line rating - it's all about the temperature

8/4/2019 Line Rating - It's All About the Temperature

1/49

Line Rating: Its all about the Temperature!

Ryan Bliss, P.E., S.E., M.ASCE

Electrical Consultants, Inc.

Inc.


2/49

Existing Line Rating Techniques

Survey

LiDar

Conventional

Finite Element Modeling (PLS-CADD, SAPS)o Temperature Calibration

Ambient

Predictive Methods

Direct Measurement Methods

Thermal Rating Analysis / Reporting


3/49

Thermal Rating Studies Questions

How accurate are the results?

What is the margin of error?

Are the results conservative? Are they too conservative?

Why do we care?


4/49

Survey Accuracy?

LiDar / Conventional

Survey Accuracy

Absolute Accuracy of +/- 6 inches

Relative Accuracy of +/- 3 inches

Sag Accuracy Factors

Span Length

Conductor Type

Conductor Temperature During Survey


5/49

Sag Accuracy Modeling/Ratings

Attachment Spotting

Insulator Length / Weight

Finite Element Graphical Sagging

Conductor Temperature Calibration

What is the Accuracy of Thermal Studies?What is the Precision of Thermal studies?

Is the study Reliable & Repeatable?


6/49

Conductor Calibration

Why is this so important? Excess Project Costs

Risk of Clearance DeficienciesHow significant is excesscosts and/or risk of clearance

deficiencies?How much Error is there inConductor Calibration?


7/49

Conductor Calibration Question

1. How does the error incalibration temperature relate

to the accuracy in thermal

rating results?

The error in the conductor

calibration is not one to one with

the accuracy in the resulting

Thermal Rating of a conductor.


8/49


Conductor Sag to aCalibration Temperature

Maximum OperatingTemperature Determined


9/49


Calibrating

Temperature

Thermal Rating

Deg (F)Difference

60 145 +85

80 170 +90

100 210 +110

120 250 +130

140 300 +160

Example of how a 20 degree F Error in Calibration temperature

could equate to 35-50 degree Error in thermal rating.

Error in Calibration temperature is not one to one withaccuracy of thermal rating.


10/49

Conductor Calibration Questions

2. How much error is there inour method of determining

conductor calibration

temperatures during survey?

3. What are the methods for

determining a conductorcalibration temperature?


11/49

Conductor Calibration Methods

Ambient Temperature Method

Predictive Methods

IEEE 738-2006

Infrared Thermography


Temperature Probe

Resistance Measurement &

Temperature Correlation


12/49



13/49


Ambient temperatures collected

during survey usually at GPS base

stations

Typically some distance from Line

Typically around 5 feet above ground

Sometimes sheltered by bushes & trees


14/49


Potential Error

Method does not account for Thermal

increase due to Electrical Load

Higher Uprating Project Costs

Assumes Conductor is not cooler than

measured Ambient temperature

Increased risk for clearance

deficiencies not getting reported


15/49

Predictive Methods

IEEE 738-2006 Calculations



16/49

Predictive Methods

IEEE 738-2006


17/49

Predictive Methods

IEEE 738-2006

because there is great diversity ofweather conditions and operatingcircumstances for which conductortemperatures and/or thermal ratings

must be calculated, the standarddoes not undertake to list actualtemperature-current relationships for

specific conductors or weatherconditions.

Is this standard applicable or helpfulto Line Rating analysis?


18/49

Predictive Methods

IEEE 738-2006

Assumptions:

IEEE 738-2006 empirical formulas will

accurately calculate conductor

temperature.

Variables can be accurately &

precisely determined or measured


19/49

Predictive Methods

IEEE 738-2006

Variables

Date & Time

Ambient Temperature

Atmosphere

Latitude & Elevation

Line Azimuth

Wind Pressure Wind Conductor Angle

Electrical Load

Emissivity

Solar Absorption


20/49

Predictive Methods

IEEE 738-2006

Assumed Accurate Variables:

Date & Time

Latitude & Elevation

Line Azimuth

Electrical Load


21/49

Predictive Methods

IEEE 738-2006

Variables difficult to be Accurate & Precise:

