Abstract: In an apparatus for parallel operation of plural uninterruptable power source devices, each power source device includes at least one of an operation mode monitor for a logic operation on the output of the AC input monitoring circuit of each of the uninterruptable power source devices to feed the result thereof as a mode controlling signal to the mode controller, a parallel synchronizing signal generator for a logic operation on the output of an oscillating circuit which drives the invertor in each of the uninterruptable power source devices and, on detection of abnormality in the AC input, feeds the result thereof as a trigger pulse to the oscillating circuit, and a synchronization monitor for a logic operation on the output from the oscillating circuit in each of the uninterruptable power source devices and, when the differences between the phase of the output from the oscillating circuit of one of the triport uninterruptable power source devices and that from the oscillating circuits of remaining triport u

Abstract: A ferroresonant three-phase constant AC voltage transformer comprising three transformer iron cores with one for each corresponding input supply phase, primary windings and secondary windings formed on each of the transformer iron cores, series reactance components or reactors connected in series, with the primary windings, automatic voltage regulating means for controlling secondary output voltages generated at the secondary windings to a predetermined target value, compensating windings formed so as to be inductively coupled to each of the series reactance components or reactors, and means for connecting the compensating windings in series with each other to form a closed loop circuit. The secondary output voltages are theoretically kept in balanced condition even when the loads or the primary input voltages or both are unbalanced.

Abstract: Primary and secondary windings of each transformer in a three-phase system each form a pair of independent windings, the first winding of each of the primary and secondary pairs formed on the iron core of one of the transformers and the second winding of each of the primary and secondary pairs formed on the iron core of the transformer adjacent thereto are connected in series to each other. These serially connected windings are regarded as one phase winding respectively, and they are connected to each other in either a delta connection or a Y connection. A variation in the voltage phase caused by a change in the load current of one of the system outputs has an influence not only on the phase of the voltage at that output but also on the phase of the voltages on the outputs adjacent thereto and consequently enables the deviation in the phase difference between the output phase voltages due to loss of balance of the load to be decreased to about one half.