1
Review of lecture 4
1. The Basic Parameters
2. The Integrated Quantities
3. The Inception and Distinction Voltages
4. Waveform Characteristics of Discharges
Contents:
Basic Parameters
cbcr uCCq )(
cba uCq
rcb
ba q
CC
Cq
cb
b
B
m
CC
C
cU
uffnN
44
aimquW2
1
2
|]||||[|1
21 amaa qqqT
I
Integrated Quantities
][1 22
221 amaa qqq
TD
][1
2211 mamaa uququqT
P
ui and ue
Review of lecture 4
q
u
eu iuFor oil-impregnated paper, ui >ue
3
Estimation of ui for several typical internal discharges:
Review of lecture 4
a dielectric with a flat cavityU
+
c
b
b
aadU
+
c
b
b
aad
CBrb
rci Edu ])([
a dielectric with a spherical cavityd c b
]3
)2([
rb
rcrbCBi
dEu
r 1
r 2
r
the flat cavity in a cylindrical
)]1ln()1
1()1ln(1
[1
2
rr
rrEu
rbrbCBi
4
Review of lecture 4
Waveform Characteristics of Discharges
q
0
9 0
1 8 0
2 7 0
0
9 0
1 8 0
2 7 0
q
a b
c
+
_
q
0
9 0
1 8 0
2 7 0
Surface discharge
Corona discharge
0
9 0
1 8 0
2 7 0
0
9 0
1 8 0
2 7 0
Internal discharge
5
Lecture 5 Dielectric Deterioration and PD Evaluation
6
ContentsContents
1. Mechanisms of Dielectric Aging by PD
2. Process of Dielectric Aging by PD
3. The Influence Factors on Aging Rate
4. PD Evaluation Approaches
局部放电老化机理
局部放电老化过程
影响老化的因素
局部放电评估方法
7
1. Mechanisms of Dielectric Aging by PD
Electrical aging is a type of dielectric deterioration under the long-term
electrical field and due to the fact of partial discharges.电老化：在电场长期作用之下因局部放电而造成的绝缘性能劣化。(1) Bombardment of charged particle 带电质点轰击
(2) Thermal Effect 热效应
(3) Resultant of Reaction 反应生成物
(4)(4) Radiation Effect Radiation Effect 辐射效应辐射效应
(5)(5) Mechanical Effect Mechanical Effect 机械效应机械效应
Broke the chemical bond and damage molecular structure of insulation material .
High temperature of discharge point accelerates thermal damage to materials
resultants, such as ozone, moisture, nitric acid, oxalic acid , erode materials.
visible light, ultraviolet radiation, X-radial,γ-radial embrittle materials.
Successive blasting discharges result in high gas pressure and crack the materials
8
2.Process of Dielectric Aging by PD
2.1 Damage of internal discharge to polymer 内部放电对聚合物的破坏
(1) Surface Erosion
A uniform surface erosion, which may be caused by bombardment of particle, thermal degradation, radiation and trapped electrons below surface, etc. Deep pits are formed and carbonized. Discharges become concentrated, some deep pits are formed, the discharges further concentrate and sometimes carbonization of the pits occurs.
在放电的各种效应作用下，逐步腐蚀气隙表面
In nitrogen gasIn air
放电集中的地方，形成一些深坑；放电进一步集中，并造成一些深坑碳化
表面腐蚀
9
2.Process of Dielectric Aging by PD
(2) Propagation of electrical tree 树枝放电的发展The dielectric breaks down over a distance of some microns. The stress at the top of the pit approaches the breakdown strength over a distance of some microns owing to the field concentration around this sharp tip.
complete breakdown. The field concentration moves to the new tip and narrow carbonization channels propagate quickly through the dielectric, initiating complete breakdown.
深坑端部一定距离内场强集中，达到了击穿场强，这些区域发生击穿。
击穿造成了新的深坑端部电场集中，碳化的狭窄通道很快在介质中发展，最后介质完全击穿。
10
2.Process of Dielectric Aging by PD
Simulation of electrical tree in XLPE cable
Two configurations of electrical tree
branched type brush type tree 刷状 丛林状
11
Development of treeing discharges
2.Process of Dielectric Aging by PD
（ a ） inception （ b ） branch growing （ c ） reaching to the opposite electrode
（ d ） complete breakdown
12
2.Process of Dielectric Aging by PD
2.2 Damage of internal discharge to oil-paper
(1)Discharges in void adjacent to the conductor attack the insulation. After some time, discharge penetrate the first layer.
(3)The tracks follow the weakest points in the insulation.
在靠近导体的气隙处发生放电，轰击绝缘表面。一段时间之后，放电穿透第一层纸
在绝缘纸存在薄弱点时，碳化轨迹容易穿透绝缘纸 .
(2) Surface discharges occur along the layers after penetrating the first few paper layers, and trees or carbonized tracks are formed.沿着层间纸的表面发生沿面放电，形成树枝或碳化通道
碳化通道达到一定的长度，击穿发生。(4)The tracks finally attain enormous lengths, ultimate breakdown occurs.
13
3. The Influence Factors on Aging Rate
3.1 Electrical field stress 电场强度nKEL
log(E)
log(L)
a
b
c
d EnKL logloglog
The principle of accelerating aging tests:
(Lb, Lc, Ld) at higher stresses (Eb, Ec, Ed) to , extrapolate La at lower stress Ea
3.2 Voltage frequency 电压频率
cb
b
B
m
CC
C
cU
uffnN
44
14
3. The Influence Factors on Aging Rate
3.3 Situation of cavity and gas contents inside 气隙状态及成分
d c b a
HV
e
(a) Single flat cavity parallel with electric field.
