Use of Converter Transformer

ok dont worry read below information.

The converter transformer is usually used as star connected on the converter side and must have either a delta primary or delta tertiary winding.
Incase it has a delta tertiary winding, it reduces the harmonic voltage distortion in the HV supply system as increasing the power factor of the load.

One of the most common use which reduce the harmonic for converter transformer can be found in Varialble speed drive (VSD) application.

A converter transformer is a three winding transformer with one primary winding and two secondary windings. The primary may either be connected in Star or Delta. But, one of the secondaries MUST be connected in Star and the other secondary MUST be connected in Delta. Now, with this arrangement, each of these secondaries is connected to a six-pulse rectifier (totally called a 12-pulse rectifier) of a non-linear load. With this arrangement, the 5th & the 7th Harmonics cancel out each other at this transformer's primary terminals. Now you have to manage only from 11th Harmonics. That is the advantage of the Converter transformer. But, you must remember that one of the secondaries is star and the other is delta. Then only the 5th & the 7th Harmonics will cancel out each other. Also, both the secondaries should be connected to the same load. Otherwise, if each one is connected to a different load, it is very difficult to maintain equal loading on both the secondaries and thus again the lower order harmonics wouldn't cancel.