Figure 10.11 Magnetic Contactors
2. Star-Ddelta Starter : It is a popular method and the industrial most used
On 3 phases motor staring
The starting electrical current of the simple 3 phase electrical motor that a delta
connected. The stating current will be high up to 4 times of the normal load therefore
to able to start the motor it is a must to use a very large circuit breaker. very thick 3
phase cable. Coil and contact in the relay or contactor must big so as to the starting
electrical current can flow through the circuit without cutting of the circuit.
To solve this problem, will starting the motor as of star starter generated the
voltage flow through each coil will reduce to 1/3 of the voltage used if coil When the
motor rotates at the suitable speed it will change the connection to the delta connection
Star-Delta Reduced Voltage Starter : The motor will connect to the power supply
through the main contactor (KM2) and connected the terminal of U1,V1,W1 of the motor
as shown in Figuer 12.10 (a) and the contact face of the star contactor (KM1) will connect
the circuit whilst starting. It is a star connection and star motor starting as shown
in Figuer 10.12 (b) and afterward the interval the timer together connectad with the
starting circuit generated the contact face of star contactor open and the contact face
of delta contactor (KM3) closed. It is a function connection of the delta motor
as shown in figure 10.12 (c).