# Star-Star (Y-Y) Connection of Three Phase Transformers

- Link: https://studyelectrical.com/2014/11/star-star-connection-of-three-phase-transformer.html
- Published: 2014-11-05T16:49:00+00:00
- Author: 

There are different types of connection employed for three-phase transformers. The
star-star (Y-Y) connection of three-phase transformers is the most economical type
of connection for small current and high voltage transformers. The advantages and
disadvantages of this connection are given below,

## Advantages of Star-Star Connection

The following are the advantages of star-star connection 

 * Phase voltage = (Line Voltage)/√3 . The voltage gets reduced in-phase and this,
   in turn, reduces the number of turns per phase and the amount of insulation.
 * There is no phase displacement between the primary and secondary voltages
 * Star points on both sides make it possible to provide a neutral connection

## Disadvantages of Star-Star Connection

The disadvantages of star-star connection of three-phase transformer are the following

 * If the load on the secondary side of the transformer is unbalanced, the phase
   voltages of load side change unless the load-star point is earthed. The difficulty
   of shifting neutral can be overcome by connecting the primary star point to the
   star point of the generator.

 * The primary of the transformer draws a magnetizing current which has third and
   fifth harmonics. If neutral of the  primary winding is not connected to neutral
   of the generator, the
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 * third and fifth harmonics current cannot flow hence the flux in the core cannot
   be of a sinusoidal wave and, therefore, the voltages will be distorted. By connecting
   primary neutral to the generator neutral, the path for the return of these third
   and fifth harmonics current is provided and, therefore, the trouble of distortion
   of voltages is overcome.

 * Even if neutral point of primary is connected to neutral of generator or earthed,
   still if third harmonic is present in the alternator voltage form, it will appear
   on secondary side. Though the secondary line voltages do not contain third harmonic
   voltage; but the 3rd harmonic voltages are additive in the neutral and causes
   the current in the neutral of tipple frequency (3rd harmonic) which will cause
   interference to the nearby communication system.

Thus harmonic phase voltages may be high in-shell type 3-phase transformers.

The star-star connection is rarely used owing to the difficulties associated with
the exciting current.

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