Post on 18-Jan-2018
description
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.
5
Pvm Esityksen nimi / Tekijä
6
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
-60
-50
-40
-30
-20
-10
0
50 145 240 335 430 525 620 715 810 905 1000
dB
MHz
Baseline
Tr167
8
-70
-60
-50
-40
-30
-20
-10
0
50 145 240 335 430 525 620 715 810 905 1000
Tr166-Baseline Tr171
-70
-60
-50
-40
-30
-20
-10
0
50 145 240 335 430 525 620 715 810 905 1000
Tr166 Baseline
Tr170
-70
-60
-50
-40
-30
-20
-10
0
50 145 240 335 430 525 620 715 810 905 1000
dB
MHz
Baseline
Tr169 - Phase T
-70
-60
-50
-40
-30
-20
-10
0
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)
9
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
10
• 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