Technical Bulletin
Technology
Title: THE USE OF OUTDOOR CABLE Unique Identifier:
240-87315751
TERMINATIONS WITH A
SPECIFIC CREEPAGE
DISTANCE OF 33MM/KV AT THE Alternative Reference Number: <n/a>
KOEBERG NUCLEAR POWER
STATION (KNPS) FOR THE
KOEBERG-ANKERLIG 132KV
Area of Applicability:
Engineering
CABLE SYSTEM PROJECT
Documentation Type:
Technical Bulletin
Revision:
1
Total Pages:
6
Next Review Date:
n/a
Disclosure Classification:
Controlled
Disclosure
Compiled by
Functional Responsibility
Authorized by
Kevin Kleinhans
Thavenesen Govender
Bheki Ntshangase
Chief Engineer – Insulation
Chief Engineer – Insulation
Senior Manager: PDE – HV
Plant
Date:
Date:
Date:
PCM Reference: <xxxxxx>
SCOT Study Committee Number/Name: <Number or name>
Document Classification: Controlled Disclosure
THE USE OF OUTDOOR CABLE TERMINATIONS WITH A
SPECIFIC CREEPAGE DISTANCE OF 33MM/KV AT THE
KOEBERG NUCLEAR POWER STATION (KNPS) FOR
THE KOEBERG-ANKERLIG 132KV CABLE SYSTEM
PROJECT
Unique Identifier: 240-87315751
Revision:
1
Page:
2 of 6
Content
Page
Revision history .................................................................................................................................................. 3
1.
Definitions and Abbreviations ...................................................................................................................... 3
1.1 Definitions ........................................................................................................................................... 3
1.2 Abbreviations ...................................................................................................................................... 3
2.
Background ................................................................................................................................................. 3
2.1 Weskusfleur (future KNPS transmission substation) air insulation level ........................................... 3
2.2 Current specific creepage distance level of the 132kV outdoor terminations .................................... 4
2.3 Cable specification ............................................................................................................................. 4
3.
Use of 33mm/kV outdoor termination .......................................................................................................... 4
3.1 Using extreme measures (no compromise on an SCD of 38mm/kV) ................................................ 4
3.2 Identified risks from the OEM associated with changing the current 33mm/kV outdoor
termination design to 38mm/kV.......................................................................................................... 4
3.3 Statistical analysis of the probability of pollution flashover ................................................................ 5
3.4 The proposed new KNPS transmission substation ............................................................................ 6
4.
Conclusion ................................................................................................................................................... 6
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When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
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Document Classification: Controlled Disclosure
THE USE OF OUTDOOR CABLE TERMINATIONS WITH A
SPECIFIC CREEPAGE DISTANCE OF 33MM/KV AT THE
KOEBERG NUCLEAR POWER STATION (KNPS) FOR
THE KOEBERG-ANKERLIG 132KV CABLE SYSTEM
PROJECT
Unique Identifier: 240-87315751
Revision:
1
Page:
3 of 6
Revision history
Date
Rev.
Compiled by
Remarks
Dec 2014
1
KD Kleinhans
This is a new Technical Bulletin.
1.
Definitions and Abbreviations
1.1
Definitions
Specific Creepage Distance: creepage distance of an insulator divided by the line-to-line value of the
highest operating voltage across the insulator
Type tests: tests which are made upon completion of the development of a new arrester design to establish
representative performance and to demonstrate compliance with the relevant standard
1.2
Abbreviations
SCD: Specific Creepage Distance
KNPS: Koeberg Nuclear Power Station
NNR: National Nuclear Regulator
RTV: Room Temperature Vulcanized
KIPTS: Koeberg Natural Pollution Test Station
OEM: Original Equipment Manufacturer
SR: Silicone Rubber
MTBF: Mean Time Between Flashover
IST: Insulator Statistical Tool
GIS: Gas Insulated Substation
2.
Background
2.1
Weskusfleur (future KNPS transmission substation) air insulation level
KNPS is in an extreme pollution environment. As such, the reason for specifying a minimum SCD of
38mm/kV for an air insulated substation at the proposed new Weskusfleur site for KNPS is clearly stated in
the Technical Instruction: 13TI-031.
