[email protected] smart grid case study: increasing the thermal rating of overhead 230-kv...
TRANSCRIPT
Smart Grid Case Study: Increasing the Thermal Rating of
Overhead 230-kV Transmission Lines from Niagara Falls, Canada
William A. Chisholm, Ph.D., P. Eng, [email protected]
Universidade de São Paulo6 Oct 2015
Abstract
• A “Smart Grid” case study allowed a significant increase in transmission line thermal rating while ensuring safe electrical clearances below the line.
• Showed operational use of sonar clearance measurements from the ground below the lines.
• Demonstrated use of the operating transmission line itself as a very long (30-km) hot-wire anemometer, compared to conductor diameter (28 to 34 mm).
Abstract
• The nature of the project involved several disciplines, including meteorology, thermodynamics, multi-span mechanical coupling, data acquisition and human factors.
• The seminar will be presented at an accessible, tutorial level with strong support from field results.
• The foundation of the seminar was invited for the first SENEV conference, sponsored by CEMIG in Minas Gerais, Brazil.
Motivation
• In Ontario, Canada, there have been ongoing restrictions in ability to transfer power from the Niagara Falls stations to load centers 100 km away.
• Capacity of a five-circuit 230-kV transmission interface to load centers is reduced when wind speed drops below 2 m/s.
• Plans to supplement existing lines with two new circuits have been frustrated.
Motivation
• In the meantime, Hydro One initiated advanced studies of overhead line clearance using:– Helicopters to perform laser surveys of the conductor
position at a known temperature– Sonar to measure the conductor heights continuously– New algorithms to invert a traditional (IEEE Standard
738) overhead line thermal rating calculation.
Motivation
• The process establishes spatially averaged wind speed along entire line sections, rather than relying on spot readings with differing exposure height and sheltering, measured at remote sites.
• This presentation will compare different methods to measure low wind speeds for line rating.
• This presentation will also cover the important mechanical response of the coupled spans.
Organization of Seminar (1), 60 minutes
• Heat Balance of Overhead Conductors• Field Observations of Temperature, Solar Flux, Wind
Speed, Direction and their Standard Deviations• Change of Tension, Sag and Clearance with
Conductor Temperature – In single span– In multiple spans with freely swinging insulators
• Field Observations of Clearance and its Predictors
Organization of Seminar (2), 30 minutes
• Ampacity Inversion – Long-Axis Hot-Wire Method– Inputs: Clearance, Line Current, Ambient Temperature,
Solar Radiation– Outputs: Spatially Averaged Conductor Temperature
and Wind Speed• Implementation by Utility and Results• Conclusions and Discussion
Heat Balance for Outdoor Conductor
• Heat Inputs– PJ , Joule Heating, I2R where R is the ac resistance at
the temperature of operation– PM , Magnetic Heating from ac currents induced in the
steel core from unbalanced stranding– PS , Solar Heating, up to 1000 W/m2 and affected by
conductor absorptivity
Heat Balance for Outdoor Conductor
• Heat Outputs– Pc , Convective cooling
• Wind speed v > 0.4 m/s, conductor diameter D =20 mm• Reynolds number Re =vD/ (mf/rf )about 1000• Nusselt number Nu is a function of Re and wind angle
– Pr , Radiative cooling, varies as fourth power of difference in absolute temperature (K)
– Pw, Evaporative cooling if the conductor is wet or sublimation cooling if it is loaded with ice
Heat Balance Model: Solar, Radiation
PS: Solar Input • Intensity • Azimuth• Elevation• (time of day)• Conductor
Absorptivity
Pr: Radiation Heat Loss• Varies as (Tc
4 –TA
4) times• Conductor Emissivity
