Everything You Should Know About The Three Phase Transformer Connections

 Three-phase transformer connections In a three-phase system, the three phases are often connected in either star or delta configuration. just just in case you are not familiar with those configurations, study the next image which explains star and delta configuration. In any of those configurations, there'll be a phase difference of 120° between any two phases.

Star delta configuration three phase

Three Phase Transformer Connections

Windings of a 3 phase transformer are often connected in various configurations as (i) star-star, (ii) delta-delta, (iii) star-delta, (iv) delta-star, (v) open delta and (vi) Scott connection. These configurations are explained below.

Star-Star (Y-Y)

Star-star connection is usually used for little, high-voltage transformers. due to star connection, the number of required turns/phase is reduced (as phase voltage in star connection is 1/√3 times of line voltage only). Thus, the quantity of insulation required is additionally reduced.

The ratio of line voltages on the first side and therefore the secondary side is adequate to the transformation ratio of the transformers.

Line voltages on each side are in phase with one another.

This connection is often used as long as the connected load is balanced.

Delta-Delta (Δ-Δ)

This connection is usually used for giant, low-voltage transformers. The number of required phase/turns is comparatively greater than that for star-star connection.

The ratio of line voltages on the first and therefore the secondary side is adequate to the transformation ratio of the transformers.

This connection is often used even for unbalanced loading.

Another advantage of this sort of connection is that albeit one transformer is disabled, the system can still operate in an open delta connection but with reduced available capacity.

Star-Delta OR Wye-Delta (Y-Δ)

The primary winding is a star (Y) connected with grounded neutral and therefore the secondary coil is delta connected.

This connection is especially utilized in a step-down transformer at the substation end of the cable.

The ratio of secondary to primary line voltage is 1/√3 times the transformation ratio.

There is 30° shift between the first and secondary line voltages.

Delta-Star OR Delta-Wye (Δ-Y)

The primary winding is connected in delta and therefore the secondary coil is connected in star with neutral ground. Thus it is often wont to provide a 3-phase 4-wire service.

This type of connection is especially utilized in the transformer at the start of the cable.

The ratio of secondary to primary line voltage is √3 times the transformation ratio.

There is a 30° shift between the first and secondary line voltages.

Above transformer, connection configurations are shown within the following figure.

transformer connection star-star-delta-delta-star

Open Delta (V-V) Connection

Two transformers are used and first and secondary connections are made as shown within the figure below. Open delta connections are often used when one among the transformers in Δ-Δ bank is disabled and therefore the service is to be continued until the faulty transformer is repaired or replaced. It also can be used for little three-phase loads where installation of a full three transformer banks makes no sense. the entire load-carrying capacity of an open delta connection is 57.7% then that might be for a delta-delta connection.

open delta or V-V connection transformer

Scott (T-T) Connection

Two transformers are utilized in this sort of connection. one among the transformers has centre taps on both primary and secondary windings (which is named as the main transformer). the opposite transformer is named a teaser transformer. Scott connection also can be used for 3 phase to 2 phase conversion.