Industrial Electrical & Maintenance
December 18, 2014, 08:24:44 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
News: SMF - Just Installed!
 
   Home   Help Search Login Register  
Pages: 1 [2]
  Print  
Author Topic: star/delta starting  (Read 46694 times)
Anonymous
Guest
« Reply #15 on: December 15, 2003, 03:06:16 PM »

Ron

You wrote
"You do realize that a star(wye)-delta motor, which has 6 leads is or can also be used as a 2 speed motor? Running it in star(wye) means it will run slower and have less torque which equates to less HP but will run as long as not overloaded."

Big mistake

The idea behind star delta is soft start.How you get it?
The motor design for two voltage Here is 400v delta/660v star.
So in Star the motor supposed to get 660V but he get 400V so he start to rotate in low current. then the coils change and you get the delta.at that time the rotor rotate and the current pick is low.
This process reduce the pick current.

If you run the motor in star for  too long he would not last,

I can agree star-delta connection is an old and outdated practice.
But the substitute is not cheap,

VFDs who coming to replace Star Delta starters are too expensive.
You cannot comper 50 hp Star Delta starter price to 50hp VFD price.
There for we have what we call soft start.
Soft start are good idea but cost more then Star Delta starter.

I use soft start when the motor have many starts in short period.
With right adjusment you can get starting cureent almost as nominal cureent.
Depend on the load.
If the motor run all the day wituot stopping its not so bad.


About the 2 speed motor it will be at soon.

Arik
Logged
rsdoran
Administrator
Jedi Master
*****
Posts: 10005



View Profile WWW
« Reply #16 on: December 15, 2003, 05:20:49 PM »

Quote
The idea behind star delta is soft start.How you get it?
The motor design for two voltage Here is 400v delta/660v star.
So in Star the motor supposed to get 660V but he get 400V so he start to rotate in low current. then the coils change and you get the delta.at that time the rotor rotate and the current pick is low.
This process reduce the pick current.


I think someone has made a mistake but not sure its me. An excerpt from what Paul stated in reply to this thread:
Quote
As you know a motor, when started direct on line (receiving full line voltage) will pull a very large initial start current. A stationary motor will behave as a transformer on short circuit, hence the very large starting current. To reduce the start current, a star/delta starting method is used.
The stator of the motor is first connected in star configuration (wye), the voltage at start is then reduced to 1/ root 3 x line volts, because the voltage is reduced then the start current is also reduced by a ratio of root3:1, then when the motor is running the stator is switched to 'delta' configuration, the motor then receives full line voltage (per phase).


I believe that states for 415v Star Connection voltage is effectively reduced to 58% or 240v.

Many motors are designed to run in a wye(star) or delta configuration...ie high voltage (415 for England and other parts of the world, 460 for the US) with low voltage being 240v. The lower voltage on an AC system is suppose to create a lower current draw, it also will reduce the speed/torque. I admit that most motors that can be configured this way use 9 leads, for wye 7,8 & 9 are connected and delta 7, 5 and 2.

I stated the above because I have seen it done numerous times. It may hurt the motor if the load is too great and the heat becomes excessive due to current draw BUT if you are in wye and the overloads are configured properly there is no reason it would hurt the motor. The apps in one of these cases were on very large motors that conveyed metal that had to be "picked from" at times so they had to run slower than when metal was "clean".

I also know that the wye/delta design was meant to lessen the current draw on startup. I also have seen it applied enough to know that it does NOT work as expected or needed in many cases.

One day I will put up my 12 lead page and its use in a wye/delta system.
Logged

Tell me and I forget, show me and I remember, involve me and I understand."
ArikBY
Jedi Knight
**
Posts: 19


View Profile
« Reply #17 on: December 20, 2003, 10:31:18 AM »



Hi guys
As I promised last week I add drawing of 2 speed motor.
This Dalander motor have something very similar to star delta conction.
When K1&K2 are on it mean speed 1.
When K2 work it speed 2.
The motor have 6 Leads  like star delta.
Its very confusing connection.You need to dig in to understand that is not star delta.
Ron
Taht what you mean for two speed motor?



Arik
Logged

rik
Barak Control Israel
engr_shafi2002
Guest
« Reply #18 on: October 13, 2004, 01:07:28 PM »

Dear sir
very very thanx for your nice reply about star delta ckt. with details...
But I wished for the PLC ladder diagram of a star delta control ckt.

something like the following:

---------| |------------------------------------------( )----------

---------| |------------------------------------------( )----------

etc. etc ......


regarding
engr. zia ashraf
Logged
PLucas
Moderator
Jedi Master
*****
Posts: 1020


torontogill@hotmail.co.uk
View Profile
« Reply #19 on: October 14, 2004, 02:59:32 AM »

engr_shafi2002,

Are you proposing to control a star/delta starter with a PLC?  Or is this just for a bit of 'practice' with a PLC?

