physical and electrical effects to nearby facilities …...physical and electrical effects to nearby...
TRANSCRIPT
Physical and Electrical Effects to Nearby Facilities When
Applying Dynamic Line Ratings to
Transmission Lines
Presented by: Rob Schaerer, P.E. Coauthored by: Bishnu Bhattarai, Jake Gentle, David Kelle (Idaho National Laboratory)
October 24, 2017
Traditional approach – Static line ratings• May vary by season• Limits line’s capacity unnecessarily
Dynamic line ratings (DLR) • Make full use of conductor capacity• Varies by temperature• Considers heat balance• Requires more data
3
Dynamic Line Ratings 101
7
Physical Impacts – Increased Sag
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BTTA cc −=
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Increased current = Increased heating• Thermal elongation = Lower conductor
» Can cause clearance violations– Thermal time constant for conductors is around 10 to 20
minutes, quickly increasing the sag
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2
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Conductors• Reduction in strength
» Caused by high temperatures for long periods of time as the aluminum anneals
Connectors• Additional cyclical heating
» Can reduce lifespan and reduce rated breaking strength
8
Physical Impacts – Conductors and Connectors
Electric fields• Related to voltage; no direct change at the
conductor• Slight increase at ground due to additional sag
Corona effects• Includes audible noise and AM radio
interference• Related to electric field gradient on the
conductor» Imperceptible change outside the right-of-way 10
Electrical Impacts – Electric Fields and Related Effects
Electrostatic/capacitive coupling• NESC 5 mA rule
» Limits discharge current on ungrounded vehicle under line to 5 mA
– If marginal, new sag could cause exceedance
• Other ungrounded objects – also slight increase» Barbwire fences on wood posts» Ungrounded above-grade pipes» Etc.
11
Electrical Impacts – Electric Fields and Related Effects (Continued)
Magnetic fields• Directly related to the current
» Could increase significantly» Public perception of increased EMF» Recommend calculation for awareness
• Smaller additional increase due to lower conductor heights
12
Electrical Impacts – Magnetic Fields and Related Effects
Magnetic fields, continued• AC interference
» Magnetic field causes induction on adjacent parallel (or semi-parallel) objects
– Pipelines» Safety, corrosion
– Railroads» Safety, misoperations
– Fences– Etc.
13
Electrical Impacts – Magnetic Fields and Related Effects
Weather• Easy to predict/measure ambient temperature• Hard to measure wind speed and direction along
the entire line
Ratings• Have to balance risk of rating exceedance with
desire to free up as much capacity as possible» Conductor temperature measurement can help
15
Prediction Risks – Weather and Ratings
Safety• Must maintain safe operation and clearances
» NERC/FERC penalties possible» Prevent accidental flashovers
• Additional heating could cause tensile failures
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Regulatory/Safety Aspects
Physical and Electrical Effects to Nearby Facilities When Applying Dynamic Line
Ratings to Transmission LinesRob Schaerer, P.E.
POWER Engineers, [email protected]
October 24, 2017