Precaution to take when connection of star delta motor
The star delta starter is a very common type of starter. Star delta starter extensively used than any other starter for starting of Three phase induction motor.The starter is used above 5HP motors. At the time of starting motor starts in star connection and when motor picks up speed of about 80% the rated speed of the motor it changes the delta from star. As a result the stator gets the supply from delta.
How we can make connection of star delta motor.When we are going to make connection of star delta starter. We need to focus on these points:-
- There are six cables in star-delta starter to motor.
- We need to connect six wires to the motor as shown in the diagram.
- Check the wires with marking and farruls. If faruls are not available check continuity in both the cables of star and delta.
- Connect the wires as shown in the figure.
Difference Between Star and Delta connection
- In a star connection, phase voltage Vph= VL/ (3)1/2. Since the induced emf in the primary winding of an alternator is directly proportional to the number of turns, a star connected alternator will require less number of turns than a delta connected alternator for the same voltage.
- For the same line voltage, a star connected alternator requires less insulation than a delta connected alternator. Due to the above reasons three phase alternators are generally star connected.
- In star connection, we get 3-phase and 4-wire system. This permits the use of two voltages (phase voltages as well as line voltages). Single phase loads can be connected between any one lie and neutral wire while the 3-phase loads can be put across the three lines. Such a flexibility is not available in delta connection
- In star connection, the neutral point can be earthed. Such a measure offers many advantages. For example, in case of line to earth fault (L-G fault), the insulators have to bear 1/31/2(57.7%) times the line voltage. Earthing of neutral also permits the use of protective devices (relays) to protect the system in the case of ground faults
- This type of connection is most suitable for rotatory conveyers.
- Most of the three phase loads are delta connected than star connected. One reason for this, at least for the case of unbalanced load, is the flexibility with which loads may be added or removed on a single phase. This is difficult to do with star connected 3-wire load
- Most of the 3-phase induction motors are delta connected