Dynamic Monitoring of Overhead Line Ratings in Wind Intensive Areas

Dr. Damian Flynn

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

Factors Affecting Line Rating

• Conductor material + dimensions• Wind speed and direction• Solar radiation• Ambient temperature• Humidity and precipitation• Average conductor temperature• Permissible conductor sag

Measurement Methods

• Conductor sag• Conductor tension• Vibration modes• Meteorological / weather data

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

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

Monitored Signals

• Wind speed + direction• Solar radiation flux• Ambient temperature• Conductor temperature • Conductor current

• 20 locations @ 5 minute intervals

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

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

Wind Speed Variability

0

5

10

15

20

0 5 10 15 20 25

Ambient Temperature (C)

Win

d S

peed

(m

/s)

Wind Tunnel Testing

Load Current Step - 550 AA

mbi

ent T

empe

ratu

re (C

)

Time (min.)

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

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

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

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

Dynamic Conductor Rating

• Estimate average conductor temperature

Conductor length

Conductor catenary sag

• Estimate maximum current per monitored section

Identify limiting line section

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

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

)

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?

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

Dynamic Monitoring of Overhead Line Ratings in Wind Intensive Areas

Dr. Damian Flynn