392 Electrical Power Systems Technology
tion from one location to another without any direct mechanical linkage.
Synchro systems are classified as two or more motor/generator units
connected together in a way that permits the transmission of angular shaft
positions by means of electromagnetic field changes. When an operator
turns the generator shaft of a unit to a certain position, it causes the motor
shaft at a remote location to automatically rotate to an equivalent position.
With this type of system, it is possible to achieve accurate control of devic-
es over long distances. Computers often employ these units to determine
the physical changes that take place in automated operations.
In synchro systems that require increased rotational torque or precise
movements of a control device, servomechanisms are employed. A servo-
mechanism is ordinarily a special type of AC or DC motor that drives a
precision piece of equipment in specific increments. Systems that include
servomechanisms generally require amplifiers and error-detecting devic-
es to control the angular displacement of a shaft.
Synchro System Operation
A synchro system contains two or more electromagnetic devices that
are similar in appearance to small electric motors. These devices are con-
nected together in such a way that the angular position of the generator
shaft can easily be transmitted to the motor or receiver unit. Figure 14-31
shows the schematic diagram of a basic synchro unit. As a general rule,
the generator and motor units are identical electrically. Physically, the mo-
tor unit has a metal flywheel attached to its shaft to prevent shaft oscilla-
tions or vibrations when it is powered. The letter G or M inside of the elec-
trical symbol denotes generator or motor functions.
Figure 14-32 shows the circuit diagram of a basic synchro system.
Single-phase AC line voltage is used to power this system. Note that the
Figure 14-30. Diagram of a three-phase, wound-rotor induction motor