£billions wasted due to poor motor sizing
August 1st 2008 Energy efficiency losses through
over sizing of pump electric motors
by engineers are commonplace
and, if the motor specification far
exceeds the application, it could be
costing industry billions of pounds
in wasted energy.
"Industry figures suggest that
around 80% of pump motors could
be the incorrect size,"commented
Andrew Glover,product manager for
WEG Motors."The majority are over
specified by as much as 10 or 15%
by engineers wanting to be 'on the
safe side'.As pumps typically account
for around 30% of an industrial
country's energy usage, this
represents a serious loss of energy.
"This takes no account of the extra
cost of a larger motor with all the
associated equipment, drives,
cabling and so on,"continued Glover,
"Electric motor manufacturers are
forever striving to increase energy
efficiency by one or two percentage
points, but incorrect specification by
an application engineer can mean
that is wasted effort.
"Where a single % point increase
in energy efficiency can save the
equivalent of the purchase price of
an electric motor over its design
life, it seems ludicrous to waste
energy through poor specification."
Undersizing is also relatively
common and should not be
ignored.An electric motor can
operate above its rated output thus
allowing for temporary overloads.
However, the motor will run
hotter as a result and if this state
continues, for example, where the
pump continues to stop and start
in its duties or a higher specific
gravity liquid is pumped than
originally specified, overheating will
cause damage.
Two points where this can directly
affect the motor life are the
bearings, which influence the motor
reliability, and the coil insulation.
Overheating degrades the
insulation more rapidly and
encourages discharges which
further degrade the insulation,
therefore shortening the motor's life.
Specification of motor size
should include starting conditions
as well as running torque.Method
of starting is also important; direct
on line starting methods will create
high torque that also impose
mechanical stresses on the pump
and hydraulic components, while
star delta starting delivers lower
torque and current.
Including a variable speed drive
or soft starter in the system
specification, matched to the
requirements of motor and pump
will overcome these problems.
Variable speed drives also improve
energy efficiency in the long term
by matching application
requirements with the correct
motor speed and thus avoid energy
wasted by, for example, belt drives,
clutches and gears. More articles from WEG Electric Motors (UK) Ltd: | 
