BOC

The challenge

BOC operates an air separation plant in Fawley that supplies gaseous oxygen and nitrogen to the Esso plant located close by. The main air compressor (CP11) at the plant is driven by an 11kV 7750kW synchronous motor, which when inspected and tested during a shutdown, was isolated due to high levels of partial discharge.

It was also discovered that the rotor had an earth fault which was due to damaged insulators on the rotor up-shaft bars. The previously retrofitted Rosenberry Hub was found to be excessively corroded and damaged which required replacing too.

Houghton International was awarded the order for the complete refurbishment of the motor and manufacture and supply of all high voltage coils.

The solution

After the motor arrived at Houghton International’s IECEx certified large machine shop, an initial inspection and assessment on the condition of it was carried out. Prior to commencement of the works, a dedicated cleanroom area was erected to prevent any contamination of the stator and windings.

The primary scope of the works consisted of refurbishment of the stator and rotor. Firstly the stator windings were stripped out under controlled conditions to prevent any possible damage to the stator core and an assessment was carried out to increase the amount of copper in the stator windings and improve the efficiency of the motor.

Existing blocking, bracing, slot wedges and coils were carefully removed to avoid damaging the slots and laminations, followed by cleaning of the stator core in preparation for the new windings. A core flux test then followed to determine condition of core.

72 HiFLEX coils, manufactured at Houghton International’s in-house coil manufacturing facility, were then wound by a specialist winding team. The unique HiFLEX insulation system helps to eliminate any partial discharge emanating from the coils as each individual coil is fully tested at point of manufacture, guaranteeing dielectric integrity. In addition, having the coils manufactured in house allowed for full traceability and assurance on the whole winding process. Following the rewind, the stator was varnished and cured with quality assurance checks and testing conducted thereafter.

In terms of the rotor, coil connections were remade, six new up-shaft leads were manufactured, and new insulators and up-shaft bars were fitted and secured. A new Rosenberry Hub was also fitted. Once the IR tests were carried out on the refurbished rotor, it was fitted into the rewound stator followed by assembly of the bearings, covers and components and a full external paint job.