Atmosphere

Ambient Temperature

Wind Pressure

Wind Conductor Angle

Emissivity

Solar Absorption


22/49

Predictive Methods

IEEE 738-2006


Atmosphere

Ambient Temperature

Wind Pressure


Emissivity

Solar Absorption


23/49

Predictive Methods

IEEE 738-2006

Atmosphere

Only Two Options:

IndustrialClear


24/49

Predictive Methods

IEEE 738-2006


Atmosphere

Ambient Temperature

Wind Pressure


Emissivity

Solar Absorption


25/49

Predictive Methods

IEEE 738-2006

Ambient Temperature

Differences between Conductor and

Weather Stations

Location

Typically weather stations are some

distance from transmission line

Distance from Ground Ambient Temperature is much cooler at

elevation, ground effect is greatest at

surface


26/49

Predictive Methods

IEEE 738-2006

Ambient

Temperature

Increased Electrical Load


27/49

Predictive Methods

IEEE 738-2006


Atmosphere

Ambient Temperature

Wind Pressure


Emissivity

Solar Absorption

P di ti M th d


28/49

Predictive Methods

IEEE 738-2006

Wind Pressure Weather Station Wind Measurements

Collected during survey usually at GPS

base stations

Typically some distance from Line

Typically around 5 feet above ground

Sometimes sheltered by bushes & trees

Helicopter Wind Measurements

Typically much higher elevation than

conductor

P di ti M th d


29/49

Predictive Methods

IEEE 738-2006Wind Pressure

Predicti e Methods


30/49

Predictive Methods


Predictive Methods


31/49

Predictive Methods


How significant is a difference of 8 ft/s?

5.5 mph


32/49

Predictive Methods

IEEE 738-2006


Atmosphere

Ambient Temperature

Wind Pressure


Emissivity

Solar Absorption


33/49

Predictive Methods

IEEE 738-2006



34/49

Predictive Methods

IEEE 738-2006


Atmosphere

Ambient Temperature

Wind Pressure


Emissivity

Solar Absorption


35/49

Predictive Methods

IEEE 738-2006

Emissivity


36/49

Predictive Methods

IEEE 738-2006


Atmosphere

Ambient Temperature

Wind Pressure


Emissivity

Solar Absorption


37/49

Predictive Methods

IEEE 738-2006

Solar Absorption


38/49

Predictive Methods

IEEE 738-2006


Atmosphere

Ambient Temperature

Wind Pressure


Emissivity

Solar Absorption

What is the overall cumulative error?

P di ti M th d


39/49

Predictive Methods



40/49

Predictive Methods


Potential Error

Emissivity & Solar Absorption

Assumptions

Background Radiation

Pixels on conductor

Distance from Lens

Scale of Lens Number of Pixels Collected by

Thermal Camera


41/49


Temperature Probe

Resistance Measurements


42/49


Temperature Probe


43/49


Temperature Probe

Accurately & Precisely Measures

Conductor Surface Temperatures to

less than 1 Degree

Limited Availability of Meter


44/49




45/49



In 1996 SensorLink Corporation invented

a process to measure current and

micro-ohm resistance on high voltage

lines. Accurately & Precisely Measures

Conductor Resistance

Average Cross Section ConductorTemperature Can Be Determined

Accurately & Precisely

Instrument has Immediate Availability


46/49

Questions & Answers

Whats the Goal or Purpose in Line

Rating?

Reduce Risk / Code Compliance

Maximize Capital Expenditure

Extend / Increase Capacity of Existing

Facilities

Accuracy and / or Precision? Are the Thermal Ratings Reliable and

Repeatable?

Concl sion


47/49

Conclusion Importance and Impact of Conductor

Temperature Calibration Direct Measurements increase Accuracy

of transmission line rating studies;

therefore, the results are:

more Reliable

more Repeatable

Better Accuracy and Precision Will Result

in Reducing Project Costs and ClearanceDeficiency Risks

C l i


48/49

ConclusionRecommendations

Use as many methods as possible IEEE 738-2006 should not be only

method used in conductor calibration

Precision & Accuracy is Critical toReliable and Repeatable Results

Direct Measurement Methods Can

Increase Precision & Accuracy, WhileReducing Overall Project Costs and

Reducing Risk of Clearance Violations


49/49

Line Rating: Its all about the Temperature!

Ryan Bliss, P.E., S.E., M.ASCE

Questions?

line rating - it's all about the temperature

Documents