Parallel Operation

Author: E.E. Kimberly

Two or more transformers may be operated in parallel from the same power line, if their primary and secondary voltages and impedances are the same. If their resistances and reactances are not similar, circulating currents will flow between them and their effective capacities and efficiencies will be reduced. Transformers intended for parallel operation should have the same per cent of impedance. If their impedances are not the same, they will share the load in approximately inverse proportion to their respective impedances. Thus, a transformer with a small internal impedance will assume a greater part of the load than will a transformer with a higher internal impedance.