Magnet repair at Didcot

Wyko has repaired a giant electromagnet used for removing metallic waste from the coal used to fuel Didcot Power Station. Following a successful contract bid, Wyko overhauled the 22 tonne overband magnet and rewound the 25kW coils ready for reinstallation above the crusher conveyors. Didcot Power Station is one of the largest in the UK, and uses a number of fuel sources including coal and renewable biomass (saw dust) to generate electricity.

Screening for unwanted tramp metal such as nuts and bolts that can easily find their way into coal deliveries during the extraction process is a vital stage in the smooth running of coal fired power stations.

To screen the many tons of coal entering the facility, the overband magnet (so called because it has a belt conveyor that travels around the magnetised area to remove any collected items) is used to attract and remove ferrous metal objects as the fuel is carried along the conveyor systems under the unit.

The coal is received in aggregate form and then crushed into a powder on site; the coal dust is blown into the burner section of the boiler to burn as close to completion as possible.

This process increases efficiency and means that firing happens at very high temperatures, enough to heat small mild steel metallic objects for example to red hot.

Any unwanted metallic objects inadvertently included in the coal can therefore cause damage to the crushing rollers and the boilers.

Routine tests by the maintenance contractor Howden Power revealed that one of the main overband magnetic screening units suspended above the coal conveyors was showing signs of an electrical fault developing.

The Howden maintenance team removed the entire unit and arranged for it to be stripped down and a full assessment carried out.

Wyko took the unit to its electromagnetic repair workshop at Digbeth in Birmingham for an overhaul and repair.

Mike Allen at Wyko Digbeth said: 'Although this 22 tonne unit is probably one of the largest in use in the UK, Wyko routinely repairs other electro-mechanical devices up to 40 tonnes'.

'Upon delivery of this unit, our team dismantled it and conducted tests to produce a full evaluation report'.

'The results of the tests showed that the coil insulation was failing and could be repaired'.

Due to the importance of the magnet and the awkward location (12m off the floor), Didcot decided on the option to have the coil completely rewound.