Difference between Star and Delta Connections – Comparison Of Y/Δ

Electrical Technology

Comparison between Star and Delta Connections

We mostly use the terms star and delta in electrical systems while discussing three phase AC circuits and electric motors. Below is a given table which compares both Star and delta connections which shows the exact difference between Star (Y) and Delta (Δ) Connections.

Star Connection:

Star connection “Y” is obtained by joining together similar ends of coils either “starting” or finishing. The other ends are joined to the line wires. The common point is called the Neutral or Star Point. This three-phase, 4-wires system is used in power distribution, transformers and small scale domestic and residential applications.

Delta Connection

Delta or Mesh Connection “Δ” is obtained by connecting the starting end of the first coil to the finishing end of the second coil and so on (for all three coils) which forms like a closed loop or mesh circuit. This three-phase, 3-wires system is used in power transmission, transformers, and large scale industrial and commercial applications.

In both systems, the Voltage between two phases (Line to Line) is known as Line Voltage, while the voltage between Phase to Neutral (Line to Neutral) is known as Phase voltage. The voltage between any line (or phase) and Neutral is single phase while voltage between all three lines (or phases) is known as three phase voltage. Keep in mind that the power in both systems are always equal and same as it is the game of different levels of voltages and currents only used in different systems based on the requirement.

Related Post: Star to Delta & Delta to Star Conversion. Y-Δ Transformation

The following table better summarizes the differences and comparison between Star and Delta Connection.

STAR Connection (Y)	DELTA Connection (Δ)
In STAR Connection, the starting or finishing ends (similar ends) of three coils are connected together to form the neutral point in the shape of letter “Y”. A common wire is taken out from the neutral point which is known as the Neutral Wire.	In DELTA Connection, the opposite ends of three coils are connected together which forms the shape of Greek alphabet “Δ”. In other words, the end of each coil is connected with the starting point of another coil, and the common joints form the three phase wires.
There is a Neutral or Star Point.	No Neutral Point in Delta Connection.
There are Four conductors in the star connection (3 Phase Wires + 1 Neutral Wire).	There are Three conductors in the delta connection (3 Phase Wires e.g. All are phases).
Three phase four wire system is derived from Star Connections (3-Phase, 4 Wires System). 3 Phase 3 Wire System is also possible in the Star Connection as Neutral is optional if not needed.	Three phase three wire system is derived from Delta Connections (3-Phase, 3 Wires System). i.e. 3 Phase, 4 Wires system is not possible in Delta Connection due to the absence of the Neutral wire.
Line Current is Equal to the Phase Current. i.e. Line Current = Phase Current I_L = I_PH	Line Current is √3 times of Phase Current. i.e. Line Current = √3 × Phase Current I_L = √3 × I_PH
Line Voltage is √3 times of Phase Voltage. i.e. Line Voltage = √3 × Phase Voltage VL = √3 × V_PH	Line Voltage is Equal to the Phase Voltage. i.e. Line Voltage = Phase Voltage VL = V_PH
In Star Connection, the total Power supplied by three Phases could be found by: P = √3 × V_L × I_L × CosФ … Or P = 3 × V_PH × I_PH × CosФ P = √3 × V × I	In Delta Connection, the total Power of three phases could be found by: P = √3 × V_L × I_L × CosФ … Or P = 3 x V_PH x I_PH x CosФ P = 3 × V × I
The speeds of Star connected motors are slower as they receive 1/√3 voltage.	The speeds of Delta connected motors are high because each phase gets the total of line voltage.
In Star Connection, Smooth starting and operation with nominal power and normal operation without overheating can be achieved.	In Delta Connection, motor receives the highest power output.
In Star Connection, the phase voltage is low as 1/√3 of the line voltage. Therefore, it needs a low number of turns, hence saving in copper.	In a Delta connection, The phase voltage is equal to the line voltage, hence it needs more turns which increase the total cost.
Low insulation required as phase voltage is low as compared to Delta.	More insulation is required as Phase voltage = Line Voltage.
Star connection is preferred for long distance transmission and distribution as it requires low insulation and has a Neutral which helps to balance the circuit.	Delta connection is preferred for shorter distance transmission and distribution as it requires more insulation and has the problems of unbalanced currents.
Two different voltage levels can be achieved by using star connection i.e. single phase and three phase supply. (3 Phases and Phase + N).	Only a single magnitude of voltage can be achieved by using the delta connection e.g. three phase supply across three phase conductors.
Star connection is preferably used in the domestic and residential applications for single phase supply (Line or Phase + Neutral = 230V AC – IEC) and three phase supply (Three Phases = 400V AC – IEC). But the case is different and complex in US – NEC).	Delta connection is generally used in the industrial and commercial applications for three phase supply (Three Phases = 400V AC – IEC). This role is not applicable in the US – NEC as they offer different levels of voltages based on the system requirement).
Star connection is commonly used for appliances which need less amount of starting current e.g. small load applications.	Delta connection is generally used for high starting torque applications e.g. large electric motors in the industries etc.
Star Connection is a common and general system which is used for both single phase and three phase power transmission & distribution.	Delta Connection is a typical system commonly used in the distribution Networks & systems and Industries.

For reference, the following table can be downloaded in the image format for later use which shows differences between star and delta configurations.

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