Power Transmission
Heat dissipation remains a major consideration for designers of motor-driven systems. Bill Bertram reports.
Cool life lessons for electric motors
F
irst, let us look at the basics of motors and their thermal management. Heat is a byproduct of the
conversion of electrical input to mechanical output, as performed by a motor or other rotating electrical machine. In fact, it is part of the ineffi ciency, as is noise. Motor designs are steadily becoming more effi cient, which means they are producing less heat – but still enough to require consideration by designers of motor-driven systems.
The simplest form of heat dispersal is through conduction into the surrounding air or structure of the driven machinery. To assist with this, a heat sink – usually a fi nned block of aluminium with a large surface area – can be affi xed to
the motor to absorb the heat and dissipate it quickly to atmosphere. A variation of this is found on many industrial motors, which have a fi nned cover over much of their body length.
Another common method for keeping electric motors cool is forced draught air cooling. Industrial motors often have an integral fan, mounted on the rear of the output shaft, so that it spins at the same rate as the driven load. This is protected by a perforated cowl, which also protects inquisitive fi ngers from the fan blades. This type of motor is often referred to as ‘totally enclosed fan cooled’ (TEFC). A variation on this, often used with servo motors, is an independently excited electric fan. A cooled motor can operate at higher load and is likely to have
Improving the effi ciency of electrical conversion and new methods of thermal management may mean that in future motors run far cooler than they do today.
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