Part Wind/ Star Delta

[reggie]

Can anyone tell me the correct timing delay on part wind and star delta motor applications.

[david.findlay]

Generally speaking it's one second for partwind & five seconds for S/D.

[reggie]

David are these figures correct for any size motor?

[Brian_UK]

Originally posted by david.findlay
Generally speaking it's one second for partwind & five seconds for S/D.
I think quoting a fixed time delay for a star delta start is a bit dangerous as it depends on the starting load, - size of motor, drive configuration and the device being driven.

As Marc said, check the starting current and wait for it to drop back to a steady figure; cross check with your stopwatch and that is your required time delay.

[Abe]

For the benefit of those members not experienced on Start Delta wiring systems, a diagram explaining the fundamentals would assist greatly in aiding our understanding.

[Brian_UK]

Somehow I screwed an edit on this post so we'll try again----

The idea behind star/delta motors is to reduce the starting load/current to acceptable levels. If this is not done then you would need to uprate the power requirements of the incoming cables/switchgear etc.

With a Star start you can generate a strong starting torgue to get the motor and the driven device up and rotating but there is a limit to the time that this winding can run for. Therefore, when the motor is up to speed and the startup torgue taken care of the Delta windings are switched into circuit and the Star winding dropped out.

You can still find manual star/delta starters in some factories; these used to be a BIG metal box with a swing lever on one side plus a huge stop button on top. The guy would wind up the machine with the lever in the start (star) position and when he thought it sounded OK would swing the lever over to the run (delta) position.....all good fun

Try this link for a more technical reply:-

Star/Delta (http://www.adwin.com/elec/star/note_01_english.html)

[Andy]

Hi,:)
correct me if I am wrong, but I thought that "star" starting was to reduce the inrush of current, to prevent switchgear overloading(the star contactor is usually the smallest of the three contactors) whilst starting and that infact more torque is generated during the "delta" phase of operation.
I have seen 150 HP compressors started DOL boy do they come up to speed fast, but their switchgear and mains cabling is huge.
Regards. Andy.:o

[Brian_UK]

Whoops, quite correct Andy....sorry folks I stand corrected. :o

[frank]

I agree Andy. When a motor runs in star it doesn't run at it's full capacity and is limited to about 85% peak power. Changing over to Delta winding at this point allows the motor to reach peak power and draw maximum current. As you say, Star start reduces the start up current.

Larger motors then go on to have part winding start or even two speed motors - all with the aim of reducing start up current.

Frank

[frank]

Hi Ayb

Try this link

http://www.seamanship.co.uk/engineering/EKsamplepages/Motor%20starters.htm

or this one

http://www.allshookup.org/specs/hydulic/stardelta.htm

this is a really good site

http://www.iserv.net/~alexx/lib/motors.htm

Frank :)

[Andy]

Hi,:)
the longest I have ever set a Star starting time to is 12 minutes. This setting was for the changeover to Delta on a milk separator in a creamery. The motor on this application is coupled to a gearbox via an oil filled fluid (slip clutch), fill the clutch too full of oil and the motor will overload during starting. Speed acheived by the separator is in the region of 29,000 rpm before the milk is introduced. Overload setting is around three times full load current, this is necessary to acheive full speed without tripping the O/L.
The thing that saves the motor is that it is usually started only once a day and after the intial 12min Star time the motor changed over to Delta where full speed is acheived within a further 20min, after which the motor current drops back to about 70% of FLA.
Regards. Andy

[Peter Croxall]

Just a thought
:(

I worked on a chiller some years ago.....It was one of those French CIAT chillers. ............ It had a soft start on it, although the compressors were part winding start

Why would you need a soft start when part winding already took care of the inrush :confused:

[Andy]

Hi, Marc:)
I aim to please. A bit of stiring keeps us all on our toes:D
If you follow the crowd it's not the thing either:eek:
Peter
the soft start is the more expensive and better way to start the compressor and necessary on some application especially where the mains is a little tight. Partwind is a good starting method, soft start is better as the voltage is increased to the windings to reduce the inrush current.
Partwind is really starting the motor in two bites and is like starting two star wound motors one after the other so current limiting is not near as good as soft start.
Regards. Andy:)

[reggie]

Anybody worked on the VRV inverter driven compressors.? Fascinating machines the way they ramp up on frequency but very expensive to repair when the didode modules blow.
Incidentally has anyone encountered phases running through salt water on start up???

[frank]

Hi Reggie

We work on VRV all the time - terrific piece of kit. Not sure what you mean about the salt water though :confused:

[Andy]

Hi,:)
small wound rotor induction motors (slip ring) are usually started by center tapping the star point of the rotor windings in a salt bath, with oil on the top to keep the salt water from boiling off.
A wound rotor motor is used where high starting torque is required or as in the past as a means of soft start.
Regards. Andy:)

[Dave Goodings]

Just one other thing on star/delta starters which no one has mentioned is that some power supply companies in some countries specify on large drives you use closed transition on starters to eliminate spikes etc just to complicate your drawings a little. LOL

[Andy]

Hi, Dave:)
supply companies in some countries specify on large drives you use closed transition on starters to eliminate
What is closed transition:confused:
Quick change-over contacts on starters and timers???
Please clarify as it is not a phrase I am familiar with.
Regards. Andy:o

[Dave Goodings]

Yes that is correct Marc a lot of centrifs I worked on overseas used this method of starting with a bank of resistors to eliminate spikes during changeover from star to delta

[Peter Croxall]

Hi Dave,
We had the same arrangment on our Trane centrifs in Saudi Arabia. :D

[FreezerGeezer]

As a matter of interest, all the Star / Delta compressor starters that I have seen on Trane screw (& larger) chillers have transition resistors. I believe that they are fitted as standard.

[Andy]

Hi,
the way I seen transition spikes delt with was sequencing of the pases on changeover so that when changing to deta you were not asking the motor to changed to a phase 180 degrees from the one it was running at.
Another point to note is star deta motors should have their direction changed if necessary at the motor terminals not the L1, L2,L3 at the top of the contactor, again to ensure that the motor is progressing unto a phase that is not out of sync by 180 degrees.
Regards. Andy.:)

[eskimo2]

copeland I believe recommend between .5 to 1 second for partwind

[eskimo2]

what does the fitting to resistors have to do with closed transition???

I always thhought it had to do with the run contactor closing before the start conatctor dropped out? or was that vice versa??
Believe York only accepted closed transition on their centrifs

been a long time but never heard of resistors being used to do 'closed transition"...are they fitted to control just arcing across contacts