Section 8
Electrical System
20412989
1-2012/Rev 08
8-2
8.3 Operation
Electrical power from the utility grid enters the main circuit breaker/disconnect on the electrical
enclosure door as 3-phase alternating current. The power is then distributed in two directions.
The 3-phase AC, at the voltage provided from the grid, is routed to the motor starter contactor(s)
and then to the main motor. Single phase AC is routed to the transformer.
Figure 8-1: Electrical Control Power
The multi-tap transformer converts the incoming voltage to 230 volt AC that is routed to both the
motor starter contactor(s) and to the power supply. The power supply then provides 24 volt direct
current to the control circuits, including the emergency stop logic, the Programmable Logic
Controller (PLC), optical relays, display screen and optional control functions.
When the
START button is pressed on the control panel, the motor control relay closes and 230
volt AC power is sent to the contactor coil(s). The coil(s) close, sending the incoming power to
the motor. When the
STOP button is pressed, the motor control relay opens, disconnecting power
to the contactor coil(s), stopping the motor.
The motor is started by either contactors or a softstarter, solenoid operated by 230 volt AC
control power.
Contactors are arranged in either a wye-delta or an across-the-line starter circuit. Wye-delta
starter circuits are typically installed in all low voltage, high horsepower machines that require
high current draw. Three, 3-phase contactors are used to start the motor slowly, minimizing the
initial current draw. Across-the-line or full-voltage starting requires a single 3-phase contactor
and is used on high voltage machines with low current draw.
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