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Freddy Manders, Marco Haverlag Philips Lighting Eindhoven Paul Aben, Job Beckers, Winfred Stoffels Technical University of Eindhoven Optical study of the.

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Presentation on theme: "Freddy Manders, Marco Haverlag Philips Lighting Eindhoven Paul Aben, Job Beckers, Winfred Stoffels Technical University of Eindhoven Optical study of the."— Presentation transcript:

1 Freddy Manders, Marco Haverlag Philips Lighting Eindhoven Paul Aben, Job Beckers, Winfred Stoffels Technical University of Eindhoven Optical study of the breakdown phenomenon in High Intensity Discharge lamps

2 Outline Introduction HID lamps Background approach Experimental Set-up Power supply Lamps under investigation Experimental results DC ignition of low aspect lamps DC ignition of High aspect lamps AC ignition Conclusions

3 Introduction Experimental set-up Experimental results Conclusions Philips One of the biggest lamp manufactures in the world In Eindhoven pre-development of all lighting sources Halogen Fluorescent Compact fluorescent LED HID etc

4 USED FOR: High efficiency High colour rendering PRACTICAL APPLICATIONS Stadiums Tennis courts Parking lots Automotive Shopping malls Beamers Burner is filled with: - Starting gas (Noble gases, e.g. Xe & Ar) - Buffer gas (e.g. mercury) - Radiation emitting substance (e.g. Na, Ce, Dy, Ca, …) Introduction Experimental set-up Experimental results Conclusions

5 Background HID lamps Ignition voltage ~ 4 kV (300 mBar, pulse ignition, standard HID lamps) ~ 18 kV (10 Bar Xe, pulse ignition, Automotive lamps) Issues 1 st electron, small lamps ( Automotive, UHP) insulation materials (cables, lamp cap, etc) Safety issues, bigger lamps More expensive electronics The lamp should always ignited We need to lower the ignition voltage of the gas discharge Introduction Experimental set-up Experimental results Conclusions

6 Approach Try to understand how breakdown in HID lamps happens Study breakdown process in model lamps with an ICCD camera and change a few parameters Gas type (Ar / Xe) Gas pressure (300 mBar, 700 mBar ) Length / diameter of the lamp Positive / negative voltage Voltage source (Pulse, AC) Introduction Experimental set-up Experimental results Conclusions

7 Experimental set-up Introduction Experimental set-up Experimental results Conclusions

8 Experimental set-up Lamps Voltage source Pulse source of 5 kV with a rise time of 10 nsec. AC voltage source from 25 kHz up to 3 MHz Low aspect ratio burners –Argon, p = 300 mbar, d = 7 mm High aspect ratio burners –Diameter = 4 mm –Argon and Xenon –electrode distance: 1.5 cm and 2.7 cm –300 mbar and 700 mbar Introduction Experimental set-up Experimental results Conclusions Voltage (kV)

9 Experimental results DC pulse ignition of low aspect lamps DC pulse ignition of high aspect lamps AC ignition Introduction Experimental set-up Experimental results Conclusions

10 Low aspect ratio: Argon 300 mBar, -4.0 kV 0 max 6 ns 7 ns 9 ns 10 ns 5 ns 12 ns 13 ns 14 ns 15 ns 0 ns 3 ns 4 ns Introduction Experimental set-up Experimental results Conclusions Grounded side High voltage side 21 ns 19 ns 18 ns 17 ns

11 Low aspect ratio: Argon 300 mBar, -4.0 kV High voltage ionization expands spherical High voltage ionization is not uniform, channels are visible, streamers. Grounded emission becomes, because of the interaction with the wall 9 nsec Introduction Experimental set-up Experimental results Conclusions

12 -4.0 kV-3.0 kV-2.5 kV 7 nsec 11 nsec 16 nsec 17 nsec 21 nsec 16 nsec 29 nsec 40 nsec 51 nsec 59 nsec 20 nsec 41 nsec 59 nsec 73 nsec 99 nsec Low aspect ratio: Argon 300 mBar Introduction Experimental set-up Experimental results Conclusions

13 Low Aspect ratio: Argon 300 mBar, -2.5 kV High voltage emission region expands spherical High voltage emission region is diffuse, burner is almost completely filled with ionization No grounded electrode emission is visible 59 nsec Introduction Experimental set-up Experimental results Conclusions

14 7 nsec 11 nsec 16 nsec 17 nsec 2 nsec 6 nsec 8 nsec 11 ns 39 nsec 60 nsec 99 nsec 128 nsec -4.0 kV +4.0 kV +2.5 kV Low aspect ratio: Argon 300 mBar Introduction Experimental set-up Experimental results Conclusions

15 Low aspect ratio: Argon 300 mBar In all 3 pictures mechanism is streamer Negative streamers are in general more diffuse. +4 kV: clearly streamer mechanism +2.5 kV: slower and more diffuse 8 nsec 16 nsec 99 nsec +4 kV -4 kV +2.5 kV Introduction Experimental set-up Experimental results Conclusions

16 Conclusions low aspect ratio lamps Introduction Experimental set-up Experimental results Conclusions At high negative over voltage (-4 kV) discharge is a streamer For lower voltage there is a transition to a Fast Ionisation wave (-2 kV) Negative streamers are more diffuse then positive Discharge always starts at powered electrode because of interaction with wall

