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C.4.1 8th International Conference on Insulated Power Cables
C.4.1
Jicable11 19 23 June 2011, Versailles - France
ON-SITE TESTING WITH COMPACT AC TEST-SYSTEM AT THE FIRST 500 KV
XLPE CABLE PROJECT IN SOUTH AMERICA
Andreas WEINLEIN, Gero SCHRDER, Sebastian EBERT, Sdkabel GmbH,
Mannheim (Germany), [email protected],
[email protected], [email protected], Harald
GEYER, agea kull ag, Derendingen (Switzerland),
[email protected] ABSTRACT The first 500 kV XLPE cable project
in South America was delivered, installed and commissioned in
Colombia as turnkey project. Due to the given local logistical and
technical requirements a new compact on-site AC high voltage
resonant test system was designed.
The test-set consists of 4 pieces cylinder reactors all placed
transport locked in a 20 ft container suitable for a fast and
reliable erection of the test system on-site. The compact test-set
is rated for 540 kV.
The on-site test was carried out successfully in September 2010
including both, high voltage and PD tests.
KEYWORDS 500 kV XLPE cable system, compact on-site AC HV
resonant test system, PD measurement on-site, compact plug-in
sealing end, mobile spare phase
INTRODUCTION The first 500 kV XLPE cable project in South
America was delivered, installed and commissioned in Colombia in
September 2010.
The entire job was handled as turnkey project. Due to the given
local logistical and technical requirements a compact on-site AC HV
resonant test system was designed to carry out the AC HV
commissioning tests.
The XLPE cable connection consists of two systems (additionally
one spare phase) rated 500 kV with individual cable length between
750 855 m. The conductor cross section is 800 mm2 aluminium. Both
circuits are laid in flat formation in a vertical saddle
arrangement inside the cavern of the Porce III Hydro Power plant.
Total 7 pieces of factory pre-tested compact plug-in SF6 sealing
ends and 7 pieces of factory pre-tested and pre-assembled compact
plug-in outdoor sealing ends were installed.
The test-set consists of 4 pieces cylinder resonant reactors (3
t each) all locked for transport in a 20 ft container with
removable roof suitable for a fast and reliable erection of the
test-system on-site. The step-up transformer and frequency
converter including control unit for voltage and PD measurement are
placed in a 10 ft container. The entire transport weight of the
test-system is less than 24 t. Extension up to 6 resonant reactors
is considered and easy to implement. Because of the module-like
set-up the handling procedure on-site is optimized. The test-set is
rated for 540 kV, 11.6 A, max.170 nF cable capacitance (set-up
resonant reactors: 2 serial, 2 parallel) or for 280 kV, 23.2 A,
max. 680 nF cable capacitance (set-up resonant reactors: 4
parallel).
A full scale commissioning test of the test-set was carried out
in the cable manufacturers factory under full load conditions with
530 kV for the duration of 2 hours at a cable drum of a capacitance
of 170 nF. Additionally, a PD measurement at both plug-in test
cable sealing ends of test set-up was carried out. The test
frequency for this set-up was 20 Hz, representing the minimum
allowable frequency for AC voltage tests after installation acc. to
IEC 62067 [11].
The on-site after installation test with 493 kV / 1 h was
carried out successfully at all cables including the spare phase in
September 2010 comprising both, AC HV tests and PD
measurements.
The testing of the spare phase was carried out by phase-plugging
of the regular cable phase inside the GIB cable enclosure which was
performed in less than one day. This was possible because of both,
the modular set-up of the test-set and the advantages of the
compact plug-in sealing end system.
PROJECT DETAILS / REQUIREMENTS A turnkey project with 5.4 km 500
kV XLPE cable of type A2XS(FL)2Y 1x800 RM/150 290/500 kV was
planned, manufactured, delivered, installed and commissioned for
the hydropower project Porce III near Medelln / Colombia (Empresas
Pblicas de Medelln E.S.P.).
The road distance to the next Atlantic sea port is more than 600
km with very frequent unpaved road quality in very high mountain
regions.
