Digital winding tester diagnoses motor faults on site

Baumuller's UK office in Coulsdon, Surrey, undertakes in-situ predictive maintenance and troubleshooting on electric motors, as well as factory-based repairs, service and parts support. The company's choice of the Baker D12R digital winding tester - supplied by Whitelegg Machines - was made in 1999 and was the first such tester in the UK; since then it has been a mainstay of Baumuller's testing programmes, approving every motor that passes through the repair shops.

Baker's D12R is a lightweight, high-voltage tester offering resistance, hi-pot and surge tests with digitised data storage for printing in real time or later. It is capable of detecting even very small insulation breakdowns within the armature or field windings, which Baumuller has found cannot be accomplished as comprehensively when using other machines.

The on-site effectiveness of the D12R was proven when Baumuller staff recently attended a major traction customer where there is a high demand on motors, with failures affecting possibly hundreds of passengers. The customer was unsure why the 'transport system' was tripping with over-voltage readings, and availability for running and the need to adhere to maintenance schedules ruled against the removal of the motor for speculative investigation

Motor problem or system problem?

This customer needed to know unequivocally whether this was a motor- or system-related problem so that a decision could be made as to whether to schedule a motor change in the short term or wait for the next major maintenance.

Baumuller's engineer, working with the D12R in portable mode, disconnected the motor supply leads and systematically tested the field winding as a whole composite, as well as the armature windings within the instrument diagnosis program.

From the in-house, outgoing test sheets, it could be seen that the values shown on this motor did not tie up with what should be experienced on the field windings. The conclusion was that further tests were necessary, as the field was tested as a whole and therefore the exact coil that was overvoltaging could not be isolated at that time.

However it could be stated that the problem was motor-related, and the data could prove this to be the case.

The customer was advised to continue running the motor but, if tripping still occurred, disrupting the system, a motor change would need to be done in the short term, prior to a full rewind.

Baumuller's engineers were able to print reports on site from the D12R and gave these, together with a copy of the motor outgoing report sheet, to the traction engineering manager. This enabled the customer to schedule a motor change at a convenient time.

The whole process took no more than one hour to complete, aided by the D12R; without it the client could have been fault-finding across his whole system for hours, if not days.

Raaland Burke, a Director of Baumuller UK, said: "Without a doubt, the D12R has been a cornerstone in our business of motor diagnosis and repair, enabling us to maintain a professional and quantifiable works programme for our clients."