Heat Balance Model: Joule, Convection
PC : Convection Heat Loss varies as (TC-TA )(Effective Wind Speed) 0.5
Wind speed, angle to conductor
Line Current• PJ
varies as I2R• PM varies nonlinearly
Convection Heat LossVaries as (TC-TA ) (Wind Speed) 0.5
Wind speed, angle to conductor
Line Current
Overall Heat Balance
Solar Input
Radiation Heat Loss(Tc
4 –TA
4 ) (T in Kelvin…)
Heat Balance for Outdoor Conductor
• Steady State, Dry Conditions
• Unsteady State
– m is mass per unit length of conductor– c is the overall heat capacity of the steel/aluminum
rcSMJ PPPPP
rcSMJav PPPPPdt
dTmc
Transient Thermal Response (IEEE 738-2012)
Rise in Conductor Temperature
from 80 to 128°C
Step Change in Current, 800 to 1200 A
Transient Thermal Response (IEEE 738-2012)
Rise in Conductor Temperature
from 80 to 128°C
Step Change in Current, 800 to 1200 A
Conductor reaches 110°C (63% of difference)
in 13 minutes
Effect of Wind Speed on Conductor Temperature (CIGRE B2 Tutorial)
Critical Wind Speed Range: 0-2 m/s (0-7.2 km/h)(m/s)
Effect of Wind Speed on Thermal Transfer:CIGRE Technical Brochure 207
(CIGRE Technical Brochure 207 Presentation)
Extra 150 MVA of Power Transfer at 2 m/s (7.2 km/h) compared to 1 m/s (3.6 km/h)
Power Transfer (MVA)
Cond
ucto
r Tem
pera
ture
(°C)
Effect of Wind Angle on Nusselt Number governing Heat Transfer
• CIGRE TB 207 Model for Wind at angle : d
• Stranding, catenary give minimum value of 0.42 Nu90 for axial flow along line (=0°).
• Older model mixes forced, natural convection based on V.T. Morgan concept.
90.0
90
08.190
sin(58.042.0:9024
sin(68.042.0:240
Nu
NuNu
Standard Deviation of Wind Direction also affects Nusselt Number
deNu
Nueff 25.022
90
sin95.005.02
1 22
Standard Deviation of Wind Direction also affects Nusselt Number
Wind angle standard deviationsd tends to increase as wind speed drops.
Standard Deviation of Wind Direction also affects Nusselt Number
Wind angle standard deviationsd tends to increase as wind speed drops.
At low wind speed, CIGRE TB207 suggests yaw angle of 45°.
Organization of Seminar (1)
• Heat Balance of Overhead Conductors• Field Observations of Temperature, Solar Flux, Wind
Speed, Direction and their Standard Deviations• Change of Tension, Sag and Clearance with
Conductor Temperature – In single span– In multiple spans with freely swinging insulators
• Field Observations of Clearance and its Predictors
Field Observations of Weather Parameters Used in Transmission Line Thermal Rating
• Historical data –hourly or daily maximum basis.• Direct observations – utility weather stations.• Predictions – numerical models based on recent
observations and/or historical trends.• CIGRE Technical Brochure 299 provides guidance
on how each dataset can be used.
Historical Weather Data: Annual, Daily Variation of Ambient Temperature
𝑇 𝐴=18.0−2.6 sin ( 2𝜋 𝐷𝑜𝑌365 )−10.2cos ( 2𝜋 𝐷𝑜𝑌
365 )¿−3.6 sin( 2𝜋𝐻𝑜𝐷24 )+2.6cos ( 2𝜋 𝐻𝑜𝐷24 )
Direct Observations: Utility Weather Stations
• Use specialized, ultrasonic or lightweight anemometers to measure low wind speeds.
• Data sampled over 10-minute periods, recording average and standard deviation (CIGRE TB 299).
Direct Observations: Wind Parameters with Sonic Anemometer and Conductor Replica
Sonic Anemometer (Vaisala)
Direct Observations : Wind Speed, Direction Standard Deviations with Sonic Anemometer
Direct Observations : Wind Speed, Direction Standard Deviations with Sonic Anemometer
Direct Observations : Standard Deviations at Low Wind Speed using Sonic Anemometer
Reminder: Standard Deviation of Wind Direction affects Nusselt Number
Wind angle standard deviationsd of 45° at 1 km/h suggests effective wind yaw angle of: 48° for cross flow (Nueff -13% ) 30° for axial flow(Nueff +55 %)
• Shaw ThermalRate (formerly Pike)• Heated, unheated portions of stranded aluminum
oriented along the line direction.
