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
Typical Eskom Transmission Structures
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Typical Eskom Transmission Structures
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Typical Eskom Transmission Structures
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Min Cost vs. Reliability vs. Maintainability
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Maintainability of designs: Structures
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Maintainability of designs: Structures
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Maintainability of designs: Structures
Nylon Rope
7.0 m
7/3 m
Tfront
149 us
244 us
244 us
244 us
244 us
Test Sequence
Test 1
No Dummy
Test 2
No Dummy
Test 3
Dummy 7/3 m from positive
Test 4
Dummy 7/2 m from positive
Test 5
Dummy 7/3 m from negative
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Maintainability of designs: Hardware
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Maintainability of designs: Hardware
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Maintainability of designs: Hardware design
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Maintainability of designs: Adaptors
Operational facts considered: TOV’s and
clearances
ToV’s Caused by:
• Switching on the network
• Lightning ….
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
Safety Clearance distances
MINIMUM SAFE WORKING DISTANCES (CLEARANCES)
ESKOM STANDARD HIGH VOLTAGE LIVE WORKING (TST 41-91, REV2)
Nominal Circuit Phase to earth (mm) Phase to phase (mm)
voltage (kV)
AC 220
1700
2800
275
2000
3400
400
2800
4800
765
5500
9700
DC 533
4250
ONE DISTANCE – KEEP IT SIMPLE !!
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
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Conventional – Stick I suspension assembly 275 kV
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Conventional Bare hand I string
Conventional Bare hand I string
Conventional Bare hand I string
Conventional – Bare hand Strain assembly 220 kV
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Conventional – Bare hand Strain assembly 220 kV
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Insulated Aerial platform Bare Hand 765 kV
– Ins. change out
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Insulated Aerial platform Bare hand765 kV
– Ins. change out
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Insulated Aerial platform Bare hand 765 kV
- Spacer replacement
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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
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Aerial under slung 400 kV Insulator change out
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Aerial under slung 400 kV Insulator change out
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Aerial under slung 400 kV Insulator change out
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Aerial under conductor work 765 kV
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Aerial “Rack” or Skid work on earth cond.
Aerial Live Spray Washing
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Live Work Risks
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
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Operational info Eskom Transmission L/L
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
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.
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Questions
Thank you