What is Start and Delta Connection?

what is star and delta connection. We mostly use the terms star delta connection in electrical systems when we  discussing three phase AC circuits especially in Electric Motor ,Generator ,Transformer connections .

Star and Delta conncetion

STAR Connection

In Star connection the similar end of the three coils are connected together to form neutral point .A common wire which is called neutral wire is taken from the neutral

There is Neutral point or star point in STAR connection. Three phase four wire system is obtained from Star Connections (3-Phase, 4 Wires System) and also derived 3 phase 3 wire system.

Star conncetion

 In Star connection the line current is equal to the phase current i-e

Line Current = Phase Current


In star Connection the Line Voltage is √3 times of Phase Voltage. i.e.

VL = √3 VPH

The Total power of three phase star connection could be found by

P = √3 x VL x IL x CosФ …. Or

P = 3 x VPH x IPH x CosФ

P = √3 V x 1

Star Coonection

The speeds of Star connected motors are slow because they receive 1/√3 voltage. The Smooth starting and operation with nominal power without overheating can be achieved by star connection of the winding

In Star Connection, the phase voltage Vph  is low as 1/√3  time of the line voltage due to which  it needs a low number of turns and  hence saving in copper.

Because the phase voltage is low therefore the low insulation is required as compare to Delta Connection. The star connection is a common and general system which is used in power transmission

Delta Connection

Delta Connection is obtained when the opposite ends of the three coils are connected together or in other words the end of each coil are connected with the starting point of another coil and the three wires are taken out from the coil joints

 In the Delta Connection there is no neutral point .The Three phase three wire system is obtained from Delta Connections(3-phase  ,3 Wires system) i-e three phase four wire system is not possible in Delta connection.

Delta Conncetion

In Delta Connection the Line Current is √3 times of Phase Current. i.e.

IL = √3 IPH

In Delta connection the Line Voltage is Equal to the Phase Voltage. i.e.

Line Voltage = Phase Voltage


The total power of three phases can be calculated by

P=√3x V x IL x CosФ ….Or

P =  3 x VPH   x IPH x CosФ

P = 3 x V (1/√3)

The Delta connected motor speed is higher because each phase gets the total of line voltage. In Delta Connection the output power is highest.

D conncetion

In Delta connection the phase voltage is equal to the line voltage therefore its required more no of turns which increase the cost  and weight of motor.

The Delta Connection required highest insulation because of phase voltage is equal to line voltage. Delta Connection is a system  which used in Distribution system and Industries.

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