BEST PRACTICES FOR OFFLINE DIAGNOSIS OF MV CABLES

Transcription

1 BEST PRACTICES FOR OFFLINE DIAGNOSIS OF MV CABLES HEIN PUTTER Productmanager cable testing and -diagnosis Megger Site Germany 1 13 th Insucon conference th Mai 2017, Birmingham, UK

2 Agenda Introduction Case Study: Acceptance/ commissioning testing Case Study: Condition Monitoring Summary & Conclusions 2

3 Introduction Offline cable diagnostics on MV cables are nowadays widely accepted and in some countries already standardized (for commissioning) This, as it is known that a pure withstand test will not identify all workmanship issues In addition, offline cable diagnostics are also very useful for condition assessment of service aged MV cables 3

4 Introduction Offline cable diagnostics we need to divide into: PD diagnostics Dielectric diagnostics Dielectric diagnostics are mainly performed on service aged cables only, most familiar method is a dielectric loss measurement (tandelta) Offline PD diagnostics can be performed with a number of excitations voltages each having their own benefits 4

5 Introduction continuous AC sinusoidal Damped AC Cosine rectangular 0.1 Hz 50 Hz Hz 0.1 Hz Hz Hz Ground wave Transition 5

6 Agenda Introduction Case Study: Acceptance/ commissioning testing Case Study: Condition Monitoring Summary & Conclusions 6

7 Case Study: Acceptance testing Commissioning test on a newly installed XLPE cable Operation voltage: 12/20 kv Cable length: 2308 m Cable type: XLPE, 3x1x240 mm 2 Joints: 7 Year of installation: 2016 Withstand test: passed (3Uo, 60 minutes) 7

8 Case Study: Acceptance testing TanDelta Measurement 8 Source: IEEE (2013) Table G.1

9 Case Study: Acceptance testing PD Uo PD 2Uo 9 DAC Excitation Voltage

10 Case Study: Acceptance testing PD Uo PD 2Uo 10 Sinus Excitation Voltage (measurement from far end)

11 Case Study: Acceptance testing Summary: Withstand test at 3Uo for 60 minutes did not identify weak spot. tandelta measurement showed further study advised, although cable is new typical behaviour for new co-polymer cables/ resistive field stress control heat shrink joints tandelta measurement did not identify local problem in phase L3 Both excitation voltages (VLF sinus 0.1 Hz and DAC) showed comparable results (PDIV, PD intensity and PD level) 11

12 Agenda Introduction Case Study: Acceptance/ commissioning testing Case Study: Condition Monitoring Summary & Conclusions 12

13 Case Study: Condition Monitoring Condition monitoring on a service aged mixed cable Operation voltage: 12/20 kv Cable length: 653 m Cable type : Mixed cable (XLPE, paper insulated) Joints: 7 Year of installation:

14 Case Study: Condition Monitoring TanDelta Measurement tandelta results Local problem in L3 14

15 Case Study: Condition Monitoring Fault located in L3 positioned at 470m, not caused by external damage, pure internal fault. 15

16 Case Study: Condition Monitoring PD Uo VLF Sinus 0.1Hz PD Uo VLF CR 0.1Hz (210Hz) 16

17 Case Study: Condition Monitoring PD 2Uo VLF Sinus 0.1Hz PD 2Uo VLF CR 0.1Hz (210Hz) 17

18 Case Study: Condition Monitoring Summary: tandelta measurement helped to identify local problem PD diagnosis with VLF Sinus 0.1Hz did not identify the fault position, VLF CR did At operating voltage cable, apart from failure position, PD free At elevated voltages several PD defects in accessories localised Trending measurement recommended after 3 years 18

19 Agenda Introduction Case Study: Acceptance/ commissioning testing Case Study: Condition Monitoring Summary & Conclusions 19

20 Summary & Conclusions Commissioning testing: Withstand testing only is not sufficient as a commissioning test tandelta diagnosis on a new cable can be misleading (copolymer/ local problem) PD diagnostics are strongly recommended Excitation voltage should be comparable to operating frequency 20

21 Summary & Conclusions Condition monitoring: For condition monitoring in addition a tandelta diagnosis is recommended A tandelta diagnosis can also identify local problems Excitation voltage should be comparable to operating frequency, differences between Sinus 0.1Hz and DAC or VLF CR have been observed. 21

22 22 Questions?