Star delta tripping issue

Hi there,

I We have some old Hydraulic Power Packs and have made some new control panels for them, as the old ones are failing.

The motor is 11kW and, with the old starters, run fine (drawing 24A max during startup).

These old starters were wired to the motor directly viqa flexi conduit, while the new starters go through a 10 pole ILME connector using these connectors (https://www.cef.co.uk/catalogue/products/1478356-16a-10-pin-female-insert-spring-terminal-connections) rated at 16A. When changing from star to delta we get a spike of around 50A and the motor "kicks" aggressively. The control circuit itself works fine. I have the timer set to 3 seconds and a 40ms delay between star and delta. Under normal running conditions the HPU only draws around 8 to 10A maximum. The issue onyl occurs when we have the valve open to the hydraulic motor and it's got me at a loss. Avy suggestions as to what is happening here?

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  • Do double check that the starter is wired correctly !

    And not for example reversing direction when changing from star to delta. This may sound basic but I have found cases of this.

  • It does not have to reverse to be awkward, the standard wiring configuration is correct for hand over with a 60 degree fallback, (*) but it is possible to create a situation where the phases are advanced by 180 degrees, and the motor then has to instantly twitch ahead to a new shaft position, while rotating at the same speed and same direction.  If there is some dead time between the start breaking and the delta making it becomes less serious, as then the core has demagnetized and the delta case is just doing a DOL onto a motor that is already spinning but without a pre-magnetised core a rather  just more sophisticated version of pulling the belt and then flicking the switch.

    Mike

    * by way of explanation

    the 3 phase to neutral voltages reach their respective peaks 60degrees offset from the peaks in the phase to phase voltages, but depending which phase to phase voltage you put across which coil there may be any multiple of 120 degrees to add to the shock the core feels.

    So  when the stator coils are energized  in time with phases 1-2-3 in star, once switched you want them to be  energized  (1-2) (2-3) (3-1) The rotating core behaves like a permanent magnet going round a touch slower than shaft speed, so the currents in the core, and which parts of the spinning iron are the north and south poles are changing steadily at few Hz (the slip frequency). This does not like to be asked to jump violently.
    Mike

  • Yeah, I've checked multiple times (going slightly crazy tbh) and the starter wiring is fine. I have had to change the motor direction at the motor terminals rather than just switch at the input, as the panel is for site use and we can't guarantee correct phase rotation. We have a phase sequence relay fitted, hence why we can't just do the simple fix. Here's the original and reversed wiring connections (in case I've made a daft mistake)

    Original wiring
    from Line Contactor  L1-U1  L2-V1  L3-W1    From Star/Delta Contactor  L1-W2  L2-U2  L3-V2

    New wiring to reverse motor

    from Line Contactor  L1-V1  L2-U1  L3-W1    From Star/Delta Contactor  L1-U2  L2-W2  L3-V2

  • The behavior seems odd.

    When it comes to incorrect phase rotation on transition from start to run, the mcb or mccb should knock off in short order, especially if starting under load.

  • In case you didn't see my solution (buried down a sub converation above), I changed out the standard star delta timer for an adjustable one and changed the star-delta delay from 40ms (as per the original starter) to 100ms and the starter is working like a dream. Thanks very much to you for your input

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