Video: PULD-40

Video transcript

How the PULD-40 hears corona, arcing and leaks that the ear cannot, how it is set up, and how an inspection is done. Corona is the ionisation of the air around a charged conductor, when the field is strong but not strong enough to strike an arc. It wastes energy, and it produces corrosive gases that degrade and embrittle the materials around it. Nothing trips, so it has to be found. Corona, arcing and leaks all emit ultrasound.

The PULD-40 listens in a narrow band centred on 40 kilohertz, from 38 to 48, well above most plant noise. That is why it still works in a noisy substation or factory. The ultrasound itself cannot be heard, so the PULD-40 converts it. A 40 kilohertz signal comes out at about 2.4 kilohertz, through the built in speaker or a headset. At the same time the level is shown in decibels and on a bar graph. 96 decibels of dynamic range.

A built in sensor optimised for 3 metres, and a parabolic sensor for 15. Four hours on a lithium ion battery, and 528 grams in the hand. The built in cone sensor is at the top. Below it, the level in decibels and the bar graph, and the battery indicator. One key switches it on, and it is ready in seconds. The external sensor port is on the side, and the speaker at the bottom. How sensitive is it? With the built in sensor, it picks up a leak 0.125 millimetres across, at 0.35 bar, from 3 metres away.

The housing is impact resistant, and it works from minus 20 to 60 degrees. The accessories: a parabolic sensor with a sight and a laser pointer, a contact sensor with magnetic holders, noise isolating headphones, an audio cable to record the signal, laser enhancement glasses, an ultrasonic noise generator, and a hard case for all of it. Before going to site, check the system with the ultrasonic noise generator. Its button selects a slow or a fast mode, shown by the blinking of its LED. Point the PULD-40 at it: the level must rise and the sound must follow.

A red blinking LED means its battery is low. The survey itself is simple. Switch on, and put on the headset in a noisy place. Aim the sensor and sweep the equipment slowly. Follow the reading and the sound up to their maximum: that points at the source. Then compare it with identical components nearby. For insulators, arresters, terminations, bushings and switches at height, the parabolic sensor goes on. Its cable plugs into the external sensor port on the side of the PULD-40.

The dish concentrates the ultrasound, and it is optimised for 15 metres. The sight and the laser pointer put the dish on the exact component. From the ground, the operator scans each element in turn, with no contact and at a safe distance, and listens for the one that is louder than the rest. Inside metal clad enclosures the sound cannot get out, so the contact sensor listens through the metal. Its magnetic holders keep it on the panel, so several cabinets can be scanned in a row:

switchgear, ring main units, cable boxes, dry type transformers and cable splices. The same ultrasound comes from mechanical wear and from leaks. So the PULD-40 also checks motors, compressors, gears and pumps, finds pressure and vacuum leaks, and checks the seals of aircraft doors and windows. Four rules. Keep the safe distances: the PULD-40 never needs to touch a live part. The contact sensor goes only on earthed metal enclosures. Never point the laser at anyone's eyes.

And charge the battery between 0 and 50 degrees. It is used for predictive maintenance in utilities and industry: to locate corona and arcing on high voltage installations, to scan switchgear and transformers, to check machines, and to find leaks, even in noisy plants. Partial discharge detection, from Amperis.