Usually the three poles on 245kV or higher breakers are such a long distance apart (to meet phase spacing requirements) that the operating shafts would be too long for one mechanism to move 3 sets of contacts consistently in the short time required for tripping or closing. Therefore a separate operating mech is used for each pole.
138kV is about the limit for having all three poles on one common frame with one mechanism to operate them. The lengths of the bushings give enough spacing to provide the necessary phase spacing at that voltage.
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245 kV Circuit Breaker Question
Re: 245 kV Circuit Breaker Question
