Member of
Case Studies of pd testing using
VLF cosine rectangular waveform
Frank Petzold
Daniel Götz
Hein Putter
Henning Oetjen
SEBAKMT / Megger
SEBAKMT / Megger
SEBAKMT / Megger
HDW / Megger
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
Group
Agenda
1.
Possible excitation voltages for PD testing
2.
VLF cosine rectangular (CR) working principle
3.
Test set up – used at Case Studies
4.
Case Study 1 – 460m XLPE in Norway
5.
Case Study 2 – 662m mixed cable in Norway
6.
Case Study 3 – 1629m mixed cable in Norway
7.
Case Study 4 – 836m mixed cable Germany
8.
Comparison table VLF CR vs. DAC – Case Studies
9.
Conclusions – Future work
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
2
Possible excitation voltages for PD testing
continuous AC
sinusoidal
0.1 Hz
Cosine
rectangular
Damped AC
50 Hz
20 - 500 Hz
0.1 Hz
Continuous
triangular
20 - 300 Hz
0.1 Hz
Ground wave
20 - 300 Hz
Transition
[1]
[1]
[1]
AC 0.1Hz
IEEE 400.2
IEEE 400.3
IEEE 400.4


AC 50Hz
AC 20-300Hz
DAC
VLF CR
Triangular





[1] Pepper D., “Grundlagenuntersuchung zum Teilentaldungsverhalten in kunststoffisolierten Mittelspannungskablen bei Prüfspannungen mit variabler
Frequenz und Kurvenform,” PhD Thesis; Berlin 2003
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
3
VLF CR – working principle
›
›
›
Charging the load capacitance
by +U / -U.
Switching of tyristor-switches
after 5sec. Establishing
resonance circuit.
Recharging to rated voltage U
+
nc
- W
+U
-U
R
S
L
C
Noise sources :
PD at switching
recharging source
PD at switching of
tyristor (stabile in phase)
Voltage depended PD of
VLF CR generator
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
4
VLF CR – noise handling
How to handle noise caused by the VLF CR generator?
Techniques for
handling
Hardware-filtering
Representative
cluster
Gating (HFCT
coupler)
Windowing
Pulse wave shape
PD recharging
source



