High Voltage Substation Surveillance using Radio Frequency Interference Measurement

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High Voltage Substation Surveillance using Radio
Frequency Interference Measurement
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(No Transcript)
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Detecting partial discharge (indirect measurement)
RFI
Thermal
Electric
Partial discharge
Pressure/ Acoustic
Light
Acoustic
Chemical
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RF pulse from a PD related source
Partial discharge pulse
RFI emission FFT frequency spectrum of PD pulse
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CASE Inkoo 110 kV CT
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• 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 measurement
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Baseline measured outside the fences Low
backround noise levels
Discharges in oil will have higher frequency
content
GSM
Typical frequency zone for air discharges lt150 MHz
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No signals
Baseline
Suspected item
Measuring points on the service road between CBs
and CTs
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Measurements
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• 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
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• 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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Advantages of RFI

• 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.

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Thanks for your kind attention! Questions?
Contact Alan Nesbitt Brian Stewart Glasgow
Caledonian University Scotland, UK ane2_at_gcal.ac.uk
Contact Micael Hellquist Hans Ove Kristiansen
Doble TransiNor AS Norway info_at_doble.no