Historical overview of MV and HV cables

1. History of Cable Systems
HISTORICAL OVERVIEW OF
MEDIUM & HIGH VOLTAGE CABLES
Nigel Hampton
Copyright GTRC 2012

2. History of Cable Systems
Objective
2
“To present the evolution of cables in time to understand
the lessons from the past: the legacy problems and their
solution”
Outline
• Timeline
• Cable components
• Legacy problems - Cables
• Current challenges

3. History of Cable Systems
Timeline
3

4. History of Cable Systems
Cable History
4
Historical perspective is
important, it tells us:
• What works
• What does not
• What is still out there
• What challenges it presents
• How large the problems may be
or become
• How to avoid mistakes

5. History of Cable Systems
Timeline 1812-1942
5
1812: First cables used to detonate ores in a mine in Russia
1942: First use of Polyethylene
(PE) in cables
1917: First screened cables
1870: Cables insulated with natural rubber
1880: DC cables insulated with jute in “Street Pipes” –
Thomas Edison
1890: Ferranti develops the concentric construction for
cables
1925: The first pressurized paper cables
1937: Polyethylene (PE) developed

6. History of Cable Systems
Timeline 1963-1990
6
1963: Invention of crosslinked polyethylene – XLPE
1990: Widespread use of WTR
materials - Be, Ca, De, Ch & US
1982: WTR materials for MV in USA & Germany
1967: HMWPE insulation on UG cables in the US (Unjacketed
tape shields)
1968: First use of XLPE cables for MV (mostly unjacketed,
tape shields)
1972: Problems associated with water trees (MV) and
contaminants (HV)
Introduction of extruded semicon screens
1978: Widespread use of polymeric jackets in US & Ca
1989: Supersmooth conductor shields for MV
cable in North America

7. History of Cable Systems
Insulation History - Global
7
Year
Voltage
(kV)
2000
1975
1950
1925
1900
600
500
400
300
200
100
0
Paper
Polymer
Type
Ref [11]

8. History of Cable Systems
AEIC Standards Development - MV
8
MV Cables
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1900 1920 1940 1960 1980 2000 2020
Year
Edition
Number
Laminated Insulation Extruded Insulation
Laminated Insulation:
AEIC CS1
Extruded Insulation:
AEIC CS8 (previous
CS5 and CS6)

9. History of Cable Systems
AEIC Standards Development – HV / EHV
9
Laminated Insulation:
AEIC CS4 (Low-
Medium Pressure)
AEIC CS2 (High
Pressure)
Extruded Insulation:
AEIC CS7, CS9 and
CG4
0
1
2
3
4
5
6
7
8
9
1920 1940 1960 1980 2000 2020
Edition
Number
Year
HV-EHV Cables
Laminated Insulation Low-Medium Pressure
Laminated Insulation High Pressure
Extruded Insulation

10. History of Cable Systems
Initial American Installations
10
Ref [7]

11. History of Cable Systems
From Edison’s to Today’s Cable
11
Edison “Street Pipe”
Picture: Brian Besconnal
Pictures: Prysmian
Picture: Southwire
Picture: Black, 1983

12. History of Cable Systems
Cable Components
12
6. Jacket (Recommended)
5. Metallic Shield
4. Insulation Shield or Screen
3. Insulation
2. Conductor Shield or Screen
1. Conductor
Picture: Southwire

13. History of Cable Systems
1. Conductor
13
“Carries the current”
• Resistance should be small to reduce power losses:
• Flexibility, weight and susceptibility to corrosion are
concerns together with economical issues such as
cost, availability, and salvage value
P = R x I2

14. History of Cable Systems
Conductor Characteristics
14
Conductor
Aluminum
Stranded Solid
Copper
Stranded
Blocked
Unblocked
Blocked
Unblocked

15. History of Cable Systems
2. Conductor Shield
15
With no conductor shield,
electric field lines are
concentrated, creating high
stress points at the
conductor/insulation interface.
“Provides for a smooth interface between the conductor and
the insulation”
Finite
Element
Simulation
High
Stress

16. History of Cable Systems
Conductor Shield Characteristics
16
Conductor Shield
Bonded
Conventional
Supersmooth
Superclean (SS/SC)
Conductor shields are semiconductive, so they are neither an insulator
nor a conductor. Semiconducting materials are based on carbon black
(manufactured by controlled combustion of hydrocarbons) that is
dispersed within a polymer matrix
On larger conductor sizes, tape shields are often used to prevent
material “fall-in” between the strands during manufacture

17. History of Cable Systems
3. Insulation
17
“Contains voltage between the conductor and ground”
• Must be clean
• Must have smooth interfaces with the conductor
and insulation shields
• Must be able to operate at the desired:
– Electrical Stress
– Temperatures

18. History of Cable Systems
Insulation - MV
18
Insulation
Laminated Extruded
PILC Thermoplastic Thermoset
HMWPE XLPE
WTR XLPE
EPR
Prior Technologies
Today’s Technologies

