23-07-2012, 01:15 PM
Star Delta Connection using Magnetic Contactor as Star Delta Starter for Star Delta Motor Control
StarDelta_Motor_Starter_Using_Miccocontroller(1).pdf (Size: 190.52 KB / Downloads: 67)
The most common motor control method for reducing induction motor starting current in any
industrial application is the star delta connection. Star delta motor connection normally
incorporates the usage of electromechanical devices which primarily consist of magnetic
contactors, a timer and a thermal overload relay.
Due to the low cost and availability of these electromechanical devices for this type of
application, the star delta connection method is still, by far, the most widely used electrical
control for reduced start up current of 3 phase induction motors which is widely known in any
industrial application.
A typical star delta control circuit wiring diagram is shown on the attached CAD drawings.
Refer to the attached star delta electrical diagrams, it is intended as a supplemental aid for
the visual comprehension of the following explanation.
Delta Connected Motor Internal Winding Terminal
Illustrated on the power circuit diagram above, the 3 phase line voltage L1, L2, L3 is supplied
from the main circuit breaker down to the main magnetic contactor and finally to the three
primary terminals of the motor coils U1, V1, W1, while shorting the other three secondary
terminals of the motor terminals U2, V2, W2 with the closing of the star contactor.
Take note that the control circuit of the star delta motor controller is specifically configured in
the manner so as to achieve the operational transfer sequence that provides the motor
terminal with a switching interchange from star connection to delta connection.
Role of the Microcontroller
The role of ATmega16 microcontroller here is to switch the circuit from Star connection to
Delta connection after a suitable delay. The microcontroller energizes the relay coils and then
contactor coils using transistor switches to achieve the above configuration.
ATmega16 Microcontroller
ATmega16 is an 8-bit high performance microcontroller of Atmel’s Mega AVR family with low
power consumption. Atmega16 is based on enhanced RISC (Reduced Instruction Set
Computing) architecture with 131 powerful instructions. Most of the instructions execute in
one machine cycle. Atmega16 can work on a maximum frequency of 16MHz.