Eskom Transmission

Live Line Maintenance

Techniques and

Practices

Eric Marshall

Chief Eng Live Work

Eskom Transmission, South Africa

OVERVIEW

• Eskom Transmission Network and environment

• Typical structures

• Maintainability of designs

• Operational facts considered: TOV’s and clearances

• Maintenance requirements

• Live Work Techniques, tools and PPE

• Live Work Risks

• Operational info of Eskom Transmission Live Work Program

• Questions

Eskom EHV Transmission Network

Eskom Transmission Network

28 790 km of OHL

220 kV = 1 217 km

275 kV = 7 476 km

400 kV = 16 913 km

533 kV DC = 1 035 km

765 kV = 1 153 km

and growing….

Consisting of:

• 80 % Glass cap and pin

insulators

• 20 % Composite insulators

• Multi bundle phase conductor

(up to 6)

• Vast family of conventional and

cross rope structures

95 % of preventative and corrective

maintenance conducted live !!

Environment

Birds and associated pollution

Fires

Lightning

“Tuff” in Africa

1010

Typical Eskom Transmission Structures

Typical Eskom Transmission Structures

11

Typical Eskom Transmission Structures

12

Min Cost vs. Reliability vs. Maintainability

13

Maintainability of designs: Structures

1414

Maintainability of designs: Structures

1515

Maintainability of designs: Structures

1616

7.0 m

7/3 m

Nylon Rope

Tfront Test Sequence

149 us Test 1 No Dummy

244 us Test 2 No Dummy

244 us Test 3 Dummy 7/3 m from positive

244 us Test 4 Dummy 7/2 m from positive

244 us Test 5 Dummy 7/3 m from negative

Maintainability of designs: Hardware

1717

Maintainability of designs: Hardware

1818

Maintainability of designs: Hardware design

1919

Maintainability of designs: Adaptors

Operational facts considered: TOV’s and clearances

Controlled and managed by:

• Inhibiting auto re-close device

• No live work under lightning and thunderstorm activity

• Closing resistors used on circuit breakers

• Bypassing series capacitor banks

ToV’s Caused by:

• Switching on the network

• Lightning ….

Safety Clearance distances

ONE DISTANCE – KEEP IT SIMPLE !!

MINIMUM SAFE WORKING DISTANCES (CLEARANCES)

ESKOM STANDARD HIGH VOLTAGE LIVE WORKING (TST 41-91, REV2)

Nominal Circuit

voltage (kV)

Phase to earth (mm) Phase to phase (mm)

AC 220 1700 2800

275 2000 3400

400 2800 4800

765 5500 9700

DC 533 4250 -

Maintenance requirements

“Constrained Transmission network” – minimal outages available

As a result 95 % plus of routine maintenance is conducted

alive using various live work techniques

Activities includes mainly:

Insulator replacements

Spacer and damper replacements

Conductor repairs

Tools and equipment

In accordance with international

standards

• Conductive clothing IEC 60895

• Insulated foam filled tubes IEC 60855

• Insulated aerial platforms ASTM A92.2

and South African Occupational Health

and Safety Act

Tools and equipment

Live Work Techniques: Eskom Tx (220-765 kV)

Generally….

Combination of Stick and Bare hand techniques

utilising the following means:

• Stick or “distance” method

• Conventional climbing and rigging ladders

• Insulated aerial platform

• Rope Hoisting method

• Helicopter based Aerial under slung & skid

Conventional – Stick V suspension assembly 400kV

2727

Conventional – Stick I suspension assembly 275 kV

2828

Conventional Bare hand I string

Conventional Bare hand I string

Conventional Bare hand I string

Conventional – Bare hand Strain assembly 220 kV

3232

Conventional – Bare hand Strain assembly 220 kV

3333

Insulated Aerial platform Bare Hand 765 kV – Ins. change out

3434

Insulated Aerial platform Bare hand765 kV – Ins. change out

3535

3636

Insulated Aerial platform Bare hand 765 kV - Spacer replacement

Rope Hoisting method Bare hand 400 kV – Ins change out

Rope Hoisting method Bare hand 400 kV – Ins change out

Aerial under slung 400 kV Insulator change out

3939

4040

Aerial under slung 400 kV Insulator change out

4141

Aerial under slung 400 kV Insulator change out

4242

Aerial under slung 400 kV Insulator change out

4343

Aerial under conductor work 765 kV

Aerial “Rack” or Skid work on earth cond.

Aerial Live Spray Washing

4545

Live Work Risks

4646

Mechanical...• Failure of line hardware and insulators

• Failure of mechanical/hydraulic tensioning equipment

Electrical...

• Insulating tool failure and flashover

• Bridging of the air gap resulting in flashover

• Insulator flashover/failure

Other...

• Falling from heights

• Aviation related

• Driving to and from work site

Operational info Eskom Transmission L/L

4747

Resources

• 97 authorised live work staff - stick, bare hand and aerial techniques

• 5 In-house single engine helicopters and 10 Pilots

• 6 Insulated aerial platforms up to 765 kV

• Centrally managed and dispatched

• 7 geographically de concentrated operational units ( 7-15 man strong)

• In house training and assessments.

Governance and control

• Live Work Technology centrally managed and controlled

• 8 Live Work Standards and 21 Live Work Procedures

• Governed by Tx LWSC and Eskom LW CG

• Aviation regulated by Civil Aviation Authority

Questions

Thank you