Direct Observations: Heated / Unheated Aluminum Conductor Replicas
Direct Observations: Shaw Sensor Rating versus Wind Speed (Including Wind Angle)
Remaining Scatter:• High Ampacity when Wet• Solar Input• Wind Direction Standard Deviation
Weather Data “Nowcasting” and Predictions:Ambient Temperature, Humidity
NOAA, http://rapidrefresh.noaa.gov/hrrrconus/
Weather Data “Nowcasting” and Predictions:Solar Radiation
NOAA, http://rapidrefresh.noaa.gov/hrrrconus/
Weather Data “Nowcasting” and Predictions:Wind at 10 m and 80 m
NOAA, http://rapidrefresh.noaa.gov/hrrrconus/
1 kt (knot) = 0.51 m/s
Best Weather-Based Line Rating Practices: Boundary Layer Modeling of Terrain Effects
Best Weather-Based Line Rating Practices: Boundary Layer Modeling of Terrain Effects
Example of down-sampling of GFS and WRF Wind Speed Models
Organization of Seminar (1)
• Heat Balance of Overhead Conductors• Field Observations of Temperature, Solar Flux, Wind
Speed, Direction and their Standard Deviations• Change of Tension, Sag and Clearance with
Conductor Temperature – In single span– In multiple spans with freely swinging insulators
• Field Observations of Clearance and its Predictors
Conductor Elongation Factors
Length As Manufactured
Increase in Length from Creep after 1 hour
Conductor Elongation Factors
Length As Manufactured
Increase in Length from Creep after 1 hourIncrease in Length from Creep after ……… 20 years
Conductor Elongation Factors
Length As Manufactured
Increase in Length from Creep after 1 hourIncrease in Length from Creep after ……… 20 years
Reversible Elastic Strain from change in Wind/Ice Loads
Conductor Elongation Factors
Length As Manufactured
Increase in Length from Creep after 1 hourIncrease in Length from Creep after ……… 20 years
Reversible Elastic Strain from change in Wind/Ice Loads
Reversible Thermal Strain from change in Temperature
Effect of Heat
• Extreme electrical power system load peaks in summer, thanks to air conditioning
• Temperature rise above ambient powered by square of current (I2R)
• Aluminum and steel expand when they get hot, reducing clearances.
• Excessive temperature rise anneals aluminum, damages splices
Organization of Seminar (1)
• Heat Balance of Overhead Conductors• Field Observations of Temperature, Solar Flux, Wind
Speed, Direction and their Standard Deviations• Change of Tension, Sag and Clearance with
Conductor Temperature – In single span– In multiple spans with freely swinging insulators
• Field Observations of Clearance and its Predictors
Multiple Spans – “Ruling Span” Theory
• Calculate behavior of “Ruling Span”
• Transform result to other spans
End
Start
End
Start
span
spanRS
)(
)( 3
RSN
Span SagRS
SpanSag
N
2
Multiple Spans with Real Insulators
• Perfect tension equalization (infinitely long insulator strings) is basis of ruling span theory.
• Horizontal component of tension up the insulator string is small but important.
• The tensions each side ofan insulator are different.
Winkleman AIEE 1959; Chisholm and Barrett PWRD April 1989; CIGRE TB 324 p. 23-25.
Insulator Displacements for IEEE Ten-Span Test Case (Motlis et al. 1999)
The predicted swing with infinite insulator length is 22° in the 750’ span. An insulator with 1.52-m length restrains swing to 8°.
Insulator Displacements for IEEE Ten-Span Test Case (Motlis et al. 1999)
Exercise: Where should the insulator swing be measured to have the best response?
Insulator Displacements for IEEE Ten-Span Test Case (Motlis et al. 1999)
According to ruling span method, spans 6 or 7.According to correct calculations, spans 7 or 8.
