36-WG11/Nuremberg2/242 Private
Experience with Composite HVDC and HVAC insulators in China: from Design to Operation
LIANG Xidong Tsinghua University , China WANG Shaowu, State Grid Corporation of China SU Zhiyi, EPRI of China 1
INDEX 1.
Introduction 2. The usage of composite insulators 3. Selection of leakage distance 4. Material selection and testing 5. Corona ring and arcing device 6. Failure analysis and maintenance 7. Insulator quality and standard 8. Conclusions 2
1. Introduction (1)
Electricity industry increased very rapid in the past 20 years in China.
Total installed capacity 353GW (20GW per year), annual generation 1600TWh.
500kV AC&DC overhead lines in Three Gorge project is 9000km.
2865km ±500kV DC lines in service, and 1955km under construction. 3
1. Introduction (2)
Pollution flashover of transmission line is a big problem.
In the past 30years, pollution flashover of overhead line is ≈ 4000, and nearly 2000 for substation.
The pollution problem under HVDC is much severer than that under HVAC.
4
1. Introduction (3)
For Ge-Shang ±500kV line, the outage rate caused by pollution is 0.17 per 100km.year under ±350kV~ ±450kV and annual cleaning.
All above mentioned flashovers are almost on porcelain insulator. The conventional measures can not prevent insulators from flashover.
Utilities are eager to have new efficient methods to solve the problem of pollution flashover. 5
INDEX 1.
Introduction 2. The usage of composite insulators 3. Selection of leakage distance 4. Material selection and testing 5. Corona ring and arcing device 6. Failure analysis and maintenance 7. Insulator quality and standard 8. Conclusions 6
2. The usage of composite insulators (1)
The first consideration of using composite insulator was the excellent pollution performance.
Therefore only HTV SR insulator is used in China.
SR insulators are widely used as the formal anti-pollution counter measure.
7
2. The usage of composite insulators (2)
More than 1.6 million SR insulators have been used by 2002.
Most of them are made in China.
After replacing porcelain insulators with SR insulators, outages caused by pollution flashover were successfully prevented.
8
500kV HVAC SR insulator in service
9
2. The usage of composite insulators (3)
The total number of ±500kV HVDC SR insulators adopted is 11167 (7866 in service and 3301 have been ordered).
Most insulators are new installed in recent years.
All of them are used in moderate or heavy pollution areas at present.
10
±500kV HVDC SR insulator in service 11
INDEX 1.
Introduction 2. The usage of composite insulators 3. Selection of leakage distance 4. Material selection and testing 5. Corona ring and arcing device 6. Failure analysis and maintenance 7. Insulator quality and standard 8. Conclusions 12
3.Selection of leakage distance (LD) 3.1
Selection of LD for HVAC composite insulators
3.2
Selection of LD for HVDC composite insulators
13
3.1 Selection of LD for AC SR insulators (1)
How to select the LD of composite insulators experienced several stages in China.
The first official document on the selection of composite insulator’s LD was approved in 1993 by the Ministry of Energy.
14
3.1 Selection of LD for AC SR insulators (2) This official document suggested:
the LD of SR insulator could be only 3/4 of that of porcelain insulators in moderate or heavy pollution areas.
This suggestion is base on the successful trial operation in China and the field test in Brighton, UK.
15
3.1 Selection of LD for AC SR insulators (3)
In 1996, another Chinese Standard JB/T 8460-1996 was approved.
It is a Chinese Mechanical and Manufacture Industrial Standard “Composite long rod insulators for use on high voltage overhead lines: dimensions and characteristics”
This standard suggestion is to simplify the manufacture.
16
3.1 Selection of LD for AC SR insulators (4) This Chinese Standard suggested:
The specific LD could be 20mm/kV for clean, light and moderation pollution.
The specific LD could be 25mm/kV for heavy and very heavy pollution areas.
For heavily polluted areas, this suggestion is actually very close to the “3/4” suggestion. 17
3.1 Selection of LD for AC SR insulators (5)
Therefore, Most SR insulators operated in pollution areas are equipped with 3/4 LD of that of porcelain insulators.
