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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