Gate 3 Liaison Group

38kV Overhead Lines

Eoin Waldron

Overhead Networks Engineer

Asset Management

ESB Networks

Original 38kV Network System Current 38kV Network System

Introduction

• First lines were built by Siemens in late 1920s and early 1930s

• Currently there is 5,700kMs of 38kV Overhead Line

• There are a large amount of original Siemens lines still in service

• Over 4,000km of network is more than 10 years old

• Almost 60% of the network is over 30 years old

KMs of 38kV Overhead Line by Conductor Type

KMs

35 & 50 Copper

1003

KMs

Other

170

KMs

150 AAAC

567

KMs

200 & 300 ACSR

435KMs

100 ACSR

3407

Other

35 & 50 Copper

200 & 300 ACSR

150 AAAC

100 ACSR

38kV Overhead Network - Age Profile

0

200

400

600

800

1000

1200

1400

1600

Pre 1940 1940-49 1950-59 1960-69 1970-79 1980-89 1990-99 2000-09

38kV Overhead Network - Age Profile

0

200

400

600

800

1000

1200

1400

1600

Pre 1940 1940-49 1950-59 1960-69 1970-79 1980-89 1990-99 2000-09

38kV Overhead Network - Age Profile

0

200

400

600

800

1000

1200

1400

1600

Pre 1940 1940-49 1950-59 1960-69 1970-79 1980-89 1990-99 2000-09

Design History

• ESB adapted the German design in the

1940’s based on their own experience

• From 1940’s to 1980’s ESB built 38kV

lines on portal structures

• Mainly built with 92mm2 ACSR conductor

• Conductor suspended from double wood-

pole structure on strings of disc insulators

• Mainly Steel Towers on angle Positions

• Designed with span lengths of between

150m to 200m.

Design History

• In the 1980’s the design was changed to a

single pole design

• Still used 92mm2 ACSR conductor

• Conductor supported on pin-insulators

• Lines look more like Medium Voltage Lines

• Used heavier wood poles than Portal lines

• Usually Wood Poles at Angle Structures

• Maximum span length of 190m

Design History

• In the 1940’s the maximum design operating temperature for 92mm2

ACSR was 40oC.

• At that time it was not envisaged that lines would be loaded above

40oC

• Over time the maximum operating temperature was increased

• In the 1980’s the maximum operating temperature for ACSR

conductor was 60oC

• Lines were designed to give a minimum of 6.0m ground clearance at

maximum operating temperature

• In older ACSR lines the grease in the conductor is the limiting factor

Current Design

• All lines are now designed to operate at 80oC

• All lines designed since 2003 are designed to have a minimum of 7.0m

of ground clearance at maximum design temperature

• 7.0m clearance required where a line is being restrung with new

conductor or thermally up-rated

• The reasons for these changes is:

• Higher operating temperature – increased thermal capacity

• Higher ground clearance – increased safety margin under 38kV lines

Case Study – No. 1

• Existing 92mm2 ACSR line built before 1980 - Of which there are 2,000km

• Designed to 50oC and 6.0m of ground clearance

• Average span length of 150m

• Increase in load requires it to be thermally up-rated to 80oC

• Increase in Load of 6MVA

Sag @ 50oC = 3.43m

Using 13m Poles

13.0m

- 2.3m Foundation

- 0.6m Insulators

- 3.43m Sag

= 6.67m GC

6.67m

Ground Clearance OK

Case Study – No. 1

• Existing 92mm2 ACSR line built before 1980 - Of which there are 2,000km

• Designed to 50oC and 6.0m of ground clearance

• Average span length of 150m

• Increase in load requires it to be thermally up-rated to 80oC

• Increase in Load of 6MVA

Sag @ 80oC = 3.95m Using 13m Poles

13.0m

- 2.3m Foundation

- 0.6m Insulators

- 3.95m Sag

= 6.15m GC

6.15m

Ground ClearanceMust Have 7.0m

Sag @ 50oC = 3.43m

Case Study – No. 2

• Existing 92mm2 ACSR line built after 1980 on single wood poles

• Designed to 60oC and 6.0m of ground clearance

• Average span length of 150m

• Increase in load requires conductor to be changed to 150mm2 AAAC

• Increase in Load of 14MVA ~ 50% increase in capacity

Sag @ 60oC = 3.61m

Using 12m Poles

12.0m

+ 0.4m Insulators

- 2.3m Foundation

- 3.61m Sag

= 6.49m GC

6.49m

Ground Clearance OK

Case Study – No. 2

Sag @ 60oC = 3.61m

Using 12m Poles

12.0m

+ 0.4m Insulators

- 2.3m Foundation

- 4.04m Sag

= 6.06m GC

Sag of Mulberry

@ 80oC = 4.04m

Must Have 7.0m6.06m

Ground Clearance

• Existing 92mm2 ACSR line built after 1980 on single wood poles

• Designed to 60oC and 6.0m of ground clearance

• Average span length of 150m

• Increase in load requires conductor to be changed to 150mm2 AAAC

• Increase in Load of 14MVA ~ 50% increase in capacity

Re-Using Existing Material

• In general when a line is rebuilt all wood poles / crossarms /

insulators etc. are replaced

• Changing from 50mm2 Copper to 150mm2 AAAC

– Wishbone crossarms are not suitable for 150mm2 AAAC

– Single poles used on 50mm2 Copper are too light for 150mm2 AAAC

– 50mm2 Copper hardware not suitable for 150mm2 AAAC

• Changing from 92mm2 ACSR to 150mm2 AAAC / 300mm2 ACSR

– Heavier crossarms required for 150mm2 AAAC & 300mm2 ACSR

– In general poles would be replaced due to pole strength and ground

clearance

Thank You

Questions??