Fig. 1: map of region Porce III in Colombia
The project consists of 2 systems with an approximate phase
length of 760 m. Additionally one spare phase of 855 m length was
supplied and installed. In total 7 pieces of factory pre-tested 500
kV compact plug-in SF6 sealing ends and 7 pieces of factory
pre-tested and pre-assembled 500 kV compact plug-in outdoor sealing
ends were installed:
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C.4.1 8th International Conference on Insulated Power Cables
C.4.1
Jicable11 19 23 June 2011, Versailles - France
Fig. 2 (left): 500 kV compact plug-in SF6 sealing end
Fig. 3 (right): 500 kV compact plug-in OSE
design AC test voltage to ground: 580 kV design impulse voltage:
1550 kV design switching impulse voltage: 1175 kV
Fig. 4: cable design
The two circuits connecting the main transformers with the
overhead lines are fixed in the cavern by means of a special
short-circuit approved cable saddle system where the cables are
laid in flat formation in vertical arrangement at 400 mm
distance.
Fig. 5 (left): 500 kV compact outdoor sealing ends
Fig. 6 (right): 500 kV cables fixed with saddle system
The concept of using the spare phase leads to a heightened final
position of the outdoor sealing end (middle phase) and a mobile
fixation of the concerning compact plug-in SF6 sealing end which
can be connected with any main transformer inside the transformer
cavern via the associated GIB enclosure. This concept allows to
replace a phase with the spare phase within a few hours. During HV
commissioning test this plug-in procedure has to be
demonstrated.
According to customers specification an AC HV test of the
insulation after installation acc. to IEC 62067 with a voltage of
1.7U0 = 493 kV for the duration of 1 h had to be carried out at
each phase including spare phase/s. For after-installation tests,
PD measurements are actually not required by IEC standards
[11].
Although each single cable and accessory is subject to routine
tests at the manufacturers lab, incidents during transport, cable
laying and installation can lead to unnoticed defects. In
consequence, after-installation tests of the insulation focus on
defects in cable accessories, e.g. interfacial problems, improper
positioning, cuts or scratches, contaminations etc. Such defects do
not necessarily lead to a breakdown during the HV test, bearing the
risk of breakdown later in service. Sensitive on-site PD
measurement significantly reduces this risk [4, 6, 8].
At each installed EHV accessory (Um 362 kV) a PD measurement is
carried out during AC voltage test of the insulation as activity of
quality assurance by Sdkabel GmbH [6, 7, 10].
Because of the required high test voltage and the secluded
region in the high mountains of South America it was nearly
unfeasible to organise AC HV test without final confirmed
completion date. As there is no appropriate test-set available in
South America and in order to be independent from test institutes
it was decided to specify an own compact AC HV test system with the
main focus on testing cable systems used as power plant links to
overhead lines, switchyard or GIS in regions difficult to reach.
The typical cable lengths of the power plant leads in EHV systems
are 200 - 1500 m, the conductor cross sections are typically 1200
mm2. For lower test voltages even longer cables can be tested.
Acc. to IEC 60840 for cables with Um 170 kV and IEC 62067 for
cables with Um > 170 kV requirements for the shape of suitable
AC test voltages and for the time of its application are
defined:
substantially sinusoidal waveform frequency between 20 and 300
Hz time of voltage application equal to 1 hour Both standards
define the AC test voltage level for on-site tests of newly
installed cable systems which depends on the cable rated voltage
with 1.1 - 2.0U0 [11, 12, 13]. Test voltages up to 1.2U0 can be
reached with insulated operation and voltage supply by a generator
which can increase the voltage step by step from approx. 20% up to
120% for short time duration (increasing of excitation voltage).
Acc. to both standards alternatively, a voltage of U0 may be
applied for 24 h. For EHV systems this method should be accompanied
by a PD measurement [4].
To cover all international and local requirements a test system
for a maximum capacitance of 170 nF at AC test voltage 540 kV was
specified. Because of limited availability of cranes on-site and
limited access routes the weight and design of one single resonant
reactor was specified to be as minor as possible also considering
the minimal allowed frequency of 20 Hz. To carry out a PD
measurement at each accessory of a cable system on-site this
compact mobile test system has to be free of internal PD and free
of corona up to the maximum test voltage of 540 kV (PD 5 pC).
