Video: AEHV

Video transcript

What the AEHV series does to transformer oil, how its high vacuum process works, and how it is built and mounted for the job. The higher the voltage and rating of a transformer, the greater the electrical stress on its insulation. That calls for oil of better dielectric quality, with less water, dissolved gas and particles, kept that way in the field. The AEHV restores that quality at the transformer, even while it is energized. The figures, in a single pass.

With oil at 27 degrees or more, the water falls from 50 parts per 1000000 to less than 5. Dissolved air falls from about 12% to less than 0.25. A 0.5 micron after-filter is standard, and 9 models cover 200 to 12000 litres an hour. The process, in 5 steps. The oil is pre-filtered and heated. In the vacuum chamber the accelerator cartridges spread it into a thin film. The vacuum strips out the water and the gases.

And an after-filter cleans it on its way back. The circuit. From the transformer, the pre-filter, the inlet pump and the heaters. The vacuum chamber, with level and foam control. On top, the vacuum line, with an optional Roots booster ahead of the vacuum pump. From the bottom, the outlet pump, the after-filter and the flow meter, back to the transformer. The oil comes from the transformer or from storage, through a 5 micron pre-filter and the inlet pump.

The heaters, of low watt density so that the oil is never burnt, raise its temperature before it enters the chamber. The accelerator cartridges are the reason one pass is enough. They make free water coalesce before it evaporates. 1000000 of glass fibres, 3 to 10 micrometres thick, spread the oil into a thin film, and their points release the gases fast. They also filter, and they are disposable and easy to change. Spray and baffle designs needed several passes.

The vacuum does the dehydration and the degassing: water, air and dissolved gases, combustibles included, leave through the pumps. The vacuum pumps go from 25 to 600 cubic metres an hour, and with a Roots booster from 150 to 4500. The treated oil leaves the bottom of the chamber through the outlet pump, crosses the 0.5 micron after-filter and the flow meter, and goes back to the transformer. Nine models, from 200 to 12000 litres an hour, from 6 to 225 kilowatts, and from 685 to 5000 kilograms.

The model is chosen by the mass of oil to treat, from 850 to 60000 kilograms, and by the flow the job needs. Each AEHV is built to order, and mounted to suit the site: on a skid, in a cargo trailer, in an open-side container, in an aluminium semi-trailer of up to 16 metres, or on a lifting frame with a tarpaulin. The series is designed for unattended operation, and it is suitable for work on energized transformers. Complete monitoring is available:

oil level monitoring for energized units, remote monitoring with a wireless emergency call-out, and hygrometers at the inlet and the outlet. Vacuum removes water, gas and particles, but not the products of ageing. For those, optional Fuller's earth filters adsorb oxidation products, thermal degradation products, dissolved varnishes, paints and acids, and the oil recovers its colour. And the options. Extra heater capacity, and an outlet heater to keep the transformer warm.

A diesel or gas boiler, or a generator on board. An inline dielectric tester or gas analyser. A touch-screen control panel. And explosion-proof or full stainless steel versions. And the difference with the AE865C. The AE865C is a 125 kilogram cart for 230 litres an hour and small volumes. The AEHV starts at 200 litres an hour, reaches 12000, and treats transformers with up to 60000 kilograms of oil. And the specification, in one table.

Insulating oil treatment, from Amperis.