½

PD switching
tyristor
½




Voltage
depended PD



comments
Best possibility, limited filtering capability at very high PD
events
Expert knowledge required
Too much Gating events could delay signal processing unit for
capturing all PDs
Dangerous in dimensioning window, best possibility in phase
stabile disturbances
All PDs will be captured, expert knowledge required
Typical PD disturbance events caused by a VLF CR generator.
High frequency switching noise
( 1. PD test set )
High frequency switching noise
of VLF CR ( 2. PD test set )
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
Low frequency switching noise
by VLF CR ( 2. PD test set )
5
Test set up – used at Case Studies
PD
coupler
HV VLF CR
HV VLF CR
VLF CR
Onsite test set up - Norway
V sync
PD
signal
Station
GND
PD measuring
Unit
Remote control PD
measuring unit
Calibration acc. IEC 60270
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
6
Case Study 1 (Norway)
VLF CR noise suppression
•Pulse wave shape
Mapping L1, L2, L3 DAC U = Uo
Mapping L1 VLF CR U = Uo
Mapping L2 VLF CR U = Uo
PDIV L2 slightly above Uo
Mapping L3 VLF CR U = Uo
PDIV L3 below Uo
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
7
Case Study 1 (Norway)
Mapping L1, L2, L3 DAC U = 1.7Uo
Mapping L1 VLF CR U = 2Uo
Mapping L2 VLF CR U = 2Uo
Mapping L3 VLF CR U = 2Uo
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
8
Case Study 2 (Norway)
VLF CR noise suppression
•Pulse wave shape
Mapping L1, L2, L3 DAC U = Uo
Mapping L1 VLF CR U = Uo
Mapping L2 VLF CR U = Uo
Mapping L3 VLF CR U = Uo
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
9
Case Study 2 (Norway)
Mapping L1, L2, L3 DAC U = 1.7Uo
Mapping L1 VLF CR U = 2Uo
Mapping L2 VLF CR U = 2Uo
Mapping L3 VLF CR U = 2Uo
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
10
Case Study 3 (Norway)
VLF CR noise suppression
•Pulse wave shape
Mapping L1, L2, L3 DAC U = Uo
Mapping L1 VLF CR U = Uo
Mapping L2 VLF CR U = Uo
Mapping L3 VLF CR U = Uo
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
11
Case Study 3 (Norway)
Mapping L1, L2, L3 DAC U = 1.7Uo
Mapping L1 VLF CR U = 2Uo
Mapping L2 VLF CR U = 2Uo
Mapping L3 VLF CR U = 2Uo
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
12
Case Study 4 (Germany)
N°
Length [m]
Insulation type
Manufacture
[year]
Service
voltage [kV]
4
837
Mixed (Paper-Mass and
XLPE)
1962
20
Phase
PDIV - DAC
PDIV – VLF CR
L1
12 kVrms
12 kVrms
L2
15 kVrms
15 kVrms
L3
13 kVrms
14 kVrms
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
Conductor
Size
13
Case Study 4 (Germany)
12.46μs
pC
Example TDR Trace of
one PD event
5μs / DIV
DAC
PD event at L2
Defect location 150m
Samples
Initiated by different
voltage sources DAC
and VLF CR.
VLF CR
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
14
Comparison DAC vs. VLF CR
Test object
criteria
PDIV
Cable 1
DAC 4.2 kV
VLF CR < Uo
Cable 2
Cable 3
DAC 4.2 kV
DAC 2.4 kV
VLF CR <= 3kV** VLF CR <= 3kV**
PD Level Uo
VLF CR > DAC
VLF CR ~ DAC
VLF CR = DAC
PD Level >Uo *
VLF CR = DAC
VLF CR ~ DAC
VLF CR = DAC
Defect location
(Mapping)
Good
correlation
Also different
spots found
Good correlation
Cable 4
Good
correlation
No PD
Good
correlation
* Not directly comparable because test voltage VLF CR = 2.0Uo, DAC = 1.7Uo
** lowest possible test voltage VLF CR = 3kV
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
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Conclusion
• VLF CR suitable for onsite PD measurement
• PD level not directly comparable to DAC
• PD level is generally not directly related to
criticality assessment of PD defects at all
• PD level VLF CR seem to be higher than DAC
– Advantage for better localization on long
cables
Common use of VLF CR will support further study of behavior
of PD Level, PDIV and Pattern analysis
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
16
Withstand test and PD test on long cables
 Long cables for on- and off-shore wind farms require high test power
 Onsite testing -> high mobilty of the test equipment needed
 Available test technologies :
- Resonance ACR 20 Hz – 300 Hz
- 0,1 Hz VLF sinusoidal waveshape
- 0,1 Hz VLF-CR cos rectangular waveshape
Case study : 3 Uo=60 kV test on 33 kV XLPE cables for windfarms
Demand for testing : routine test in the cable factory combined with pd test of
factory joints, after transportation and laying on the ship, after laying
Cross sections up to 800 mm² , length up to 40 km
 Test capacitance up to 25µF (three phase testing))
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
17
Withstand test and PD test on long cables
Test power :
Test voltage :
Capacitance of test object :
3 Uo = 60 kV rms
max. 25 µF
required test power
Resonance
50 Hz
0,1 Hz VLF
Sinusiodal
0,1 Hz VLF
Cos rectangular
28260 kVA
power consumption of test equipment
188 kVA at Q = 150
56 kVA
73 kVA (app. 1,3x P Test)
56 kVA
8 kVA (app. P test / 7)
Inductive energy
storage
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
18
Example field application of 0,1 Hz VLF-CR Cosine-rectangular
for 60 kV 25 µF test capacitance
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
19
Thanks for your attention
Questions?
IEEE/PES ICC Fall 2012 Meeting, Sub F - St Petersburg Beach /FL 12-15.Nov. 2012
20
Grace Jiang, 3M and
Tim Hayden, National Grid