Delta Zigzag transformer question

[n1mr0d]

Hi, at my work we got a 70kV Delta-Zigzag transformer that i am currently analysing. The primary side is 3.3kv, the secondary is 400V and the vector group is Dzn0 (Delta-zigzag + neutral(grounded) 0 phase shift). The primary is connected to a generator (wye connected) and the secondary is connected to a diode bridge rectifier with a inductive/resistitive load. Firstly, can the secondary be interpreted as delta or wye with no phase shift. Secondly, what is the purpose of a neutral; has it something to do with the harmonics caused by the bridge rectifier?

 

[cuky2000]

The Delta-Zigzag grounded has the following characteristics:
a) Suitable for ungrounded source in the generator primary side.
b) Suitable for 4-wire service in the secondary side.
c) Suppressed triple harmonic to the generator in the primary side.
d) At difference of the Wye-ZZG, Delta primary connection does no have phase-shift HV to LV. Therefore, the wye connection cannot be interpreted as equivalent connections to D-ZZG.

Primary neutral grounding in wye-zigzag (Y-ZZ) configuration is not recommended for the following reasons:
• SLG fault make the primary system vulnerable since furnish a contribution to ground fault current
• Coordination of protective devices becomes extremely difficult or virtually impossible due to multiple ground sources.
• Open conductor faults cause the added duty witch could exceed several time transformer rating.