This article describes the most prominent differences between the star and delta connection and their basic introduction.
Electric circuits can be divided into the following two types.
- Single-phase AC circuit
- Three-phase AC circuit
Single-phase AC circuits transmit power and current in one phase across a single wire. While three-phase circuits produce and transmit power in three phases each phase having a phase shift of 120 degrees from each other.
Three-phase circuits are further subdivided into two kinds of connection namely –
- Star connection circuit
- Delta connection circuit
What is Star Connection?
Star connection is a type of electrical connection of a three-phase AC circuit, comprised of four conducting wires. Three of the four wires are carrying each of the three-phase currents and the fourth wire is the neutral wire.
The three-phase wires carry the line currents at a phase difference of 120 degrees each. A star connection is the most preferred type of three-phase circuit connection for transmitting power and current over long distances, due to the presence of the neutral wire in the star connection.
The neutral wire is used to safeguard the electrical equipment such as the transformers from over-current and over-voltage flow across it.
The star circuit connection can either be balanced or unbalanced. In the balanced condition of the star connection, the same magnitude of current flows through each of the three-phase wires, and the current flowing across the neutral wire is zero.
Thus, the star-connected circuit is said to be balanced, and this balanced flow of current is the desired condition in a three-phase power system, to ensure the safety of the electric equipment connected to it.
On the other hand, an unbalanced condition of the star-connected circuit is achieved when uneven current flows across the three-phase wires. In this scenario, the neutral wire comes into action. In the unbalanced condition, the neutral wire carries the unbalanced current and passes it to the ground, thus protecting the electrical equipment connected to the supply system.
Thus, the neutral wire plays a crucial role in converting the unbalanced current flow in the three-phase system to a balanced current flow, which would otherwise be harmful to the connected electrical and electronic equipment.
Figure 1 shows the star-connected circuit. The relation between the three-phase line voltage and phase voltage, and the line current and phase current is given below.
The line voltage is equal to √3 times the phase voltage or neutral voltage as shown in equation 1. While the phase current and line current remain the same as shown in equation 2.
What is a Delta Circuit Connection?
Delta connection is a type of three-phase circuit connection comprised of only three conducting wires carrying three-phase currents without a neutral wire. The three-phase wires are connected in the form of a delta. The delta connection is also called the mesh connection.
Due to the absence of a neutral wire in the delta connection, there persists an unavoidable unbalanced current flow in the phases of the circuit. That is why a delta circuit connection is used in three-phase systems requiring short-distance transmission of power and current.
Figure 2 depicts the three-phase representation of three phase delta circuit connection.
In the case of a delta circuit connection, the line current of each phase of the three phases is equal to √3 times the phase as shown in equation 3. While the line voltage and phase voltage are equal in magnitude as shown in equation 4.
Difference Between Star and Delta Connection
The table below highlights the important differences between the three-phase star connection and delta connection of electronic circuits –
| Parameter | Star connection | Delta connection |
| Description | Each end of a star-connected wire is connected to a common point in the circuit, thus forming a star-shaped connection. | The three conducting wires of the delta connection are connected to each other in order to form a closed loop. |
| Number of wires | The star connection consists of four wires. Three of these are the phase wires and the fourth one is the neutral wire connected to the ground. | Delta connection is only comprised of three-phase wires with no neutral wire. |
| Neutral wire | The neutral wire connection is present at the point of intersection of the three-phase wires, also called the neutral point. | The neutral wire is absent in the case of a delta-connected circuit. |
| Mode of transmission | Star connection circuits are used for long-distance transmission of electric current and power. | Delta connection circuits are used for short-distance transmission of electric current and power. |
| Balanced / Unbalanced | Star connections are primarily balanced circuit connections due to the presence of the neutral wire, that carries the unbalanced current to the ground. | Delta connections are mostly unbalanced circuit connections due to the absence of the neutral wire. |
| Relationship between line voltage and phase voltage | The line voltage is equal to √3 times the phase voltage in a star connection. | The line voltage is equal in magnitude to the phase voltage in the delta connection. |
| Relationship between line current and phase current | The line current is equal in magnitude to the phase current in the star connection. | The line current is equal to √3 times the phase current in a delta connection. |
| Rate of operation | The rate at which star-connected power systems operate is relatively slow as the phase voltage is equal to 58 % of the line voltage. | The rate at which delta-connected power systems operate is relatively high as the phase voltage is equivalent in magnitude to the line voltage. |
| Insulation | The insulation requirements for the phase and neutral wires are relatively low because the phase voltage is less than the line voltage. | The insulation requirements for the phase wires are relatively more because the phase voltage is equal to the line voltage. |
| Applied voltage | 230 volts is carried by the star connection windings. | 440 volts is carried by the delta connection windings. |
| Applications | Star connections find their application in transmitting power over long distances due to the balanced flow of current in it. It is also used for single phase and three power to consumers. | Delta connections find their application in distributing power across households in residential areas over short distances. It is primarily used in the high-voltage transmission of power. |
Conclusion
In conclusion, this article discusses the differences between star and delta connections used in the transmission and distribution of power. The main difference between the two of these types of connections is that the star-connected systems achieve a balanced condition due to the presence of a neutral wire that carries the unbalanced current to the ground, while the delta-connected systems are mostly unbalanced systems due to the absence of a neutral connection.
Therefore, for this reason, star connections are used to transmit three-phase AC power over long distances, while delta connections are used to distribute three-phase AC power over short distances.