19. History of Cable Systems
MV Cable “Installed Capacity” In USA
19
Oldest Youngest
Ref [18]

20. History of Cable Systems
MV Extruded Cable Installed in USA
20
Year
MV
cables
installed
in
the
US
(Millions
of
ft)
2000
1994
1988
1982
1976
1970
1964
7000
6000
5000
4000
3000
2000
1000
0
EPR
TR XLPE
XLPE
HMWPE
Data courtesy of Glen Bertini
Ref [18]

21. History of Cable Systems
Insulation – HV / EHV
21
Insulation
Laminated Extruded
Self
Contained
Thermoset
XLPE
EPR
– HV only
Pipe Type
PPL
- EHV only
Paper
Prior Technologies
Today’s Technologies

22. History of Cable Systems
Examples of Laminar Insulation Cables
22
Picture: Southwire
Pictures: Prysmian

23. History of Cable Systems
Examples of Extruded Insulation Cables
23
Pictures: Southwire
Pictures:
Prysmian

24. History of Cable Systems
4. Insulation Shield
24
“Keeps the voltage and stress within the insulation”
With no insulation shield,
electric field lines are
concentrated, creating
high stress points on the
outside surface of the
insulation.
Finite
Element
Simulation
High
Stress

25. History of Cable Systems
Belted Cables
25
• Early laminated cables had a “belt” of insulation over the
core insulation.
• This led to
tangential
stresses that
were a cause of
a lot of early
failures
Finite
Element
Simulation

26. History of Cable Systems
Conductor and Insulation Shield (CS & IS) Effect
26
When both shields are:
• smooth
• intact
Then, electric field lines
are uniform, with a
controlled electrical
stress distribution.
Finite
Element
Simulation

27. History of Cable Systems
Insulation Shield – MV, HV, and EHV
27
Laminated Insulation
Carbon Black Paper
Perforated metallized paper
Preferred in North America, Asia & parts of
Europe.
Thought to permit easier termination & splicing
of cables but service performance is very
dependent upon the workmanship / training of
the installer, which is often variable
Often same
compound as CS

28. History of Cable Systems
Types of Metallic Shields
28
Metallic Shield
Tape
Copper
Aluminum
Copper
Laminated
Sheath
Stainless
Steel
Aluminum
Copper
Lead
Corrugated
Sheath
Concentric
Copper Wire
Wire
Flat Strap
Extruded
Aluminum Aluminum

29. History of Cable Systems
Examples of Metallic Shields
29
Courtesy of Southwire
A B C D E
A – Welded Copper Corrugated Sheath
B – Welded Aluminum Corrugated Sheath
C – Concentric Copper Neutrals
D – Copper Neutrals with Copper
Composite Laminate Sheath
E – Copper Neutrals with Aluminum
Composite Laminate Sheath
Pictures: Southwire

30. History of Cable Systems
Types of Jackets Materials
30
Jacket
Semiconductive
Special
Carbon black filled
co polymers Neoprene
Nylon
Polypropylene
LSF
Hypalon*
Standard
PE PP
PVC
LLDPE
MDPE
HDPE
* No longer available
Enhanced Grounding Chemical / Thermal Resistance

31. History of Cable Systems
Legacy Issues
Cables
31

32. History of Cable Systems
PILC Cables
32
• Differing designs
– Belted vs. shielded
– Jacketed vs. unjacketed
• Lead corrosion (PILC)
• Temperature performance and stability of impregnants
• Draining of compounds
– Dry insulations
– Collapsed Joints
• Overheating due to high dielectric losses
• Moisture ingress leading to overheating
• Loss of impregnant due to lead sheath leaks
• Combinations of the above

33. History of Cable Systems
Remaining PILC in US Networks
33
Where PILC
remains on the
system it retains
a significant
presence
Estimated for US
Utilities in 2010
(some utilities
segregated)
Ref [15]

34. History of Cable Systems
The PILC experience teaches us that today’s decisions
will be with engineers for a very long time
34
Ref [15]

35. History of Cable Systems
Extruded Cables
35
• Differing designs
– Jacketed vs unjacketed
– Extruded shields vs graphite shields
• Dirty insulation compounds (PE, early XLPE)
• Insulations that were susceptible to water treeing (PE , early XLPE)
• Poor manufacturing processes
– Open compound handling procedures
– Changing Formulations (EPR)
• Inadequate cable designs
– Unblocked conductors
– Unjacketed cables
– Cables with inadequate neutral designs
• Combinations of the above

36. History of Cable Systems
Current Challenges
36

37. History of Cable Systems
37
Percentages of failures of each component
Termination
1.4%
Joints
55.4%
Cable
43.2%
Accessories: Joints or splices, and Terminations
Percentage of Failures per each Component
Ref [17]

38. History of Cable Systems
38
Failure Modes
Overheat
4%
Dielectric
breakdown
10%
Aging
6%
Corrosion
4%
Moisture
4%
Event
3%
Manufacturing
problem
14%
Overload
2%
Maintenance failure
2%
Mechanical Damage
1%
Contamination
1%
Poor
workmanship
49%
Ref [17]

39. History of Cable Systems
Building a Reliable Cable System
39
Customer
Service
Application
Design Specs
Materials Manu-
facturing
Testing
Installation
Operation
Awareness