Types and connection of three phase transformer ~ MONU TUTORIALS ACADEMY

Three phase transformer connection

Three phase transformer consists of three transformer either separate or combined on one core.the primary and secondary of any three phase transformer can be independently connected in either a star or a delta.

Delta primary-delta secondary
Star primary-star secondary
Delta primary-star secondary
Star primary-delta secondary.

Delta delta connection

In figure a show the delta delta connection of three identical single phase transformer for three identical windings on each of the primary and secondary sides of the three phase transformer. The secondary winding a1 a1 corresponds to the primary winding A1 A2 the terminal A1 and a1 have same polarity. The polarity of terminal a connecting A1 and C2 is the same as that of a connecting a1 and C2.

In figure b show the phasor diagram for lagging power factor cos phi magnetising current it and voltage drop in impedance have been neglected. Under balance condition the line current are √3 times the phase winding current are displaced behind the phase current.in the delta delta configuration the corresponding line and phase voltage are identical in magnitude on both primary and secondary side.

It is to be noted that in figure each winding is drawn along the line of the measure of its induced voltage. The voltage and current phase II are determined very easily from the winding drawn in this manner.

It is seen from the phasor diagram that the primary and secondary line voltage are in phase the connection is called zero degree.

Star star connection

In this figure show the star star connection of three identical single phase transformer all the three identical winding on each of the primary and secondary sides of the three phase transformer.the phasor diagram of drone in the similar manner as done in delta delta connection. The phase current is equal to the line current and they are in phase. The line voltage is √3 times the phase voltage. There is a phase separation of 30 degree between line and phase voltage. This figure show the star star connection 40 degree phase shift and this figure be there is a phase shift of 180 degrees between primary and secondary system.

Delta star connection

A a delta star connection of three phase transformer is shown in figure a.in delta star connection the primary line voltage is equal to the primary phase voltage. The relationship between secondary voltage is Vls=√3Vps. Therefore, the line to line voltage ratio of this connection is,

In figure b show the phasor diagram for the delta star connection supplying balanced load at a power factor cos phi lagging. It is seen from the phasor diagram that the secondary phase voltage Van leads the primary phase voltage v a n by 30 degree. This is also the face relation ship between the respective line to line voltage. This connection is called positive 30 degree connection.

by reversing the connection on either side the secondary system voltage can be made to leg the primary system by 30 degree as shown in figure this connection is called negative 30 degree connection.

Star delta connection

the star delta connection of three phase transformer is shown in figure in this connection the primary line voltage is equal to √3 times the primary phase voltage. The secondary line voltage is equal to the secondary phase voltage. Therefore, line to line voltage ratio of star delta connection is,

The phasor diagram can be drawn with the help of winding diagrams. There is a phase shift of 30 degree lead between the respective line to line voltage. Similarly a phase shift of 30 degree lead exist between respective phase voltage. This connection is called positive 30 degree connection.

in this figure show the star delta connection of transformer for a phase shift of 30 degree lag. This connection is known as negative 30 degree connection.

The star delta connection or delta star connection has no problem with unbalanced load and third harmonic. The delta connection as your balance phase voltage on the star side and provides a path for the circulation of the third harmonic and their multiples without the use of neutral wire.

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