IQ_Partial_Discharge_Presentation.ppt

1. I Q S e r vic e s
An Introduction to On-line
Partial Discharge Surveys

2. I Q S e r vic e s
PARTIAL DISCHARGE
When high voltage insulating material
breaks down Partial Discharges are
created, measured in units of charge
known as pico-Coulombs or millivolts.

3. I Q S e r vic e s
WHAT IS PARTIAL
DISCHARGE?
• Electrical discharges occurring inside medium and
high voltage insulation (flaws, cracks, voids,
irregularities).
• These imperfections create voltage stresses and
cause eventual failure of the insulation.
• Insulation failures begin with and are characterized
by small but detectable releases of energy or Partial
Discharge.

4. I Q S e r vic e s
• For many years partial discharge testing has been
an IEEE/ANSI standard to identify insulation
problems in electrical apparatus before it leaves
the factory floor.
• Many U.S. and International standards have been
developed for partial discharge testing.
• Until recently Partial Discharge testing was
limited to testing at manufacturer’s laboratories.
• Now computers and sophisticated equipment can
isolate and detect Partial Discharge occurrences in
the field.
PARTIAL DISCHARGE
TESTING USED FOR QUALITY
ASSURANCE

5. I Q S e r vic e s

6. I Q S e r vic e s
NO OUTAGE EVALUATION
These proven technologies exist today to evaluate medium or
high voltage systems while the system is energized.
1. Oil testing/DGA – limited to oil transformers
2. Infrared testing – visible loose connections only
3. Visual inspections – problems may not be visible
4. Power Quality – cannot detect insulation failures
5. Vibration – limited to motors and transformers
6. Partial Discharge Testing – single best all-around test

7. I Q S e r vic e s
PARTIAL DISCHARGE
VS. INFRARED
How are Partial Discharge Inspections
different from Infrared Inspections?
• Infrared identifies electrical current problems (loose
connections) that result in heat. The specimen must be
visible to the naked eye for the infrared camera to detect a
problem.
• Partial Discharge identifies voltage problems that result in
insulation breakdown and generation of Partial Discharges.
The specimen does not need to be visible for Partial
Discharges to be detected.

8. I Q S e r vic e s

9. I Q S e r vic e s

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11. I Q S e r vic e s

12. I Q S e r vic e s
INSULATION BREAKDOWN
Why should we be concerned with insulation
breakdown and Partial Discharges?

13. I Q S e r vic e s
• NFPA 70B states that insulation breakdown
is the number one cause of electrical
failures.
• In medium and high voltage equipment,
partial discharges are the first indication of
insulation breakdown.
INSULATION BREAKDOWN

14. I Q S e r vic e s
Component Percentage of insulation failure
Transformers 84%
Circuit Breakers 21%
Disconnect Switches 15%
Insulated Switchgear Bus 95%
Bus duct 90%
Cable 89%
Cable Joints (splices) 91%
Cable Terminations 87%
Based on IEEE Gold Book Table 36
Total Failures due to Insulation
Breakdown

15. I Q S e r vic e s
WHAT TYPE OF FACILITES
ARE AFFECTED?
• INDUSTRIAL - Large Manufacturing,
Cogeneration
• COMMERCIAL - Research Parks, High Rises
• INSTITUTIONAL - Campuses, Hospitals
• GOVERNMENTAL - Military Bases, Large
Office Complexes
• UTILITY - Investor Owned, Municipalities

16. I Q S e r vic e s
WHERE DO PARTIAL
DISCHARGES OCCUR?
• Electrical Systems > 600V (2.4KV, 4.16 KV,
12KV, etc.)
• Types of Equipment Subject to Partial
Discharge
-Cables -Transformers
-Circuit Breakers - Instrument Transformers
-Switchgear (CT’s, PT’s)
-Insulators - Bushings
-Generators - Motors
-Surge Arrestors - Capacitors

17. I Q S e r vic e s
ADVANTAGES OF PARTIAL
DISCHARGE SURVEYS
• PREDICTIVE - failures can be prevented.
• NO OUTAGE NECESSARY - does not interrupt
operations.
• NON-DESTRUCTIVE - no damage to electrical
system.
• TRENDING - comparison to previous tests
possible
• PRIORITIZE MAINTENANCE ACTIVITIES -
determine which equipment to service first.
• PLANNING - allows time to schedule repairs.
• FINANCIAL CONTROL – repairs can be budgeted.

