Voltage Sag Effect on Three Phase Five Leg Transformers

The behavior of three phase five leg transformer under voltage sag is studied in this paper. This paper proposes a simple, practical model of a three phase-five leg, saturated transformer with accurate performance. Transformer saturation is produced when the voltage sag is recovered and it causes inrush current in transformer. Effects of voltage sag depth, duration and initial point on wave have been analyzed in this paper. Initial point on wave can produce maximum inrush current in five leg transformers while comparing with three leg transformers. The magnetic circuit symmetry of five leg transformer produces the more symmetrical shape of inrush current curves versus initial point on wave and sag duration than three leg transformer. The simulations show that current peak has a periodical dependence on sag duration and linear dependence on sag depth. Inrush current that is produced in three phase five leg transformer is higher than three phase three leg transformer.




References:
[1] X. S. Chen., P. Neudorfer, "Digital Model for Transient Studies of a
three-phase five-legged Transformer", IEE Proceeding, Vol.139, No4,
July. 1992.
[2] S. Garcia, A. Medina, " State Space Three-phase Multilimb Transformer
Model in the Time Domain: Fast Periodic Steady State Analysis", IEEE
Transactions on Power Delivery, Vol.18, No.4, Oct. 2003.
[3] Pedra, J., Corcoles, F., Sainz, L., Lopez, R.and Salichs,M.,"PSPICE Computer Model of a Nonlinear Three-Phase Three-Legged
Transformer", IEEE Transactions on Power Delivery, Volume:
19, Issue: 1, Jan 2004 ,pp.200 - 207.
[4] Pedra, J., Corcoles, F., Sainz, L, "Symmetrical and Unsymmetrical
Voltage Sag Effect on Three Phase Transformers ", IEEE Transactions
on Power Delivery, Volume: 20 No.2, April 2005, pp.1683 - 1691.
[5] Pedra, J., Corcoles, F., Guasch, L, "Effect of Symmetrical Voltage Sag
On Three Phase Three-Legged Transformers ", IEEE Transactions on
Power Delivery, Volume: 19, No.2, April 2004, pp.875 - 883.
[6] M. H. J. Bollen, "Voltage Recovery after Unbalanced and Balanced
VoltageDips in Three-Phase System", IEEE Transactions on Power
Delivery, Vol.18, No.4, Oct. 2003.
[7] M. H. J. Bollen, " Understanding Power Quality Problems: Voltage Sags
and Interruptions", NewYork: IEEE Press, 2000.