PD Testing Considerations for MV Plant Cables

Cable Testing Philosophy Repair Mistake Aging Damage Damage

Manu- Trans- In- Operation Power frequency facturing portation stallation 50/60 Hz

Power frequency 50/60 Hz Factory Factory Testing Acceptance Acceptance Testing Maintenance Maintenance Testing

Cable Aging Management- SLIDE 2 Various Manufacturing Defects

1. Cavity at shield 5. Protrusions 2. Cavities due to shrinkage or 6. Splinters gas-formation in insulation 7. Fibers 3. Defects in the insulation 8. Contaminants in the shield insulation shield 4. Loosely bound solid particles Cable Aging Management- SLIDE 3 Electrical Trees (XLPE)

• Often begins near – Protrusions at the shield – Protrusions at the conductor – Near impurities – At water trees • Two Types – Branch type trees – Bush type trees

Cable Aging Management- SLIDE 4 Partial Discharge Theory

1 xE )( = R x ln r 3ε E = xE )( void + 21 ε 3ε 1 = + ε R 21 x ln r

4 Voltage/Electric Field Voltage/Electric

Phase Angle 0 0 45 90 135 180 225 270 315 360

-2

-4 Appl. Voltage [kV] Background Field [kV/mm] Void Breakdown Strength Void Field [kV/mm] Cable Aging Management- SLIDE 6 -6 Partial Discharge Theory 20 Electrical Field Conditions

10 Return Voltage/Electric Field Voltage/Electric Initial Discharge Second Discharge Discharge 5

Phase Angle 0 0 45 90 135 180 225 270 315 360

-5

-10

Appl. Voltage [kV] -15 Background Field [kV/mm] Void Breakdown Strength Void Field [kV/mm] -20 Cable Aging Management- SLIDE 7 40 Partial Discharge Theory Electrical Field Conditions

20 Voltage/Electric Field Voltage/Electric

Phase Angle 0 0 45 90 135 180 225 270 315 360

-10

-20

Appl. Voltage [kV] -30 Background Field [kV/mm] Void Breakdown Strength

Void Field [kV/mm] Cable Aging Management- SLIDE 8 -40 PD Testing

• Diagnostic Test • Can be performed on-line or off-line • With respect to commissioning testing often performed either during a HiPot test or after HiPot test • Should preferably be done at.. – At near power frequency – Elevated voltages to identify problem prior to in-service failure • Most PD monitors require experts for operation and data interpretation ⇒ expert test • No standard for field PD testing – (IEEE 400.3 is a guide) • Should be performed by independent third party

Cable Aging Management- SLIDE 9 © Kinectrics Electrical Trees (XLPE)

Apparent Charge at

discharge location VPD

Measured Apparent R

Charge

Attenuation Attenuation

C iPD

VPD iPD VPD R Measured Apparent R Charge

Cable Aging Management- SLIDE 11 © Kinectrics TDR on Tape Field Cable

Cable Aging Management- SLIDE 12 Cable Testing Philosophy Repair Mistake Aging Damage Damage

Manu- Trans- In- Operation Power frequency facturing portation stallation 50/60 Hz

Power frequency 50/60 Hz Factory Factory Testing Acceptance Acceptance Testing Maintenance Maintenance Testing

Cable Aging Management- SLIDE 13 Acceptance & Maintenance Tests

Types of Tests Standards • Soaking • IEC 60502, IEC 60840, IEC 62067 • DC HiPot Testing Guides • AC HiPot Testing • IEEE 400 • VLF Testing – 400.1 DC Testing • Damped AC – 400.2 VLF Testing • Partial Discharge – 400.3 PD Testing – 400.4 Damped AC Testing – 400.5 AC Withstand • Cigre 182 • Cigre 279 Cable Aging Management- SLIDE 14 VLF Testing After-laying field tests Pros Cons • Inexpensive compared to AC • Still discussion on test levels versus HiPot Non-Resonant testing test time • Effective in finding watertree’d • Issues with charge injection and cable for field aged, distribution trapped charge when testing at class cables frequencies less than 0.1 Hz • Not as effective in finding weak • Easy to perform spots in the insulation as a • Non-expert test conventional AC HiPot. • IEEE Std 400.2 • Voltage wave may not be sinusoidal (depends on test kit).

