Parallel Operation of Load Ratio Control Transformers Using Reverse Reactance Compensation [includes discussion]

When transformers with automatic load ratio control are operated in parallel, a miethod of preventing excessive circulating current is required. Some of the methods used are extremely complex, requiring additional equipment and control connections between units. The combination of resistance compensation to produce constant voltage at the load center as well as reverse reactance compensation to limit the circulating current between units is applicable to many circuits where more complicated means of parallel operation are now used. This system has the advantage of requiring no additional equipment and no control connections between units. The relations developed show that satisfactory performance in limiting circulating current between units and maintaining voltage can be secured in many cases. The best performance is obtained when the power factor of the circuit is high and substantially constant, and when the power factor of the circulating current is low. However, variations in load power at light loads have little effect on the performance. Equations for calculating the performance of this control on paralleled circuits are derived.