Video: PADD

Video transcript

How the PADD finds the one faulty arrester on a live medium voltage line, how it is used from a hotstick, and how to read its 6 levels. A metal oxide arrester with a defect can develop partial discharges, inside or on its surface. Those discharges radiate radio frequency, and they show up as interference on radio, communication systems and television. The complaint arrives, but the source is very hard to find. Directional radio frequency equipment points at an area,

where there may be several arresters. The PADD works the other way round: by direct contact, on the conductor right next to each arrester. So it tells exactly which one is faulty, and only that one is replaced. It works on overhead lines up to 69 kilovolts, 45 kilovolts phase to neutral. Six levels in two colour zones, visual and audible. A built in self test, and a single 9 volt alkaline battery. The hook electrode goes on the conductor.

The label on the body carries the legend of the 6 levels and the status LED. At the bottom, the universal adapter for an insulated hotstick. The whole unit is very light, so it can be handled at the end of a long stick. The reading is a pattern of blinking lights. 1, 2 or 3 blue lights are the 3 low levels. 1, 2 or 3 red lights are the 3 high levels. At very high activity a tone sounds as well, so the operator does not need to see the unit to know.

A green LED tells the state of the unit. Blinking slowly, it is on standby. Steady, it is sensing more than 4 kilovolts on the conductor. Blinking fast, the battery is low and has to be replaced before carrying on. The standard electrode is a 60 millimetre hook, which hangs on the bare conductor. AY shaped electrode is the alternative, when the layout of the conductor or the accessory suits it better. Both travel in the carrying case with the unit.

Before going up to the line: fit the electrode, check the battery, and run the Auto Test, which confirms the detector is working. Then mount the unit on the insulated hotstick with its universal adapter. Where to touch: the hook goes on the bare conductor, as close as possible to the arrester being checked. The green LED turns steady when the line voltage is sensed. Read the level, then move to the next arrester, one by one.

The operator stays at the far end of the insulated stick. Reading the result is direct. Blue levels mean low activity. Red levels mean high activity, and a tone joins them at the top of the scale. Because each arrester is checked on its own conductor, the one that stands out is the source. The same principle checks other medium voltage accessories in service: dry type transformers, bushings and insulators, always by contact on the conductor next to the part being checked.

Four rules. Only on lines up to 69 kilovolts. Always from an insulated hotstick, never by hand. Follow the live line working rules of the site. And run the Auto Test before every inspection. It is used to find the arrester behind radio or television interference, and in preventive maintenance programmes for arresters on overhead distribution networks, together with the other medium voltage accessories. Partial discharge detection, from Amperis.