ABB
10
ABB | Motors and Generators
| Synchronous motors
The right excitation method for every application
At ABB we take care to ensure that the excitation system
meets the very high overall standards of reliability that
we have set for our synchronous motors.
For fixed speed applications and variable speed applications
with less demanding dynamic control requirements, a brushless
exciter and automatic voltage regulator are generally provided.
The brushless system has no wearing parts, and the external
excitation power requirement is low.
The brushless exciter is a separate AC generator mounted
on the motor shaft at the non-drive end. In most fixed speed
motors the field winding is DC fed; in variable speed motors
(and fixed speed motors with LCI starting) the field winding
is AC fed. The exciter is vacuum pressure impregnated using
the MCI method, ensuring that the windings are sealed and
secured. The advanced and yet straightforward design has
a low component count and effective protection functions,
and it offers high reliability and easy access for maintenance.
For variable speed applications where very fast and accurate
speed or torque control are required, the motor is generally
equipped with brushes and a slip ring unit to allow excitation
and control of the motor from the frequency converter.
The slip rings are mounted on the motor shaft with access
via removable inspection covers. In general the slip rings
and mounting flange or hub are made of steel, and they are
normally mounted as a single unit. Slip ring units with brass
rings, as well as split flange mounted units, are available on
request. The slip ring unit is fitted with brass connection
pins to facilitate installation.
No excitation system is needed for variable speed motors
with permanent magnet rotors.