SVC无功补偿方案设计
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工 程 举 例
1. 已知条件
某钢厂110kV 变电站,通过AC120×2的架空线与供电局110kV 变电站相连,长 11km ,钢厂110kV 母线系统短路容量Skmax=694.3MVA ,Skmin=540.5 MVA ,并作为公共电网联接点(PCC 点),钢厂主变T 1=50MVA , 三线圈变压器,110kV/35kV/6kV,变压器阻抗百分比 高—中:9.5%,高—低17.43%,中—低6.53%,中压35kV 侧通过AC 240/4km 连至钢厂电炉车间35kV 母线。
电炉车间有一台40t 电弧炉,炉变25MVA 阻抗8%(343V ),电炉变一次侧配有12%的前置电抗器,电弧炉(EAF 炉)短网0.65+j2.65m Ω
另有一台精炼炉(LE 炉),炉变7MVA ,阻抗8%(240V ),LE 炉短网为0.5+j2.5m Ω
2. 技术要求
2.1按国家标准设置动态无功补偿装置 2.2 PCC 点功率因数≥0.95
3. 方案设计
3.1.1 绘制钢厂所在电网系统简图 3.1.2 根据系统简图计算系统等值阻抗
a )由系统最小短路容量Skmin 和最大短路容量Skmax 值计算阻抗标幺值 Xkmin ,Xkmax (基准容量Sj 取100MVA )
Xkmin=
5.540100
min 100=
Sk =0.185 Xkmax===3
.694100
max 100Sk 0144
b )三线圈主变压器等阻抗
·先进行三角——星形变换(参见5.2节)
UT11=
%2.10%2
53
.643.175.9=-+
UT12=%7.0%2
43
.1753.65.9-=-+
UT13=
%23.7%2
5
.953.643.17=-+
·用变压器短路电压(U T %)计算各绕组阻抗标幺值
X T11=100×(U T11%)/Se
=
204.050
102
.0100=⨯
X T12=-0.014 X T13=0.145
c) 架空线AC240/4km 等值阻抗计算(参见4.2节)
X 0=5105.0lg 6.4-⨯⎪⎪⎭
⎫
⎝⎛+u r D pj ω (Ω/km ) = 0.144×4
.126
.1700lg
⨯+ 0.016 = 0.419Ω/km
X L1=2
0Ue L
100⨯⨯X
= 100×0.419×2
354
=0.137
d) 电弧炉前置电抗标幺值 D k =12%(参见6节)
X DK =
48.0%1225
100
=⨯ e )电弧炉变压器(EAF 炉)等值阻抗(参见5.1节)
X T2=
25
08
.0100⨯=0.32 f) EAF 炉短网等值阻抗值(参见8节)
X EAF =B ×2100
Z
S =2
343.01000100
65.2⨯⨯=0.225
g) 精炼炉(LF 炉)等值阻抗 X T3=
7
08
.0100⨯=1.143 h )LF 炉短网等值阻抗 X LF =
2
240.01000100
55.2⨯⨯=4.43
3.2 计算各负载通路总阻抗∑X,最大无功冲击Qmax ,相对无功冲击max Q ∆
a )∑X EAF (min )=X smin +X T1+X T2+X L1+X DK +X T2+X EAF
=0.185+0.204+(-0.014)+0.137+0.48+0.32+2.25
=3.562
∑X EAF (max )=3.521
Q EAF(min )=
562.3100
=28.1Mvar Q EAF(max) =521.3100
=28.4Mvar
(min)EAF Q ∆=28.1×(cos Ф)2
=18.0Mvar (max)EAF Q ∆=28.4×0.64=18.2Mvar
注:电弧炉平均功率因数cos Ф=0.8,精炼炉cos Ф=0.85 b )∑X LF (min )=6.085 ∑X LF (max )=6.044 Q LF (min )=16.4Mvar Q LF (max )=16.5Mvar (min)LF Q ∆=11.9 (max)LF Q ∆=12.0 3.3 二炉叠加
(m ax)Q ∆=2
(min)2
(min)EAF LF Q Q + (min)Q ∆ =225.164.20+
=224.161.28+=32.5Mvar =32.8Mvar
(min)
Q ∆∑=229.1118+ (max)Q ∆∑=2
2122.18+ =21.6Mvar =21.8Mvar 3.4 电炉炼钢引起的电压波动d 和闪变P st (参见9.3节) 3.4.1 EAF 炉
d EAF (min )=%35.35.5401.18= d EAF (max )=
3.6942
.18=2.62% P st (min )=(min)21
EAF d =1.675 P st (max )=1.31
3.4.2 LF 炉 d EAF (min )=
%2.25.5409.11= d EAF (max )=3
.69412
=1.73% P st (min )=1.1 P st (max )=0.66
3.4.3 二炉叠加
∑(min)
d
=22%)2.2(%)35.3(+
∑(max)
d
=22)73.1()62.2(+