Zig Zag vs. Broken Delta

[LBolt]

We have a 2300V ungrounded system that we want to convert to a High resistance grounded system. Are there any advantages/disadvantage to using a zig zag transformer with a resistor in the neutral leg verses 3 single phase grounding transformers connected in Wye primay and broken delta secondary with the resistor in the delta?

 

[busbar]

One difference is that the zigzag-connected resistor will see 2300V in a ground fault, while the broken-delta resistor can be 600V-class, usually 208V. Some discussion in Detjen+, Grounding transformer applications and associated protection schemes, Industry Applications Society Conference Record, 1990

 

[jbartos]

Suggestion: Reference:
Donald Beeman "Industrial Power Systems Handbook," 1st edition, McGraw-Hill Book Co., Inc., 1955
Section: Zig-Zag Grounding Transformers on page 347
The Zig-Zag transformer is applied without the neutral resistor. The short-time kVA rating of a grounding transformer is equal to rated line to neutral voltage times rated neutral current. A grounding transformer is designed to carry its rated current for a limited time only, such as 10sec or 1min.
Hence, the transformer is usually about one tenth as large, physically, as an ordinary three-phase transformer for the same rated kVA.
Y-Delta Grounding Transformers
The Y neutral has added resistance and it is grounded. Delta is closed to provide a path for the zero sequence current. The Y-winding must be of the same voltage as the circuit it is which is to be grounded.

 

[Modula2]

Would you like to measure the ground fault by (1) zero sequence CT around phase conductors, by (2) CT on transformer neutral to ground conductor, or by (3) voltage across open delta resistor?