All the insulators work well and no any failure or damage which related to the shorter LD were reported.
18
3.1 Selection of LD for AC SR insulators (6)
The ageing of composite insulators is still worried by some utilities.
In recent years, some utilities suggested that silicone rubber insulator should have the same LD as porcelain insulators.
19
3.2 Selection of LD for DC SR insulators
Porcelain insulators present very poor pollution performance for ±500kV overhead lines.
After analyzing the experiences in Gezhouba-Shanghai HVDC line, the following suggestion is made for ±500kV overhead lines in China.
20
Selection of LD for ±500kV insulators For light pollution areas Unit:
34 cap-and-pin insulators
Installation height (H):
34×170 = 5.78m
Leakage distance (LD): 34×545 = 18.5m Specific leakage distance (SLD): 18530mm/515kV = 36mm/kV
21
Selection of LD for ±500kV insulators For moderate pollution areas Porcelain Unit: H: LD: SLD:
40 ~ 44 6.8 ~ 7.5m 21.8 ~ 24m 42 ~ 44mm/kV
SR insulator
5.4m 18m 35mm/kV
The LD or SLD of SR insulator is much shorted than that of porcelain one. 22
Selection of LD for ±500kV insulators For heavy pollution areas Porcelain Unit: H: LD: SLD:
SR insulator 6.29m 22.7m 44mm/kV
Porcelain/glass insulator could not be used in this kind of areas. 23
Table 2 Number of ±500kV HVDC NCI used in China HVDC Projects
Capacity Length Commission MW km year
Project status
Number of NCI
Notes
Gezhouba -Shanghai
1200
1045
1989.09
in service
́̀̽̓
̈́́̿ from 2000.12 ̾́̾ͅ from 2001.12 ̿̾́̓ from 2002.12
Tianshengqia -Guangzhou
1800
960
2000.12
in service
̾̽̓̽
̓̿ͅ from 2000.12 ̀̈́ͅ from 2002.2
Three Gorge -Changzhou
3000
860
2002.12
in service
̿͂̽̽
double string, all from 2002.12
Three Gorge -Guangzhou
3000
975
2004.02
Constructing
̿̿̽̾
Constructing, all in double strings
Guizhou -Guangzhou
3000
980
2004.12
Constructing
̾̾̽̽
Constructing
̾̾̾̓̈́
̈́̓̓ͅ in service, ̀̀̽̾ ordered
Total
12000 4820
24
INDEX 1.
Introduction 2. The usage of composite insulators 3. Selection of leakage distance 4. Material selection and testing 5. Corona ring and arcing device 6. Failure analysis and maintenance 7. Insulator quality and standard 8. Conclusions 25
4. Material selection and testing
4.1 Tracking and erosion resistance of shed material 4.2 Hydrophobicity of shed material
4.3 Artificial pollution test 4.4 Brittle fracture
26
4.1 Tracking and erosion resistance of shed material (1)
The early stage of composite insulators in China, tracking and erosion test became a very important test.
The Inclined-plane test is often used.
In the early stage, SR insulators was required to pass through the 6.0 kV level in Inclined-plane test. In recent years, the requirement was adjusted to 4.5kV and hydrophobicity was also required.
Then 1000h salt HVAC test is easy to pass. 27
4.1 Tracking and erosion resistance of shed material (2)
While the 1000 h salt fog tracking and erosion test under HVDC failed at the beginning. A modified Inclined-plane test under DC voltage was suggested for fast selecting the shed material. The modified Inclined-plane test require: +4.5 kV & 0.2ml/min liquid flow rate. 28
4.1 Tracking and erosion resistance of shed material (3)
After the +4.5kV Inclined-plane test, the 1000 h salt fog test under HVDC could then be passed easily under the SLD of 35mm/kV. ±500kV HVDC SR insulators work well. In field operation, no composite insulators under HVAC or HVDC were reported for the tracking and erosion failure. Composite hollow insulators with LSR were found several tracking problem. 29
4.2 Hydrophobicity of shed material (1)
Hydrophobicity was not quantitatively required for SR insulator even though pollution performance is the most important consideration.
