3 phs D to Wye for starting?

[SailorDaniel]

I've been noticing several chillers where it looks like it has a double set of contacts/heaters/starters on the power coming in. I've been told they are for several differnent things.

Explanation #1) Some of these I know are just for phase loss protection on each leg but was also told that some are for converting a high leg system to a regular 3 phase sytem? Does this make any sense, is it true, any why would you want to do that?

#2) I was also told that it is for converting the Delta system to a Wye system for start up(or vice-versa)?? What would be the benefit and why would they do this anyway? Does it preserve windings or something?

[SailorDaniel]

or were people just blowing smoke up my compressor because they had no idea and didn't want to admit it....................?

[genduct]

Seems I heard the explanation that your start Y run delta because the delta is the max HP and torque except that also means max LRA on startup on deltal as well
So you have a chiller that is building up resistance/load/ HP required as it ramps up, ( as opposed to say starting an air compressor with pressure against it) and you don't need the high starting torque of the delta and Y will get you going.

Make sense, I hope I heard it right and repeated what I had heard

[Tech Rob]

Lots of manufacturers of large horsepower motors use reduced inrush and reduced voltage starters. Wye-Delta is a reduced inrush starter that starts in wye, and then "transitions" and sequences the contactors in a way so that it runs in delta.

The instant a motor starts, it draws locked rotor amps. Wye-Delta starters limit the amperage to around 33% of locked rotor. This limits the demand on the utility and also limits the heat generated by the motor at startup.

Hope that makes sense to you.

[trouble time]

Lots of manufacturers of large horsepower motors use reduced inrush and reduced voltage starters. Wye-Delta is a reduced inrush starter that starts in wye, and then "transitions" and sequences the contactors in a way so that it runs in delta.

The instant a motor starts, it draws locked rotor amps. Wye-Delta starters limit the amperage to around 33% of locked rotor. This limits the demand on the utility and also limits the heat generated by the motor at startup.

Hope that makes sense to you.

This guy know his starters......:bump:

[fool4school]

I work on a Dunham Bush that is between 25-30 yrs old that starts 3 phase
with the in coming power switches from delta to wye. on start up. Think that is dose start the widings seperatly

[Tech Rob]

Thanks.

Fool4school, every DB screw that I have ever seen has been part winding start, which is different from wye-delta. Only similarities is that they are both reduced inrush starters that utilize "start" and "run" contactors, and typically have 6 lead motors. Part winding starters generally just have a time-delay relay that energizes the run contactor a half-second behind the start contactor. It's akin to starting two separate motors that are connected to the same load.

[RichardL]

Some numbers quoted earlier are in error....
When starting a Wye-Delta motor in the Wye configuration, the motor will pull 133% of Full Load Amps on start.
The same motor starting in the Delta configuration can pull as much as 600% of Full load amps.
A "Part-Winding" start on say a 40hp compressor has two identical 20hp windings, and one motor winding is energized briefly before the other.
Wye-Delta start therefore has a much lower starting current than even the best "Part-Winding" start.

[Tech Rob]

Here's an illustration of the difference between closed transition Wye-Delta and Part Winding.

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