An update on the paralleling of OLTC power transformers

The procedures for successfully controlling the on-load tap changers of power transformers in parallel have changed little for many years. The two most common procedures used today-minimum circulating current and master/follower-are well known and proven by experience. The most common implementations of each of these procedures, however, remain the traditional approaches of discrete analog circuits involving current transformers to isolate particular aspects of the load circuit or banks of relays to assure the identical tap operation of the transformers. Digital electronics presents the opportunity to modernize the technology of paralleling, using either of the popular methods, by communication of the required information between the respective OLTC controls using serial communications. This eliminates the analog circuitry of paralleling balancers and multiple status relays. The resulting system is much simpler to install and less prone to operational error.