ABB Surge Arresters Contribution to Power Quality Line Side Protection

Transcription

1 James Taylor, Technology Support Manager / Principal Specialist May 2013 ABB Surge Arresters Contribution to Power Quality Line Side Protection May 6, 2013 Slide 1

2 Availability of electric power supply EHV Transmission substation Transformer HV HV Main substation Secondary substation MV Distribution substation LV May 6, 2013 Slide 3 At each point, the consumer of electricity is concerned about Number and Duration of interruptions (plus associated costs)

3 Lightning Costs and Losses from Attributed Sources Lightning in South Africa is responsible for 65% of damage in distribution networks and 26% of the total number of line faults in transmission networks ( ) Faults on transmission lines in Korea ( ) Transmission Voltage Total Faults Lightning caused faults % 66kV % 154kV % 345 kv % SUM % Examples of plant losses due to lightning-induced electrical outage: South African South Deep JV mine lost 1 month production (2005) Porgera JV mine in Papua New Guinea lost 50% of electrical power for more than three months at a production loss of US$750,000/day (2006) Tennessee smelter pot line frozen. 164 pots have to be dug out by hand. Production is shut down for seven weeks. (2007) May 6, 2013 Slide 4

4 Acceptable outage rate A moving target Single circuit Power in Transmission line Power out Substation Transformer equipment Typically poor overall availability Substation equipment is not the critical factor during normal operation Line and transformer are dominating causes for unavailability Double circuit Two lines in parallel Two transformers in parallel Power in S/S Power out May 6, 2013 Slide 5 Lightning is a significant contributing factor to the outage rate Line availability remains critical with common towers Double line failures must be avoided

5 Line interface protection At the line entrance bay to take care of multiple lightning strokes in combination with circuit breaker operations Line entrance surge arrester protects the line breaker and the instrument transformers at the entrance. Furthermore it gives improved protection to the power transformer. Surge Arresters marked with blue May 6, 2013 Slide 6 Arresters placed Always as close as possible to the power transformer With safe silicone insulated arresters, optimal place is on the power transformer

6 ABB PEXLIM arresters Flexibility at its Best Solid design with silicone-housing directly bonded onto active parts incorporating unique open-cage design with patented belt-winding Reliable, secure and safe design Low weight facilitates flexible installation Vertical upright Inverted Suspended Horizontal Angular Benefits: Saves space Saves money on structures Saves money on foundations Can be placed directly on power transformers for best protection May 6, 2013 Slide 7

7 Station protection Line entrance bays Arresters always located adjacent to the power transformers; being the most costly item of plant With line breaker closed, these arresters are often all that is needed to protect apparatus connected to the same line within the substation With the breaker opened, no protection exists for the line side of the breaker making it and other equipment vulnerable Incoming lightning surge may cause flashover of the breaker or insulation failure of other line-side equipment May 6, 2013 Slide 8

8 Station protection Line entrance bays Prolonged opened breaker condition normally dictates that the breaker disconnecting switches are also opened and grounded. If not, some form of protection should be used to prevent surges impinging on the breaker. More likely during normal operation is that damage to the line breaker occurs as a result of subsequent strokes of the lightning flash during the open-close cycle Flashover across the line breaker is particularly severe since the consequence will normally be a busbar fault in the substation With the breaker open, equipment on the line side is also unprotected May 6, 2013 Slide 9

9 A likely scenario Line CB X Substation arresters Relay protection 3 Line 4 1 May 6, 2013 Slide Lightning strikes the line, resulting in a flashover and earthfault. 2. Lightning surge travels into the substation. Line CB is closed and substation arresters function to limit the overvoltage. 3. Relay protection senses the fault and line CB opens (in about 50ms). Fault current is cleared by the CB. Autoreclosure would normally occur in about 300ms. 4. Multiple lightning stroke occurs in the same channel as before in the interval ms after initial stroke. Subsequent surges occur while the CB is open (dead time during autoreclose operation) 5. The lightning overvoltage is reflected at the open line end, doubling the amplitude. Line breaker is unprotected and overvoltage exceeds the breaker insulation withstand strength.

