Independent Diagnostic Service
SFRA measurements with different measurement voltages in factory and at commissioning Lars Adeen HVdiagnose AB Sweden +46 705395848
[email protected]
The reality Grey 0.1 V Light Blue 0.5 V Blue 1 V Brown 2 V Black 5 V Green 10 V p-p
The ”problem”
The reason
Region 1: < 2kHz, Main Core, Inductance Region 2: 2 kHz to 20 kHz, Bulk Component, Shunt Impedance Region 3: 20 kHz to 400 kHz, Main Windings Region 4: 400 kHz to 5 MHz, Main & Tap Windings, Test Leads
SFRA Test with PAX or Omicron ? FRAX (Pax Diagnostics)
FRAnalyser (Omicron)
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10 V peak-peak Option: 1-10 V peak-peak 2.82 V peak-peak possible 10 V common voltage as Doble M5100 and M5200
2.82 V peak-peak = 1 VRMS History: HP Network Analyser, 1 VRMS
• Same cable praxis: PAX and Omicron • 50 Ohm coaxial cables • Short braids for earth connection of cable screen
• Generator • 20 V -> 10 V @ bushing terminal • 5.64 V -> 2.82 V @ bushing terminal
Shortest braid concept Most important factor …
First case 2007
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A number of new rectifier transformers SFRA test at factory with Omicron FRAnalyser Demand from customer to perform SAT SFRA with Omicron Was our PAX FRAX (Megger) not compatible? Started up the project with rental of Omicron equipment Involved Dr. Peter Werelius PAX (Megger) Several comparable test were performed at site
The transformer(s) 2 cores with: - 1 HV winding - 2 LV 31.5 / 0,6 / 0,6 kV 34 MVA - HV (1U, 2V, 3W) - LV2 (u2, v2, w2) - LV3 (u3, v3, w3)
Test of compatibility
Ideal ambient conditions for skiing
Omicron: Verkprüfung v.s Site Test
Verkprüfung
Site Test
Different cable and clamps
Tests were performed with both types of cables and clamps. No difference!
PAX Site Test : 2.8 v.s. 10 V
2.8 V
10 V
We lowered the FRAX-101 output voltage to 2.5 V peak (still higher than the FRAnalyzer) and got measurements much closer to FRAnalyzer also at the lowest frequencies FRAnalyser, 1.4 Vpeak (Red curve) • FRAX-101, 2.5 Vpeak (Gray curve) • FRAX-101, 2.5 Vpeak, 5 Vpeak, 2.5 Vpeak (Light green curve)
• FRAX-101 5 Vpeak (Dark green curve)
2.8 V @ site : PAX v.s. Omicron
Omicron
PAX
Summary FRAnalyzer manufactured by Omicron and FRAX-101 manufactured by PAX Diagnostics gave exactly the same results except at the lowest frequencies (20Hz to 200 Hz). At these lowest frequencies, the response on the open high voltage winding (only this measurement) was voltage dependent and the fact that the FRAX-101 applied 5 V peak and the FRAnalyzer only used 1.4 V peak gave the difference.
The voltage dependence was verified by lowering the output voltage in additional FRAX-101 measurements.
