1) The document discusses online partial discharge (PD) measurement of medium voltage and high voltage power cables to prevent unplanned outages. It describes PD theory, cable structures, sensors used for online PD detection, and case studies demonstrating the technology. 2) Qualitrol offers both portable and permanent online PD monitoring systems using sensors like high frequency current transformers and transient earth voltage sensors to detect PD pulses in energized cables. 3) Case studies demonstrate the system separating noise from PD signals to accurately detect and locate incipient faults in cables in high noise environments like GIS substations and switchgear.

1. Prevent Unplanned Outages with On-line PD
Measurement of MV/HV Power Cables
Cable Partial Discharge Measuring Systems
Ammar Khan
Technical Application Specialist – Cables CBM
1Dated: June 21, 2016

2. • Partial discharge theory
• Power cable structure
• PD detection and localization
• Why online PD measurement
• Sensors used for online PD measurement
• Qualitrol offerings
• Case Studies
Overview
2

3. PARTIAL DISCHARGE
THEORY
3

4. • According to IEC 60270
Partial discharge (PD) is a localized electrical
discharge that only partially bridges the insulation
between conductors and which may or may not occur
adjacent to a conductor.
• The term ‘partial discharge’ includes a wide group of discharge
phenomena
– (i) internal discharges occurring in voids or cavities within solid or
liquid dielectrics;
– (ii) surface discharges appearing at the boundary of different
insulation materials;
– (iii) corona discharges occurring in gaseous dielectrics in the
presence of inhomogeneous fields;
– (iv) continuous impact of discharges in solid dielectrics forming
discharge channels (treeing).
What is Partial Discharge?
4

5. PD Phenomenon
5
HV across conductor
PD Pulses
Breakdown in cavity

6. The detection and measurement of discharges is based on the exchange of
energy taking place during the discharge. These exchanges are manifested
as:
– (i) electrical pulse currents
– (ii) dielectric losses
– (iii) E.M. radiation (light)
– (iv) sound (noise)
– (v) increased gas pressure
– (vi) chemical reactions
Results of Partial Discharges
6

7. POWER CABLE STRUCTURE
7

8. • Designed life of power cables is approximately 40 years
• Cable Types that can be tested using Qualitrol Online PD Technology:
– XLPE (Cross Linked PolyEthylene)
– EPR (Ethylene Propylene Rubber)
– PE (PolyEthylene)
– PILC (Paper Insulated Lead Covered)
Power Cable, its Basic Structure
8

9. A Power Cable Circuit
9
Joints
Terminations Cross-bonding Links

10. Multi point grounding
10
Solid grounding

11. Distributed PD measurement
11
Zone 1 Zone 2 Zone 3

12. PD DETECTION AND
LOCALIZATION
12

13. PD Detection into Cables
13
Long Cable
Defect
Measurement EndRemote End
PD at Cable Terminations
• PD in cable induces HF signals
• The signals travel in both
directions
• Signals attenuate during
propagation and reflect back at
terminations
• Detection Principle
• Capture the HF signals emitted
by PD at termination point
• Analyse signals to identify PD
fault and differentiate with Noise
or External PD signals
Long Cable
Defect
Measurement EndRemote End
PD in Joints and inside the Cables

14. PD Fault Localization
14
• Time Domain Reflectometry (TDR)
Principle is used to locate PD.
 Measure time difference between
main and reflected HF signals (∆T)
• For Longer cables, reflected pulse
may not reach to the measurement
end
 Requires a signal injector at the
other end to inject same HF signal
• For accurate localisation requires
 Accurate length of cable
 Cable Return Time (Tr)
Long Cable
Defect
Measurement End
Remote End
ΔT
Long Cable
Measurement EndRemote End
Tr

15. WHY ONLINE PD
MEASUREMENT
15

16. • No need to de-energize the cable system
• Non destructive testing
• Accurate Detection of Incipient Faults under operating conditions
• Accurate Localization or Zoning of Incipient Faults
• Trending Fault Severity via regular CHECKUPs
• Helps in scheduling maintenance and planned outage
• Ensure that cable is defect free after repair / workmanship
Why Online PD Monitoring?
16
• Most of the incipient faults or defects in power cables
generate PD signals well before the actual failure except water
trees.
• PD monitoring helps in identifying the incipient faults before
the break down -> Saves cost of UNPLANNED OUTAGE

