Difference Between Star And Delta Connection (Comparison)

Star and Delta Connection are the two types of connections in a 3 – phase circuits. A Star Connection is a 4 – wire system and a Delta Connection is a 3 – wire system. Before going in to details of the Star Connection, Delta Connection and comparing those two, let us have a very brief note on three – phase electric power.

A single phase system consists of just two conductors (wires): one is called the phase (sometimes line, live or hot), through which the current flows and the other is called neutral, which acts as a return path to complete the circuit.

In a three – phase system, we have a minimum of three conductors or wires carrying AC voltages. It is more economical to transmit power using a 3 – phase power supply when compared to a single phase power supply as a three – phase supply can transmit three times the power with just three conductors when compared to a two – conductor single – phase power supply.

Hence, most of the power generated and distributed is actually a 3 – phase power (but majority of households will receive a single phase supply). To know more about single phase and three phase, read the Difference Between Single Phase and Three Phase Power Supplies tutorial.

Further, the three – phase electric power system can be arranged in two ways. They are: Star (also called Y or Wye) and Delta (Δ).

Star Connection

In a Star Connection, the 3 phase wires are connected to a common point or star point and Neutral is taken from this common point. Due to its shape, the star connection is sometimes also called as Y or Wye connection.

If only the three phase wires are used, then it is called 3 Phase 3 Wire system. If the Neutral point is also used (which often it is), the it is called 3 Phase 4 Wire system. The following image shows a typical Star Connection.

Delta Connection

In a Delta Connection, there are only 3 wires for distribution and all the 3 wires are phases (no neutral in a Delta connection). The following image shows a typical Delta Connection.

Difference Between Star And Delta Connections

Let us understand more about these connections by using the following Comparison between Star and Delta Connections differences.

Star vs Delta Connection Comparison

Comparison of the key features of star and delta connections, discussed within the same paragraphs for each feature:

Configuration

In a star connection, each of the three phase windings is connected to a common central point known as the neutral or star point, typically resulting in a four-wire system, though the fourth wire (neutral) is optional. Conversely, a delta configuration connects the end of each phase winding to the start of another, forming a closed loop in the shape of a triangle (delta). This arrangement always uses a three-wire system and does not incorporate a neutral.

Implication

The star configuration’s neutral wire provides stability and allows for dual-voltage systems, which is advantageous for applications needing both single and three-phase power from the same source. On the other hand, delta connections, lacking a neutral, are more straightforward and robust, suited for applications requiring consistent, high power delivery without phase balancing.

Voltage

In a star connection, the line voltage is root three (√3) times the phase voltage, which allows for operating flexibility in various voltage environments. Delta connections have their line voltage equal to the phase voltage, simplifying the electrical design but limiting flexibility because only one voltage level can be utilized.

Current

Star connections have their line current equal to the phase current, facilitating simpler infrastructure for current handling. In contrast, in delta connections, the line current is root three (√3) times the phase current, necessitating robust components capable of handling higher currents.

Power Calculation

Power in a star connection can be calculated using either $P=3\times VP\times IP\times \cos (\varphi )$ or 𝑃=3×𝑉𝐿×𝐼𝐿×cos⁡(𝜙)P=3​×VL×IL×cos(ϕ), providing measurement flexibility. Similarly, power in a delta connection follows the formula $P=3\times VP\times IP\times \cos (\varphi )$ or 𝑃=3×𝑉𝐿×𝐼𝐿×cos⁡(𝜙)P=3​×VL×IL×cos(ϕ), though the implications for component sizing differ due to the current and voltage characteristics.

Insulation

Star connections require less insulation on each phase due to the lower phase voltage compared to the line voltage, which can reduce material costs and complexity. Conversely, in delta connections, the same voltage is applied across each phase as is across the line, necessitating higher insulation levels to safely handle the increased voltage.

Usage

Star connections are typically used in both transmission and distribution networks where the flexibility of a neutral wire is advantageous, suitable for long distances and diverse applications requiring less starting current. Delta connections, preferred for their high starting torque, are prevalent in applications involving heavy machinery and motors, where robust power delivery over shorter distances is prioritized.

By understanding these differences and the specific conditions they are suited for, professionals can effectively decide which configuration to implement based on the operational requirements and environmental constraints.