Houghton International is a specialist in the repair, maintenance and life extension of rotating electrical machines. When engineers at the company carried out a HST alternator overhaul and rewind project for a rail industry customer, they applied their usual quality and verification procedures, which included a full range of tests using their SKF Baker AWA static motor analyser.
Unusually, the winding failed the test. Based on the design of the windings in the machine, the waveforms generated during the surge test should be closely balanced. In this case, unbalance was very high, at more than 60 per cent. That result surprised the Houghton International team. As one of the UK’s leading rail industry service providers, the company’s rail division has extensive experience in the repair, maintenance and life extension of AC & DC traction motors, motor alternator (MA) sets and HST alternators for customers in the UK and around the world.
Surge waveform imbalances can be caused by several issues, including short circuits or windings with an incorrect number of turns and misconnections. But when Houghton International inspected the new windings, and checked their work against the specification provided by the original manufacturer of the equipment, they could not find any reason for the test failure. On further investigations Houghton International engineers realised a reversed polarity winding connection in the circuit, and requested a third party confirmation before advising the customer and taking further actions.
Houghton International engineers then contacted SKF to discuss the results and also emailed the raw data to allow closer analysis for an independent review. SKF Engineer, Tony Ruane, then requested the winding data, and when he similarly drew out a winding diagram he also realised that the number of poles of the winding did not match the specification, and by reversing one connection within the circuit, the number of poles were then correct.
To confirm this, Houghton International then made the change of connection on the winding itself and subsequent testing showed that the surge waveforms were now closely balanced.
The finding was highly significant for Houghton International, but even more important for their customer, who learned the reason for some of the issues experienced with the equipment over the last 30 years. The customer contracted Houghton International to check and resolve the issue across its fleet.
Michael Mitten, CEO at Houghton says: “For us, this case underlined the value of the Baker Test equipment in helping to identify and resolve difficult problems in electrical machines. Thanks to the AWA Analyzer, and to the excellent support we received from SKF, we were able not just to fix this problem, but also help our customer address a longstanding fleet-wide issue.”
Go to www.skf.co.uk to learn more.