Benchmarking of cable condition monitoring methods ... · 6 different cables XLPE/CSPE ......
Transcript of Benchmarking of cable condition monitoring methods ... · 6 different cables XLPE/CSPE ......
Benchmarking of cable condition monitoring methods – lessons learned from a recent IAEA
co-ordinated research programme
Dr Sue BurnayJohn Knott Associates Ltd, UK
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Objectives of IAEA programme
Identify practical condition monitoring methods for cable insulation & jacket materials of interest to NPPs Methods that can trend degradation Suitability for ageing assessment
Assess the reproducibility of these methods Benchmarking using different test laboratories Identify ways to improve test methods
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Participants & materials
17 active participants from 13 different countries, plus several observers
6 different cables XLPE/CSPE (Rockbestos, USA) EPR/EVA (Eupen, Belgium) PEEK/XLPO (Habia, Sweden) SiR/SiR (Hew, Germany) XLPO/XLPO (Shanghai Special Cable, China) EPR/EPR (Changzhou Bayi Cable Co., China)
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CM methods included in programme
Mechanical Elongation at break (EAB) Indenter (IM) Recovery time
Chemical/thermal Oxidation induction time
(OIT) Oxidation induction
temperature (OITP) Thermogravimetric analysis
(TGA) Fourier transform infrared
spectroscopy (FTIR)
Electrical Dielectric loss (Tan delta) Dielectric spectroscopy Insulation resistance (IR) Time domain reflectometry
(TDR) Frequency domain
reflectometry (FDR)
Other Ultrasonic velocity Density
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Overall plan
Each lab decided which materials and CM methods to test
Labs prepared their own samples from whole cable
Test method agreed at start of programme Comparison of unaged data initially, method revised if
necessary Labs did thermal ageing at agreed temperature Limited no. of radiation aged samples Data collated in standard format
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Main concern – variability between labs
Initial results on unaged material – update to test methods
On aged materials, variability was considerable for some CM methods
Important to understand reasons for variability
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Variability between labs – EAB (1)
CSPE jacket (Rockbestos)
0
100
200
300
400
500
600
0 500 1000 1500 2000 2500
Ageing time at 120˚C (hr)
EAB
(%)
AMSLABOR-SCKVEIKIVUJENIST
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Variability between labs – EAB (2)
EPR Insulation (Eupen) - Black
0
100
200
300
400
500
600
700
0 2000 4000 6000 8000 10000
Ageing Time at 135˚C (hr)
EAB
(%)
AMS
CNEA
LABOR-SCK
SECRI
VEIKI
VUJE
UJV
NIST
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Variability between labs – EAB (3)
EVA jacket (Eupen)
0
100
200
300
400
500
600
0 4000 8000 12000
Ageing time at 120 C (hr)
EAB
(%)
AMSLABORSECRIVEIKIVUJECNEANISTUJV
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Cable types
CSPE jacket – reasonably uniform thickness, easy to cut dumb-bell samples for EAB
EVA jacket – non-uniform thickness, moulded around insulated wires
EPR insulation on solid tinned Cu – very difficult to strip
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Reasons for variability - EAB
Test method – type of extensometer used Optical extensometer Clip-on extensometer Cross-head movement
Sample preparation – biggest source of variability Dumb-bell samples – removal of surface irregularities,
dual layers, wrap materials Tubular samples – method used to extract wire from
insulation Difficult to prepare specimens from aged cable
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Variability between labs – IM (1)
CSPE Jacket (Rockbestos)
0
5
10
15
20
25
30
35
0 500 1000 1500 2000
Ageing Time at 120⁰C (hr)
IM (N
/mm
)
AMS
KHNP
LABOR
AECL
INSS
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Variability between labs – IM (2)
XLPO Insulation (Shanghai)
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
0 1000 2000 3000 4000 5000 6000 7000
Ageing Time at 135⁰C (hr)
IM (N
/mm
)
AMSINSS (corrected)SECRIAECL
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Variability between labs – IM (3)
XLPO Jacket (Shanghai)
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
55.0
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Ageing Time at 135⁰C (hr)
IM (N
/mm
)
AMSSECRILABORINSS (corrected)AECL
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Reasons for variability - IM
Probe tip diameter (correction to standard) Sample temperature Force range used for analysis Clamping force Variation in sample thickness
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Recovery timeXLPO jacket (Shanghai)
0
1
2
3
4
5
6
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Ageing time at 135⁰C (hr)
Reco
very
tim
e (s
)
AECL
Only 1 lab testing this method Often shows larger change than for indenter e.g for this XLPO,
IM changes by factor of 2 and recovery time by factor of 5
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Variability between labs – OIT (1)
EPR insulation (Eupen)
0
10
20
30
40
50
60
70
80
90
100
0 1000 2000 3000 4000 5000 6000 7000
Ageing time at 135⁰C (hr)
OIT
at 2
40⁰C
(min
)
KHNP-green (250C)
SECRI-green
SECRI-black
SECRI-blue
