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VOOZH | about |
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VOOZH | about |
Star and delta connections are the types of three-phase circuits. Electric circuits are divided into Single-phase AC circuits and Three-phase AC circuits. A Single-phase system consists of two conductors, one is called phase (through which current flows) and the other is called neutral ( acts as a return way to complete the circuit). A Three-phase system consists of three conductors, which is the more economical way to transmit power than a single-phase system. In electrical circuit analysis there are certain type of complex circuits that have resistances connected in either series or parallel. These complex arrangements are usually connected in the T, Y, Delta or pi connections. Among these star and delta are some common types of connection.
Table of Content
Star connection is denoted by ' Y '. It is a 4-wire system and one of the type of Three-phase circuit. It consists of 3 phase wires and 1 neutral. There are two types of star connection, 4 βwire 3 β phase system (three-phase wires and one neutral wire) and 3 β wire 3 phase system (three-phase wires). Star Connections are mainly used for the Power Transmission Network for longer distances. This type of connections are required when there is need for a neutral point. It is mostly used in low and medium voltage distribution systems.
The Common point of the Star Connection is called Neutral or Star Point. Consider VR, VB , VY are three phase voltages and VRB, VBY , VRY are line voltages:
Now from the figure above,
|VR|=|VB|=|VY|=|VPhase|
Let VPhase= VP,
|VR|=|VB|=|VY|=|VP|
We can write VRY as,
VRY = VR + (-VY)
VRY = VR -VY
To find the magnitude use parallelogram law of vectors,
we know that |VR|=|VB|=|VY|=|VP|, VRY=VL (Line voltage)
and ,
Then,
VL =β3 VP
where VL is line Voltage
VP is Phase Voltage
From the circuit shown above in star connection line is in series with its phase winding,
IR= IB = IY = IP
IL = IP
Where, IL is line current
IP is phase current.
It is also called mesh connection. Delta connection is a 3- wire system and all the three wires are phases. No neutral wire in delta connection. Delta connection is denoted by Ξ . Delta Connection is generally used in distribution networks. It is sometimes also in the shape of pi and mostly in shape of a triangle or can be referred to as delta. there is no common or neutral point available in the system. In this connection every wire is connected to two adjoining wires in the form of a triangle Ξ, all three points form the three phases as shown below.
Consider IR , IB , IY are the Line Currents and IRB , IBY , IRY are the Phase Currents in Delta connection as shown below:
From the above connection,
|IRB|=|IBY|=|IRY|=|IPhase|=|IP|
From the above diagram we can write,
IR = IRB - IRY
IY = IRY - IBY
IR = IBY - IRB
Use the parallelogram law of vectors to find the magnitude,
Use,
Neutral point does not exist in the delta connection the phase voltage and line voltage are equal,
VRB = VBY = VRY = VL (Line voltage)
VL = VP
where VL is line Voltage
VP is Phase Voltage
IL =β3 IP
where IL is line Current
IP is Phase Current
Consider three resistances RAB, RBC , RCA are connected in delta to the terminals A,B,C as shown below:
From the figure above,
Resistance between A and B for star connection = Resistance between A and B for delta connection
RA + RB = RAB || (RBC + RCA)
For example,
Then
β (1)
Similarly,
β (2)
β (3)
Subtracting equation (2) from equation (1)
β (4)
Add equation (3) and (4)
β (5)
Similarly,
β(6)
β(7)
Here RA,RB,RC are the Resistors in star connection.
To get the delta connection resistors RAB,RBC,RCA from the star connection, Consider the star connection as shown below:
Divide equation (5) by equation (6),
RCA=(RARBC)/RB
Similarly divide equation (5) by equation (7),
Substitute RAB, RCA in equation (5),
Similarly,
Find the equivalent delta connection of the circuit in star with resistances 2, 4 and 6 ohms respectively.
Consider the circuit,
RA= 2β¦, RB=4β¦, RC=6β¦
Substitute these values into the conversion formulas,
Similarly,
Similarly,
For the resistances RA= 2β¦, RB=4β¦, RC=6β¦ in star connection the Equivalent resistances in delta connection are RAB=22/3 β¦,RBC=22 β¦,RCA= 11 β¦
Star Connection | Delta Connection |
|---|---|
Also called as ' Y' or 'Wye' connection | Also called as Mesh Connection. |
It is a 4- wire connection | It is a 3- wire connection |
The common point in star connection is called Neutral or star point. | There is no neutral point in delta connection. |
Line Voltage is root three times phase voltage i.e. VL=β3 VP | Line Voltage is equal to the phase voltage i.e. VL=VP |
Line current is equal to the phase current i.e. IL=IP | Line current is root three times phase current i.e. IL=β3 IP |
Star connection is used for long distances | Delta connection is used for short distances. |
In conclusion, this article discusses the star and delta connections used in the transmission and distribution of power. We discussed about star and delta connection starting with their definition, advantages, disadvantages, applications. In this article we can see that the star-connection is used for long distances due to the insulation required is less and achieve load balance because of neutral wire or conductor compared to the delta connection which doesn't have any neutral wire unless if we provide it artificially. Based on the preferences and usability star connection can be converted into delta connection and vice versa, so that the advantages like Higher reliability, lesser cost delta connection is used and for the application of both transmission and distribution networks star connection is used.
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