(b) Single flat cavity , perpendicular with electric field.
(c) Double cavities, in series in the direction of electric field.
(d) Double cavities, in parallel in the direction of electric field.
单个扁平气隙，平行电场方向单个扁平气隙，垂直于电场方向
两个串联气隙两个并联气隙
(e) Cavities, adjacent to electrodes. 紧邻金属电极的气隙
（ a ） is more harmful than (b)（ c ） is more harmful than (d)（ e ） is more harmful than the cavities bounded by dielectric.
15
3. The Influence Factors on Aging Rate
3.4 Temperature and humidity 温度和湿度
the upper limited operating temperature of insulation. 绝缘的最高允许工作温度。
heat resistant grades of insulation 绝缘耐热等级
G ra d e Y A E B F H C
Pe rmiss ib le
te mp e ra tu re (oC )9 0 1 0 5 1 2 0 1 3 0 1 5 5 1 8 0 >1 8 0
3.5 Mechanical force 机械应力
)exp(RT
EAk aa Ea - activation energy (kJ/mol-1)
k - aging rate
Aa - pre-exponential factor
T – temperature (K)
16
4. PD Evaluation Approaches
4.1 Estimation by the basic parameters
(1) Apparent charge, qa
The maximum qa at 1~1.5 rated voltage of HV equipment should be smaller than the permissible discharge magnitude.
通常在 1~1.5 倍额定电压下测量设备视在放电量，需小于规定的允许放电水平Disadvantages:(1) The qr is quite different with qr 视在放电量和真实放电量有差别 r
cb
ba q
CC
Cq
(2) qa is often transient and fluctuant. qa 是瞬变的和无规则波动的
(3) qa only indicates the maximum of discharge magnitude corresponding to the defects in the largest size. 仅代表最大缺陷中的最大放电量
(2) Discharge energy and power, W and P
17
4. PD Evaluation Approaches
(3) The phase angle of pulses When partial discharges act more excitedlythe pulses occur at the wider range of phase angle. 放电相位变宽Inception pulses will shift to zero or a negative phase angle. 起始脉冲 朝着过零点或者负半周移动Average phase angle of pulses in a power-frequency half cycle also becomes smaller. 平均放电相位也变小
(4) Ui and Ue Under the same test voltage, higher discharge magnitude or more pulses exist in the tested equipment with smaller inception and extinction voltages.
在同样的实验电压下， ui 越低，放电量 qa 越大，放电次数 n 也就越多
18
4. PD Evaluation Approaches
4.2 Estimation by distribution (statistical) graphs采用分布 (统计 )图谱评定
t
q a( t )
q i
t i
u i
))(,( iii tutq )),(,,( iiiii nunq
ff
nt iii 360
Every PD activity is a sequence of PD pulses qi(ti)
0 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020
-0.5
0
0.5
19
4. PD Evaluation Approaches
(1) q-φ graph ， H(q, φ)
q
0 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020
-0.5
0
0.5
t
0 50 100 150 200 250 300 3500
0.2
0.4
0.6
0.8
φ
The average, (maximum, sum) pulse height distribution: the average (maximum, sum) amplitude in each phase window as a function of the phase angle,
The phase range is divided into 2n parts firstly, each part is a phase window.
0 50 100 150 200 250 300 3500
0.2
0.4
0.6
0.8
q ave
统计每个相位窗中的放电量平均（最大，之和）值
放电量 -相位分布图
20
(2) n-φ graph ， H(n, φ)
4. PD Evaluation Approaches
The pulse count distribution: the number of observed discharges in each phase window as a function of the phase angle.
放电次数 -相位分布图
0 50 100 150 200 250 300 3500
0.2
0.4
0.6
0.8
φ
统计每个相位窗中的放电次数
0 50 100 150 200 250 300 3500
2
4
6
8
10
12
N (
tim
es)
21
4. PD Evaluation Approaches
(3) n-q graph ， H(n, q)The q range is divided into 2n parts firstly, each part is a q window.
the number of observed discharges in each q window as a function of the discharge magnitude.
将放电量等分为 2n 份，每一份为一个放电量窗
统计每个一个放电量窗中脉冲的个数
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80
10
20
30
40
q(mV)
N(t
imes
)
(4) w-n graph ， H(w, n)
iiquW2
1
the number of observed discharges in each w window as a function of the discharge energy.
22
4. PD Evaluation Approaches
4.3 parameters extracting from graphs (statistic operators)
图谱的特征参数提取 ( 统计算子 )(1) Skewness, sk 偏斜度
f(x)
x
f(x)
x
f(x)
x
（ a ） sk>0 （ b ） sk=0 （ c ） sk<0
3
3)(
ii px
Sk
ii
iii
iiii
px
px
xxp
22 )(
/
(2) kurtosis, ku 陡峭度
4
4)(
ii pxku
(3)others 其他
23
4. PD Evaluation Approaches
4.3q-u hysteresis curve Q-u 迟滞曲线
q
u
eu iu
The area surrounded by curve. Larger area means poorer performance to absorb gas
Δu=ui-ue. Difference of ui and ue.曲线包围面积，越大材料吸气性能越差
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The end