Therefore, SR insulator’s hydrophobicity performance is not stable. 30
4.2 Hydrophobicity of shed material (2)
In March 1998, a test and evaluation method for the hydrophobicity of SR insulator was first suggested.
Hydrophbicity was divided into 4 parameters and each one were suggested a test method and an acceptable criteria.
These 4 parameters are: Hydrophobicity on clean surface (Hc) Hydrophobicity loss property (H l ) Hydrophobicity recover property (Hr ) Hydrophobicity transfer property (Ht) 31
4.2 Hydrophobicity of shed material (3)
Table 3 Hydrophobicity requirement for SR insulators Static CA
Parameters
Test conditions
Ȭ Ȭ av
Hydrophobicity on clean surface ͕Ͱ
Clean surface, at standard lab environment (200C±5K, and 40% ~ 70%RH)
Hydrophobicity
De-ionized water immersion for 96h at room temperature Loss property ͕ Natural rest for 48h at Hydrophobicity standard laboratory environment after water recover property ͕Ϳ immersion Polluted by salt and kieselguhr Hydrophobicity at the level of SDD/NSDD = transfer property 0.1/0.5 mg/cm2, and then rest for 96h at standard lab ͕ environment
Hydrophobicity Class for 5 specimens min
100º 90º
HC1~HC2, HC3 less than 1
90º 85º
HC3~HC4, HC5 less than 1
95º 90º
HC2~HC3, HC4 less than 1
110º 100º
HC2~HC3, HC4~HC5 less than 1 32
4.2 Hydrophobicity of shed material (4)
This method has been accepted by Chinese Electric Power Industrial Standard DL/T 810 - 2002 “Technical Specification of ± 500kV HVDC Composite Long Rod Insulator” and other Chinese standards on SR insulators.
The accept criteria in table 3 is only the basic requirement for SR insulators, and isn’t a high requirement.
Manufactures must notice the importance of the balance between tracking and hydrophobicity. 33
4.3 Artificial pollution test (1)
Effective evaluation of insulator’s pollution performance is very important. In China, solid layer pollution test is more suitable than salt fog one.
But, pollution applying and hydrophpbicity simulation are very difficult. That makes the repeatability and reproducibility of the test become poor.
A modified solid layer artificial pollution test method which suitable for SR insulators was suggested and published at 1999 ISH. 34
4.3 Artificial pollution test (2)
The key point of this method is to shield the hydrophobicity temporarily by applying a very thin layer of kieselguhr at first.
After been polluted, wait for 4 days. Pollution layer will change gradually from hydrophilic to hydrophobic.
By this method, pollution layer applying becomes easier, and hydrophobicity status could be simulated easily. 35
4.3 Artificial pollution test (3)
This method has been accepted as Chinese standard for SR insulator testing.
This method has also been accepted by CIGRE taskforce 13-13-01 at “Polluted insulators: Guidelines for selection and dimensioning, Part 1: General principles and the a.c. case”
36
Brittle fracture on 500kV HVAC insulator
4.4 Brittle fracture (1)
Brittle fracture is the most serious problem for composite insulators.
Up to now, there are 13 brittle fractures in China. And 10 of them happened on 500kV HVAC overhead lines.
60% 500kV brittle fractures are on the imported foreign products.
37
4.4 Brittle fracture (2)
In DL/T 810-2002, stress corrosion test for FRP rod is included. The test is done under the acid solution of 1 N HNO3 and 67% SML tensile mechanical load for 96 hours at room temperature.
For ±500kV HVDC transmission line, only this kind FRP rod are used.
In recent years (1999 ~ 2000), FRP rod manufactures in China could supply FRP rod with good stress corrosion property and good electrical & mechanical property. 38
4.4 Brittle fracture (3)
±500kV HVDC SR insulator
Sometimes, doublestring was adopted to increase the safety factor.
The price of ±500kV SR insulator is only ≅ 1/3 of DC porcelain or glass insulators. Doublestring is still acceptable due to the cheaper price. 39
INDEX 1.