Span, m 229 290 457 Insulator Displacement, RS Model (°) 22 23 -12
1.52 m Insulator Displacement, SWING (°) 8 10 -11
Multiple Spans – Sag/Temperature Slope
More Sag Change with Temperature for Short Spans:
15 mm/C° versus 11 mm/C°
Multiple Spans – Sag/Temperature Slope
Less Sag Change with Temperature for Long Spans:
42 mm/C° versus 47 mm/C°
Multiple Spans – Sag/Temperature Slope
Different Sag Changes with Temperature for Spans of
Same Length in Different Positions
Influence of Correct Tension Balance Model:– Estimated using 100°C with Ruling Span
Organization of Seminar (1)
• Heat Balance of Overhead Conductors• Field Observations of Temperature, Solar Flux, Wind
Speed, Direction and their Standard Deviations• Change of Tension, Sag and Clearance with
Conductor Temperature – In single span– In multiple spans with freely swinging insulators
• Field Observations of Clearance and its Predictors
Typical Clearance Limits for Overhead Lines
• Legal Vehicle Height 4.3 m.• Added Electrical Buffer set to withstand
Switching Surge Flashover Voltage.• Examples of Total Clearance Requirement:
– 5.5 m for 115 kV– 6.1 m for 230 kV
Clearance-Based Thermal Observations
• Measure Weather Parameters• Measure Line Current • Perform Heat Balance Calculation• Estimate the Conductor Temperature• Calculate Thermal Expansion of Conductor• Measure the Tension Change from Known State
(recent manual survey)• Measure Catenary of Reference Span• Estimate Catenaries of Other Spans
Clearance Monitoring with Sonar
Distance (m)
Echo
Lev
el (d
B)
Phase Conductor Echo
Phase Conductors
Clearance Monitoring with Sonar
Distance (m)
Echo
Lev
el (d
B)
Overhead GroundwireEcho
Overhead Groundwire
Permanent Installations to monitor Clearance and Weather
Weather Sensors: Sonic Anemometer, Temperature, RHShaw Sensor (Conductor Replica)
Sonar Clearance Sensors on Wood Crossarms
Standalone System on 4” ABS Pipes with Solar Panels Sonar Clearance Sensors
on 4” ABS Plastic Pipes and Line Power
Permanent Installations to monitor Clearance and Weather
Permanent Installations to monitor Clearance and Weather
Empty (new) Distribution Transformer Case
Clearance Measurement Analogy:Four Parallel Circuits
You
Clearance Measurement Analogy: Along Right-of-Way
You 2 cars ahead
………
Clearance Measurement Analogy: Along Right-of-Way
You 2 cars ahead
………
8 or 98 cars ahead
Good to Excellent Correlation:Clearances Along One Line, Especially Within Section
Tension-Based Thermal Observation
• Measure Weather Parameters• Measure Line Current • Perform Heat Balance Calculation• Estimate the Conductor Temperature• Calculate Thermal Expansion of Conductor• Measure the Tension Change from Known State
(recent manual survey)• Calculate Catenary of “Local Ruling” Span• Estimate Catenaries of Other Spans
Tension (kg)
Clearance (m)(Nascimento et al)
Tension-Based Thermal Observations (CEMIG)
Ambient Adjusted Rating Analogy
Estimate Speed Based on Fuel Consumption, 7 liters/100 km(equivalent: Line Current)
… adjusted for Temperature
Weather-Based Thermal Rating
• Measure Weather Parameters• Measure Line Current• Perform Heat Balance Calculation• Estimate the Conductor Temperature• Calculate Thermal Expansion of Conductor• Calculate the Tension Change from Known State
(stringing, 30-60 years ago)• Calculate Catenary of “Ruling” Span• Estimate Catenaries of Other Spans
Estimate Speed Based on Fuel Consumption, 7 liters/100 km(equivalent: Line Current)
Static Rating Analogy:Line Current
Regression Coefficient as “Grade”
• Ranked nine predictors of clearance in a span:– Other clearances in same line section– Tension– Other clearances on adjacent lines within right-of-way– Other clearances on parallel lines, 3 -15 km away– Conductor surface temperature, 3 spans away– Clearance, 32 km away– IEEE 738 (Ambient, Wind, Solar, Current)– Ambient– Line Current
Ranking Using Linear Regression Coefficient
Predictor of Clearance Pearson R2 Square of Load Current 0.38-0.53 Ambient Temperature 0.53-0.69
IEEE 738 (Ambient, Load Current, Wind Speed, Solar)
0.65-0.78
Clearance in Another Stringing Section (98 spans away, different line direction)
0.69
Conductor Temperature 3 spans away 0.77
Clearance in Parallel Right-of-Way, 3-15 km Away 0.85
Clearance in Adjacent Line on Same Right-of-Way 0.94
Tension in Same Stringing Section 0.94
Clearance in the Same Stringing Section >0.99