SECRI-brown
NIST-black (230C)
NIST-green (230C)
AMS-yellow
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Variability between labs – OIT (2)
EPR insulation (Changzhou)
0
10
20
30
40
50
60
0 1000 2000 3000 4000 5000 6000 7000
Ageing time at 135˚C (hr)
OIT
at 2
40˚C
(min
)
SECRI
NIST
AMS
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Variability between labs – OITP
EPR insulation (Eupen) - yellow/green
150
170
190
210
230
250
270
290
310
0 1000 2000 3000 4000 5000 6000 7000
Ageing time at 135 C (hr)
OIT
P ( ⁰C
)
VUJE-blue
SECRI-Blue
SECRI-yellow/green
SECRI-brown
KHNP-yellow/green
NIST-black
NIST-yellow/green
SECRI-black
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Reasons for variability – OIT/OITP
Must use same set temperature throughout series of tests for OIT
Sample preparation for both OIT and OITP Particle size and packing Selection of sampled material (colour, dual layers) Analysis method – specified in IEC/IEEE standard but
may need to be done manually
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Variability between labs – FTIR
XLPE insulation (Rockbestos)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0 1000 2000 3000 4000 5000 6000 7000
Ageing time at 135C (hr)
FTIR
Pea
k ra
tio
KHNP 1735:1351NEL 1732:2917NEL 1507:2917NEL 3400:2917
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Reasons for variability – FTIR
Main problem is determining which peaks to compare –often not known before ageing programme starts
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Potentially useful CM methods
These have only been tested by 1 or 2 labs so there is no data on variability between labs
Methods showing trends with ageing (for at least some materials) Ultrasonic velocity Dielectric spectroscopy Frequency domain reflectometry (FDR)
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Ultrasonic velocityXLPO Jacket (Shanghai)
1400
1600
1800
2000
2200
2400
2600
0 1000 2000 3000 4000 5000 6000 7000
Ageing Time at 135°C (hr)
Ultr
ason
ic V
eloc
ity (m
/s) SNPSC
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Dielectric spectroscopy
Highlights the problem of electrical measurements on thermally aged materials – large step change in values as cable is dried
For irradiation at constant temperature, trends are more visible
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Frequency domain reflectometryEPR insulation (Eupen)
0%5%
10%15%20%25%30%35%40%45%
0 1000 2000 3000 4000 5000 6000
Ageing Time at 135 C (hr)
% C
hang
e fr
om B
asel
ine
Refle
ctio
n Co
effic
ient
AMS - blue (black)
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Summary of practical usefulness of CM methods for materials tested
Used a colour code to indicate practical usefulness of each CM method tested
This is specific to actual materials tested
Example – very useful
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Example - useful
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Example – potentially useful
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Example – not useful
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Summary of practical usefulness of CM methods for materials tested
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Lessons learned
Three critical areas for practical use of CM methods in ageing assessment Specification of test method Sample preparation method Data analysis
Specification of test method
All aspects must be tightly defined and consistent throughout monitoring programme Type of test equipment e.g. grips, extensometer for
EAB Test parameters e.g. OIT set temperature Identify those parameters that are critical to
reproducibility Not all parameters are critical e.g. cross-head speed in
EAB tests Ensure enough measurements are made to reduce
standard deviation of measurements
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Sample preparation
The most important factor in inter-lab variability For EAB need to define
Size of dumb-bells Surface treatment Removal of conductors from insulation Use of end-tabs for tubular insulation Type of grips
For OIT/OITP/TGA Selection of sample material e.g. dual layers Method of size reduction and particle size Packing of particles in test pan
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Data analysis
Check algorithms used in test equipment May need to analyse manually e.g. to define baseline
and threshold for OIT, OITP; force range used for IM In EAB, measurement of elongation relative to
start of test If using cross-head movement (not recommended)
define gauge length to be used Define how mean and standard deviation are
reported Do you discard outliers?
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Summary
Toolbox of useful CM methods available Several potentially useful methods identified Suitable CM methods are material dependent Test methods must be very well defined
Including sample preparation and data analysis Standards are being developed/revised for some CM
methods
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For more information
Summarised results are in IAEA-TECDOC-1825, can be downloaded from
http://www-pub.iaea.org/books/IAEABooks/11164/Benchmark-Analysis-for-Condition-Monitoring-Test-Techniques-of-Aged-Low-Voltage-Cables-in-Nuclear-Power-Plants
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