Analysis of bus voltage regulation and OLTC performance on mismatched parallel-connected transformers

This paper analyzes the regulation of bus voltage when master-follower or master-slave tap change control method is used when two mismatched-transformers are operated in parallel. Bus voltage regulation at a distribution substation relies on the use of the AVR relay that controls the OLTC. The circulating current method yields expected performance regarding bus voltage regulation when mismatched transformers are operated in parallel. When the master-follower/slave method is used, the standard voltage set-point of 103% results in low voltages being experienced by the customer at the end of the feeder. The simulations done on the network suggests that the voltage set point of each AVR relay be determined with the consideration of the upstream and downstream AVR relay settings.