1 UHF PD DIAGNOSIS at HV CABLE TERMINATIONS HEIN PUTTER Productmanager cable testing and -diagnosis Megger Site Germany 13 th Insucon conference – 16 -18 th Mai 2017, Birmingham, UK
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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 ?