Table of Contents
Why is the star contactor switched first then the main in the star delta starter?
WHY?! Star delta starter is used to reduce the starting current drawn by the motor. Start the motor in STAR and then, when the motor has gained sufficient speed, change its connections to DELTA to allow the motor to run at its full speed and torque from then on.
How does a star Delta contactor work?
In star delta starting an induction motor is connected in through a star connection throughout the starting period. Then once the motor reaches the required speed, the motor is connected in through a delta connection. A star delta starter will start a motor with a star connected stator winding.
How many power contactors are used in star delta starter?
three contactors
Component: The Star/Delta starter is manufactured from three contactors, a timer and a thermal overload. The contactors are smaller than the single contactor used in a Direct on Line starter as they are controlling winding currents only. The currents through the winding are 1√3 = 0.58 (58\%) of the current in the line.
What is the function of timer in star delta starter?
Star delta timer is an electronic timer which counts the time of its coil energize and trip the circuit when the time exceed presetting time.
What is the function of contactor in electrical circuit?
A contactor is an electrical device which is used for switching an electrical circuit on or off. It is considered to be a special type of relay.
What is Star contactor?
The star contactor serves to initially short the secondary terminal of the motor U2, V2, W2 for the start sequence during the initial run of the motor from standstill. This provides one third of DOL current to the motor, thus reducing the high inrush current inherent with large capacity motors at startup.
How is Star Delta contactor size?
Size of Star Contactor =33\%x13 = 4 Amp. Size of Main Contactor (Starting-Transition-Running) = 58\%X Full Load Current (Line). Size of Main Contactor =58\%x13 = 8 Amp. Size of Delta Contactor (Running Condition) = 58\%X Full Load Current (Line).
What is the difference between relay and contactor?
Control Relay: It is a device through which contacts in one circuit are operated by an alteration in conditions in the same circuit or in associated circuits. Contactor: It is a device which is used for repeatedly establishing and interrupting an electric circuit under normal conditions.
How long should a star delta timer be set for?
Set the timer to the time recorded on the stop watch. In star Delta usually we consider that the load and motor torque are equal when the motor reach 75-85\% of the speed. At this time you stop the star connection to go with delta connection, the time is around 30 to 50 milliseconds, to avoid short-circuit.
What is the major difference between a contactor and a motor starter?
The contactor applies voltage to a contactor coil to close the contacts and to supply and interrupt power to the circuit. A motor starter is simply a contactor PLUS an overload relay and is rated by motor HP or amperage. If there is no overload relay it is not a starter any longer. It’s back to being just a contactor.