High Voltage Substation Surveillance using Radio Frequency Interference Measurement

Partial discharge

RFI

Thermal

Light

Chemical

Pressure/ Acoustic

Electric

Detecting partial discharge(indirect measurement)

Acoustic

Partial discharge pulse RFI emission FFT frequency spectrum of

PD pulse

RF pulse from a PD related source

CASE Inkoo 110 kV CT

• Selective testing targeting mainly old 110 kV CTs discovered a unit with a high C2 power factor ~0,95 %. (Strömberg KOTU F41 type, manuf. 1972)

• A DGA follow up showed considerable gassing TCG 18 000 ppm (H2 12037 ppm, CH4 4839 ppm, C2H6 1058 ppm) diagnosed as D1 low energy discharge

• Suitable test case...?• Doble were asked for a PDS100

blind test.

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Pvm Esityksen nimi / Tekijä

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Baseline measurement7

GSMTypical frequency zone for air discharges <150 MHz

Discharges in oil will have higher frequency content

Baseline measured outside the fencesLow backround noise levels

-70

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50 145 240 335 430 525 620 715 810 905 1000

dB

MHz

Baseline

Tr167

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-70

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50 145 240 335 430 525 620 715 810 905 1000

Tr166-Baseline Tr171

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50 145 240 335 430 525 620 715 810 905 1000

Tr166 Baseline

Tr170

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50 145 240 335 430 525 620 715 810 905 1000

dB

MHz

Baseline

Tr169 - Phase T

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50 145 240 335 430 525 620 715 810 905 1000

Baseline

TR168 Phase R

Measuring points on the service road between CBs and CTs

Suspected item

No signals

Baseline

Measurements

The faulty unit was succesfully located– A small PD signal was registered ~15dB

above baseline– Attennuation of high frequencies is useful in

the location process– The 110 kV CT was replaced - no signal

after replacement (one month later)

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HV Lab testing of the CT

• PD Ignites at 74 kV phase-to-earth voltage (128 kV main voltage), apparent charge was 50-60 pC

• Extinguishing voltage is considerably lower around 45 kV (77 kV main voltage)

• At 1,2 x Um/ (85 kV) discharge level was 150 pC• Internal pressure 0,75 bar (0,6 considered normal)• Tandelta slightly increasing as a function of voltage up to 70 kV,

0,43...0,59 % • Tandelta increases rapidly when PD ignites at 74 kV being 1,76 %

at 123 kV• CT passed the 0,75 x 230 kV, 50 Hz 1 min overvoltage test

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• Non-invasive, no need for physical or electrical connection.

• Does not require equipment under test to be taken out of service.

• May be adopted for first-line substation surveillance.

• Rate and severity of discharge can be monitored and trended.

Advantages of RFI

Thanks for your kind attention!Questions?

Contact:Alan NesbittBrian StewartGlasgow Caledonian UniversityScotland, UKane2@gcal.ac.uk

Contact:Micael HellquistHans Ove Kristiansen Doble TransiNor AS

Norwayinfo@doble.no