10 Line entrance bays Reliability and improvement Example 420kV (LIWL kV) Incoming surge 2000kV, 2000kV/ms Voltage at breaker Voltage at transformer Voltage at breaker - kv Breaker closed, Line arrester and CVT Breaker closed, Line arrester and no CVT Breaker closed, No line arrester and no CVT Breaker closed, No line arrester but CVT Breaker open, Line arrester and CVT Breaker open, Line arrester and no CVT Breaker open, No line arrester but CVT Breaker open, No line arrester and no CVT Voltage at transformer - kv Line arrester and CVT No line arrester but CVT Line arrester and no CVT No line arrester and no CVT Range of insulation levels Distance transformer-arrester to transformer - m Clear advantage with additional arresters (and CVT) in front of the line breaker May 6, 2013 Slide 11

11 Cause of lightning flashovers on HV transmission lines Backflashover High footing resistance Shielding failure No OHSW Poor shielding angle Induced flashover Lightning flashes to ground seldom exceed 200 kv Neglected on HV transmission lines due to high LIWL May 6, 2013 Slide 12

12 Transmission Lines Reliability and availability improvements Duplicate system Very expensive and often impractical. Compromise with two lines on one tower. Increase insulation withstand Expensive and creates insulation co-ordination problems Improve footing impedance Often difficult and expensive Shield wires Requires low tower footing impedance. Problems of their own. Difficult to retrofit. Unlikely to achieve demanded reliability. Do not improve switching performance. Protect line insulation by surge arresters May 6, 2013 Slide 13 Arresters connected in parallel with line insulators at selected towers. Line Surge Arresters (LSA)

13 Line protection Arresters installed on selected towers eliminates disturbances caused by overvoltages Prevents lightning-induced flashover across line insulators on the tower Controlled switching surge overvoltage profile along the line Assists to extend line circuit breaker life and maintenance-interval Gapless design preferable May 6, 2013 Slide 14

14 Line protection (LSA) Lightning-induced flashover at a tower Total risk for complete line is the sum of the risk at each tower (as a function of individual tower parameters) With arresters in one circuit risk for a double-circuit fault is practically eliminated at the particular tower LSA are an effective method for reducing overall line outage rate Number of lightning Risk of flashover strokes per km line X Span length x 0.6 X per lightning stroke per year as function of tower footing resistance May 6, 2013 Slide 15

15 4,50 Line protection (TLA) EHV and UHV line switching Traditional solution for limitation of switching overvoltages is to fit pre-insertion resistors on the line breakers decreases the amplitude of the travelling wave induced during closing / reclosing effective, but can be problematic Overvoltage(p.u.) 4,00 Range of SIWL used for line towers 3,50 3,00 2,50 No Control Closing Resistors Line Ends Modern, innovative and more robust alternative is instead to place TLA s on specific towers along the line 2,00 1,50 ABB 1,00 Group May 6, Slide Distance in Percentage of Line Length (%) Line Ends & Mid-point 3-phase fast reclosing of 200 km, 550 kv non-compensated line after 1-phase ground fault

16 PEXLINK Secure supply all the way Assures disturbance-free operation of transmission lines Suitable for all voltage levels Station Class PEXLIM silicone-housed arrester with line & earth fixing hardware and earth lead disconnecting device Configurable to meet standard and special installations Easy to install Mechanically robust and secure Fail-safe design with visible indication May 6, 2013 Slide 17

17 Application example Eskom (South Africa) 275 kv Transmission Lines with PEXLINK Line name (275 kv) Line length (km) Units installed Performance (Faults/100km/year Before After Eiger-Prospect Eiger-Fordsburg Glockner-Olympus N/A 6.97 Taunus-Princess Esselen-Pelly Bighorn-Pluto Hera-Watershed Source: Cigré 5th Southern Africa Regional Conference, October 2005 May 6, 2013 Slide 18

18 PEXLINK Monitoring (EXCOUNT-II) Of interest to monitor surges through individual LSA Sensor fitted to each LSA Remote communication Statistical analysis (software) Leakage current measurement only of academic interest May 6, 2013 Slide 19

19 PEXLINK A future necessity to help keep the lights on? Sensitive processes are all the more dependent on constant and reliable energy supply Momentary loss of supply may be as costly as a prolonged blackout to a process industry Consumers have become more conscious and demanding and are likely to be even more so into the future Deregulation of the electricity market allows for performance based contracts with stiff penalties for Utilities that don t measure up May 6, 2013 Slide 20

20 Acceptable outage rate is a moving target Securing Power Quality in a changing world Effects of lightning in future years? If the theory of global warming is correct, we could see double or triple, even more, in the number of lightning strikes by midcentury. Source: Dr. Martin Uman, Univ. of Florida Lightning Research Center, quoted in article in New York Times, Sept. 9, Chinese scientists have warned that global warming is likely to intensify extreme weather patterns, and severe storms in recent years may be a prelude to this. Source: China Meteorological Administration, July 30, PEXLINK Secure supply all the way May 6, 2013 Slide 21

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