This is definitly my favourit use of high voltage :-). Note: sparks are near instantaneous discharges, whereas arcs are continuous. To get long sparks, you need high voltages, but not necessarily high discharge currents; for long arcs, you need only a moderatly high voltage, but high discharge currents. To initiate the discharge, move the electrodes together until the voltage arcs over, then pull them apart again. Some examples:
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This was done with the 60kV pulses device. The porcelain plate is about 25cm in diameter, the electrodes from the two ignition coils touch it in about the middle on both sides. The discharges go along the plate surface round the edge. Photo: sensitive film (200 or 400 ASA), shutter open for about 10 sec (several discharges) plus flash to make the equipment visible. Room must be absolutely dark. |
This is an arc produced with the 4kV 2000VA mains transformer . The electrodes are about 5cm apart. To ignite the arc, I brought a copper wire with long plastic handle between them; after the arc appeared, I pulled the wire away again. The arc has a upside-down-"V"-like shape, because the ionized air is extremely hot and therefore rises. If the electrodes were not bent upwards, the arc would not be stable because of this tendency to rise. Photo: nothing particular. The arc is bright enough to light the whole scene. |
Another arc with the above transformer. To avoid the difficulties with the rising air, I arranged the electrodes vertically. This way, the arc can be pulled to a length of nearly 15cm. The upper metal ball gets hot very quickly. |
Jacob's ladder: two electrodes arranged in "V" shape. The arc is ignited at the point of smallest distance (bottom) and rises up till it reaches the end of the electrodes, gets too long and breaks off. Transformer: 4kV 2000VA mains. Photo: open shutter, ignite arc, wait till it has broken off, close shutter. Set the aperture to a high value (11 or 16). |
Arc at the end of Jacob's ladder. Photo: just shot a the right moment. |
Another nice photo of high voltage sparks is in the super-cascade section.