Current-Limiting Reactors Their Design, Installation and Operation

The essential features in the design, installation and operation of current-limiting reactors are pointed out. The application of reactors to different circuits is not treated because a number of good papers dealing with this subject has been presented at Institute meetings. Design.-A current-limiting reactor should have low reactance at low currents and high reactance at high currents. Such a reactor has been developed and is known as the ``saturated core´´ reactor. It has not been used as yet for current-limiting protection to any extent. A reactor having an iron core and only an a-c. winding gives a drooping voltage-ampere characteristic and, therefore is not suitable for current-limiting protection. Reactors with air cores have straight line volt-ampere characteristics and, therefore, are well adapted for this protection. Since the only function of current-limiting reactors is to limit the current during short circuits to safe values, they should be capable of performing this function when other apparatus is being destroyed, due to excessive current. For this reason, heat resisting materials should be used for holding and insulating the conductor of a reactor. A useful formula is given for determining short-circuit temperature rises. A current-limiting reactor functions as such only when there are short circuits on the system. Short circuits are almost sure to be preceded or accompanied by voltage disturbances of abnormal value. Therefore, the insulation factor of safety in a reactor should be relatively high.