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A common requirement of a distribution system is to serve a combination of single-phase lighting loads and a three-phase induction motor. Two transformer connections for providing this combination service are the ungrounded wye--delta and the open wye--open delta. Each connection has its good points and bad points. Of concern are the three-phase voltages provided the induction motor. If the voltages are unbalanced, depending upon the degree of unbalance, the induction motor is subject to overheating. Sources of the voltage unbalance can be the unequal spacing between conductors of the primary and secondary lines, the transformer ratings and connection, and the amount of single-phase load relative to the three-phase load. This paper utilizes previously published models of the primary and secondary lines, transformer connections, and induction motors. A simple system is developed to demonstrate the voltage unbalance created by these components under normal and abnormal conditions and the effect of the resulting unbalances on the induction motor. The system model also provides an insight into the voltages that can appear across the transformer terminals during abnormal operating conditions. Index Terms--Distribution, induction motors, transformer connections, unbalanced voltages.

This paper documents the detailed analysis of the three-phase ungrounded wye-delta transformer bank serving a combination three-phase induction motor and single-phase lighting load. A 3 x 3 transfer function matrix is developed that makes it possible to determine the load line-to-line voltages with a knowledge of the primary voltages of the transformer bank. Included in the transfer function matrix are the transformer impedances, unsymmetrical secondary impedance matrix, and the impedances of the motor and single-phase lighting load. Index Terms--Distribution, induction motor, transfer function, transformer connection models.

A common load on a distribution feeder consists of a combination single-phase lighting load and a three-phase load such as an induction motor. This combination load can be served by a wye-delta transformer bank. The question is whether the wye connection should be directly connected to ground, connected to ground through a grounding resistor or left ungrounded. During normal loading conditions, each connection has advantages and disadvantages. However, during a short-circuit condition, a grounded wye-delta bank will provide a “backfeed” short-circuit current for an upstream ground fault. This paper will develop methods for the analysis of the backfeed currents for an upstream line-to-ground fault. [ABSTRACT FROM AUTHOR]

Step voltage regulators are the workhorse of distribution feeders for maintaining the voltage at every customer's meter to be within the ANSI standards. A step voltage regulator can be viewed as a tap-changing autotransformer. This paper will apply a model of the step voltage regulator. The IEEE 13 Node Test Feeders will be used to demonstrate how the regulator is controlled in order to maintain the desired voltage for full-, light-, and future-load conditions. The coordination of step voltage regulators with shunt capacitors will be included. [ABSTRACT FROM AUTHOR]

It is fairly common in a distribution system to find instances where distribution lines are ‘physically’ parallel. The parallel combination may have both distribution lines constructed on the same pole or the two lines may run in parallel on separate poles but on the same right of way. For example, two different feeders leaving a substation may share a common pole or right of way before they branch out to their own service area. It is also possible that two feeders may converge and run in parallel until again they branch out into their own services areas. The lines could also be underground circuits sharing a common trench. In all of the cases, the question becomes how should the parallel lines be modeled and analyzed? The purpose of this paper is to develop the models for the parallel lines and demonstrate how they can be analyzed using the new models. [ABSTRACT FROM AUTHOR]

Presents a method of analyzing an induction motor in the phase frame with unbalanced voltages that can lead to excessive heating. Induction-machine model; Analysis of the sequence networks; Demonstration analysis of an induction motor in the phase frame; Conclusions.