17 High aspect ratio burners Argon, p = 300 mbar, d = 1.5 cm, V = +4kV 52 ns 94 ns 8 ns58 ns 99 ns 15 ns69 ns 107 ns 23 ns75 ns 109 ns 25 ns84 ns 121 ns 39 ns85 ns 93 ns 48 ns 0 ns Introduction Experimental set-up Experimental results Conclusions

18 High aspect ratio burners: Ar300 mBar, +4kV streamer along burner wall very little branching grounded emission expands spherical and is diffuse 85 nsec Introduction Experimental set-up Experimental results Conclusions

19 Ar 300 mBarAr 700 mBarXe 300 mBar 23 ns 52 ns 75 ns 85 ns 121 ns 109 ns 99 ns 23 ns 51 ns 71 ns 85 ns 115 ns 98 ns 89 ns 22 ns 39 ns 57 ns 85 ns 140 ns 135 ns 106 ns High aspect ratio burners: +4kV Introduction Experimental set-up Experimental results Conclusions

20 Ar300: little branching, intense emission at grounded electrode Ar700: much branching Xe300: much branching, very little emission at grounded electrode High aspect ratio burners: +4kV 85 nsec, Ar 700 mBar 85 nsec, Ar 300 mBar 85 nsec, Xe 300 mBar Introduction Experimental set-up Experimental results Conclusions

21 97 ns269 ns 9 ns108 ns272 ns 20 ns143 ns301 ns 21 ns188 ns303 ns 29 ns212 ns313 ns 39 ns242 ns 257 ns 54 ns 0 ns 320 ns 340 ns High aspect ratio burners: Ar 700 mBar - 4kV Introduction Experimental set-up Experimental results Conclusions

22 High voltage ionization (negative voltage) very diffuse and at a very low intensity At grounded electrode streamers are formed Two different mechanisms during one discharge 257 nsec Introduction Experimental set-up Experimental results Conclusions High aspect ratio burners: -4kV

23 Conclusion high aspect lamps Introduction Experimental set-up Experimental results Conclusions More interaction with the wall because the distance to the wall is smaller Positive discharge branch more then negative Negative discharge is more diffuse and slower The higher the pressure the more branching Xe branches more then Ar

24 Comparison of velocities at + 4 kV velocity / (10 6 m/s) d = 1.5 cmd = 2.7 cm Ar ± ± 0.1 Ar ± ± 0.1 Xe ± ±0.1 Xe ± ± 0.1 Introduction Experimental set-up Experimental results Conclusions

25 Introduction Experimental set-up Experimental results Conclusions 1.2 velocity / (10 6 m/s) d = 1.5 cmd = 2.7 cm Ar ± ± 0.1 Ar ± ± 0.1 Xe ± ±0.1 Xe ± ± 0.1 Comparison of velocities at + 4 kV

26 Introduction Experimental set-up Experimental results Conclusions 1.4 velocity / (10 6 m/s) d = 1.5 cmd = 2.7 cm Ar ± ± 0.1 Ar ± ± 0.1 Xe ± ±0.1 Xe ± ± 0.1 Comparison of velocities at + 4 kV

27 Introduction Experimental set-up Experimental results Conclusions velocity / (10 6 m/s) d = 1.5 cmd = 2.7 cm Ar ± ± 0.1 Ar ± ± 0.1 Xe ± ±0.1 Xe ± ± Comparison of velocities at + 4 kV

28 Conclusions velocity measurements Introduction Experimental set-up Experimental results Conclusions Out of the camera pictures it is possible to calculate the velocity of the discharge. The speed are all in the order of 10^6 m/s which is normal for a streamer discharge The velocity results for the high aspect ratio lamps with 4 kV show that there are some relations: The factor the velocity changed Distance between electrodes changed from 1.5 cm to 2.7 cm 1.2 Gas pressure changed from 300 to 700 mBar 1.4 Gas type changed from Ar to Xe 1.1

29 Breakdown voltage for AC ignition for high aspect lamps -29% -26% Introduction Experimental set-up Experimental results Conclusions For DC pulse ignition ~ 4 kV is needed to ignited the 700 mBar Xe lamps so AC lowers the breakdown voltage with ~ 50 %

30 Experimental results (AC ignition - Xenon) Two regimes in which the burners can ignite Introduction Experimental set-up Experimental results Conclusions

31 Experimental results of 300 mBar Xe (AC ignition)

32 Low frequencies: Discharge travels via the wall Looks like pictures of pulse ignition (streamer-like channels, branching) High frequencies: Discharge travels through the gas Ionisation channel has the shape of a streamer … 30kHz 80kHz 140kHz 200kHz 300kHz 400kHz Introduction Experimental set-up Experimental results Conclusions 700 mBar of Xe

33 Maximum velocity of ionisation front: Shape looks like a streamer-like discharge Maximum velocity of the ionisation channel is in the order of those in Townsend discharges. Contradiction: 300 mBar Xenon at 200 kHz Introduction Experimental set-up Experimental results Conclusions

34 Introduction Experimental set-up Experimental results Conclusions Conclusions on AC ignition AC ignition voltage about 50-60% lower than pulse ignition voltage Ignition voltage is a decreasing function of frequency At relatively low frequencies the ionisation channel travels along the wall At relatively high frequencies the ionisation channel travels through the gas Ionisation channel builds up step-wise over many periods Ionisation channel only grows during voltage maximum Possible explanation: Due to alternating E-field more charged particles stay in the volume, and are able to ionise for a longer time. The higher the frequency, the more charged particles stay in the volume.

35 Thank you for your attention!

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