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.