The Scott transformer is widely used in electric railway systems when there are two unbalanced single-phase loads as this transformer can reduce unbalance currents. This paper investigates whether or not the Scott transformer can also reduce harmonic current. Our study shows that it can reduce the harmonic current when single-phase loads have identical harmonic characteristics. This harmonic reduction occurs through the cancellation of harmonic currents of single-phase loads in the transformer windings. Our studies also show that there is some degree of cancelation even when the loads do not have identical harmonic characteristics. The cancellation depends on load balance factor and harmonic order.
nullH. MAZIN and J. GALLANT, "A Probabilistic Analysis on the Harmonic Cancellation Characteristics of the Scott Transformer," Journal of Electromagnetic Analysis and Applications, Vol. 2 No. 1, 2010, pp. 18-24. doi: 10.4236/jemaa.2010.21003.
[1] Y. Mochinaga, Y. Akatsuka, K. Arai, and M. Ono, “ Development of three-winding transformer for shinkansen auto-transformer feeding system receiving extra high voltage,” The Institute of Electrical Engineers of Japan, Vol. 111-d, No. 3, pp. 237–244, 1991.
[2] B. K. Chen and B. S. Guo, “Three phase models of specially connected transformers,” IEEE Transactions on Power Delivery, Vol. 11, No. 1, pp 323–330, January 1996.
[3] T. H. Chen and H. Y. Kuo, “Network modeling of traction substation transformers for studying unbalance effects,” IEE Proceedings Generation, Transmission and Distribution, Vol. 142, No. 2, pp. 103–108, March 1995.
[4] S. Chen, R. Li, and P. His, “Traction system unbalance problem - Analysis methodologies,” IEEE Transactions on Power Delivery, Vol. 19, No. 4, pp. 1877–1883, October 2004.
[5] H. Erfanian and W. Xu, “An investigation on the effectiveness of Scott transformer on harmonic reduction, power and energy society general meeting - Conversion and delivery of electrical energy in the 21st century,” 2008 IEEE, pp. 1–4, 20–24, July 2008.
[6] A. Cavallini and G. C. Montanari, “A deterministic/ stochastic framework for power system harmonics modeling,” IEEE Transactions on Power Systems, Vol. 12, No. 1, pp. 407–415, February 1997.