Organization of Seminar (2)
• Ampacity Inversion – Long-Axis Hot-Wire Method– Inputs: Clearance, Line Current, Ambient
Temperature, Solar Radiation– Outputs: Spatially Averaged Conductor Temperature
and Wind Speed• Implementation by Utility and Results• Conclusions and Discussion
Clearance-Based Thermal Rating
• Measure Clearance in Reference Span• Estimate Clearances of Other Spans• Estimate Tension Change from Known State (recent
LIDAR survey of line at known temperature)• Calculate Thermal Expansion of Conductor• Estimate Conductor Temperature• Measure Ambient Temperature and Current• Perform Heat Balance Calculation• Estimate Average Wind Speed• Calculate Limited-Time Rating
Clearance-Based Thermal Rating
• Measure Clearance in Reference Span• Estimate Clearances of Other Spans• Estimate Tension Change from Known State (recent
LIDAR survey of line at known temperature)• Calculate Thermal Expansion of Conductor• Estimate Conductor Temperature• Measure Ambient Temperature and Current• Perform Heat Balance Calculation• Estimate Average Wind Speed• Calculate Limited-Time Rating
Four Conductor Temperature Estimates from Individual Clearance Readings
Non-Physical
Tconductor > Tambient
Standard Deviation of Four Temperatures (obtained from Clearances) versus Currents
Organization of Seminar (2)
• Ampacity Inversion – Long-Axis Hot-Wire Method– Inputs: Clearance, Line Current, Ambient Temperature,
Solar Radiation– Outputs: Spatially Averaged Conductor Temperature
and Wind Speed• Implementation by Utility and Results• Conclusions and Discussion
Running in Reverse, Item 3:Wind Speed from Clearance
• With known line currents and conductor temperatures estimated from clearances, iterate wind speed until heat balance converges.
Organization of Seminar (2)
• Ampacity Inversion – Long-Axis Hot-Wire Method– Inputs: Clearance, Line Current, Ambient Temperature,
Solar Radiation– Outputs: Spatially Averaged Conductor Temperature
and Wind Speed• Implementation by Utility and Results• Conclusions and Discussion
Background: Power and Weather
The black line shows the expected effect when the weather is normal for that time of year.
Blue lines indicate days when the weather effect was less than normal. • Warmer than normal days
during the winter months• Cooler than normal days
during the summer
Red lines indicate days when the weather effect was greater than normal. • Below-normal
temperatures in winter• Above-normal
temperatures in summer
The weather effect takes into account temperature, wind, lighting, and humidity. The normal effect is determined by analyzing thirty years of records. Source: IESO
Addition to Base Load (MW), Ontario 2004
Background: Why Niagara?
Two new 230-kV circuits were constructed to supplement five existing parallel 230-kV lines.
These would have increased limits by 800 MW and enable Sir Adam Beck plants to deliver an additional 1.6 TWh/year. However, a land dispute delays the in-service date.
In the meantime, a significant generation upgrade was carried out that made the line thermal rating issues even worse.
Background: Why Niagara?
The largest hard rock Tunnel Boring Machine in the world finished drilling a massive tunnel deep beneath the City of Niagara Falls in May 2011.
Background: Why Niagara?
The new tunnel is 12.7 meters (41 feet) wide and 10.2 kilometers (6.3 miles) long.
Background: Why Niagara?
In March 2013, the tunnel was filled with water and now provides additional 500 m3 / s to generate clean, renewable hydroelectricity at the existing Sir Adam Beck stations.
The increased output is still carried along the same, five 230-kV circuits forming the QFW interface, that have been thermally limited since 2002.
The sonar clearance-based dynamic line rating system is used to manage and maximize the energy transfer, at times allowing 2400 MW to flow safely rather than the static 1800 MW rating.
Organization of Seminar (2)
• Ampacity Inversion – Long-Axis Hot-Wire Method– Inputs: Clearance, Line Current, Ambient Temperature,
Solar Radiation– Outputs: Spatially Averaged Conductor Temperature
and Wind Speed• Implementation by Utility and Results• Conclusions and Discussion
Conclusions: Heat Balance of Overhead Conductors
• Thermal Models (IEEE 738, CIGRE Brochure 207) balance I2R (Joule) and sunshine heat inputs with losses from convection and radiation.
