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UHF PD DIAGNOSIS at

HV CABLE TERMINATIONS

HEIN PUTTERProductmanager cable testing and -diagnosis

Megger Site Germany

13th Insucon conference – 16 -18th Mai 2017, Birmingham, UK

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Agenda■ Introduction■ PD defects and their behavior in the frequency spectrum■ International case studies of UHF measurements on HV

cable terminations■ Summary & Conclusions

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Introduction High voltage terminations are essential components in high voltage

cable systems

During commissioning these components can be properly tested

Once installed, the effort for an offline test is high, online methods are preferred

UHF PD diagnosis could be a solution for this

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Agenda■ Introduction■ PD defects and their behavior in the frequency spectrum■ International case studies of UHF measurements on HV

cable terminations■ Summary & Conclusions

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Corona discharges

300MHz

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Corona discharges

300MHz

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Surface discharges (Toepler)

Streamer like discharge

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Surface discharges (Toepler)

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Large cavity/ void discharges (Ø 5mm)

Towsend like discharge

300MHz

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Large cavity/ void discharges (Ø 5mm)

300MHz

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Small cavity/ void discharges (Ø 0.5mm)

Streamer like discharge

950MHz

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Small cavity/ void discharges (Ø 0.5mm)

950MHz

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Agenda■ Introduction■ PD defects and their behavior in the frequency spectrum■ International case studies of UHF measurements on HV

cable terminations■ Summary & Conclusions

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International case studiesTypical procedure for UHF PD measurements:

Analysis of the ambient noise/ background noise (Antenna)

Measurement of spectrum at test object itself • If no pre-installed couplers comparing with noise• If pre-installed couplers also by comparison of the

phases

Analysis of the characteristic frequencies in time domain (PRPD pattern)

Documentation

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Case study 1UHF PD measurement using pre-installed UHF couplers

Direct comparison of phases

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Case study 1 Frequency spectrum

Frequency spectrum L1 (Blue) - L2 (Pink) Frequency spectrum L2 (Pink) – L3 (Blue)

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Case study 1 PRPD patterns of by example of phase 3

PRPD @ 337MHz PRPD @ 850MHz

PRPD @ 677MHz

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Case study 2UHF PD measurement using pre-installed UHF couplers

Previous failure in a similar termination, causing local black-out

UHF PD couplers installed during an outage

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Case study 2 Frequency spectrum

Discharges detected in Phase 2 customer replaced them

L1 L2 L3

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Statistics7%

15%

26%52%

NoiseNo PD activitySurface / VoidCorona

Nr. of measured HV terminations 18

Nr. of terminations with pre-installed UHF Coupler 11

Total nr. of measurements* 27* For this paper

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Statistics

7%15%

26%52%

40%

40%

20%

<= 300MHz<= 600MHz<= 1GHz

PRPD Pattern Surface / void discharges

Frequency content of surface/ void discharges

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Agenda■ Introduction■ PD defects and their behavior in the frequency spectrum■ International case studies of UHF measurements on HV

cable terminations■ Summary & Conclusions

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Summary & Conclusions Surface discharges can also be visible in ranges above 300MHz

Frequency content of cavity/ void discharges, depending on the type of discharge, can be limited to 300MHz as well PRPD Pattern needed to be able to segregate between corona and internal PD

Of the 18 inspected terminations, 4 needed further study due to classification to surface or void/cavity discharges. In these cases trending was recommended

The evaluation of the absolute level and the grade of activity (pulses per cycle) is seen as an important criteria for future trending measurements

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Questions ?