Star-Delta Stater for Which KW?

Which kW do you have???

35kw...

Then it depends upon the resilience of the incoming supply, the nature of which has not been shared with the forum.

• 55kW DOL? No problem, if the incoming LV supply is robust enough.

I just did a project with 5 x 200HP (150kW) 480V starters for pumps on a municipal water supply system. It was designed to be Autotransformer starters, I bid it with Solid State Soft Starters and won. But before the order was released, the end user got permission from their utility to go with Full Voltage (DOL) so we are being asked to change them. I spoke up about the benefits of using reduced voltage starters soft starters, they don't care...they are only thinking about the initial capital expenditure. They will regret it later no doubt.

look at the rating of the SD starter.. that will tell you! That would be the name plate details on the side of the unit!

There is no clear-cut dividing line; practice varies from place to place.

As Tornado says, there is no standard. But many times, it is the local power provider that makes those rules, because they are the ones that suffer the consequences. They will not have a rule that specifically states star-delta, but they will have a rule that dictates at what point you must use reduced voltage starting, of which one method is star-delta.

In strong grids even 100kW could be started by DOL but in weak grids(third world poor countries) motors rated more than 5HP are started by star-delta starter.

As the guys have said it depends on the supply you are coming from. If you are deep in an industrial estate or have thin over lines then star/delta is likely the way forward.

On a power station you would still be on DOL.

If you try DOL and the supply isn't man enough you will cause a 'brown out' or dip and likely bring out other drives and kit.

You know the situation and really this is your call.