• Not straight forward to interpret PD data acquired during VLF conditions • Research still to be done on the effectiveness in detecting, for instance, interfacial phenomena

1 0.1HZ 0.5

0 0 1 2 3 4 5 6 7 8 9 10

-0.5

-1

1 20HZ 0.5

0 0 1 2 3 4 5 6 7 8 9 10

-0.5

-1

1 60HZ

0.5

0 0 1 2 3 4 5 6 7 8 9 10

-0.5

-1

VLF AC Withstand Cable System Installation Acceptance Maintenance Acceptance Maintenance Waveform Rating ( φ-φ) (φ-∅) ((φ-∅)) (φ-∅) (φ-∅) (φ-∅)

[kV] [kV rms] [kV rms] [kVrms] [kVrms] [kVrms] 5 9 10 7 13 9 8 11 13 10 15 19 21 16 26 23 25 291 32 241 Sinusoidal 28 32 361 27 42 36 35 39 44 33 46 51 57 43 67 58 69 75 84 63 72

Cable Aging Management- SLIDE 18 AC HiPot Testing

• Stipulated in IEC 60502 (MV), IEC 60840 (HV) and IEC 62067 (EHV) as well as most cable testing standards • Testing at power frequency from 20 Hz to 300 Hz • Recommended high potential test level for acceptance testing ranges from 1.25U0 to 2U0 but typically 1.7U0. • High potential voltage applied for 60 minutes • AC HiPot testing is gaining ground in Europe and North- America • Proven test methodology for identifying installation related defects.

Pros Cons • Proven test methodology; • Not a diagnostic test test levels and duration well • Requires heavy equipment established • Not necessarily cheap • Based on IEC standards • Reliable equipment available. • Decades of experience with tests • Can perform PD testing during AC HiPot tests • Gets ‘soft’ failure so meaningful forensics can be performed

i L R C

iR CCable

Cable Aging Management- SLIDE 21 MV Test Spec (Plant Cables)

Rated AC Testing DC Testing Voltage Hipot Test Partial Discharge Test Equipment (kV) Test Level Time Extinction Allowable Pulse Time Test Level Time (kV) (mins) Level (kV) Mag. (pC) (mins) (kV) (minutes) Power Cable

Unshielded: 4.16 N/A N/A N/A N/A N/A 25 (35) 5

Shielded: 4.16 9 (13) 5 4.5 (4.5) 3 (3) 2 25 (35) 15 (including cable bus) 8 13 (18) 5 7.5 (7.5) 3 (3) 2 35 (45) 15 13.8 19 (27) 5 13 (13) 3 (3) 2 55 (70) 15 Bus Duct

Isolated Phase Bus 25 45 (60) 1 19 100 2 64 1

Metal-Enclosed Rigid 13.8 27 (36) 1 10.5 (10.5) 100 (100) 2 38 (50) 1

Switchgear 4.16 14 (19) 1 3.5 (3.5) 100 (100) 2 N/A N/A

13.8 27 (36) 1 10.5 (10.5) 100 (100) 2 N/A N/A

Cable Aging Management- SLIDE 22 PD Interpretation Criteria

Comm. Testing (Off-Line) Maintenance Testing (On-Line) • Measure PDIV, PDEV • Assess individual PD sources • Measure PD Level & Intensity separately • Identify signature partial • Identify location of partial discharge pattern discharge source • Identify location of partial • Assess impact of individual PD discharge source sources (insulation materials, ⇒ Guiding criterion is that the experience) cable system should be PD ⇒ Develop individual free at the specified test assessment/ranking of joints voltage at commissioning fro and cable sections HV &EHV systems ⇒ Less then 3pC or 3pC for MV systems using conventional systems

Pros Cons • Can help identify insulation • No standard or acceptance defects which does not cause criteria failure during an AC HiPot test • For long lengths of cable a • Can use external, non-invasive distributed PD measurement sensors should be performed (at each • Can be performed continuously accessory) at each accessory using daisy • Requires an expert to perform chained PD systems the test and evaluate the data • Cannot compare factory PD tests to field tests • May be practically difficult to perform (manhole access, traffic control)

Cable Aging Management- SLIDE 24 Off-Line vs. On-Line

Off-Line On-Line • Requires cable disconnected and • Non-invasive test cable conductors exposed. • Done at rated voltage • Requires external power source • PDIV and PDEV cannot be • Done at elevated voltage measured • Can perform meaningful • Often, multiple PD sources from sensitivity assessment various types of HV equipment • Can measure PDIV, PDEV are detected • For cross-bonded cable systems, • Can only detect sources present SVLs must be shorted and, at the time of testing! preferably, the cross links • Can be performed continuous removed thus creating a over long lengths of time thus continuous sheath characterizing the dynamic PD behaviou

Cable Aging Management- SLIDE 25 © Kinectrics PD Monitors

Measurement Parameters Types of Monitors • Magnitude • Traditional PD • Phase Angle Monitors ⇒ Derive pulse count • Conventional PD rate Monitors • Signal Shape • Modern Partial Discharge Monitors