17. SENSORS USED FOR ONLINE
PD MEASUREMENT
17

18. • HFCT (High Frequency Current Transformers)
– To detect any PD signal coming from Cable insulation
– One for each Cable
– Installed at termination / joints
• TEV (Transient Earth Voltage)
– To detect any external PD signals coming from termination
or nearby Switchgear Panel
– One for each Termination
– Installed near the openings or vents of terminations
• RF Antenna (Radio Frequency)
– For Noise gating
– One for each Termination
– Installed near to termination (Either TEV or RF Antenna)
Sensors used for Online PD Measurement
18

19. • High Frequency Current Transformers
– Inductive type sensor
– Split core to install sensor easily
– Different variants to fit the purpose (current (up to 1000A), diameter
(up to 150mm internal diameter))
– Sensitivity: Up to 10mV / mA
– Frequency Response: 200kHz – 15MHz
• Installation requires
– Individual cable earth
– Cable insulation gland
– Installation is done while the
cable is energised
Sensors: HFCT, Options for Installation
19

20. • Transient Earth Voltage Sensor
– Capacitive type sensor
– Integrated magnets help to attach it to
metallic body
– Sensitivity: Up to 100mV / V
• Installation requires:
– Metal Switchgear should not be double
skinned / walled
• RF Antenna
– Can be used in place of TEV
– Used to perform noise gating
20
Earthed metal clad
TEV
HFCT
Vent
Sensors: TEV and RF Antenna Installation

21. Sensors Positioning
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HFCT

22. Sensors Positioning
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23. Online Cable PD Measurement Topology
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Sensors
(HFCT, TEV)
Termination
Portable System /
Permanent Installation
Sensors cables

24. QUALITROL OFFERINGS ON
CABLE PD MEASUREMENT
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25. Field Service
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• Field Service
•Sit Survey and feasibility of Online PD measurement
•Risk Assessment
•Method statement document shared with the customer
•Testing of 6-9 cables per day
•Detailed report with further recommendations within 5 days as standard or
more days depending on the number of days of testing

26. Portable System
26
•Portable System (Periodic Measurement)
•Main Unit (4 simultaneous channels)
•Accessory Box
•Sensors
•Cables

27. Sensors
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•High Frequency Current Transformers (HFCT)
•Transient Earth Voltage Sensor (TEV)
HFCT-150
1000A
3mV/mA
HFCT-100
500A, 1000A
3-5mV/mA
HFCT-60
50A, 500A,
5-10mV/mA
HFCT-30
50A
10mV/mA

28. Continuous Monitoring Solution

29. Continuous PD Monitoring Software
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30. Continuous PD Monitoring Software
30

31. CASE STUDIES
HIGH NOISE ENVIRONMENTS
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32. Case Study 1: Lab Verification of Technology
Maximum magnitude phase
resolved distribution of mixed
signals including noise, PD,
interference were applied
together to test the system and
separated out by the system

33. Case Study 2: GIS Substation
33
 Cable Termination
 GIS termination
 220kV, XLPE
 Around 500m
length
 Cable Termination
 Remote end
 Terminating to
Overhead lines

34. Case Study 2: High Noise Environment
34
Before performing any filtering on
Channel A single cycle data, high noise
level and too much interference can be
seen.
Not sure which is PD or which is noise.
Also not sure that there is any PD?
After filtering, white noise level is
decreased. Interference signals can still
be seen at the same locations.
However, some more pulses appeared
in the middle.
These pulses in the middle may or may
not be PD

35. Case Study 2: Extracted Noise Pulses
35
Channel A noise pulse shape, its
maximum magnitude phase resolved
distribution and pulse count phase
resolved distribution

36. Case Study 2: Extracted PD Pulses
36
Channel A PD pulse shape, its
maximum magnitude phase resolved
distribution and pulse count phase
resolved distribution By TDR, it states
that PD is located at remote end.

37. Case Study 3: Metalclad Switchgear
37
 Cable Termination
 Metal clad
 10kV, XLPE
 Around 1367m
length
 One HFCT on the
earth shield of
cable
 Other two beneath
the metal housing
as earth shield
was available
there

38. Case Study 3: Interference and PD
38
Before performing any filtering on
Channel A single cycle data, low noise
level but too much interference can be
seen.
Not sure which is PD or which is noise.
Also not sure that there is any PD?

39. Case Study 3: Extracted Noise Signals
39
Noise pulse shape, its maximum
magnitude phase resolved distribution
and pulse count phase resolved
distribution

40. Case Study 3: Extracted PD Signals
40
Channel A PD pulse shape, its
maximum magnitude phase resolved
distribution and pulse count phase
resolved distribution. By TDR, it states
that PD is located at remote end.

41. Case Study 3: Extracted PD Signals
41
Channel C PD pulse shape, its
maximum magnitude phase resolved
distribution and pulse count phase
resolved distribution

42. THANK YOU
End of Session
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