From this Technical Instruction we based our recommendation for any future air insulated equipment at
KNPS on specific reasons/requirements:
1)
In relation to the proposed Weskusfleur substation, the NNR wanted assurance that all reasonable
steps are taken to avoid the tripping of any busbars at a substation connected to KNPS, as well as
its feeder to the off-site supply (thus the current Acacia 132kV and the future Ankerlig 132kV
feeders).
2)
The historical measurements taken at Duine s/s were used as a good representative base for the
calculations of an SCD of air insulated equipment to be used in the KNPS area, and would thus
use these analyses for future KNPS expansions and the associated area.
3)
Only an open / aerodynamic and alternating shed profile would be used for air insulation in this
area. This requirement will not be compromised.
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Document Classification: Controlled Disclosure
THE USE OF OUTDOOR CABLE TERMINATIONS WITH A
Unique Identifier: 240-87315751
SPECIFIC CREEPAGE DISTANCE OF 33MM/KV AT THE
Revision:
1
KOEBERG NUCLEAR POWER STATION (KNPS) FOR
THE KOEBERG-ANKERLIG 132KV CABLE SYSTEM
Page:
4 of 6
PROJECT
4)
Assumptions were made around the type of material used in testing. Only LAPP silicone rubber
longrods and hollow core insulators were used in the tests. Historically the LAPP material has
performed well at KIPTS, however it was accepted being a representative measure of silicone
rubber materials currently being manufactured.
5)
According to IEC60815, the respective SCD’s for pollution levels (in mm/kV) are sequential in the
following manner: 16, 20, 25, 31, 38, 45, etc. This was the reason for doing the statistical iterations
at 31mm/kV and then at 38mm/kV, and so on.
6)
All statistical analyses were based on the amount of outdoor insulators to be used in an air
insulated substation at Weskusfleur substation.
2.2
Current specific creepage distance level of the 132kV outdoor terminations
The reason for specifying a minimum SCD of 38mm/kV is based on the above requirements, and for ease of
interchangeability for any future outdoor HV equipment at KNPS. Currently, the maximum SCD for 132kV
outdoor terminations at KNPS is not more than 31mm/kV and additionally for porcelain, RTV silicone rubber
coated. These current outdoor terminations have shown excellent pollution performance and to date have
had zero pollution-related flashovers.
2.3
Cable specification
The required 132kV cable specification for the current Acacia 132kV and the future Ankerlig 132kV feeders
were completed, and the tender for the installation was awarded before the Technical Instruction: 13TI-031
was introduced to the business. This project became aware of the Technical Instruction by the time that
installation of this 132kV cable was being executed.
3.
Use of 33mm/kV outdoor termination
3.1
Using extreme measures (no compromise on an SCD of 38mm/kV)
There are certain extremes that we could follow:
a)
To be absolutely sure, we would have to redo the insulator pollution curves for this 33mm/kV
outdoor termination unit (costing in excess of R1million per test, and taking at least 6 months to 1
year).
b)
The other option would be to re-design the cable sealing end to conform to a minimum SCD of
38mm/kV. This would mean a total re-test of the entire cable system (as is required by IEC), and
this would cost 3-4 times more than option (a), and take even longer.
3.2
Identified risks from the OEM associated with changing the current 33mm/kV
outdoor termination design to 38mm/kV
The OEM was consulted in the decision to change the current 33mm/kV outdoor termination design to a
38mm/kV design, and even though a 38mm/kV outdoor termination unit had been conceptually designed, the
OEM commented that “although the changes are possible, it needs to be noted that the desired outdoor
termination bushing was not type tested in the proposed arrangement and there is a probability of
unforeseen risks performing these changes with regard to the sealing method for the cable at the bottom of
the outdoor termination, possible oil leaks over the installation life, and the bushing behaviour in the event of
flashover”.