Cable Aging Management- SLIDE 27 Broad Band PD Measurements

Cable Aging Management- SLIDE 28 Sensor Connections

HFCT For Voltage Reference LFCT For Voltage Reference

Cable Aging Management- SLIDE 29 AC HiPot & Unconv. PD Testing

• The frequency content of a partial discharge pulse depends on… – Duration • Strength of the electrical field • Length of the partial discharge it self – Pulse propagation path ⇒ different PD sources have different frequency content

Cable Aging Management- SLIDE 30 • Off-line Hi-Pots (ac, VLF) Dielectric loss measurements Partial Discharge testing

Cable Aging Management- SLIDE 31 Summary of Partial Discharge Data

Cable ID (Phase) AC Hipot DIV (kV) DEV (kV) PD @ 13 kV (pC) 2ENA02NC1-AA/AG (Red) Passed 10.8 10.6 185 2ENA02NC1-AA/AG (Black) Passed 16.8 16.1 0 2ENA02NC1-AA/AG (Blue) Passed 13.9 13.7 0

2ENA02NC1-AB/AH (Red) Passed 11.9 10.7 190 2ENA02NC1-AB/AH (Black) Passed 17.5 16.0 0 2ENA02NC1-AB/AH (Blue) Passed 16.5 15.0 0

2ENA02NC1-AC/AI (Red) Passed 18.9 17.3 0 2ENA02NC1-AC/AI (Black) Passed >19 >19 0 2ENA02NC1-AC/AI (Blue) Passed 14.2 13.4 0

2ENA02NC1-AD/AJ (Red) Passed 15.7 14.8 0 2ENA02NC1-AD/AJ (Black) Passed 11.6 11.2 330 2ENA02NC1-AD/AJ (Blue) Passed 16.8 15.4 0

2ENA02NC1-AE/AK (Red) Passed >19 >19 0 2ENA02NC1-AE/AK (Black) Passed >19 >19 0 2ENA02NC1-AE/AK (Blue) Passed >19 >19 0

2ENA02NC1-AF/AL (Red) Passed >19 >19 0 2ENA02NC1-AF/AL (Black) Passed 18.6 18.0 0 2ENA02NC1-AF/AL (Blue) Passed 17.7 16.1 0

Cable Aging Management- SLIDE 32 Example 1: On-Line PD • 142 circuits of single conductor 5 kV EPR • 19 years to 21 years old • All cables feeding 4.2 kV induction motors

Cable Aging Management- SLIDE 33 Example 1: On-Line PD (5kV)

• Partial discharge activity detected through out the system • However, of 142 cables, only 7 subjected to partial discharge activity from the cable system it self – In one case, partial discharge activity was detected from a cable splice – The remaining six cases related to tracking along cable termination surfaces • The remaining discharge activity detected originated from the 4.2 kV induction motors, the bus system or other connected HV equipment

Cable Aging Management- SLIDE 34 Example 2: On-Line PD (27.5)

• Industrial client • 42 cable sections, 27.5 kV XLPE • 12 years old • Cable circuit constitute single supply line to the plant ⇒ crucial to avoid unforeseen failure • On-line partial discharge measurements performed routinely as a maintenance test

Cable Aging Management- SLIDE 35 Example 2: On-Line PD (27.5)

Cable Aging Management- SLIDE 36 Ex 3: Periodic/Remote Monitoring

• Custom made sensor – Cable length – Cable specifications • Non-invasive install, can be performed live • Connected to termination box

Cable Aging Management- SLIDE 37 Ex 3: Periodic/Remote Monitoring

Cable Aging Management- SLIDE 38 Ex 3: Periodic/Remote Monitoring

• Permanent installation at substation • 1 day installation • Suspected faulty equipment PROCESSING • PD measured from vacuum bottle • Verified during subsequent off-line testing

Cable Aging Management- SLIDE 39 Remote Monitoring Setup – Example 1

Cable Aging Management- SLIDE 40 Cable Testing also involves… Being nice to stray doggies at work sites - even while you’re busy!

“The greatness of a nation and its moral progress can be judged by the way its animals are treated.. I hold that, the more helpless a creature, the more entitled it is to protection by man from the cruelty of man" - Mahatma Gandhi (1869 - 1948)

Cable Aging Management- SLIDE 41 Contact information

Terry Herrmann Rick Easterling Structural Integrity Associates Kinectrics [email protected] [email protected] (303) 542-1415 (804) 550-3109

Steve Biagiotti Mark Fenger Structural Integrity Associates Kinectrics [email protected] [email protected] (303)542-1402 (416) 300-8464

www.structint.com Howard Sedding Kinectrics [email protected] (416) 207-6000 x6172

www.kinectrics.com

Cable Aging Management- SLIDE 42