1 conductor aluminium, round stranded
2 conductor screen conductive XLPE-compound
3 insulation XLPE
4 insulation screen conductive XLPE-compound
5 bedding swelling tape, semi-conducting
6 wire screen copper wires
7 bedding swelling tape, semi-conducting
8 bedding fabric tape, semi-conducting
9 metallic sheath copolymer-laminated aluminium
10 outer sheath HDPE, outer conductive and flame-retardant
layer
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C.4.1 8th International Conference on Insulated Power Cables
C.4.1
Jicable11 19 23 June 2011, Versailles - France
DESIGN OF TEST-SET A system was designed with following
characteristics:
power supply (50/60 Hz): 3 x 400 V power: max. 150 kVA output
voltage: 0 540 kV output current: max. 11.6 A nominal power: 6265
kVA frequency range: 20 144 Hz capacitance range: 3.3 nF 170 nF
duty cycle (at 20C / 100%): 2 h ON / 10 h OFF quality factor: >
100 weight reactor: approx. 3000 kg nos. reactors: 4 pieces weight
exciter transformer: approx. 1400 kg weight frequency converter:
approx. 330 kg humidity (no condensation): < 95% system weight
incl. containers: approx. 18 t + 6 t erection time of test-set
on-site: < 4 h
Fig. 7: 540 kV layout of test system
High test power can only be efficiently generated by mobile
resonant test systems, where the weight to-power ratio and feeding
power demand is relatively low and the transport volume is
manageable [2]. When operated at resonance, the feeding power is
reduced to the real power loss in the test circuit. Only the actual
power loss has to be supplied in order to maintain the test
voltage. The quality factor Q is the ratio of reactive power and
real power. The losses in the resonant reactors are by far higher
than inside the XLPE cable system. Frequency tuned resonant
circuits (ACRF) consist of constant inductance(s), the capacitive
load and a control module with frequency converter unit [5].
Fig. 8: design of resonant reactor size DSH6W
The design of the reactor is based on the experience with
smaller units which were developed for on-site testing of GIS
installations since 1979 [01]. The reactors consist of two high
voltage windings in series. Both windings enclose a common bar core
at half potential. In difference to most other reactors, the DSH6W
has no closed iron core with divided air gaps. The magnetic field
generated in the iron core closes back via the air. This has to be
taken into consideration during erection of the test circuit.
The result of this design is a compact reactor with low weight
compared to its testing power. Each resonant reactor is designed
for 280 kV and 5.8 A (inductivity: 360 H). The entire height of the
540 kV set-up is approx. 5.1 m. The HV divider is of three parts
type.
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
A A
B B
C C
D D
E E
F F
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Fig. 9: 540 kV set-up of 4 reactors
The concept of the design considers a 20 ft transport container
with a removable roof suitable for sea transports and fast and
reliable erection of the test-system on-site. All resonant reactors
are fixed inside the container with special holding devices locked
for transport. All toroidal corona rings are dismantled and stored
volume optimized.
Fig. 10: 20 ft transport container with removable roof
All corona rings are made of conductive hard plastic. This
technique avoids perturbing buckles as noticed very often on
metallic hollow surfaces. To prevent from corona at test voltages
of 300-540 kV the diameter of the plastic pipes is 300 mm with an
outer ring diameter of 1.5 m.
Between resonant reactor(s) and HV divider a HV filter is
integrated to protect the set-up in case of breakdown of the test
object and to improve the quality of the PD measurement at the test
object.
The step-up transformer and the frequency converter including
the control unit for voltage and PD measurement are placed in a 10
ft container.
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C.4.1 8th International Conference on Insulated Power Cables
C.4.1
Jicable11 19 23 June 2011, Versailles - France
Fig. 11: conductive hard plastic corona rings
Further accessories of the test-set are a full size safety
circuit, a 50 m long connection cable of 200 kVA (5 x 400 V), a 12
m robust telescope HV connection (diameter 250 mm), a 20 m long
medium voltage cable (1 x 25 kV) and for each resonant reactor an
oil-sump including post insulators for isolated installation.
Fig. 12: 10 ft control container
The entire test-set is upgradeable with two further resonant
reactors type DSH6W to be stored in a second 10 ft container. With
this upgrade cables with a maximum capacitance of 255 nF can be
tested up to 540 kV.
Alternatively the entire test-set can be built up for 280 kV
use. Test voltage 280 kV covers most of the tests (approx. 90%).
