1. An Introduction to On-line Partial Discharge Surveys

2. 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. 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. PARTIAL DISCHARGE TESTING USED FOR QUALITY ASSURANCE
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.

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

7. 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.

12. INSULATION BREAKDOWN
Why should we be concerned with insulation breakdown and Partial Discharges?

13. INSULATION BREAKDOWN
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.

14. Total Failures due to Insulation Breakdown

15. 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. 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. 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. TYPICAL MEDIUM VOLTAGE POWER CABLE CONSTRUCTION

19. TYPICAL HIGH VOLTAGE UNDERGROUND CABLE SYSTEM
Load Unit Substation
Source Switchgear
Visible Cable
Terminations
Visible Cable
Terminations
Ground Level
Underground Cable in Conduit (not visible)

20. 3 STAGES OF CABLE INSULATION FAILURE

21. Imperfections and voids
STAGE 1
No problems, minor voids therefore minor partial discharges
Jacket, Shield, Semi-conducting shield
INSULATION
Imperfections and voids
/ / / /CONDUCTOR / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
voids
INSULATION
Jacket, Shield, Semi-conducting shield

22. STAGE 2
Tracking begins
Jacket, Shield, Semi-conducting shield
INSULATION
/ / / /CONDUCTOR / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
INSULATION
Jacket, Shield, Semi-conducting shield

23. STAGE 3 CABLE FAILURE! Blow-up Phase-to-ground
Jacket, Shield, Semi-conducting shield
INSULATION
Blow-up
Phase-to-ground
/ / / /CONDUCTOR / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
INSULATION
Jacket, Shield, Semi-conducting shield

24. 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. Test Equipment & Sensors

26. Partial Discharge detection of a flaw in a dry type transformer using capacitive coupling
Transformer Coil
Capacitive
sensor
Detector

27. Propagation of Transient Earth Voltages (TEV) in Switchgear
High Voltage Bus
Metallic Switchgear cover (signal detected outside)
Partial discharge site (inside)

28. Measurements using Capacitive PD sensors

29. Switchgear failure due to internal tracking

30. Tracking on epoxy resin busbar

31. Start of tracking on insulation

32. Failed Switchgear Insulation

33. Detecting PD Using Airborne Acoustic (Ultrasonic) Sensors
Busbar
Sensor
Insulator

34. Airborne Acoustic Sensor

35. Insulator Failure Prevented

36. Partial Discharge detection of a void in a shielded cable using inductive coupling.
Insulation +
Void
Shield (grounded)
Conductor
Detector
Inductive Sensor

38. High Frequency Current Transformer Used to Test Cable in High Voltage Substation

39. Failing Terminations

40. Molded Cable Accessory Failure

41. Splice Void

42. Shield Delamination Causing Partial Discharge

43. Poor Workmanship Causing Partial Discharge

44. Testing 15kV cables Case Study On-line testing of cables
PD damage to termination

45. Identifying & Prioritising Circuits Most at Risk Using On-Line PD Survey

46. PD Survey - Worst 30 Results

47. 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. 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. We apologize to every electrical professional for taking 252 years
We apologize to every electrical professional for taking 252 years
to prevent your failures.
Benjamin Franklin discovered electricity
in 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!