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Lightning Arresters and Their Application (System Reliability Enhancement)
2011 SWEDE Conference
Steve Brewer Hubbell Power Systems/Ohio Brass
SWEDE Conference - April 2011
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Outline
• Disconnector Reliability• Line Insulator Protection• Practical/Safety Topics• Track Resistant Bracket
SWEDE Conference - April 2011
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Disconnector Reliability
SWEDE Conference - April 2011
Proper Isolator Operation• Ground lead separated
• Normal overcurrent sequence – Protection operates– System re-energized– Voltage holds– Service to end user restored
• Visual indication of failure
SWEDE Conference - April 2011
Improper Isolator Operation
• Ground lead remains intact
• Normal overcurrent sequence – Protection operates– System re-energized– System trips until lock-out occurs– Service to end user NOT restored
• No visual indication of failure
SWEDE Conference - April 2011
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Resistor Graded Disconnector Time-Current Curve
0.01
0.1
1
10
10 100 1000
Current (A)
Tim
e (s
)
SWEDE Conference - April 2011
Capacitor Graded Disconnector Time-Current Curve
SWEDE Conference - April 2011
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Line Insulator Protection
SWEDE Conference - April 2011
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The Enemy
SWEDE Conference - April 2011
Traveling Wave/ Overvoltage Protection
• Lightning hits mid-span
• Current divides and then propagates
• V = I x R
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Surge Arresters - Concept
• Surge causes traveling voltage wave
• Voltage would be enough to flash-over insulation
• Surge arrester high resistance at L-G voltage
• Surge arrester low resistance at surge voltage
• Surge is diverted to ground
• Surge arrester high resistance again after surge
• Conduction time is too short for breakers to react
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Case Histories
SWEDE Conference - April 2011
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National Grid
• Champion International Paper Co.– Operates 363 days/year, 24 hours/day– One interruption costs $50-100k
• No. 2 line - 115 kV, 70 years old – Hired PTI – Installed new OHSW– Improved footing resistances
SWEDE Conference - April 2011
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National Grid 115 kV Line without Surge Arresters
SWEDE Conference - April 2011
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National Grid 115 kV Line with Surge Arresters
SWEDE Conference - April 2011
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Suspended Line Arrester Configuration
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Typical Dead-End Line Arrester Configuration
SWEDE Conference - April 2011
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Practical/Safety Topics
SWEDE Conference - April 2011
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Practical Issues• Must use right rating and type
– Too large as bad a too small• Lead length affects protection• Conductor Size - Min. # 6 AWG
– Ground lead must be flexible• Reuse of arresters
– Not recommended• Testing of Arresters
– Thermal Imaging holds most promise• DOT shipping considerations
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Safety Issues
• Porcelain arresters– Most dangerous if do not blow up
• Disconnector operation– Brings line voltage to base of unit
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Track Resistant Bracket
SWEDE Conference - April 2011
