A Study of Some Three-Phase Systems

The star-star, delta-delta, delta-star and star-delta connections are taken up in order and their individual peculiarities and characteristics, precautions that must be taken in operation to avoid trouble, and where and when the system may be grounded with best results, are discussed. The question of delta-delta vs. delta-star is considered: (1) For moderate voltages the delta-delta system has the advantage on account of its greater flexibility. (2) For high voltages the delta-star connection is preferable, chiefly on account of its greater strength and lower cost. There is a probability that a delta-star bank of transformers will cause less disturbance in switching than one that is delta-delta connected. (3) There are much greater possibilities of development in transformers designed for delta-star connection than for any other. (4) Past and present practise upholds the use of the delta-star connection in preference to the delta-delta for high-voltage transmission.