Transformer tap changing under load

Attention is called to the need for voltage and power-factor regulating equipment on lines used for tying together large generating stations and for interconnection of systems. Such lines must be capable not only of transferring large amounts of energy in either direction, but must also be suitable for connecting generating sources operating at essentially equal voltages. The important characteristics of the three principal methods for voltage regulation on interconnecting lines, — namely, synchronous condensers, tap changing under load, and induction regulators, — are presented, discussed and compared. The comparison includes such factors as first cost (including installation) reliability, ease of operation, losses, effect on system power factor and losses, maintenance, adaptability to reversible energy transfer and ability to give close voltage regulation. The requirements of regulating equipment, particularly from the operator´s standpoint, are discussed with the idea of bringing out the necessity of obtaining a high degree of reliability, ease of operation and flexibility to meet the various operating conditions. The fields of application of various methods of regulation are discussed, showing the advantages of each for different requirements and pointing out that in some cases the best solution of the problem lies in the application of a combination of two different methods of regulation to secure the best overall results. Brief descriptions of three installations (two of tap changing under load, and one of induction regulators) for voltage regulation and power factor control on lines of The Philadelphia Electric Company are included.