Gas / Electric Arcing Interactions

Transcription

1 Gas / Electric Arcing Interactions Michelle Gallardo Senior Engineer Alan Mulkey Consulting Engineer Gas System Integrity May 20, 2015

2 Puget Sound Energy (PSE) PSE is Washington state s oldest local energy company, serving 1.1 million electric customers and 770,000 natural gas customers in 10 counties. 2

3 Outline Overview of electric system operations Regular Operations Ground Faults/ Intended Return Paths How gas system can become affected Why does arcing happen? Conditions that increase risk Typical Damage Characteristics What does arcing look like? How we respond An Event 3

4 Electric Distribution System 4

5 Electric Distribution System 5

6 Intended Return Paths In most cases Ground Fault Current will travel through the earth and use the electrical system grounds to complete the circuit (return to source). Grounds ground plates, ground rods, or ground grids are placed on distribution overhead and underground circuits and equipment Neutrals connect grounds with substation 6

7 Events that lead to Ground Faults Overhead Conductors Conductor falls to ground Grounded object contacts conductor Underground Conductors Insulation breaks down Neutral Corrosion 7

8 When is the Gas System at Risk? Low probability and possible high consequence Both of the following items must occur to have an issue: The Electric System releases ground fault current. AC fault can last 1/10 of a second or longer Intended return path not continuous - theft The Gas System is in close proximity to the fault or in close proximity to another metallic object in close proximity to the fault 8

9 Close Proximity Other conductive objects may provide a parallel path to complete the circuit: Water Gas Underground tanks Sewer Cable TV Telephone 9

10 Where does the damage occur? Metal loss occurs when DC current leaves our pipe, with AC it is entering and leaving our pipe at 60 hertz, therefore metal loss occurs where it enters and leaves our pipe 10

11 When gas piping becomes part of the return path Damaged coating Damaged equipment (RTU s, rectifiers, bond wires) Metal loss and possible leaking gas Extreme heating may weaken or rupture pipeline Gas may ignite Personnel may get injured 11

12 Typical Damage Characteristics Field personnel will be working a leak and discover Two metallic pipes in close proximity, possibly touching 12

13 How do we know electricity is involved? 13

14 Typical Damage Characteristics When fully exposed Bright shiny metal hole, Metal spatter, from metal heating and cooling quickly Can be cone shaped hole Melted PE Damaged tracer wire 14

15 Fire at meter set, meter set and fuel line in close contact 15

16 Close up of Regulator with microscope 16

17 Water line and gas service in close contact Coating damaged, burnt and brittle Copper plating on gas pipe 17

18 Initial Response If there is one leak there may be others: Metal loss occurs both when current leaves or enters the pipe; Confirm leak is Caused by Electricity Mobilize Leak Investigation Team Request Corrosion Control Assistance Establish Leak Investigation Boundary 18

19 Mobilize Leak Investigation Team Mobile and walking leak investigators; Notify Fire Department if assistance needed: Evacuations; Accompanying leak investigators; Look for; Down power lines; Burned electric meters; Electric utility vehicles and workers; Water company vehicles and workers; Electric outages in the area; 19

20 Leak Investigation Boundary Initiate leak investigation: Center the leak investigation at the largest hole and increase area as more holes are found; Start in the neighborhood; and Electrically continuous metal pipe; Expand leak investigation boundary: As additional leaks are found; To include circuit back to substation. Conduct follow-up leak investigations Leaks could be from initial fault or subsequent attempts to restore power. 20

21 Check Cathodic Protection System Damaged rectifiers; Abnormal readings on RMUs Shorted insulating fittings; Burned bond wires; Perform post event surveys. 21

22 Be Prepared Underground cable failures occur more often in summer; Down overhead electric lines occur more often in winter; Power company will try to reenergize to check if fault is cleared Know your local power company(s), establish contacts; Public awareness: Mobilize communication team to inform residents and respond to news media; What did people see Overhead line on the ground arcing? Any other utilities in area performing troubleshooting Develop job aids for first responders. 22

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24 Seattle, Wa Lake Forest Park Kenmore Shoreline Substations Line Down Seattle

25 8TH AVE NE 8TH AVE NE 9TH AVE NE 11TH AVE NE ROOSEVELT WAY NE 14TH AVE NE 15TH AVE NE 15TH AVE NE 14TH AVE NE 12TH AVE NE 16TH AVE NE 15TH AVE NE 12TH AVE NE 16TH AVE NE 10TH PL NE ROOSEVELT WAY NE ROOSEVELT WAY NE 9TH AVE NE 14TH AVE NE 14TH AVE NE North Acres Park NE 127 th St NE 125TH ST NE 123RD ST NE 120TH ST 3RD AVE NE Sewer Svc 3RD AVE NE Oil vent 3RD AVE NE NE 125TH ST NE 123RD ST NE 120 th St Overhead Splice Failed Chain link Fence RAMP I-5 FRWY RAMP NE 120TH ST 5TH AVE NE 5TH AVE NE 5TH AVE NE 5TH AVE NE 5TH AVE NE NE 123RD ST 5TH AVE NE NE 125TH ST NE 124TH ST NE 123RD ST NE 126TH ST 8TH AVE NE 8TH AVE NE 8TH AVE NE 8TH AVE NE NE 128TH ST ROOSEVELT WAY NE NE 127TH ST NE 127TH ST NE 127TH ST NE 127TH ST NE 125TH ST NE 125TH ST Seattle NE 123RD ST NE 122ND ST NE 120TH ST NE 120TH ST NE 120TH ST NE 120TH ST 10TH AVE NE 10TH AVE NE 10TH AVE NE NE 125TH SR ST NE 126TH ST NE 123RD STNE 123RD ST 10TH PL NE 12TH AVE NE 12TH AVE NE NE 125TH ST Abandoned water service NE 125TH ST NE 124TH ST NE 123RD ST NE 120TH ST 14TH AVE NE NE 127TH ST NE 125TH ST NE 123RD ST NE 120TH ST 15TH AVE NE 15TH AVE NE Pinehurst Playground Water svc NE 125TH ST NE 123RD ST NE 120TH ST NE 120TH ST Branch Fell Bonded Test Lead Wires & Valve Box Extension Bonded Test Lead Wires I-5 FRWY 3RD AVE NE I-5 FRWY 5TH AVE NE 7TH AVE NE 8TH AVE NE 5 th Ave NE 12 th Ave NE PINEHURST WAY NE 25

26 Summary of leaks 1016 NE 127 th St (abandoned water svc) 1 by NE 122nd St (Water svc) 2,200 ft 0.48 by

27 Summary of leaks th Ave NE (Oil tank vent) 2,700 ft 0.3 by th Ave NE (Sewer svc) 3,500 ft Interior Exterior