Three-phase circuits are used in transformers, generators, distributors to generate electric power. It has three voltages which are interconnected using either star or wye connection or delta or mesh connection to save copper and make the system less expensive. The angle between the line currents of resistors is 120 degrees.
Star Connection vs Delta Connection
The main difference between Star Connection and Delta Connection is that star connection is used in the long-distance transmission lines, and delta connection is used in short distance distributed network. The star connection uses 4 wires, three for connection to the external circuit and one for the neutral point. The delta connection uses three wires to form a mesh loop.
In the Star connection system, the starting or finishing ends are connected to the neutral point. It uses four wires to connect to the external load circuit, out of which three wires for the external circuit and the fourth fire are for neutral connection forming a three-phase star connection. A voltage between each line and the neutral point is a phase voltage, and a voltage between the two terminals of connection is a line voltage.
Delta Connection is a system the starting end is connected to the finishing end of the phase forming a mesh loop. A delta-connected system does not have a neutral point. So only three wires are used to form a delta connection. Delta connections are used in the sum of voltages at any closed paths equals zero.
Comparison Table Between Star Connection and Delta Connection
| Parameters of Comparison | Star Connection | Delta Connection |
| Definition | It is a three-phase four-wire start connected system generally used in long-distance transmission of power in the distributed network. | It is a three-phase three-wire delta connected system generally used in the short-distance transmission of power in the distributed network. |
| Neutral point | It has a neutral point where all the starting or ending points of each resistor meet. | There is no neutral point in the delta; instead, the starting point of one resistor is connected to the ending point of the other resistor forming a mesh loop. |
| Line Voltage | Line voltage = √3 *Phase voltage | Line voltage is equal to phase voltage. |
| Line Current | Line Current is equal to Phase current. | Line current=√3 * phase current |
| True Power | √3*Line Voltage *Line Current*CosΘ Where Θ is the difference between phase voltage and phase current | √3*Line Voltage *Line Current*CosΘ Where Θ is the difference between phase voltage and phase current |
What is Star Connection?
Star connection is one of the forms to interconnect the three-phase circuit. It has a neutral point N where all the similar ends of the resistors either start or finish joins. The star-connected system forms a Y or T shape or reverses Y shape using four wires, three for three phases, and the last one is for neutral point. The phase voltage is the voltage between the phase windings, and line voltage is the voltage between the two terminals of the winding. Every pair of the terminal has a two-phase winding that is opposite to each other as they have similar ends.
A balanced star-connected system has an equal voltage in all the phases with the 120-degree angle between each line voltage, and it has an equal current in all the phases with 30 degrees of angle between phase voltages. In this system, the line current and line currents are equal. The potential energy at a neutral point is zero.
Formulae
EL (line Voltage) =√3*Eph (phase Voltage) or Eph = EL
Actual power (p) = √3*EL*IL* CosΘ here Θ is the angle obtained between phase voltage and phase current.
Apparent power=√3*EL*IL
What is Delta Connection?
The delta connection is the other form to interconnect a three-phase circuit. In this circuit, the phases have dissimilar ends where the start point of a resistor is connected to the endpoint of the other resistor to form a mesh loop. The delta-connected systems have higher starting torque than star connected system. Hence they are used in a distributed network of the shortest distance. In the delta-connected system, the phases are connected in series form.
In the balanced delta-connected system, the line voltage and phase voltages are equal. This system does not have a neutral point. Therefore, only three wires are used in the system. The line currents are separated by 120 degrees, and each line current is 30 degrees behind its phase current. If the load is not connected to the system, then no current will pass in the mesh.
Formulae
IL (line current) =√3*Iph (phase current) or Iph = IL
Actual power (p) = √3*EL*IL* CosΘ here Θ is the angle obtained between phase current and phase voltage.
Apparent power=√3*EL*IL
Main Differences Between Star Connection and Delta Connection
- Star connection system is a three-phase four-wire system with a neutral point, whereas Delta connection system is a three-phase three-wire system without a neutral point.
- Star connection systems are used for both low and heavy loads of power transmission in long-distance, whereas Delta connection systems are used for heavy load transmission in a shorter distance.
- In the Star connection system, Line voltage and phase voltages are the same, whereas, in the Delta connection system, phase voltage and line voltages are the same.
- The Star connection three-phase circuit forms a Y shape, and the Delta connection three-phase circuit forms a mesh loop.
- Star connection systems have less starting torque, whereas the Delta connection system has a high starting torque.
Conclusion
The three-phase circuit is used in transformers, generators, distributors to transform power. To reduce the complexity of the circuit and price of the product, the phases in the three-phase circuit are interconnected with each other using either star or delta connection. These systems reduce the use of copper and hence make the power distribution less expensive.
The star connection systems are used in generators and alternators to transfer power. The Delta connection systems are used in small-distance power distributed networks. Star connected system requires less insulation than delta connection hence preferred for long-distance power transmission systems.
References
- https://www.google.co.in/books/edition/Basic_Electrical_Engineering/e-ZbzLvhKzAC?hl=en&gbpv=1&dq=basic+electrical+engineering+by+uma+rao+and+jayalakshmi&pg=PA3&printsec=frontcover