• Convection depends on wind speed at 1-2 m/s.• Convection depends on wind yaw angle to line.• Wind direction standard deviation increases
remarkably as wind speed decreases below 2 m/s. This usually increases the convective cooling.
Conclusions: Change of Tension, Sag and Clearance with Conductor Temperature
• A line between strain towers functions as a single unit, averaging the effects of wind, solar and temperature over distances of 5-50 km.
• Calculating tension from clearance requires the same care as calculating clearance from tension.– No ruling span approximation allowed!
Conclusions: Field Results, Predictors of Clearance
• It was practical, inexpensive and reliable to measure clearance with ±6cm accuracy from ground level with standard industrial sonar outdoors over a wide temperature and humidity range.
• It was better to:– predict clearance using another clearance measurement,
taken 98 spans away on the same circuit,• than to:
– use the IEEE Standard 738 thermal model with load current and weather data directly under the conductor.
Conclusions: Wind Speed Observations
• Agreement between heated conductor heat balance (Shaw Sensor) and effective wind speed from nearby sonic anemometer was rather good.
• Neither measurement of wind was a good predictor of line clearance with present methods.
• Calculating conductor temperature from clearance is robust and has standard deviation less than 3C°.
• It is possible to invert the ampacity calculation process to establish the cross-wind speed V90 averaged over an entire 5-50 km stringing section.
• The process gives noisy results that differ from the measured wind speed under the line.
Conclusions: Reverse Rating Process to obtain Distributed Wind Speed
Conclusions: Utility Implementation
• Clearance-based thermal rating offers strong advantages, especially when multiple lines present a combined limitation to power transfer.– Inexpensive and autonomous installation– Practical in-service calibration– Multiple vendors, standard industrial technology– Directly useful for estimating clearance of other
spans• Distributed wind speed provides a sound basis
for thermal rating when line current exceeds 200 A.
Open Questions for Further Study
1. Measure component state (line, cable, transformer etc) in two or more ways.• They will disagree.
2. What are good measures of agreement? • Static case – X tracks Y with scatter• Dynamic case – X lags Y with delay
3. What is the composite effect of:– thermal time constant of conductor (10 minutes)– mechanical time constant of coupled spans in
series (1 minute travel time end to end, poorly damped)
Open Questions for Further Study
4. Rank of Other Predictors– Ultrasonic wind speed / direction– Shaw (Hot wire) sensor– Sag at 150’ from insulator (Video Sagometer)– Insulator tilt angles (Sagometer, others)
5. Rank of Same Predictors, Other Sites– Limited comparisons with tension– Limited comparisons on lines with poorly
correlated load currents– No comparisons in sheltered terrain
CIGRE and IEEE References forThermal Rating of Lines
• CIGRE Technical Brochure 207 (Thermal behavior of overhead conductors)
• IEEE Standard 738 (Standard for calculating the current temperature of bare overhead conductors)
• CIGRE Technical Brochure 299 (Guide for selection of weather parameters for bare overhead conductor ratings)
• CIGRE Technical Brochure 324 (Sag-Tension calculation methods for overhead lines)
• CIGRE Technical Brochure 601 (Guide for thermal rating calculations of overhead lines)
About the Author
William A. (Bill) Chisholm, F (IEEE), Ph.D., P.Eng, managed the Hydro-One Niagara to Hamilton Real-Time Thermal Rating project, starting in 2001 and ending in 2006 with commissioning of permanent clearance observation sites.
• BASc in Engineering Science, University of Toronto, 1977• M.Eng (part time), University of Toronto, 1979• Ph.D. (part time) in Electrical Engineering, University of
Waterloo, 1983. • 38 years of research background in power system lightning
protection, icing and thermal rating• Retired as Principal Engineer at Kinectrics, 2007• Professor, Université du Québec à Chicoutimi, 2007-8
– Wrote book, Insulators for Icing and Polluted Environments– Taught graduate course, Protection contre la foudre
• Panelist, Conductors sessions at IEEE-PES meetings• Member, joint IEEE/CIGRE Task Force B2.12, Weather
Parameters for Bare Overhead Conductor Ratings• Bronze medal, 200m fly, 2010 World Masters Championships