Dynamic Thermal Ratings for Overhead Lines Philip Taylor, Irina Makhkamova, Andrea Michiorri Energy Group, School of Engineering Durham University

Dynamic Thermal Ratings for Overhead Lines

Philip Taylor, Irina Makhkamova, Andrea Michiorri Energy Group, School of Engineering

Durham University

Energy GroupSchool of Engineering

Overview• Research Overview• Overhead Line Thermal Modelling

– Lumped Parameter– Computational Fluid Dynamics– Comparisons

• Thermal State Estimation• Further work


Research Aims• The use of dynamic thermal ratings to:

– Increase utilisation of existing power system assets.

– Facilitate increased capacities and energy yields for DG

– Develop a real time controller


Project Consortium

• Part funded by DIUS


Project Phases

• Thermal Modelling (OHL, UGC and TFMR)• Thermal State Estimation• DG constrained connection techniques• System Simulation• Network and Meteorological

Instrumentation• Open Loop Trials• Closed Loop Trials


What Do We Mean By Dynamic Thermal Ratings? Aim

To increase the energy transferred through the network under normal operating conditions

Without reducing component lifetime or network security

Measurements Availability of a limited

number of environmental measurements

Electrical measurements available from SCADA

How Exploit headroom which is available for a reasonable amount of time Never exceed the standard component continuous operation design

temperature

Lumped Parameter Modelling

of the Thermal State of OHL Conductors


Lumped Parameter Model – Standard comparison

IEC TR 61597 IEEE 738CIGRE WG 22.12 in ELECTRA 144 – 1992

The IEC model has been selected

0

400

800

1200

0 2 4 6 8 10 12v [m/s]

I [A

] IEEE

IEC

CIGRE'

Maximum current carrying capacity – models comparison

Conductor ACSR 175mm2 LYNX

Wd=90º, Ta=25 [ºC], Sr=0 [W/m2]

A

B

C


Lumped Parameter Model – Simulation

33kV

132kV

132kV

400kV

132kV

33kV

Local load

Local loadLocal

Generator

Network diagram and line characteristics

Voltage: 132kV, line length: 7km, conductor: ACSR 175mm2 LYNX

Town A

Town B

The network and its geographical location

Costal area, west coast, subject to sea breeze

Three directions for the line, the smallest rating has to be considered


Lumped Parameter Model – Simulation results

GWh/year

Yearly (summer) rating

762

Seasonal ratings 879

Daily ratings 1393

Hourly ratings 16960

200

400

600

800

1000

1200

1400

Jan

Mar

May

Jun

Aug

Oct

Dec

Time [months]

Rat

ing

[A].

Seasonal

Daily

Minimum daily rating compared with seasonal ratings

Weather data from Valley (Anglesey)

Comparison of energy transfer capacity for different rating period

The simulations suggest that consistent headroom is available when using daily or hourly ratings

CFD Modelling of the Thermal State of OHL

Conductors


Modelling the thermal state of ACSR 410 conductor exposed to cross wind

The outer diameter is 28.5mm

ASCR410: 7 steel strands surrounded by 27 aluminium strands.

Simplified geometry

M. Isozaki and N. Iwama. Verification of forced convective cooling from conductors in breeze wind by wind tunnel testing. (0-7803-7525-4/02, 2002 IEEE).

Outlet Conductor Inlet

Air domain

2-D calculation scheme


Modelling thermal state of ACSR 410 conductor exposed to cross wind

0

20

40

60

80

100

120

140

160

180

200

220

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Wind velocity, m/s

Tem

per

atu

re r

ise,

K Published data

Empirical data (text book)

CFD data


Modelling the thermal state of LYNX conductor exposed to cross wind

Lynx consists of 30 strands of an aluminium wire and 7 strands of a steel wire.

Outer diameter is 19.5 mm

Real geometry Simplified geometry Computational grid


Modelling the thermal state of Lynx conductor exposed to cross wind

292

294

296

298

300

302

304

306

308

310

312

314

316

318

320

322

324

326

328

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Wind velocity,m/s

Tem

per

atu

re i

n t

he

con

du

cto

r, K

2-D model

3-D model

Design core temperature (ER P27)

The ambient temperature is 293 K; I = 433A.

