Automatic star delta starter control circuit diagram with timer

fully automatic star delta starter

Star delta starter troubleshooting star-delta starter control wiring diagram principle circuit diagram and explanation

star delta starter control 

 Introduction fully automatic star delta starter 

A three-phase motor has three windings with terminal numbers A1-A2, B1-B2, and C1, C2. In some motors, the terminal numbers are U1-U2, V1-V2 and W1-W2. These three windings are known as star connections or delta connections. In the motor nameplate we can get the motor type as a three-phase AC induction motor, 5kw 10 kW as KW, voltage 230 or 400, star or delta connection full load current power factor efficiency duty cycle, etc.

 

Star Connection: -

                  Star Connection

 The instar connection is connected to the second point of each winding i.e. A2, B2, C2 one point (shorted), from which one point is known as the star point. And the remaining three points A1, B1, and C1 are connected to the 3 phase supply points R phase Y phase, and B phase respectively. The connection is shown in the figure. In the STAR connection, each voltage is equal to the line voltage / 1.732 (Route 3), known as the phase voltage. And the phase current is equal to the line current.

Delta Connection: -

                       Delta Connection

 In delta connection, the second point A2 of the first winding is connected to the first point B1 of the second winding. The second point B2 of the second winding is connected to the first point C1 of the third winding. And the second point C2 of the third winding is connected to the first point A1 of the first winding. It forms a triangle-shaped closed circuit with three windings on the side of the triangle, hence it is known as a delta connection. In delta connections, the winding phase voltage is equal to the line voltage of the supply. But phase current line is current / route 3.

 

So a motor can be connected to a star or delta connection according to the nameplate voltage and connection.

If a motor nameplate shows a delta connection, it can be run first in the star and then in the delta. This motor can be used with a star-delta starter.

If a motor is a 400-volt star connection it cannot be used with a star-delta starter because the motor cannot be connected in a delta connection.

 

Principle of Star Delta Starter: - During starting the motor a 3 phase supply is given to the motor by the contactor. There is too much current when giving direct full voltage to the motor which causes a line voltage drop. A method used to reduce the current is known as reducing the voltage start and a full voltage running scheme is used. This is achieved in two ways

 

Using l star delta starter

2. Using the autotransformer rater

 

Here we will discuss the star-delta starter.

 

In the old times, a manual star delta starter was used. But now automatic star-delta start is used.

 

Construction; - It consists of three starters and one time relay and two push-button overload relays. All parts are connected as shown in the circuit diagram.

When the start button has pressed the contactors c1 and c3 pick up and the motor starts in the star connection with a low voltage taking voltage. After a few seconds when the motor operates the speed time relay contacts C3 drop and C2 pickup which changes the motor connection for the delta. Now the motor runs at full voltage. The overload relay provides protection from overload conditions by tripping the motor. When the stop button was pressed both contacts and the motor stopped. The time relay coil is connected in parallel with the c1 contactor coil. The c2 and c3 NC contacts are used in interlocking so that c2 can be lifted only when c3 falls. Likewise, c3 can only pick up when c2 drops.