Polluted Outdoor Insulators Maintenance and Washing

Transcription

1 Polluted Outdoor Insulators Maintenance and Washing Ali Naderian, PhD, PEng, SM IEEE Toronto, Canada February برگزار کنندگان ایکهربا سامانه تجهیزات صنعت برق ایران کارشناسان توزیع برق ایران

2 Training Contents: 2 1. Contamination and Flashover 2. Insulator Failure ( Ceramic & Polymeric) 3. Polluted Insulators : 1- Washing (Hot or Cold) 4. Polluted Insulators : 2- Polymeric Insulators 5. Polluted Insulators : 3- RTV Coatings 6. Standards: IEC , IEEE Summary and General Industry Practice

3 Insulator Types: Cap&Pin, Post, Bushing 3

4 Insulator Types: Porcelain and Glass Cap & Pin 4

5 Insulator Types: Cap and Pin Insulators 5

6 Insulator Types: Composite (Polymeric) 6

7 Why Polymeric? Compact Line 7 400kV compact line assembly built on 132kV ROW

8 How Flashover Happens? 8 Contamination + Moisture Dry-band arc Flashover

9 Dry-band arc leading to Flashover (Video) 9

10 Effect of Humidity? 10 at 80% RH the electrical field stress is concentrated near the top of the support insulator. Higher temperature was also observed here, indicating that moisture was evaporating due to the presence of small leakage currents

11 Insulator Flashover 11

12 Insulator Flashover

13 IEC Selection of Insulators for Use in Polluted Conditions 13 Type A: Desert Type B: Coastal Site Pollution Severity (SPS) a Very light; b Light; c Medium; d Heavy; e Very heavy Type A Type B

14 IEC

15 Polymeric Insulators Advantage for Pollution 15 Light weight Hydrophobicity do not allow the accumulation of water on their surface, thus preventing surface currents and flashovers. High mechanical strength Vandalism

16 Hydrophobicity: 16

17 Polymeric or Ceramic? 17

18 Polymer Degradation 18

19 Mechanical Failure 19

20 Polymeric Insulator Inspection 20

21 Polymeric Insulator Inspection 21

22 Polymeric Insulator Inspection 22

23 Polymeric Insulator-230kV failure 23

24 Corona Ring Installation 24

25 Typical Methods to Overcome Pollution: 25 Water washing Increasing insulation level/creepage distance Resistive glaze insulation Greasing Polymeric insulators Silicone Room Temperature Vulcanized (RTV) coatings

26 Reduce Flashover Accidents: Adjusting creepage distance to reinforce insulation, mainly by increasing the number of discs in a string or by using so-called anti-pollution insulators, which in China typically consist of double or triple layer aerodynamic sheds on each disc; 2. Increasing frequency of washing, mainly live-line but also manual cleaning with lines de-energized; 3. Coating surfaces of porcelain and glass with a thin layer of hydrophobic material or applying silicone rubber composite insulators.

27 Application of RTV Coatings

28 RTV Coating Leakage Current

29 Visual Observation, 300 hrs Salt Fog Test 29 RTV-A : almost no erosion- Midsun RTV-C : CSL Tracking close to pin and edge of insulator RTV-B : Dow corning Several tracking path near pin

30 Simulation of Effect of Acid Rain on RTV Coatings 30 Loss of Hydrophobicity is caused by: - Wetting in coastal regions - Acid-rain in industrial regions which often causes depolymerization Midsun 570 Dow Corning CSL (Sicoat) RTV-A New RTV-B New RTV-C New The most severe influence of acid rain on RTV coatings is depolymerization. Accelerated acid rain aging: 1 month soaking in nitric acid, ph=3.9 at 90 ºC is equivalent to 90 months natural aging the field (345 kv substation, Connecticut, USA). RTV-A Aged RTV-B Aged RTV-C Aged

31 Typical Live Washing Techniques Handheld jet nozzle 2. Remote-control jet nozzle 3. Fixed-spray nozzle 4. Helicopter-mounted nozzle

32 Fixed spray (substation) 32

33 Helicopter Washing 33

34 What is important in Hot Line Washing? 34 Leakage Current : 1mA to 2mA? What influences the leakage current? Line voltage : 230kV- 345kV-500kV- 750kV Distance from the nozzle tip to the energized parts Water resistivity or conductivity Water pressure Nozzle orifice diameter Wet and Dry AC Flashover Lightning Impulse Flashover Switching Impulse Flashover

35 Water Resistivity and Pressure 35 Rule of thumb: IEEE Std Water resistivity >1,300 Ω.cm for warm weather (above 10 degc) High Pressure > 2750 kpa(400 psi) Cold weather ( below 5 deg C) use de-ionized water -water resistivity> 50,000 Ω.cm

36 Typical Live Washing Steps 36

37 Max. No. of Defective Units for Live-Line Work Based on 2.0 pu switching overvoltage (SO) System voltage kv Typical number of insulator units per chain Maximum number of defective units

38 Summary of Recommendation for 500kV line 38 Minimum working distance [m/(ft)] Nozzle orifice diameter [mm] Nozzle Pressure [kpa/(psi) ] Minimum water Resistivity [Ω.cm] IEEE Std (20) Max (550) 3, (14) Max (800) 50,000 Old Ontario Hydro 4.3(14)* (900) 3,000 CESI/CEPRI 6.1(20) for K OV = (435) 2, (14) for K OV =2 Chinese Research 5.5 (18 ft) 4 to 8 Not known 10,000 SCE 4.3 (14 ft) (400) 20,000 PG&E 6.1(20 ft) (400) 1,000 New Ontario Hydro 4.8 (16 ft) (750) 3,000

39 Standards 39 ANSI/NEMA C American National Standard for Insulators - Porcelain and Glass IEC Insulators for overhead lines with a nominal voltage above 1kV : Glass and Ceramic IEC : Composite station post insulators for substations with a.c. 1 KV up to 245 kv Definitions & tests IEEE IEEE Guide for Cleaning Insulators IEC Guide for the selection and dimensioning of high-voltage insulators for polluted conditions IEC 60507:2013 Artificial pollution tests on high-voltage ceramic and glass insulators to be used on a.c. systems

40 What is updated IEC and

41 Example: Persian Gulf Arab Countries 400kV Double Circuit Kuwait, Bahrain, Qatar, the United Arab Emirates, Oman and Saudi

42 To Prevent flashover: 42 Insulators, and hardware should be inspected prior to the cleaning program. Start from lowest phase conductive. Begin to wash from the lower part of the insulator until finishing in the upper part. The water should not fall directly on a dirty insulator. Keep in mind the direction of the wind.

43 Summary of Insulator Pollution Issues? 43 Polymeric had advantage but has many issues. Specially at 230kV and higher. Best practical performance for HV polluted over-headlines is High Quality RTV Coated Cap&Pin or Glass Insulator Is existing design working? Revisit Pollution Site Severity and Creepage Distances for each Geographic Area Establish live-line washing practice for HV lines Emergency planning guideline, Equipment, Manpower, Training

44 Thanks for Listening! Ali Naderian, PhD, PEng, SM IEEE Toronto, Canada February برگزار کنندگان ایکهربا سامانه تجهیزات صنعت برق ایران کارشناسان توزیع برق ایران