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Tips for Westinghouse DH breakers that trip free or won’t close

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    Tips for Westinghouse DH breakers that trip free or won’t close

    Hey guys, after working on some vintage Westinghouse DH breakers for the first time this weekend I wanted to share some lessons learned.


    My company was doing some maintenance at a rather large facility and the crew I was on had the privilege of maintaining some old Westinghouse DH breakers over at the outdoor 4160V substation.

    These breakers were manufactured in the 1950-60’s and had not been maintained since mid 1990, so this should give you an idea of the condition that they were in.

    We were working with two different style breakers:

    50 DH 250D, Style 1640186-A, 4.76kV, 1200A, Mfg. 9/1953
    50 DH 250E, Style 416D200G41, 4.76kV, 1200A, Mfg. 2/1966

    Fortunately the customer had all of the original maintenance tools available so we had the umbilical cord for electrical operation, slow close bar, racking handle and transport wheel.

    Lessons learned

    The first breaker we pulled out of the cell (Style 1640186-A) was tripping free when trying to close electrically. Mounted on the front of the breaker underneath of the trip paddle is a solenoid. The plunger on this solenoid will sometimes stick after tripping the breaker which keeps the trip paddle slightly raised.

    Click image for larger version. 

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    To the untrained eye this condition looks perfectly normal because the trip paddle naturally rests on the plunger but this slight elevation in the trip paddle will cause the breaker to trip free. We manually reset the solenoid by pushing the plunger down by hand and the breaker closed.

    Always try a slow close before electrical operation to prevent blown fuses. The next breaker in the group blew a fuse when trying to close it electrically. After trying a slow close it was obvious something was wrong. We could push slow close bar down about a half inch before the mechanism locked up. What happened before was now obvious: the solenoid could not close the breaker which caused the fuse to blow.

    So the next logical question was “what’s going on with the mechanism?”

    This particular model DH circuit breaker (Style 416D200G41) was equipped with a racking mechanism interlock that prevents closing operations when the circuit breaker is in an intermediate racking position. The interlock was stuck, leaving it slightly engaged, which was mechanically blocking the breaker from closing and thus blowing the control fuse.

    The interlock is located behind the operating mechanism and is directly connected with the racking mechanism. Looking at the rear of the breaker on the left hand side is a spring loaded rod. Old nasty grease was causing this rod to stick. It could not be moved and had to be worked loose with channel locks. After lubricating the piston it could easily be pushed back and forth using only a finger.

    Click image for larger version. 

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    After working the racking mechanism in and out we could tell the interlock was now operating as it should. Slow closing was now effortless. We replaced the control circuit fuses and the circuit breaker operated electrically with no problems.

    When performing maintenance on late 50’s era Westinghouse DH circuit breakers, always try a slow close before electrically operating, especially if they haven’t been out of the cell in over 20 years. Slow closing the circuit breaker should be smooth and effortless. If the circuit breaker will not slow close, check the racking mechanism interlock, it could be stuck.

    If you have a Westinghouse DH breaker that is tripping free, check the trip solenoid and paddle. Sometimes the solenoid plunger does not fall back down all of the way causing a slight elevation on the trip paddle.
    Last edited by SecondGen; May 10, 2015 at 09:20 AM.


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