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

High Level DLR Overview

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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

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Dynamic Line Ratings 101

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Example Approach – Weather Based DLR

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High Level Effects on Adjacent Objects

Physical Impacts

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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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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

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Physical Impacts – Conductors and Connectors

Electrical Impacts

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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.

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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

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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.

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Electrical Impacts – Magnetic Fields and Related Effects

Other Aspects to Consider

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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

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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, Inc.Rob.Schaerer@powereng.com

October 24, 2017