18. I Q S e r vic e s
TYPICAL MEDIUM VOLTAGE
POWER CABLE
CONSTRUCTION

19. I Q S e r vic e s
Source
Switchgear
Ground Level
Underground Cable in Conduit (not visible)
Visible Cable
Terminations
Load
Unit Substation
Visible Cable
Terminations
TYPICAL HIGH VOLTAGE
UNDERGROUND CABLE
SYSTEM

20. I Q S e r vic e s
3 STAGES OF CABLE
INSULATION FAILURE

21. I Q S e r vic e s
STAGE 1
Imperfections
and voids
voids
INSULATION
/ / / /CONDUCTOR / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
INSULATION
No problems, minor voids therefore minor partial discharges
Jacket, Shield, Semi-conducting shield
Jacket, Shield, Semi-conducting shield

22. I Q S e r vic e s
INSULATION
/ / / /CONDUCTOR / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
INSULATION
Tracking begins
Jacket, Shield, Semi-conducting shield
Jacket, Shield, Semi-conducting shield
STAGE 2

23. I Q S e r vic e s
INSULATION
INSULATION
CABLE FAILURE!
Jacket, Shield, Semi-conducting shield
Jacket, Shield, Semi-conducting shield
Blow-up
Phase-to-ground
/ / / /CONDUCTOR / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
STAGE 3

24. I Q S e r vic e s
HOW CAN PARTIAL
DISCHARGES BE DETECTED?
Discharges are detected by special signal processing equipment designed to
eliminate outside interference.
Capacitive Methods - For Unshielded Components
- Dry Type Transformers
- Instrument Transformers
- Switchgear
Inductive Methods - metal enclosed components
- Shielded Cables and Components
- Oil Filled Transformers
- Rotating Apparatus
Acoustic Emission Methods
- Dry & Oil Transformers
- Switchgear
- Unshielded Cables

25. I Q S e r vic e s
Test Equipment & Sensors

26. I Q S e r vic e s
Partial Discharge detection of a flaw
in a dry type transformer using
capacitive coupling
flaw
Transformer Coil
Capacitive
sensor
Detector

27. I Q S e r vic e s
High Voltage Bus
Metallic Switchgear
cover (signal detected
outside)
Partial discharge
site (inside)
Propagation of Transient Earth
Voltages (TEV) in Switchgear

28. I Q S e r vic e s
Measurements
using
Capacitive PD
sensors

29. I Q S e r vic e s
Switchgear failure due to internal tracking

30. I Q S e r vic e s
Tracking on epoxy resin busbar

31. I Q S e r vic e s
Start of tracking on insulation

32. I Q S e r vic e s
Failed Switchgear Insulation

33. I Q S e r vic e s
Detecting PD Using Airborne
Acoustic (Ultrasonic) Sensors
Insulator
Busbar
Sensor

34. I Q S e r vic e s
Airborne Acoustic Sensor

35. I Q S e r vic e s
Insulator Failure Prevented

36. I Q S e r vic e s
Partial Discharge detection of a void in a
shielded cable using inductive coupling.
Insulation
+
Void
Shield (grounded)
Conductor
Detector
Inductive Sensor

37. I Q S e r vic e s

38. I Q S e r vic e s
High Frequency Current Transformer Used to Test Cable in
High Voltage Substation

39. I Q S e r vic e s
Failing Terminations

40. I Q S e r vic e s
Molded Cable Accessory Failure

41. I Q S e r vic e s
Splice Void

42. I Q S e r vic e s
Shield Delamination Causing
Partial Discharge

43. I Q S e r vic e s
Poor Workmanship Causing
Partial Discharge

44. I Q S e r vic e s
Testing 15kV cables
On-line testing of cables PD damage to termination
Case Study

45. I Q S e r vic e s
Identifying & Prioritising Circuits Most at Risk
Using On-Line PD Survey
L IV E L INE P ART IAL D IS C HARG E S URV E Y RE S UL T S
O F 6 2 9 HV F E E D E RS
0
100
200
300
400
500
600
700
800
900
1000
1
2
1
4
2
6
3
8
4
1
0
5
1
2
6
1
4
7
1
6
8
1
9
0
2
1
1
2
3
2
2
5
3
2
7
4
2
9
5
3
1
6
3
3
7
3
5
8
3
7
9
4
0
0
4
2
1
4
4
2
4
6
3
4
8
4
5
0
5
5
2
6
5
4
7
5
6
8
5
8
9
6
1
0
FEEDERS
m
V
D
i
s
c
h
a
rg
e
A C TIO N
C O N C E RN

46. I Q S e r vic e s
PD Survey - Worst 30 Results

47. I Q S e r vic e s
PERFORMING A PARTIAL
DISCHARGE SURVEY
• Analyze the single line drawing to develop plan
• Onsite Measurement
– Removal of equipment covers.
– Record field data.
– Obtain signatures of atypical components.
• Offsite Data Analysis
– Correlate measurements to single line drawing.
– Compare atypical results to like insulation from database.
– Analyze signatures.
– Trend Results.
• Report Generation
– Recognize immediate failure possibilities.
– Recommend possible repairs.
– Recommend possible resurvey frequency.

48. I Q S e r vic e s
SUMMARY
• Electric Insulation will fail.
• Predicting failures is now possible through
Partial Discharge Analysis.
• No outage is required to survey the
equipment.
• Results can be prioritized and trended.
• Partial Discharge Surveys should be
performed annually.

49. I Q S e r vic e s
We apologize to every electrical professional for taking 252 years
to prevent your failures.
Benjamin Franklin discovered electricity
in 1752. This year we launched an easy
to use, cost effective “no-outage” electrical
inspection technology that detects
medium and high voltage equipment
problems before they fail!