Fulfilling role as a fault finder

Two motor testing units made by the Baker Instrument company and supplied by UK agent,Whitelegg Machines,have helped GE Energy find a fault on a motor that drives an oil mist eliminator at a UK power station, avoiding down time and lost revenue estimated at up to £150,00

Based in Dartford, Kent, GE Energy provides a wide range of technical services for businesses and authorities that generate, transmit, or use electricity.

These include test and inspection contracts on electric motors, transformers and switch gear. The company works in all areas of the energy industry. To support its expanding work programme, GE Energy took delivery in August 2009 of two advanced motor testing units.

Motor condition testing, off-line: The AWA Winding Analyser is an offline test unit that checks the integrity of insulation systems within electric motors and transformers.

The Baker AWA off-line tester: The AWA unit provides automatic testing capabilities for winding resistance with automatic temperature compensation, megohm, PI, DC step voltage and surge tests.

Recently GE's Tony Ruane visited a UK Power Station to perform an annual test and inspection on 45 motors over three days. On testing the fifth motor, a fault was detected.

Surge test failure When performing the surge test, a fault was detected at 1670 volts and the test was stopped automatically.

The fault was detected using pulseto- pulse 'EAR' software, designed to detect turn-to-turn insulation weakness or arcing. However, since the test was performed from the motor control cabinet Ruane was unsure as to whether the fault lay with the motor itself or the power cables.

The next step was to go to the motor terminal box to isolate the fault location. Power cables were disconnected from the motor and the motor tested again. This time, the pulse-to-pulse software detected no insulation weakness and therefore attention turned to the power cable.

A third test was then performed on the cable itself, with it still disconnected. This time the pulse-topulse 'EAR' fault returned at a similar voltage to the original fault.

As time was short, a decision was taken to restart the motor. Since the voltage level at which the fault was detected was relatively high, Ruane was confident that the motor would restart.Motors which see a lot of start ups each day under heavy load and which have weak insulation are more likely to fail in the short term.

Since the motor is question typically runs for several months without stopping, the risk of shortterm failure was less likely.

Oil mist eliminator The motor in question was a 15kW machine which drives an oil mist eliminator unit. This is a critical piece of equipment on the gas turbine unit and works by drawing a vacuum on the outer bearing oil seals to extract oil vapour from the bearing cavity into a separator.

If this unit were to fail, the pressure inside the bearing cavity would create an oil leak forcing oil vapour into the rest of the surrounding environment creating a fire hazard, especially in the load tunnel. It has been estimated that subsequent down time and lost generating revenue would be in the region of £100,000 to £ 150,000.

Whitelegg Machines has represented Baker in the UK for more than 20 years, providing technical sales, training, after sales service and calibration.