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SALONEN–FI–RIFS2–1270

Electrical Safety in LVDC Distribution System. Pasi Salonen Researcher - Working towards Ph.D. degree Lappeenranta University of Technology Finland Electrical safety analysis focusing on human safety Contact voltage and touch current Indirect customer-end insulation faults

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SALONEN–FI–RIFS2–1270

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  1. Electrical Safety in LVDC Distribution System Pasi Salonen Researcher - Working towards Ph.D. degree Lappeenranta University of Technology Finland • Electrical safety analysis focusing on human safety • Contact voltage and touch current • Indirect customer-end insulation faults • Single and double fault situations SALONEN–FI–RIFS2–1270

  2. Electrical Safety in LVDC Distribution System • Low voltage direct current (LVDC) system • Low voltage directive (LVD) 2006/95/EC • Maximum allowed voltage 1500 VDC • Bipolar system with ± 750 VDC pole voltages • Neutral isolated system SALONEN–FI–RIFS2–1270

  3. Electrical Safety in LVDC Distribution System • Simulation environment • PSCAD based LVDC simulation model • 35 kVA transformer (Ddy) with two secondary outputs • ± 750 VDC network length 200 m, AXMK 4x35 mm2 cable • Two 10 kVA customers with 1-phase 230 VAC inverters • Installation cable length 25 m, MMJ 3x2.5 mm2 cable • PE circuit created with equivalent resistance against ground SALONEN–FI–RIFS2–1270

  4. Electrical Safety in LVDC Distribution System • Equivalent human impedance • Parameters for normal conditions Zhuman = Human total impedance, RP = human skin impedance, 500 Ω, CP = Human skin impedance, 1.5 μF, RI = Human internal impedance, 600 Ω. • Parameters for hard conditions R = Equivalent resistance, 250 Ω. SALONEN–FI–RIFS2–1270

  5. Electrical Safety in LVDC Distribution System • Indirect faults at customer-end • All galvanic parts (sinks etc.) are grounded • Human contact in parallel with PE-conductor RP = 500 Ω CP = 1.5 μF RI = 600 Ω SALONEN–FI–RIFS2–1270

  6. Electrical Safety in LVDC Distribution System • To ensure human safety during faults • Std. contact voltage limit for DC is 120 V • Contact current for DC (at 5 % risk) is 150 mA (1000 ms) • Std. contact voltage limit for AC is 50 V • Contact current for AC (at 5 % risk) is 40 mA (1000 ms) • LVDC system voltage and current are mixed values • AC limits should be used for LVDC system SALONEN–FI–RIFS2–1270

  7. Electrical Safety in LVDC Distribution System • Single fault • Normal condition • Results, RE=5 Ω • Ihuman = 1.9 mA • Uhuman = 1.2 V • Icircuit = 6.2 A • Results, RE=1 Ω • Ihuman = 2.6 mA • Uhuman = 1.6 V • Icircuit = 8.3 A U I SALONEN–FI–RIFS2–1270

  8. Electrical Safety in LVDC Distribution System • Single fault • Hard condition • Results, RE=1 Ω • Ihuman = 6.0 mA • Uhuman = 1.6 V • Icircuit = 8.4 A U I SALONEN–FI–RIFS2–1270

  9. Electrical Safety in LVDC Distribution System • Double fault • Normal condition • Results, RE=5 Ω • Ihuman = 19.0 mA • Uhuman = 27.0 V • Icircuit = 146.0 A • Results, RE=1 Ω • Ihuman = 37.0 mA • Uhuman = 54.0 V • Icircuit = 293.0 A U I SALONEN–FI–RIFS2–1270

  10. Electrical Safety in LVDC Distribution System • Double fault • Hard condition • Results, RE=1 Ω • Ihuman = 220.0 mA • Uhuman = 54.0 V • Icircuit = 293.0 A U I SALONEN–FI–RIFS2–1270

  11. Electrical Safety in LVDC Distribution System • Conclusions • Safety analysis made in PSCAD simulation environment • Single faults are not dangerous even at hard conditions • Double faults can introduce values above dangerous limits • Possibility of double fault is relatively small compared to single fault • Fault clearance always at first fault situation • Current restriction in converter decreases values • Current limiting to 140 AAC value in customer-end converter • Contact current and voltage value below dangerous limits • Future work • Analytical calculation of currents and voltages SALONEN–FI–RIFS2–1270

  12. Electrical Safety in LVDC Distribution System Thank you for your intrest! Questions? Pasi Salonen Researcher LUT Energy / Department of Electrical Engineering Lappeenranta University of Technology, Finland Email: pasi.salonen@lut.fi SALONEN–FI–RIFS2–1270

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