Ungrounded Wye - Delta Transformer Protection
Ungrounded Wye - Delta Transformer Protection
(OP)
Does anybody know what causes the voltage spike when energizing a three phase ungrouned wye - delta transformer using three single phase switches. Upon energization of the last phase a MOV was blown as well as fuses.






RE: Ungrounded Wye - Delta Transformer Protection
RE: Ungrounded Wye - Delta Transformer Protection
A reasonable overview may be §7 in ANSI/IEEE Std C57.105-1978 …Transformer Connections in Three Phase Distribution Systems standards.ieee.org
RE: Ungrounded Wye - Delta Transformer Protection
The ungrounded-wye—delta configuration is in the referenced “Connections Susceptible to Ferroresonance” table.
RE: Ungrounded Wye - Delta Transformer Protection
Also, it is not clear which voltage level is involved, and whether or not the transformer consists of three single phase transformers or one three phase transformer.
E.g. 500kV line three single phase transformers can be turned on via three single phase switches, when unloaded.
RE: Ungrounded Wye - Delta Transformer Protection
RE: Ungrounded Wye - Delta Transformer Protection
R.A. Walling, R.K. Hartana, W.J. Ros "Self-Generated Overvoltages due to Open-Phasing or Ungrounded-Wye Delta Transformer Banks," IEEE Transactions, Volume 10, Number 1, pp 526-531, January 1995 covers "Disconnection of one phase of an ungrounded-wye delta transformer bank from the source that can result in severe overvoltages due to neutral shift and ferroresonance (more exactly self-ferroresonance of the transformer).
RE: Ungrounded Wye - Delta Transformer Protection
Should extra ‘ammunition’ be desired, two papers are
Bohmann, L.J.; McDaniel, J.; Stanek, E.K.; Lightning arrester failure and ferroresonance on a distribution system; IEEE IAS Transactions, v29n6, Nov-Dec 1993
Rusch, R.J.; Good, M.L.; Wyes and wye nots of three-phase distribution transformer connection;, IEEE IAS Transactions, v26n4, Jul-Aug 1990