Sughrue, Mion, Zinn, Macpeak & Seas
Apparatus for protecting vacuum interrupter type on-line tap changer
 An apparatus for protecting a vacuum interrupter type on-line tap changer in which a cross current flows between taps through a current limiting resistor for a predetermined time by shorting selected taps therebetween at the time of tap changing operations. Vacuum interrupters are employed as current switching elements. A dial switch selects the position of the tap of the tap changer. A limit switch closes only at a predetermined position of the dial switch during tap changing operations. Thus, a cross current between the taps or a load current flowing for a long time due to a drop in the degree of vacuum of the vacuum interrupters is detected, thereby preventing burn-out of the current limiting resistor and damage to contacts of a disconnecting switch due to interruption of the current. 
Fuji Electric Co., Ltd.
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additional inventional additional
Tetsuo
Watanabe