電抗*，%*，%1*(如圖5.19 (a)所示)求出電源1和電源2對(duì) 10kV母線的轉(zhuǎn)移電抗，等效網(wǎng)絡(luò)如圖5.19 (b)所示，圖中產(chǎn)生變化的各等效電抗計(jì)算如下:X12*X13*圖5.19電力系統(tǒng)及其等值電路=0.1157 + 0.21 X12*X13*圖5.19電力系統(tǒng)及其等值電路=0.1157 + 0.21 + 0.1157 * 0.21 = 0.37930.45340.4534 x 0.21=0.4534 + 0.21 += 1.4860.1157(二)計(jì)算電抗的計(jì)算短路發(fā)生在110kV母線時(shí)X= 0.1157 x 50 = 1.446，jsS 1*100短路發(fā)生在10kV母線

6、時(shí)1250 x.s1* = 0.3793x 而了 = 4.741，(b) Y/變換后350X = 0.4534 x = 1.587jsS 2*100350 x = 1.486 x = 5.2jsS 2*100(三)查計(jì)算曲線，得短路電流周期分量標(biāo)幺值(1)短路發(fā)生在110kV母線時(shí)I- = 0.715, I- = 0.65 TOC o 1-5 h z S1*S2*（2）短路發(fā)生在10kV母線時(shí)因?yàn)?x.s1* = 4.741 3.45 , 1,2* = 5.2 3.45 ,故I- = 1/4.741 = 0.211, I- = 1/5.2 = 0.1923S1*S 2*(四)計(jì)算基準(zhǔn)電流(1)短路發(fā)生在110kV母線時(shí)，歸算到短路點(diǎn)所在電壓級(jí)的各電源的額定電流分別為-1250350I= 3115 = 6.2757kA，I= = = 1.7572kA(2)短路發(fā)生在10kV母線時(shí)，歸算到短路點(diǎn)所在電壓級(jí)的各電源的額定電流分別為 HYPERLINK l bookmark45 o Current Document 1250350NS1 = “3x10.5 =，NS2 .-3 X10.3 =5（五）計(jì)算短路電流的有名值（1）短路發(fā)生在110kV母線時(shí)I ” = 0.715 x