Page 251 - Introduction to Marine Engineering

Steering gear 227

exciter field is part of a control circuit, although in some circuits control
is directly to the field current of the generator with the exciter omitted,
When the control system is balanced there is no exciter field, no exciter
output and no generator output, although it is continuously running.
The main motor which drives the rudder has no input and thus is
stationary. When the wheel on the bridge is turned, and the rheostat
contact moved, the control system is unbalanced and a voltage occurs in
the exciter field, the exciter, and the generator field. The generator then
produces power which turns the rudder motor and hence the rudder,
As the rudder moves it returns the rudder rheostat contact to the same
position as the bridge rheostat, bringing the system into balance and
stopping all current flow.

Supply

Starter

Motor

Rudder
rheostat

Figure 12.10 Ward-Leonard steering gear

In the single motor system the motor which drives the rudder is
supplied directly from the ship's mains through a contactor type starter.
Reversing contacts are also fitted to enable port or starboard
movements. The motor runs at full speed until stopped by the control
system, so a braking system is necessary to bring the rudder to a stop
quickly and at the desired position.
The usual electrical maintenance work will be necessary on this
equipment in order to ensure satisfactory operation.