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Dynamic Monitoring of Overhead Line Ratings in Wind Intensive Areas
Dr. Damian Flynn
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Overhead Line Dynamic Ratings
• Wind farms located in remote locations• Upgrade transmission + distribution networks ?• … network capacity lags wind farm expansion• Equipment ratings are normally seasonal• Overhead line cooling dependent on wind speed• Switch from static to dynamic equipment ratings ?• … delay requirement for network expansion
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Factors Affecting Line Rating
• Conductor material + dimensions• Wind speed and direction• Solar radiation• Ambient temperature• Humidity and precipitation• Average conductor temperature• Permissible conductor sag
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Measurement Methods
• Conductor sag• Conductor tension• Vibration modes• Meteorological / weather data
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N. Ireland Power System
NIE TRANSMISSION NETWORK – PINCH POINTS
>250MW of Wind
275 kV double cct275 kV single cct110 kV double cct110 kV single cctMoyle HV DC linkPower station275 kV substation110 kV substation
Power flow controller
Mech switched capacitance
Omagh
Coolkeeragh
Dungannon
Ballylumford
Moyle I/C
Kilroot
to Letterkenny
to Swanlinbar
Louth
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Monitoring Methodology
• Omagh - Dungannon 110 kV line (ACSR conductor)• A & B circuits at 10 locations• GPS time stamping of data• Daily GPRS burst to remote server
Tnet Controller
GPRS
Serial RS 232
ISM Band Radio
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Monitored Signals
• Wind speed + direction• Solar radiation flux• Ambient temperature• Conductor temperature • Conductor current
• 20 locations @ 5 minute intervals
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Static Conductor Ratings
0
5
10
15
20
00:00 06:00 12:00 18:00 00:00
Time (hr)
Am
bien
t Tem
pera
ture
(C
) Winter day
Spring day
Summer day
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Solar Radiation
0
200
400
600
800
1000
00:00 06:00 12:00 18:00 00:00
Time (hr)
So
lar
Rad
iatio
n (
W/m
2)
Winter day
Spring day
Summer day
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Wind Speed Variability
0
5
10
15
20
0 5 10 15 20 25
Ambient Temperature (C)
Win
d S
peed
(m
/s)
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Wind Tunnel Testing
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Load Current Step - 550 AA
mbi
ent T
empe
ratu
re (C
)
Time (min.)
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CIGRE Physical Model
joule heating
+ magnetic heating
+ solar heating
+ corona heating
=
convective cooling
+ radiant cooling
+ evaporative cooling
• Transient model – thermal mass cooling term
• Engineering judgment required to select individual model parameters
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PLS (Dynamic) Model Structure
Conductor temperature =
ao + a1 * ambient temperature (t)
+ a2 * exp(-b * average wind speed (t) c)
+ a3 * average wind speed (t)
+ a4, a5 * average wind speed (t, t - 1)* sin(δ)
+ a6, a7, a8 * solar radiation (t, t - 1, t - 2)
+ a9, a10, a11 * conductor current (t, t - 1, t - 2) 2
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Temperature Prediction - November
00:00 12:00 00:00 12:00 00:00 12:00
2
4
6
8
10
12
14
16
Time (hr)
Con
duct
or
Te
mp
erat
ure
(°C
)
PLS temperatureCIGRE temperatureMeasured temperature
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Temperature Prediction - March
00:00 12:00 00:00 12:00 00:00 12:00
4
6
8
10
12
14
16
Time (hr)
Con
duct
or
Te
mp
erat
ure
(°C
)
Measured temperatureCIGRE temperaturePLS temperature
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Dynamic Conductor Rating
• Estimate average conductor temperature
Conductor length
Conductor catenary sag
• Estimate maximum current per monitored section
Identify limiting line section
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Conductor Rating Prediction
06:00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:001000
1200
1400
1600
1800
Time (hr)
Cur
rent
(A
)
PLSCIGRE
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Critical Span Determination
06:00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00600
800
1000
1200
1400
1600
1800
2000
Time (hr)
Cur
rent
(A
)
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Outstanding Issues
• Is the critical span being monitored?– define virtual poles, incl. wind speed up factors
• Conductor temperature vs. mid-span sag?• Resolution and reliability of weather data• Limited (high current) PLS training data• Ratings for other in-circuit components?• Modified network protection settings• Likelihood of joint hotspots?
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Future Plans
• 10-20% line rating increase expected in most sheltered locations– High wind, low load, one circuit out of service
• Re-conductoring and pole raising programme– Increase summer minimum rating
• Extension to other circuits• Dynamic line rating, dependent on (1+ hr)
weather forecast
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Dynamic Monitoring of Overhead Line Ratings in Wind Intensive Areas
Dr. Damian Flynn