For this application all 4 pieces of resonant reactors have to be
connected in parallel:
Fig.13: 280 kV layout of test system
output voltage: 0 280 kV output current: max. 23.2 A frequency
range: 20 206 Hz capacitance range: 5 nF 680 nF
duty cycle (at 20C / 100%): 2 h ON / 10 h OFF quality factor:
> 100 nos. of reactors: 4 pieces erection time of test-set
on-site: < 3 h The entire height of the 280 kV set-up is approx.
3.8 m. The HV divider consists of two parts. With the upgrade by
two further reactors cables with a maximum capacitance of 1020 nF
can be tested up to 280 kV.
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
A A
B B
C C
D D
E E
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890
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300
Fig. 14: 280 kV set-up of 4 reactors
REAL HEATING TEST The factory acceptance test of the AC HV
test-set without load capacitance at manufacturers test bay was
carried out for each single resonant reactor with 336 kV / 1 min.
and 280 kV / 30 min. at fTest = 112 Hz (including PD measurement).
Additionally the 540 kV set-up and the 280 kV set-up with 4
reactors each was tested at 540 kV / 1 h (at fTest = 130 Hz) resp.
280 kV / 1 h (at fTest = 125 Hz) without load.
Fig. 15: set-up 4 x 280 kV / 1h
As final acceptance test the entire set-up was tested under real
heating conditions connected with a HV XLPE cable. A cable length
of approx. 1000 m was prepared with 2 pieces of 500 kV SF6-plug-in
compact sealing ends. One end was connected via a gas filled
bushing with the test-set. The other side of the cable was closed
with a gas filled dead-end pipe. The entire capacitance of cable
including sealing ends, bushing and HV divider was approx. 170
nF.
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C.4.1 8th International Conference on Insulated Power Cables
C.4.1
Jicable11 19 23 June 2011, Versailles - France
test voltage: 530 kV test duration: 2 h test capacitance: 170 nF
test frequency: 20.2 Hz test current: 11.5 A At both cable sealing
ends a synchronous PD measurement was carried out with inductive
sensors.
Fig. 16: heating test with 530 kV / 2 h / 170 nF
ON-SITE TESTS Besides the transport logistic of shipping the
test-set to site a concept was created to test all 7 phases with
minimal alteration works of resonant reactors considering 11 m
phase distance at outdoor sealing ends. Only one alteration of the
resonant reactors had to be performed.
Fig. 17: sequence of testing 7 phases
After the 3rd test (spare phase) the spare phase was un-plugged
from GIB at transformer no. 4 and the primary compact plug-in SF6
sealing end was plugged into GIB no. 4 (4th test). With all 6
pieces of 500 kV transformers approx. 6 m GIB pipe was HV tested
together with the cable. All links to transformer were removed
during the tests.
The test set-up for on-site PD measurements should be
corona-free. Therefore, corona toroids and connections of suited
diameter have to be used. Sufficient clearance from HV connections
to any part of the construction should prevent PD from earthed or
potential free components. At both sealing ends an inductive sensor
(HFCT) was used connected with a multi-channel PD detection system
whose acquisition units were connected with optical fibres to
controller and laptop in the control container. The voltage signal
for synchronization of PD measurement was directly taken from the
frequency converter. The voltage was increased step by step PD
controlled.
Fig. 18 (left): sensor and PD acquisition unit at OSE Fig. 19
(right): sensor and PD acquisition unit at GIB
Fig. 20: voltage time characteristics of all tests
test voltage: 493 kV test duration: 1 h test capacitance: 102 -
117 nF test frequency: 24.5 - 26.2 Hz test current: 8.2 - 8.8 A
Fig. 21: set-up test phase no. 1
Fig. 22 (left): PD measurement at 493 kV at OSE Fig. 23 (right):
PD measurement at 493 kV at GIB
Synchronized two-side PD measurements enable time-of-arrival PD
localization. In contrast, single side PD detection is restricted
to time domain reflectometry for PD localization, which results in
lower sensitivity and accuracy [9, 4].
(7)
(6)
(5)
(4)
(3)
(2)
(1)
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C.4.1 8th International Conference on Insulated Power Cables
C.4.1
Jicable11 19 23 June 2011, Versailles - France
Fig. 24: set-up test phase no. 7
ON-SITE RE-PLUGGING PROCEDURE For this project a special spare
phase design and concept was developed. The spare phase is mobile
fixed at a special carriage system under the ceiling of the
transformer cavern.
