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Star delta periodically tripping

GFaw

I have an 11kW/21A motor which is attached to a hydraulic power pack.

I have replaced the old panels with new, using the same star delta starting. When connected to a 415V outlet protected by a C32 breaker, the breaker will periodically trip. This has only manifested since the new panels, but the new control circuit is just a basic star delta (open transition) circuit. The only difference is the motor connection on the panel is now pluggable (to allow for quick changeover in the event of a failure).

I've tried "rolling" the connections in the motor (as suggested by an old hand elsewhere) to no effect.

The pump has to be started onload for operational reasons (doesn't trip offload) and this is when the MCB trips; for info, the old starters do not trip the external breaker.

I've checked starting currents using my fluke in max/min and, on average, get around 24A at both the star and delta phases of startup (at the incoming MCCB feed) and then the running load is 10.7A. When the C32 breaker trips, there is no current spike captured on my Fluke.

If I switch to a D32 MCB fed socket, the issue goes away (obviously), but my guys can't be guaranteed they will have a D type breaker on the site sockets provided.

Anyone dealt with this or have a suggestion as to what I can do to fix the issue? I've wired many star deltas over the decades and never experienced this issue.

p.s. Softstarting not an option as the guys have to inch the motor frequently, and the starts per hour don't even remotely suit one.

UPDATE : OUT OF SHEER FRUSTRATION I CHANGED OUT THE ABB CONTACTORS AND ACCESSORIES FOR SCHNEIDER LC1D RANGE AND THE ISSUE IS MASSIVELY IMPROVED (AROUND 1 TRIP IN 100 STARTS, RATHER THAN EVERY 3 OR 4. THOUGHTS?)

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  • 0

    When does it trip? Immediately the star contactor closes? On c/o to delta? Randomly? Is everything else the same as before, just the starter panel changed?

    I've experience tripping on change over before, cured by ensuring there is a slight delay between star contactor opening and delta closing.

    Otherwise it's a head scratcher!

Reply
  • 0

    When does it trip? Immediately the star contactor closes? On c/o to delta? Randomly? Is everything else the same as before, just the starter panel changed?

    I've experience tripping on change over before, cured by ensuring there is a slight delay between star contactor opening and delta closing.

    Otherwise it's a head scratcher!

Children
  • 0 in reply to Chris Willmott

    Yeah, it trips on transition to delta and the control circuit just bog standard star delta. I have a star delta timer and have tried every delay from 20ms to 140ms with the same result

  • 0 in reply to GFaw

    Interesting the new contactors have changed things. If you'd only changed the starter and everything else remained the same, it was almost certainly something to do with the new panel. Did anything in particular prompt you to change those, or was it just the frustration as you say? 

    If you've ruled everything else out then can you not put a 'D' type MCB in? The average current readings you've measured with your current clamp are not representative of the inrush at start-up and the secondary spike on delta contact closing. Unless the MCB is faulty, it would seem probably that it's the instantaneous electromagnetic component causing the MCB to trip rather than the overload.

    Have you checked the motor? Do you have a coincidental fault with the MCB? For the cost it might be worth changing that out too as the previous repeated tripping could have damaged it.

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