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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?

Parents
  • It could well be down to the delay that you have set between switch over, 40ms is two cycles at 50Hz but if your delay isn't accurate and takes into account the phase difference between the star and delta configurations your change over might be closing onto a reasonable voltage difference driving the increase in current and the kick.  I dont have any data on changeover times for conventional starters but my guess is that they could be shorter.  If you have flexibility you could try incremental adjustments (say +/-1ms)in the delay to see which direction reduces the spike and then optimise the delay in that direction to minimise the spike. Ofc grid frequency varies throughout the day and that will limit what you can ultimately achieve.  +/- 0.5Hz is allowed but normally its much tighter.  That would suggest fine tuning in sub 1ms increments would not be worthwhile.  Let us know how you get on.

    One other possibility would be differences in switching times between phases.  You dont say what sort of switching you are using but any differences would produce spikes and kicks.

    Hope this helps

  • Is the motor up to full speed before change over? Usually you can hear it. I'd lengthen the change over time to something like 5-6 seconds to ensure that the motor is up to full speed in Star before changing over to Delta. Also, are you starting up off-load? I.E. with no hydraulic circuits activated before change over? There should be a by-pass which dumps straight back to the oil tank when none of the valve spools are operated.

Reply
  • Is the motor up to full speed before change over? Usually you can hear it. I'd lengthen the change over time to something like 5-6 seconds to ensure that the motor is up to full speed in Star before changing over to Delta. Also, are you starting up off-load? I.E. with no hydraulic circuits activated before change over? There should be a by-pass which dumps straight back to the oil tank when none of the valve spools are operated.

Children
  • Motor is up to full speed in star before changeover. If we start offload the issue is reduced but not resolved.

    The issue does seem to be from the new control panel, as I've hooked it up to one of the old HPU motors and the problem still exists. If the old panel is put back in circuit the problem goes away.

    In answer to Satter, the old panels have a basic star delta timer fixed at 40ms with no issue but, to be thorough I've tries 20/40 and 60ms all of which have no meaningful effect