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When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
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Document Classification: Controlled Disclosure
THE USE OF OUTDOOR CABLE TERMINATIONS WITH A
SPECIFIC CREEPAGE DISTANCE OF 33MM/KV AT THE
KOEBERG NUCLEAR POWER STATION (KNPS) FOR
THE KOEBERG-ANKERLIG 132KV CABLE SYSTEM
PROJECT
3.3
Unique Identifier: 240-87315751
Revision:
1
Page:
5 of 6
Statistical analysis of the probability of pollution flashover
Consider the table below, focussing on the lines highlighted in red:
400 kV
132 kV
Mean Time Between Flashovers (Years)
SCD (mm/kV)
31
Pollution Type
A
B
A
B
A
B
A
B
Porcelain Post (189)
0.1
<2
10
<2
> 300
6
> 300
872
RTV SR Coated Porcelain Post (Mace) (189)
18
19
> 300
>20 000
> 300
> 20 000
> 300
> 20 000
RTV SR Coated Porcelain Post (Midsun)
(189)
0.3
2
> 300
> 20 000
> 300
> 20 000
> 300
> 20 000
SR Hollow Cores (294)
> 300
29
> 300
> 20 000
> 300
> 20 000
> 300
> 20 000
SR Composite Longrods (387)
> 300
90
> 300
15 238
> 300
> 20 000
> 300
> 20 000
Porcelain Post (211)
0.1
<2
9
<2
> 300
6
> 300
847
RTV SR Coated Porcelain Post (Mace) (211)
15
18
> 300
> 20 000
> 300
> 20 000
> 300
> 20 000
RTV SR Coated Porcelain Post (Midsun)
(211)
0.3
<2
> 300
> 20 000
> 300
> 20 000
> 300
> 20 000
SR Hollow Cores (162)
> 300
37
> 300
> 20 000
> 300
> 20 000
> 300
> 20 000
SR Composite Longrods (489)
> 300
89
> 300
14 172
> 300
> 20 000
> 300
> 20 000
38
46
55
NOTE: Pollution Type A is forty Pre-deposited ESDD2% = 0.165 mg/cm2 pollution events with natural critical wetting per year,
and Pollution Type B is one Instantaneous conductive fog pollution event with ESDD = 0.4 mg/cm2 per year.
The rows in red represent the statistical analyses performed on the LAPP composite hollow cores (294
x 132kV units, and 162 x 400kV units), and we can see that statistically for Type A pollution (pre-deposit) the
composite hollow core at 31mm/kV has an exceptionally low chance of flashing over during its lifetime with a
MTBF in excess of 300 years. If we focus on the column for Type B pollution (with one Instantaneous
pollution event @ 0.4 mg/cm2 per year), we have a statistical probability of flashover every 29 years at
132kV.
Using the IST we calculated the statistical probability of flashover for the 33mm/kV outdoor terminations only
(since we are still dealing with GIS), and the following results were obtained:
Mean Time Between Flashovers (Years)
SCD (mm/kV)
Pollution Type
132 kV
Cable Terminations (3)
33
A
B
> 1000
> 1000
KNPS had requested that any Transmission installation connected to it shall at minimum have a probability
of flashover of not more than 1 in 100 years. Based on the preceding results, a reasonable inference can be
drawn that the flashover rate will meet this performance limit. The above, even though for a smaller sample
one would have a larger error, does still give us confidence that the installed cable would easily comply with
the KNPS requirement.
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When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
to ensure it is in line with the authorized version on the WEB.
Document Classification: Controlled Disclosure
THE USE OF OUTDOOR CABLE TERMINATIONS WITH A
SPECIFIC CREEPAGE DISTANCE OF 33MM/KV AT THE
KOEBERG NUCLEAR POWER STATION (KNPS) FOR
THE KOEBERG-ANKERLIG 132KV CABLE SYSTEM
PROJECT
3.4
Unique Identifier: 240-87315751
Revision:
1
Page:
6 of 6
The proposed new KNPS transmission substation
The existing 400/132kV GIS at KNPS is now due for major refurbishment in order to improve the reliability of
the system. KNPS also intends to increase generated power through a project called Thermal Power Uprating. The increased power will result in the existing 400kV GIS busbars being overloaded under certain
contingencies. Thus a new 400/132kV Transmission yard will be constructed at KNPS, starting in the next 2
years. This would mean that any current installations would only be operational for the next ±5 – 8 years,
before being linked to the new Transmission yard. It means that this 132kV Brugg cable would be installed
and operated for not more than 8 years, further limiting the risk of a flashover during this period.
4.
Conclusion
Considering the above, the 33mm/kV outdoor termination from Brugg Cables can continue to be used in this
application. This does however not detract from the fact that the Technical Instruction: 13TI-031 is still valid
and in force for the remaining equipment to be installed.
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