Page 161 - Electromechanical Devices and Components Illustrated Sourcebook

Chapter 6 Rotating Components 123

The unit may use a 24-VDC input and produce a 600 VAC,
400 Hz output that is specified for a special piece of equip-
G M ment. Dynamotors have been almost completely replaced by
solid state power supplies.

Schematic Symbol
Single- to Three-Phase Converters
Shaft Coupling
Synchronous Motor 50 Hz Generator In some applications it is necessary to operate a three-phase
piece of equipment in a building or locations that are only
served with single-phase power. In these cases a single- to
three-phase converter can be used to generate the appropriate
power. Figure 6-74 shows a typical single- to three-phase rotary
converter. The unit is constructed from a three-phase motor that
is set up to operate on single phase. The single-phase power is
wired to one of the three coils. As the rotor turns, it induces
Base
power into the two unused coils. Three-phase power can be
Figure 6-71 Motor/Generator Set to Produce 50 Hz Power
taken off of the three coils.
Figure 6-75 shows a schematic representation of a three-
phase rotary converter. The unit must be set up with a starting
circuit. In this case a start capacitor is connected to the second
Lifting Eye Control Cabinet
coil through a delay off relay. When the converter is energized,
Motor Side Generator Side the start capacitor is connected for a predetermined time and
Brush Cover
Brush then automatically disconnected. The run capacitors are primar-
Cover ily used to tune the phase angle of the two generated phases.

Power Switch Controller
Feet
Figure 6-72 Motor/Generator DC Arc Welding Machine
Three-Phase Motor
(Less Output Shaft)

American companies producing electrical equipment for mar-
kets that use 50 Hz power. Figure 6-72 shows a motor/generator
arc welder. These units were very common before the avail-
Figure 6-74 Standalone Single- to Three-Phase Converter
ability of high-power rectifiers. The motor operates from stan-
dard AC power and the generator produces low-voltage,
high-current DC power.
240-VAC Single Phase Input
Neutral
Dynamotors
240-VAC Three-Phase Output
Small, packaged Motor/generator sets, as shown in Figure 6-73,
are commonly referred to as dynamotors. These units were Run Capacitors
very common in aircraft built from the 1930s through the 1970s. Three-Phase Motor
Start
Capacitor

T
On Button
Off Button
Output
Delay Off Relay
Input
2 Pole Contactor w/Auxiliary Contact Set
Figure 6-73 Dynamotor Figure 6-75 Single- to Three-Phase Converter Schematic