CFD predicts 16 K headroom existence


Impact of solar radiation on the conductor temperature

•Additional source of heat emanates from solar radiation

•q = α · d · s •α = solar absorption coefficient, this • varies from 0.3 to 0.9•d = diameter of conductor (m)•s = intensity of solar radiation (W/m2), • a typical value being 800 (W/m2)

20

27.37 27.7829.6 30.9

33.3

0

5

10

15

20

25

30

35

Te

mp

era

ture

, d

egre

es

C

1 2 3 4 5 6

Temperature in the Lynx conductor

1 Ambient temperature

2 Temperature of the conductor taking into account convection and radiation losses

3 Temperature of the conductor taking into account convection and radiation losses and temperature – dependent resistivity

4, 5, 6 Temperature of the conductor taking into account convection and radiation losses, temperature – dependent resistivity and solar radiation with insolation of 240W/m2, 400 W/m2, and 720 W/m2, respectively.

Initial conditions: Cross wind = 2 m/s, Current = 433A, T ambient = 293 K


Lynx conductor exposed to cross wind - comparison with measured data on distribution

network

DateTim

eAmbient Temperat

ure(deg. C)

Wind

Speed(m/s)

Windspeed Avg

(m/s)

Wind Directio

n(deg.)

Solar Radiati

on(W/m2)

Line

temperature

(deg C)

I (A)

Case 1:

27/03/2008 12:50 8.4 (0.4) 1.3 189 232 15.5 30.59

Case 2:

27/03/200820:15 7.6 (2.2) 3.5 86 0 10.0 83.13


CFD Model: the Lynx conductor exposed to cross wind - comparison with real data

Case 1

Case 2

280

281

282

283

284

285

286

287

288

289

290

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Wind velocity, m/s

Tem

per

atu

re,

K

data (deg C) CFD (deg C) Difference (deg C)

Case 1 15.5 9.9 5.6

Case 2 10.0 7.8 2.2


Lynx conductor exposed to parallel wind

The ambient temperature is 293 K; I = 433A

Calculation scheme

ConductorOutlet

Inlet Air domain

290

300

310

320

330

340

350

360

0 2 4 6 8 10 12 14 16

Te

mp

era

ture

, K

Cross wind

Parallel wind

Temperature of the conductor vs. velocity for cross and parallel wind conditions

Wind velocity, m/s

Tem

pera

ture

, K

Aluminium

Steel core

Conductor

Comparison Between CFD and Lumped Parameter

Modelling of the Thermal State of OHL

Conductors


CFD / Lumped comparisonCross wind, temperature

295

300

305

310

315

320

325

0 1 2 3 4 5

Ws [m/s]

Tc

[K]

T [K] Lumped

T [K] CFD

Conductor temperature. CFD/Lumped parameter comparison

Conductor: ACSR 175mm2 LYNX, Ta=20'C, I=433A, Wd=90'


CFD / Lumped comparisonParallel wind, temperature

Conductor temperature. CFD/Lumped parameter comparison

Conductor: ACSR 175mm2 LYNX, Ta=20'C, I=433A, Wd=0'

300

310

320

330

340

350

360

0 1 2 3 4 5

Ws [m/s]

Tc

[K]

T [K] Lumped

T [K] CFD

Thermal State Estimation


State Estimation - Objectives Produce reliable estimates of maximum current carrying capacity of power system components Identify minimum and most probable value Possibility to calculate a rating for a given probability/risk P

DF

min maxmode

variance

1

CD

F

min max

average

P

Rating


0

50

100

150

200

250

00 02 04 06 08 10 12 14 16 18 20 22 00

Time [h]

Rat

ing

[MV

A]

min

mean

max

Static

State Estimation – Simulation results

Minimum, mean and maximum hourly rating


Conclusions

• Encouraging results regarding potential headroom

• Lumped parameter models more conservative than CFD

• Initial comparisons to real data encouraging• Need to further validate models with real data• Need to validate state estimation with real data• Site installation• Trials (open and closed loop)

Documents

Dynamic Thermal Ratings for Overhead Lines Philip Taylor, Irina Makhkamova, Andrea Michiorri Energy Group, School of Engineering Durham University