ieee 2012 tutorial on significance of using proper conductor temperature

7/29/2019 IEEE 2012 TUTORIAL on Significance of Using Proper Conductor Temperature

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Dale DouglassPower Delivery Consultants, Inc.

NERC Alert Task Force:

Guidelines for Determining Conductor Temperatures During

Measurement of Sag Along Overhead Transmission Lines

February 7, 2012

Management of Existing Overhead Lines WG Meeting

Tampa, Florida

Significance of Using Proper

Conductor Temperature


2/11

Purpose of Talk

The goal of this presentation is to

quantify the impact of errors in

determining conductor temperatureduring LiDAR surveys on the resulting

high temperature sag estimates for a

variety of lines and conductors.


3/11

Consequences of conductor temp errors

during LIDAR measurements

1. The final sag is

measured using LIDAR at

an actual ruling span

cond. temp = 30C.

2. If cond. Temp is

estimated to be 40C, sagat 95C is too low &

clearance problems may

be missed!

3. If cond. Temp is

estimated to be 20C, sag

at 95C is too high & the

lines thermal capacity

may be underestimated.GROUND LEVEL

Minimum Electrical

Clearance

Sag Meas with LIDAR &

actual Cond Temp = 30C

Calculated Sag @95C for

calc Cond Temp = 40

Cwith LIDAR meas

Calculated Sag @95C for

calc cond. Temp = 20C

with LIDAR meas

Span Length


4/11

Field Data Required

In order to calculate the clearance at high

temperature, the conductor temperature must

be calculated or measured during the LiDAR

survey.

If conductor temperature is calculated, the line

current and weather conditions along it must be

measured.

If conductor temperature is measured, weather and

line current are not needed but may be useful for

verification of measurements.


5/11

Span and Line Section

Temperature

In most lines, there is very good tension equalizationbetween suspension spans so the sag clearancedepends on the average temperature within each linesection.

There is little temperature equalization along bareoverhead conductors.

At high current levels (> 0.5 amps/kcmil), the normalvariations in wind speed and direction along the linecan yield significant variations in conductor

temperature from span to span. If we measure or calculate conductor temp. at one

location within a line section, it may not be close to theaverage of all spans, especially at high line currents.


6/11

0

50

100

150

200

250

0 1 2 3 4 5 6 7 8 9 10

ConductorTemperature-degC

Span Position Along the LIne

26/7 795 kcmil Drake ACSR conductor temperature variation with wind

speed and direction along the line as a function of line current.

For all locations, Tair = 40C & Solar Heat is for Summer Noon

200a

400a

600a

800a

1000a

1200a

1400a

1600a

4fps,90o

4fps,45o

4fps,22o

3fps,45o

3fps,90o

3fps,22o

6fps,45o

6fps,22o

6fps,90o


7/11

Impact of Line Current

If the line current during the LiDAR survey is small(< 0.5 amps/kcmil), then the error in estimating theconductor temperature during a LiDAR survey is

usually small (0.5 amps/kcmil), then errors in determining the

average conductor temperature can translate intosignificant errors in calculation of high temperatureelectrical clearances.


8/11

40

45

50

55

60

65

70

75

80

85

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

CalculatedConductorTempat40Cair,0.8emiss&

absorp

Current Density - amps/kcmil

795 kcmil, Drake ACSR Conductor Temperature Calculated with IEEE 738

TC- 2 ft/s&FullSun

TC-4 ft/s&FullSun

TC- 8 ft/s&FullSun

With 160 amps, the conductor

temperature is between 40Cand 53C regardless of the wind

speed and direction and the

maximum temp meas error is

probably < 5C.

Air Temperature = 40C

With 640 amps, the

conductor temperature is

between 40C and 70C and

the maximum temp meas

error can be larger (>10C) direction.


9/11

Final Sag-LiDAR Temp Errors


10/11

Other errors in estimating high

temperature sag

Selection of weather conditions for

Thermal Ratings. Use of 4 fps wind can

yield a 20C error conductortemperature* ( 2 ft sag)

Calculation of thermal elongation can

yield errors of 1 to 3 ft (10 to 30C)**

* - CIGRE TB 299 ** - CIGRE TB 324


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Conclusions

Possible errors in determination of conductor

temperature during LiDAR surveys are a

function of line current. At line currents above 0.5 amps/kcmil, the

error in estimating high temperature sag can

be 1 to 2 ft in typical lines.

This is comparable to errors related to

selection of rating weather assumptions and

thermal elongation of ACSR.

ieee 2012 tutorial on significance of using proper conductor temperature

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