Friday, May 29, Update on Testing Medium Voltage Cable and Switchgear Systems

Transcription

1 Update on Testing Medium Voltage Cable and Switchgear Systems Friday, May 29, 2015 Presented by: Ashley Harkness Electrical Reliability Services

2 Value--- When we find the one serious problem You can focus Effort / Manpower Maintenance $$$-- In the right place.

3 What we will look at: On Line Partial Discharge System Test No Outage Required Passive Diagnostic Technique Finding Water Tree Damage Non-destructive Tan Delta measurement 3

4 Take Aways. Best for your System Condition / Age Understand: Different Test / Different Results: Diagnostic Tests: Yield Trended Data On-Line tests: No Outage 4

5 MV System Life Estimate Hypothetical Cable System Failure Profile Failures Term. & Splice Failures Cumulative Term. & Splice Failures Cable Failures Cumulative Cable Failures Cumulative Total Failures Infant Mortality Normal Performance End of Life Time

6 Something to Consider Insulation breakdown is the leading cause of electrical failure. Partial Discharges (PD) are the first indications of insulation deterioration.

7 On Line PD Examples A Laboratory on a hill had three failures in December.

8 Outdoor Switchgear, Three Project Issues No shutdown. 2. No opening Hot gear 3. Survey---NOW! Main Distribution Air Switch and Transformer SF-6 Switches

9 12 kv Air Switch Insulator Support Tracking Damage Due to Dirt

10 Three Outdoor Switchgear Problems--- Found from Outside 1. Arcing to ground between A107-A Unshielded Cables Touching. 3. Insulator Tracking. PD data for multi Channels #1 # # PD Magnitude (mv) Phase (Degrees)

11 #1 SWITCHGEAR DAMAGE Arcing damage at insulator transition from cubicle to cubicle

12 #2 CABLE DAMAGE CORONA DAMAGE

13 #3 SWITCHGEAR DAMAGE Corona damage on the insulator and support structure Tracking damage on the insulator

14 Transformer Termination PD PD data for multi Channels Phase (Degrees) PD Magnitude (mv) BNK 303 Upper BNK 303 Lower

15 Termination: What Was Found Surface corona damage to the cable termination

16 What is Partial Discharge? Small electrical sparks within and across high voltage insulation. PD results in electrical breakdown of air PD erodes insulation PD causes insulation failure.

17 The Partial Discharge Process HEAT / CHEMICAL REACTIONS ACOUSTICS, SOUND LIGHT ELECTROMAGNETIC WAVES, PULSES

18 BASIC PROBLEM---

19 Insulator Tracking Damage The Insulator is a fiberglass and polymeric material.

20 Deterioration = Life Damage Due to Installation High installation side wall stresses Tight Cable Bends: shield deformation Cuts, scrapes: Broken jackets and shields Workmanship issues Damage Due to Operations Severe Loading, Short circuits; Temperature Extremes: Conductor Migration, Dielectric Changes Gaps and Voids, Semi-con / insulation separations

21 Load Break Elbow Dirt + Moisture + Poor Workmanship = Tracking, Failure, Shutdown

22 Metal-tape shield Outer Jacket Insulation shield Insulation Conductor shield Electrical Conductor Picture Provided by Okonite

23 Installation Damage

24 The Role of Cable Damage Shield Corrosion Disconnected Shield conductor Damaged Jacket/ water penetration Bending radius damage

25 The Role of Cable Damage Shield Conductor Corrosion:

26 The Role of Aging: Elevated Temperature accelerates aging Limits useful life Typical aging : Loss of volatile constituents Oxidation of materials leading to embrittlement Molecular changes due to hydrolytic interaction of insulation with water Chemical breakdown of constituents Organic materials change physical properties

27 Transients Weaken Insulation Transient PD voltage Unrecoverable fault Impulse 1 Impulse 2 Impulse 3 Impulse 4 Impulse 5 Time 7200V

28 And Then, There Were Rats How did we know?

29 How Do We Detect Online PD?

30 How Do We Detect Online PD? Apply Magnetic External Sensors Transient Earth Voltage (TEV) Internal local PD (Tracking, Leakage) No shutdown Does NOT evaluate the Cable Insulation

31 How the TEV Works Internal PD signals Leak out through openings External capacitive TEV senses the leaking RF The resulting signal images the PD

32 Permanent Sensors

33 Cable Mapping Finding the PD s Location along the cable.

34 LIKE RADAR Cable PD pulses time of flight = Distance

35 Mapping the Cable Run 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1, PD Map of Circuit 1500kVA XFMR N. (from POA 3) All Joints Location (% along cable) Mapping showed the PD at ~85% of cable length: ~1031 ft.

36 Waste Water Treatment Plant, Cable PD

37 Waste Water Treatment Plant Severely bent cables

38 On Line Partial Discharge Testing Advantages: NO OUTAGE NEEDED For Cables, etc., (HFCT) and Enclosure (TEV) For Switchgear/Transformer Encl. (TEV Only) Yields termination, insulator, and bushing: corona and tracking Partial Discharge testing can detect, trend, and locate hidden system damage before an unplanned outage.

39 On Line PD Test Methods

40 Initial Field Survey

41 Placing the TEV Sensors

42 Permanent Sensors External connector

43 Remember our opening--- When we find the one serious problem You can focus Effort / Manpower Maintenance $$$-- In the right place.

44 STAY SAFE! Contact me at: Electrical Reliability Services