Testing Buchholz Relays Using Dry Air Pumps

Buchholz Relays

Dry Air Pumps

The Dry Air Pump from PBwel provides a portable solution for on-site testing of Gas and Oil operated Buchholz Relays.

A charge of air is created in the polycarbonate cylinder by means of a foot-operated pump. The cylinder contains an indicating silica gel which absorbs the moisture present in the air. The pressure of the air charge is monitored on the built-in pressure gauge.

When a suitable pressure has been attained, the air charge is then quickly passed to the Buchholz via a flexible tube by opening the ballvalve fitted to the cylinder. To prevent backpressure forcing oil back down the flexible pipe, a non-return valve is incorporated in the unit.

The indicating silica gel is a crystalline material, which absorbs moisture readily. The properties of the crystals can be easily regenerated by heating/drying. The crystals are impregnated with Iron compounds which give them an orange colour.

Upon absorption of moisture, these crystals change from their orange colour to a pale yellow and then become colourless.
When the crystals change to pale yellow, they should be regenerated. This gel is not classified as dangerous.

Dry Air Pump By Pbwel

On-site testing of Buchholz Relays

These instructions are for guidance only. All testing should be carried out in accordance with substation guidelines and safety procedures.

Place pump on stable area of ground
Open unit and attach flexible pipe to non-return valve outlet using suitable spanner. Do not overtighten Brass fasteners
Ensure that outlet valve is closed at right angle to ballvalve body
When access clear, connect flexible hose to TEST ballvalve upon Buchholz. Open TEST valve
Connect suitable test meter to Buchholz terminals in accordance with substation requirements. It is recommended that the switch resistances be measured to avoid damaging switches
On the ground, unfasten the foot pump. Pump air into the polycarbonate cylinder until the pressure gauge reads a value of approximately 40 p.s.i.
Quickly open the ballvalve on the unit, and monitor the TRIP switch, which should operate and then return to its “normal” position
The air passed into the Buchholz during the test should be sufficient to operate the ALARM switch
Air should be removed from the Buchholz by opening the GAS ballvalve
It should be noted that where a long length flexible hose is used, the pressure might need to be increased due to the loss of pressure this causes.
Repeat test as necessary with increasing pressures
After satisfactory testing close TEST ballvalve, remove flexible hose and replace dust caps
Remove test meter from Buchholz terminals and refit terminal box cover
Fasten foot pump and close ballvalve on unit and refit dust cap
Inspect silica gel and if orange colour faint, regenerate as detailed

Technical Details

Max Recommended Operating Pressure – 60 p.s.i.g
Size – 475 x 250 x 128mm.
Weight – 8kg

The Dry Air Pump is self contained in a rugged steel case with plated fasteners and a carrying handle to ease transportation. The provided flexible hose is 7mtr and has fittings to suit 1/8” BSP ballvalves. The hose can be transported in the case. Damaged units can be returned to our premises for a quotation on repairs.

PBwel is a globally recognised designer, manufacturer and supplier of temporary portable earthing, voltage detectors, Buchholz relays and electrical safety products.

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