Introduction 2. The usage of composite insulators 3. Selection of leakage distance 4. Material selection and testing 5. Corona ring and arcing device 6. Failure analysis and maintenance 7. Insulator quality and standard 8. Conclusions 40
5. Corona Ring and Arcing Device
There is no arcing device for porcelain insulators ≤ 220 kV, and corona rings play the role of arcing device for 330 kV and 500 kV insulator strings.
For composite insulators, corona ring is sometimes used at the high voltage end for 110 kV and used at both end for 220 kV and above. 41
INDEX 1.
Introduction 2. The usage of composite insulators 3. Selection of leakage distance 4. Material selection and testing 5. Corona ring and arcing device 6. Failure analysis and maintenance 7. Insulator quality and standard 8. Conclusions 42
6. Failure analysis and maintenance (1)
Table 4 Failures of composite insulator by 1998
Type of failure
FRP rod/tube puncture
Proportion
21%
Interface Brittle breakdown fracture
29%
19%
FRP rod FRP rod Installation broken pull out damage
12%
7%
12%
Table 5 Flashovers of composite insulator by 1998
Type of flashover
Lightning
Proportion
50%
Reason Bird Pollution Strong Rain Other unknown drooping flashover wind flashover
15%
9%
4%
0%
2%
20%
43
6. Failure analysis and maintenance (2)
Compared with 0.8 million installed SR insulators in 1998, 42 failed insulators and 245 flashovers are not a large number.
Utilities in China are satisfied with composite insulators up to now.
Composite insulators not only successfully prevent the pollution flashover but also save many maintenance costs. 44
6. Failure analysis and maintenance (3)
For the 20% reason unknown flashovers, it is because there is no obvious bird excrement trace on insulator surface.
Most reason unknown flashovers are most probably caused by bird drooping.
45
6. Failure analysis and maintenance (4)
Maintenance work for SR insulator is only the periodical visual inspection from ground and sampling insulators to do further testing in laboratory.
The test items including: visual inspection, hydrophobicity inspection, dry and wet withstand voltage test, steep-front impulse voltage test, mechanical tensile test, etc.
Unfortunately, the effectiveness of these tests is not very good. 46
INDEX 1.
Introduction 2. The usage of composite insulators 3. Selection of leakage distance 4. Material selection and testing 5. Corona ring and arcing device 6. Failure analysis and maintenance 7. Insulator quality and standard 8. Conclusions 47
7. Insulator quality and standard
7.1
Ageing and insulator quality
7.2
Standard and insulator quality
48
7.1 Ageing and insulator quality
Ageing is an old problem for composite insulators. Ageing should be considered and studied seriously under the polluted environment.
It is necessary to distinguish the failures of composite insulators. Is it failed for the poor quality of individual insulator or for the ageing of whole insulators
Ĥ
It is difficult for present test standard to evaluate composite insulator’s long-term performance.
49
7.2 Standard and insulator quality
Manufactures want to decrease their cost. Then the quality is doubtful. Standards give the bottom line.
In the new standard “DL/T 810-2002 ”, the importance of material test is emphasized.
Several material tests are designed to stable insulator’s quality.
Research work on the standard should be emphasized in the future. 50
INDEX 1.
Introduction 2. The usage of composite insulators 3. Selection of leakage distance 4. Material selection and testing 5. Corona ring and arcing device 6. Failure analysis and maintenance 7. Insulator quality and standard 8. Conclusions 51
8. Conclusions (1)
1.6 million HVAC SR insulators and about 11000 ±500kV HVDC SR insulators are used in China.
Most of them operated in pollution areas. SR insulator has been taken as the formal anti-pollution counter measure.
The application of SR insulators successfully prevented the pollution flashovers. 52
8. Conclusions (2)
Ageing is always the problem for composite insulators, especially when they operated in pollution areas.
New standard was published in China to stable SR insulator’s quality based on emphasizing the importance of material tests.
Composite insulator’s standard should be further studied. 53
Thanks ! LIANG Xidong, Tsinghua university Fax:8610-62783057 Email:
[email protected] 54
