电力变压器的局部放电及测量

U2 =1.3 m / 3 U
During observation, some impulses occasionally occurring with high magnitude can be neglected. 在整个试验时间内连续观测，个别较高的脉冲可以忽略 The noise level is required to be less than 50% magnitude of the highest detected impulse. 外围噪声水平应低于规定的视在放电量的50% When test voltage is raised to U2 and decreased from U2, the inception and extinction voltages are recorded. 在电压升至U2及由U2降低的过程中，记录起始可能的放电电压和熄灭电压
电力变压器的局部放电及测量
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Contents 1. Significance of PD detection in Transformer
电力变压器测量局放的重要性
2. PD Propagation in Windings
局部放电在绕组中的传播
3. Test Procedure and Permissible Apparent Charge
L
& I
Байду номын сангаас
e
Currents through L and C while the two elements connected in parallel
e
u
Voltages across L and C while the two elements connected in series
& Ic
u
C
2
Review of Lecture 7
5s U1 U2 5min 30min
U1:pre-applied Voltage 预加电压 U2:measuring voltage 测量电压
U1 = 3 m / 3 =Um U
U2 =1.5Um / 3
Um :the maximum line voltage
q ≤ 500 pC
q ≤ 300 pC
induced voltage
X x Z
x
Z
(c)
√
(d)
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4. Detection Circuits for Transformers
4.2 Detection Circuits for Three-Phase Transformers 三相变压器的测试回路
A B C + Z X + – a Y + – b Z – +c o
Um :the maximum line voltage
q ≤ 500 pC
q ≤ 300 pC
During the first step under the test voltage U2, the maximum apparent charge is recorded. 在电压U2的第一阶段应读数并记录 No record is required under test voltage U1. 在U1阶段无需观测记录 During the second step under the test voltage U2, discharge impulses need to be observed continuously and the maximum apparent charge is recorded. 在电压U2第二阶段整个时间内，应连续地观测和记录局部放电水平
umx =
unx =
Qcoshα(l x) CK[tghα(l x0 ) + tghαx0 ]coshα(l x0 ) Qcoshαx
(x0 ≤ x ≤ l)
CK[tghα(l x0 ) + tghαx0 ]coshαx0
α = CK (0 ≤ x ≤ x0 )
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2. PD Propagation in Windings
Detection circuits
Zm Cx e Ck=Cx Zd
A o
Straight detection circuits
Zm Cx1 e Zd1 Zd2
A
Cx2
o
Balanced detection circuit
3
Review of Lecture 7
Some problems need to be noticed Detection impedances is required to withstand large current. Several detection impedances are needed to match the capacitor samples Connection types of capacitor elements influence detection results.
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3. Test Procedure and Permissible Apparent Charge
5s U1 U2 5min 30min
U1:pre-applied Voltage 预加电压 U2:measuring voltage 测量电压
U1 = 3 m / 3 =Um U U2 =1.5Um / 3 U2 =1.3 m / 3 U
Review of Lecture 7
Contents: 1. Partial Discharge in Power Capacitors 2. Parameters and Standard 3. Electrical Detection of PD in Capacitor
Parameters to estimate the PD of capacitor Apparent charge, q Extinction voltage, Ue Inception voltage, Ui Change of q with voltage applying time
Voltage response along the winding 沿绕组的电压响应
u x
u p
x
0
x0
l
ul =
Q ck [tghα(l x0 ) + tghαx0 ] coshα(l x0 )
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3. Test Procedure and Permissible Apparent Charge
变压器局部放电的电气定位方法
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1. Significance of PD Detection in Transformer
power frequency withstand test 工频耐压试验 impulse withstand test 冲击耐压试验
PD often affects the transformer’s properties in a long-term period. The withstand strength in a short time does not change significantly. 局部放电通常影响变压器的长期运行性能，而对短时的耐压强度影响不大。 Withstand test is destructive, the voltage is so high that insulation is easy to be damaged. 耐压试验是有损试验，容易对绝缘造成破坏 The voltage of PD test is much lower, and the testing duration is longer (0.5~1h). 局部放电试验的试验电压相对较低，试验持续时间也较长
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2. PD Propagation in Windings
n O
k / dx Cdx
P du dx
Cb
m A P Cb
Cn uc Cb Cm Cc
uc+ C c –
xo
x l
Equivalent circuit of a winding with a cavity discharge source
Cd U Ck ' C C (n 1) K= d = = 1+ k d U d ' 1 + Cd C x (Ck + Cd ) Ck 1+
Ck
Cx Cx
Ck
Cx Cx
Ux
Cx Cx
Rd
Cd
Ud
Ux
Cx Cx
Rd
Cd
Ud '
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Lecture 8 PD Detection in Power Transformers
To use high voltage leads as short as possible. 采用尽量短的引线 To execute the test with required voltage on both main insulation and longitudinal insulation. 在试验中对主纵绝缘都能同时得到所应施加的电压
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4. Detection Circuits for Transformers
Two ways of the test：induced voltage test and applied voltage test. 两种试验方法：感应加压方式，直接加压方式 Principles of PD circuit selection 试验回路选择
1
Review of Lecture 7
Power Source Compensation reactor is used in series or parallel with Cx so that to decrease the capacity of testing transformer
u
& IL
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4. Detection Circuits for Transformers
4.1 Detection circuits for single-phase transformers 单相变压器的测试回路
A a
A CK a
Z X x
applied voltage
Z X
x
(a)
a A
(b)
a
A CK X
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2. PD Propagation in Windings
O L K C
Equivalent circuit of a transformer winding
C-ground capacitance per unit length
A
单位长度对地电容
K-series capacitance per unit length, longitudinal capacitance 单位长度的串联电容 L-inductance per unit length, parasitic inductance 单位长度的电感，即寄生电感 O-neutral point 中性点 A-high voltage end 高压端
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3. Test Procedure and Permissible Apparent Charge
If the following results are obtained, the PD experiment can be passed. 如果满足两个条件，则试验合格 During the test procedure, the test voltage never suddenly decreases. 试验过程中，试验电压不产生突然下降 During the last 30 minutes, the magnitudes of all observed impulses are smaller than the permissible apparent charge and do not increase towards the permissible apparent charge. 在施加电压U2的第二阶段的30分钟内，所有测量的视在放电量连续维持在 低于规定的限值，并且不表现出明显地、不断地倾向允许最大限制值增长 的趋势
测试程序和允许放电水平
4. Detection Circuits for Transformers 5. 6. The Influence of Discharges in Bushing
套管放电的影响 变压器局部放电的测试回路 Calibration 校正
7. Electrical Location of PD in Transformers