Heinputter 2

Recommendation for commissioning testing
of medium voltage cables

The recommendation
© 2011 SebaKMT – MADE in GERMANY 2
Recommendation for commissioning
testing of medium voltage cables.
Includes:
 Sheath testing
 Withstand testing
 PD testing

 The treatment recommendation was created by the same work group,
which was responsible for the development of the VDE Cable Data Base
 Members of this working group are specialists of
- 18 Power Utilities
- 4 Universities
- 4 Service providers for testing and diagnosis
- 1 Accessory manufacturer
- 1 Cable consulting company
- 4 Manufacturers of PD measuring systems
Note: VDE cable database is a web-based database where PD measurements are stored
and where also the PD affected accessories has been inspected. This get a better
knowledge about the type of faults and its remaining life time. (www.VDE-Kabeldatenbank.de)
Initiators

 The experience of 20 years commissioning testing with 0.1 Hz VLF test
voltage indicate, that by a voltage test, only the very serious workmanship
failures are detected.
 There is a large variety of workmanship failures, which pass the com-
missioning tests, and fail only after several months or years of operation.
Target
 Fulfillment of the statutory requirements of the Operation Safety Act, the
BGV A3 and the VDE 0105 in respect to the commissioning test of newly
installed resp. modified electrical systems.
 Quality control of newly installed cables/ accessories by PD testing
 Gaining information for the condition assessment of cable systems
Motivation

Sheath Material PE PVC
Identification 2Y Y
Cable types (examples) NA2XS(F)2Y NA2XSY
Test voltage type DC DC
Test voltage level < 5 kV < 3 kV
Test duration < 5 min < 5 min
Typical leakage current < 100 µA/km < 800 µA/km @ 3 kV
Table 1: Test voltage levels and requirements
Contents
Cable sheath testing

N A 2X S 2Y 1 x 150 rm /25 12/20 kV
Norm cable acc. to DIN VDE
Conductor Material (A = Al / C = CU)
Shield (S = Cu / K = Pb)
Dielectric (2X = XLPE / Y = PVC)
Sheath (2Y = PE / Y = PVC)
Description of German abbreviations of cables
Contents
Cable sheath testing

Table 2: Overview of the voltage levels and durations to be used for plastic
and paper mass impregnated MV cables after repair or reallocation.
Insulation DC AC 45 Hz < f < 65 Hz AC f = 0,1 Hz
Test Level
UT = x Uo
Test
duration
min
Test
Level
UT = x Uo
Test
duration
min
Test Level
UT = x Uo
Test
duration
min
PVC Uo/U=6/10 kV
34 to 48 kV
Uo/U=12/20 kV
67 to 96 kV
Uo/U=18/30 kV
76 to 108 kV
15 to 30 2 30
XLPE, PE 2 60 3 60
PILC and mixed
cables with PVC
Uo/U=6/10 kV
34 to 48 kV
Uo/U=12/20 kV
67 to 96 kV
Uo/U=18/30 kV
76 to 108 kV
15 to 30 2 30 3 30
Mixed cables of
XLPE/PE with
PVC and PILC
2 60 3 60
Contents
Cable withstand testing (aged/ in-service cables)

Experiences of 20 years commissioning tests with 0.1 Hz VLF test voltages
indicated that this reveals only the very serious workmanship failures. There
is a large variety of workmanship issues which pass the VLF commissioning
tests, and fail only after several months/ years of operation under load.
Field statistics on newly installed cables indicates that test failures appear
within 15 to 30 minutes of operation. Test durations of 60 minutes produced
no additional information or results. Therefore, a test duration of 30 minutes
is considered as sufficient.
A significant amount of the faults that are probably not detected during the
withstand tests can be detected and localized by an additional partial
discharge measurement.
Testing of cable insulation after new installation of pure XLPE Cables
Contents
Cable withstand testing (new cables)

PD Measurements for commissioning tests
PD measurements allows to check the cable installation quality as well
as the condition of the complete system installation. Potential fault
spots can be detected in an early stage, and an evaluation of the
system and a budgeting of the required investments can be made.
A fundamental rule is:
Partial discharges occurring at U0 indicates a high risk of operating.
PD measurement test systems with the following type of voltages are
commercially available:
 0.1 Hz VLF (VLF – Very Low Frequency)
 20 – 300 Hz AC (AC – Alternating Current)
100 – 500 Hz damped AC ( DAC – Damped AC)
Contents

PD Measurement for quality assurance on newly installed systems
Newly installed cable accessories are, with a correct installation, PD free up
to at least 1.7 U0.
Field experiences showed that some types of accessories require several
load changes resp. temperature cycles, before they are PD free. This has
to be considered during the evaluation, or the PD test has to be repeated
after some load cycles.
The voltage has to be increased in steps up to the maximum test voltage
level. Possible PD signal have to recorded.
The test voltage has to be present for a sufficient duration to enable a
reliable detection of fault spots and to confirm the dielectric strength.
Contents

PD Measurement for quality assurance on newly installed systems
For different voltage types, the following test procedure is recommended:
0,1 Hz VLF - Stepwise increase of the test voltage up to 2 U0
- 10 minutes stress duration @ 2 U0 to test the
dielectric strength and operational readiness
20 – 300 Hz - Stepwise increase of the test voltage up to 2 U0
- 5 minutes stress duration @ 2 U0 to test the
100 – 500 Hz DAC - Stepwise increase of the test voltage up to 1.7 U0
- VWD (multiple test 50 cycles) @ 1.7 U0 to test the
Contents

Test result Evaluation Recommendation
No detectable
PD
Test passed Requirement BNL < 100 pC (BNL = background noise level)
For cables with high attenuation (during calibration with 1000 pC, no end
reflection detectable) the PD measurement must be performed from
both ends.
Ui < Uo Test not passed Replacement of the affected accessories, new measurement on the new
installed accessory (confirmation of the PD fault spot only based on
visible installation errors, there are not PD tracks visible)
Entry into www.VDE-Kabeldatenbank.de)
For operational reasons, a temporary net operation after passed test
acc. to table 2 is permittable.
Ui between 1
and 1.7 Uo
Commissioning
of the cable
system possible,
but repeated
tests after 4 to 8
weeks
Result of the repeated measurement:
- If Ui  1.7 Uo the test is passed
- If Ui < 1.7 Uo the test is not passed
-Replacement of the affected accessories (visual inspection to identify
the installation errors and PD fault spots (Voids, de-lamination,
tracking/PD erosion) Entry into www.VDE-Kabeldatenbank.de)
In exceptional situations, at Ui between 1.2 and 1.7 Uo, the system can
be released for continuous operation. In this case annual repeated
measurements to control the stability of Ui have to be performed.
Contents
Table 3: Evaluation and recommendation of measurement results

Case Procedure Requirements
New cables
(completely new installation)
- Sheath testing
- 0.1 Hz VLF test
alternatively
- PD measurement
Table 1
Table 2, Part 2.2
Table 3
Aged cables
(Fault elimination, partial
replacement, re-jointing, loop
insertion
- Sheath testing
- 0.1 Hz VLF test
alternatively
- PD measurement
Table 1
Table 2, Part 2.2
Table 3
The PD measurement has to be considered as a qualitative valuable part of the
commissioning test
Contents
Final recommended procedures
Table 4: Recommendation for testing of MV cables

Contact
Name: Hein Putter
Telefon: 0049-1759361560
E-Mail: putter.h@sebakmt.com
Thank you for your attention!

For more info please visit our website:
www.sebakmt.com

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