Video: AGTU

Video transcript

What the AGTU is for, how its gas circuit works, and how it recovers, transfers and cleans the SF₆ of small equipment. A small breaker or a compartment holds only a few kilograms of SF₆, but the rules are the same as for a large one. The gas cannot be vented: it has to be recovered, kept, and put back clean. And a high capacity recovery cart is out of proportion for that job. The AGTU does 3 jobs in one portable box: it recovers the gas, it consolidates part-used cylinders into one,

and it transfers the gas back into the equipment at a regulated pressure. It is designed for breakers and equipment up to 69 kilovolts, and it weighs 34 kilograms. Everything is built around one compressor: oil-less, direct drive, with a compression ratio of 1000 to one. Being oil-less, it adds nothing to the gas. Its high discharge pressure liquefies SF₆ even on a hot day, and a pressure switch stops it at the maximum allowable pressure.

On the panel: the suction gauge, which reads both pressure and vacuum, and the discharge gauge. The high pressure alarm light, and the start and stop buttons. The two valved gas connections. And the condenser fan, on the side. At the back, the treatment line. The drier canister, D one. The colour change moisture indicator beside it. The particle filter, F one, down to 0.1 micrometres. The power switch.

And the 3 metre hoses, supplied with the unit. This is the circuit, in one line. The inlet regulator, with the suction gauge. The compressor, a check valve and the condenser. The discharge gauge and the pressure switch. Then the treatment: two driers with activated alumina, a molecular sieve for the arcing by-products, the particle filter and the moisture indicator. And at the outlet, a regulator for filling equipment.

Recovery. The gas leaves the equipment through the regulated inlet, and is compressed and condensed. On its way out it is dried, purified and filtered, so it reaches the storage cylinder clean. The equipment is emptied down to 100 millibar, or below one millibar with the optional XDS vacuum module. In outline: the hoses from the equipment to the unit, and from the unit to the cylinder.

Start the compressor, and watch the suction gauge fall as the equipment empties. Stop at the residual pressure you need. If the discharge pressure reaches its limit, the unit stops by itself. Recharging runs from the cylinder. The regulated inlet takes a high pressure bottle directly, with no need to throttle it by hand. The gas crosses the filters once more, and the outlet regulator sets the filling pressure for the equipment.

Consolidation. The gas left in several part-used cylinders is gathered into one, through the same circuit, and cleaned on the way. The unit works with tanks, bottles or carts, and an auxiliary storage tank is available as an option. Every pass cleans the gas. Activated alumina takes out the moisture, a molecular sieve removes the decomposition products of arcing, and the particle filter stops everything above 0.1 micrometres. The specification gives water down to 10 parts per 1000000 by weight, or less.

Maintenance is simple. When the moisture indicator changes colour, the filters are changed, without disconnecting any tubing and without special tools. A run time meter counts the compressor hours, and an equalisation circuit lets the compressor restart against high pressure. And the specification, in one table. Recovery to an auxiliary tank, pressure regulated recharging of switchgear, consolidation of part-used cylinders, and purification of the gas.

SF₆ gas handling, from Amperis.