In areas supplied by underground transmission systems load division among several parallel connected cables may not be satisfactory. Phase-angle-connected TCUL transformers may be used to provide the phase shift necessary to equalize the cable loading and to provide voltage regulation at the load. A means for automating the TCUL adjustments to provide satisfactory current balance and voltage regulation was sought. This problem was attacked by first expressing the system performance (the unbalance of cable currents and load voltage magnitude) in terms of a system performance function. An optimal policy of control is defined as the selection of the particular TCUL transformer which provides the greatest improvement in the system performance. A negative gradient optimization routine is used to determine the required adjustment. A derivation of the adjoint network relationships for a phase-angle-connected transformer is given. These relationships provide a means for readily determining the gradient of the performance function. This approach is developed to provide a means for continuously monitoring and automatically controlling the system performance. A discussion of two ways in which this approach might be implemented physically is given. The optimally adjusted TCUL controller was incorporated in a digital computer model of a small underground power system. Simulated operation of the system under widely varying load conditions demonstrated the ability of the controller to maintain very small cable current unbalance while simultaneously holding voltage variations to +2.9 percent of nominal. A significant advantage of this approach is that the optimal sequence of adjustments required to restore the system to a satisfactory level of performance may be obtained and verified without making any actual adjustments to the TCUL transformers. This is important from a maintenance point of view. A possible disadvantage of the method is that an accurate model of the system must be available. / Ph. D.