Drives Demonstrating their Strengths...
DC drives are able to show the full range of their virtues in many
areas of application. Which drive system best satisfies the requirements
of the user must be decided in each individual case, after all the
relevant technical and economic factors have been taken into account.
The advantages of DC drives however, are manifold. Tried and tested
in practice and without complicated operating procedures DC drives
are characterised by their linear closed-loop performance. The speed
of the motors is controlled by altering the armature voltage whereas
the torque is proportional to the current and can be kept at a constant
level throughout the whole control range (armature control range).
The speed control range can also be extended by weakening the excitation
current for the field (field-weakening operation), the output in
this range remaining constant.
Since only a relatively simple conversion of three-phase current
into DC current is necessary, the units are especially compact and
easy to handle. Equipped with the latest state of the art in processor
technology, the drives can satisfy all and any of the requirements
of modern machine and plant engineering. Reliable and user friendly
Thanks to the simple relationship between voltage and speed, the
control system is very easy to understand and the converter extremely
simple to operate. The user can therefore make all the settings
needed for highly complex drive tasks just as precisely as simple
The development of DC motors in recent years has concentrated on
improving the use of the space available and reducing the maintenance
effort. With the help of computer-aided methods of calculation,
both thermal and magnetic utilisation have been optimised as well.
The result is a perfectly co-ordinated system which, in conjunction
with improved materials, now allows a brush service life of more
than 15,000 operating hours. The bush service life today is approximately
the same as the interval between maintenance work on the bearings.
High-quality insulation materials ensure the high thermal safety
of the machines, and thus the high level of availability of modern
DC drives. Fully digitised converters The fully digitised converters
are user-friendly and easy to operate. A keyboard with a display
of the drive data directly fitted on the unit enables simple adjustment
of the necessary control parameters during operation. Remote parameterisation
and remote monitoring/diagnosis are also possible centrally via
standard interfaces and a bus system. With the user-specific software,
extra functions can be implemented at any time due to the additional
options available. Linecommutated thyristor converters make up the
core of the power section. They operate with a high level of efficiency
but with low forward losses and minimal switching losses. The feed
back of power into the supply system with simple means - in the
case of reversing operation for example - lowers the consumption
of energy and therefore costs as well. The blocking voltage of the
thyristor enables use of the converters where there are high supply
voltages. This is especially the case with DC technology.