Fig. 25: spare phase carriage fixation in cavern
This design allows to reach each of the 6 pieces of horizontal
GIB cable enclosures to plug-in the 550 kV compact plug-in SF6
sealing end of the spare phase. As part of the commissioning tests
this procedure shall be demonstrated. First the spare phase was
tested, subsequently the regular phase in the same GIB cable
enclosure (transformer) was tested with 493 kV. The re-plugging
procedure was performed in less than one day. This was possible
because of both, the modular set-up of the test-set and the
advantages of the plug-in sealing end system.
Fig. 26 (left): carriage system for spare phase
Fig. 27 (right): ready installed spare sealing end
CONCLUSIONS For EHV projects in secluded regions a compact AC
test system has a lot of benefits. The typical cable lengths in
such projects are less than 1500 m. A mobile test system as the
described one meets the specification in all matters. AC resonant
testing in combination with distributed multi-channel PD
measurements using PD sensors at each accessory ensures best
efficiency for EHV XLPE extruded cable systems. The modular
upgrading of the test system with two further resonant
reactors for extensive projects allows for more flexibility
regarding capacitance, set-up and above that it provides
redundancy. The on-site test was carried out successfully in
September 2010 including both, HV and PD tests.
REFERENCES
[1] F. Bernasconi, W.S. Zaengl, K. Vonwiller, 1979, A new
HV-series resonant circuit for dielectric tests, 3rd ISH Milan,
paper 43.02
[2] W. Hauschild, W. Schufft, W. Spiegelberg, 1997, Alternating
voltage on-site testing of XLPE cables: The parameter selection of
frequency-tuned resonant test systems, 10th ISH Montreal, Vol. 4,
pp 75-78
[3] W. Schufft, W. Hauschild, 2000, Resonant test systems with
variable frequency for on-site testing and diagnostics of cables,
HV Testing Monitoring and Diagnostics Workshop, Alexandria,
Virgina
[4] U. Hermann, A. Kluge, R. Plath, 2007, After-installation
testing of HV/EHV extruded cable systems procedures and
experiences, Jicable07
[5] W. Hauschild, W. Schufft, R. Plath, U. Herrmann, K. Polster,
2002, The technique of AC on-side testing of HV cables by
frequency-tuned resonant test systems, CIGRE Session, paper
33-304
[6] R. Plath, U. Herrmann, K. Polster, R. Heinrich, W. Kalkner,
J. Spiegelberg, P. Coors, 1998, On-site PD measurement on an
extra-high voltage XLPE cable line, Jicable98
[7] S. Sutton, R. Plath, G. Schrder, 2007, The St. Johns Wood -
Elstree experience testing a 20 km long 400kV XLPE-insulated cable
system after installation, Jicable07
[8] CIGRE WG 21.16, 2001, Partial discharge detection in
installed HV extruded cable systems, CIGRE technical report no.
182
[9] R. Plath, 2005, Multi-channel PD measurements, 14th ISH,
Beijing, China
[10] J. Kaumanns, E. Plieth, R. Plath, 2003, On-site AC testing
and PD measurement of 345 kV / 2500 mm2 XLPE cable systems for bulk
power transmission, Jicable03, paper A8.4
[11] IEC 62067 Ed.1.1 2006-03, Power cables with extruded
insulation and their accessories for rated voltages above 150 kV
(Um = 170 kV) up to 500 kV (Um = 550 kV) - Test methods and
requirements
[12] IEC 60840 Ed.3 2004-4 Power cables with extruded insulation
and their accessories for rated voltages above 30 kV (Um = 36 kV)
up to 150 kV (Um = 170 kV) - Test methods and requirements
[13] IEC 60060-3 Ed.1.0, 2006-02, Definitions and requirements
of on-site tests
GLOSSARY
AC Alternating Current ACRF Frequency Tuned Resonant Circuits
(E)HV (Extra) High Voltage GIB/GIS Gas Insulated Bushing /
Switchgear HDPE High Density Polyethylene HFCT High Frequency
Current Transformer OSE Outdoor Sealing End PD Partial Discharge(s)
Q Quality Factor XLPE Cross-Linked Polyethylene
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