STAR AND DELTA CONNECTIONS
A a.c generator is usually equipped with 3 separate winding connected at 120 degree of space interval around stator.Each winding produce identical peak voltage but each is timed to peak one-third of a cycle after its predecessor.The three windings are distinguised by calling them as red,blue,yellow or A,B,C or U,V,W
Each winding has two ends called R & R’,Y&Y’ and B&B’.
- Generally each winding supplies one element of a 3 phase load.It may happen that the three loads require the same amount of voltage,inthis case the circuit is said to be balanced .unless otherwise stated in the question students should assume it to be a balanced circuit.
- Each winding of the 3 phase circuit has two ends .so to connect each winding with the each load two connecting wire are needed.
- This is the most easiest way of connection,but is seldom used because it involves 6 wires so more copper loss.
What is done is to make each phase share one conductor with the other.
- here in this thpe of connection the inner terminals of the 3 phase winding are connected together to a single point,similarly the 3 inner terminals of the load are connected together to a single point.then this two points are connected together by a single wire.This connecting wire is called as neutral wire.
- now each outer terminal of the the winding is connected independently with the outer terminal of the 3 phase load.
- this type of connection is known as star connection.
There is another way by which the winding share conductors
- in this type of connection two adjacent winding are connected with each other like as shown in the diagram .now R’ is connected with B B’ is connected with Y and finally Y’ is connected with R.
- As a result of this three conductor points are formed.the load is connected in the form of a star.
- The three conductor points are then connected to the respective terminal of the load
- In Delta connecction there is no need of any neutral wire.
DIFFERENCE BETWEEN STAR AND DELTA CONNECTION
- In star connection it will be seen that the line current from generator to load must be same as the generator winding phase current as they are in series.In a delta connection however the line current is divided between two phases.
- In delta connected circuit the voltage across lines is same as that voltage across winding as they are connected in parallel.
DRAWING OF STAR AND DELTA CONNECTED APPARATUS
Theoritically the star connection is shown by a star or Y and the delta connection is shown by a traiangle.But for practical purpose they are shown as
QUESTION AND ANSWERS SECTION
1.WHY STAR OR DELTA CONNECTION IS NEEDED?
ANS star or delta connection uses less wires as compered to conventional connection,due to which there is less copper loss and less heat generation.
2.WHICH IS BETTER STAR OR DELTA CONNECTION?
ANS delta connection is more cost effective as compered to star connection.
3.WHAT IS A NEUTRAL WIRE?
ANS A neutral wire is that which connects a star connected winding to the star connected load between the two common condustors.
4 .WHAT IS A THREE PHASE WINDING?
ANS A 3 phase winding is that where the three winding are connected in 120 degree phase difference.
5.HOW THE WINDINGS ARE DISTINGUISED?
ANS The windings are distinguised by calling them as red,yellow,green or R,B,Y.