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IntroductionUnlike internal combustion
engines, electric motors are generally
characterised by very high efficiency. In fact,
ongoing engineering efforts have pushed the
degree of efficiency of modern motors to within a
few percentage points of 100%, depending on the size
of a given motor. Today, an efficiency of 96% has virtually
become the standard, and even 97% is not infrequently
achieved. At the same time, soaring energy costs have
become a powerful stimulant that drives redevelopments and
the engineering progress toward further improvements in thedegree of efficiency, the idea being to save on resources
and to lower the operating overhead.
Notwithstanding these efforts, the operation
of electrical motors continues to involve
certain energy losses in the form
of friction losses, core losses,
hysteresis losses, all of which
manifest themselves as
waste heat. In order to
prevent an impermissible
heating of the motor
and specifically of the
winding, it is necessaryto dissipate this
heat.
Mathis Menzel, Menzel
Elektromotoren GmbH,
Germany, discusses
the advantages and
disadvantages of different
types of motor coolers.
Motor
Variants
Reprinted from October 2008World CemenTwww.worldcement.com
7/27/2019 Method of Cooling
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Cooling methodsWith smaller motors (depending on the type and
size, generally up to somewhere near frame size
560 mm, which translates into a performance
envelope of about 2 MW), the standard cooling
method is surface cooling (usually using ribbed
housings). In the case of larger motors, the type
most commonly used is a modular construction. In
fact, slip ring motors in the medium voltage segment(nominal currents above 1000 V) are manufactured
almost exclusively in the form of modular motors.
A characteristic feature of such motors is that the
electric part is identical for any of the various cooling
types, so that the differences are mainly associated
with the added cooling system.
ComparisonIn principle, motors of the cooling types IC 01
and IC 81W are identical except for the respective
heat exchanger, as the cooling performance of an
ambient-air system practically matches that of a
water-cooled system (assuming that the air fedinto the motor does not exceed a temperature of
40 C). By contrast, the cooling effect of air-to-air
heat exchangers (where the internal circuit and the
external circuit both use air) is markedly inferior,
resulting in a performance loss of about 30%
depending on frame size, even though the electrical
construction is identical. The difference is also
reflected in the decidedly higher procurement costs
for a motor of the IC 611 cooling type, the power
output being the same.
Today, motors of the IC 611 cooling type
equipped with a mounted air-to-air cooler are
predominantly used in the cement industry (serving
as drives for mills, crushers, and fans), among other
applications. Few motors, and least of all large mill
drives, follow the IC 01 cooling type: i.e. the open-
circuit cooled design.
In the cement industry, for one, the IC 81
cooling type is rarely found. Then again, its specific
advantages cause it to be the motor of choice in
a variety of other sectors, such as power plant
technology or the paper and steel industry, where it
accounts for an overwhelming share of the electric
motors deployed. It is unlikely that the IC 81W
cooling type will ever gain a substantially higher
Table 1. Advantages and disadvantages of different cooling systems
Cooling type IC 611 air-to-air heat exchanger IC 81 W air-to-water heat
exchanger
IC 01 open-circuit ventilation
Advantages Winding is protected against
environmental impact.
System is independent from any
cooling water circuit.
Winding is protected against
environmental impact.
Cooling pipes and motor winding
remain clean from deposits.
The ambient temperature has a
negligible impact.
System is marked by a superior,
constant cooling effect.
System involves lowest
procurement costs.
Cooling pipes, in which deposits
might collect, are not required.
The cooling method is very
effective.
Disadvantages System involves the highest
procurement costs, comparativelyspeaking.
The frame size is larger than with
the other cooling types due tothe less effective cooling method.
System requires an increased
cleaning effort.
A cooling water system is
required.
System is more expensive than
IC 01 type motors.
Ambient, airborne pollutants are
drawn into the motor.
Figure 2. Workings of the IC 01 open-
circuit ventilation cooler.
Figure 1. IC 01 open-circuit ventilation cooler.
Reprinted fromWorld CemenT October 2008www.worldcement.com
7/27/2019 Method of Cooling
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share of the market in this sector than it has today,
not least because the use of water in any given
process is avoided as much as possible in the
cement industry.
By contrast, the deployment of water-cooled
motors is particularly sensible wherever water-cooled
drives are already part of a given process. This is
often the case with water-cooled gear units, in which
the use of a shared cooling circuit seems the obvious
answer.In terms of its basic design, the IC 611 cooling
type with air-to-air heat exchanger representing the
established standard in the cement industry has
the one major advantage in that it requires neither
water nor a clean environment. Then again, a motor
of this type does require regular monitoring and
visual inspection to make sure that the cooling ducts
are not clogged by deposits that would prevent the
dissipation of heat into the environment. Failure
to dissipate the heat would eventually cause the
motor to overheat and as is to be hoped trigger
an alarm by the temperature control, assuming a
thermostat is properly installed and set.
ConclusionIn closing, it should be added that it is impossible
to make an unqualified recommendation for any one
cooling type over all others. Here as everywhere,
the specific conditions and requirements of a given
facility and location always need to be taken into
account. At the same time, it is safe to diagnose
a tendency in the cement industry to favour
open-circuit cooled motors of the IC 01 cooling
type. This is explained by the fact that, on the one
hand, the required output and with it the size of
the motors keeps increasing, while, on the other
hand, the environmental conditions of newly raised
cement plants continue to improve, causing the
advantages of lower acquisition costs to outweigh
the disadvantages of pollution. In short, the choice of
cooling type is ultimately subject to a combination of
factors, including deployment context, environmental
aspects, the value-for-money ratio, and market
forces._________________________________________________l
Figure 3. IC 81W air-to-water heat exchanger.
Figure 4. Workings of the IC 81W
air-to-water heat exchanger.
Figure 5. IC 611 air-to-air heat exchanger.
Figure 6. Workings of the IC 611 air-to-air heat exchanger.
Reprinted from October 2008World CemenTwww.worldcement.com