Most of us here are also members of PLC's.Net, on that forum we tend to follow certain unwritten rules regarding 'doing peoples homework' and posting full ladder solutions.  We normally ask for what you have done so far, then we can point you in the right direction.  In other words we give advice while the person posting the question does the work, that way they learn how to do it and not just copy someone elses work.

If you look at my first reply to this post, you will see a schematic and an explanation of how the diagram works.  Use this to 'convert' the schematic to ladder logic, then post what you have here and we will see what we can do.

Paul
Logged

There are 10 types of people in this world....
Those that understand binary and those that don't!
BobB
Jedi Knight
**
Posts: 86



View Profile
« Reply #20 on: October 15, 2004, 07:32:01 AM »

If you wish to control YD with a PLC, it is easy with a couple of timers. Post your homework here for review and there are many people who will help. Do not expect us to do it for you if you are not prepared to give us what you have done.

By the way, I use PLC's for this every week.
Logged

he Old Pfhaart
calvinthecat
Jedi Knight
**
Posts: 18


View Profile
« Reply #21 on: October 16, 2004, 06:26:32 AM »

The other people posted good stuff for this subject and I enjoyed it !
The ideas make sence and for grins and laughs remember the locked rotor current of most motors is around 6 times the running current or 600%
I have usually wired all of the ones that I worked on as delta and do away with all the extra crap or use a VFD but my use has been fans so it might not be good with belt conveyors and ect to go straight delta.
                         meow
Logged
Eric Nelson
Global Moderator
Jedi Master
*****
Posts: 887



View Profile WWW
« Reply #22 on: October 16, 2004, 07:00:30 AM »

Quote from: "calvinthecat"
meow


Have you met Pierre yet?... Tongue

:prost

-Eric
Logged
affzal
Guest
YD
« Reply #23 on: July 07, 2005, 02:51:58 AM »

you can control by using timer only input and output are necessary doesnt need a complex wiring....only for the wiring of the motor only are require.the output from PLC can energize the contactors..
Logged
rsdoran
Administrator
Jedi Master
*****
Posts: 10005



View Profile WWW
« Reply #24 on: July 07, 2005, 08:16:10 AM »

Quote from: "affzal"
you can control by using timer only input and output are necessary doesnt need a complex wiring....only for the wiring of the motor only are require.the output from PLC can energize the contactors..

It could be done simple but not sure if your simple is the same as mine. With a star-delta start you have to make sure that the contactors will never be engaged at the same time. This may require using mechanical and/or electrical interlocks, I prefer to use both. This should not be difficult because its just a basic start/stop ckt that will start a contactor and a timer, when timer is done it releases (turns off) the first contactor then after X period of time (to verify contactor has released using the electrical interlocks) you engage the delta contactor.
Logged

Tell me and I forget, show me and I remember, involve me and I understand."
BobB
Jedi Knight
**
Posts: 86



View Profile
« Reply #25 on: July 07, 2005, 06:10:21 PM »

Quote
This may require using mechanical and/or electrical interlocks


Absolutely agree. The only difference is I use the PLC in lieu of the electrical interlocks.
Logged

he Old Pfhaart
Anonymous
Guest
« Reply #26 on: December 08, 2005, 10:05:24 PM »

Quote from: "David Emmerich"
Hi Group,...It's funny, every time a  :patchn topic that is just a little off-the-normal comes along, it seems like I am just about to need the info, or I have just found out something about it!!!!  Cool Like Rons' mention of 12 lead motors and partial winding starting...I just changed out a 6 lead 125Hp mixer motor that was on a star/delta MS, and put in a 12 lead 125 Hp on a new mixer, which I rebuilt the starter panel for ,using an older telemecanic softstart, and one of the old star/delta contactors as a bypass. Inside the motor pecker head cover were 8 different wiring plans ...high/low volt, partial, star/delta...heck,you needed a guide book to read the cover!!!! But it came up running the right way on the first try, so the motor fairies must have had pitty on me and sprinkled their magic stuff ( maybe portland cement dust? ) on the job!!!! :mrgreen:
Eric,how did Mr.Plow do this weekend? Did he earn his keep for another year?
Well group, its been a long 5 days,just under 1000 miles, and now I leave in the morning for a job in Lexington....I did rebuild the CO2 regulator for my keg last night, so its  :prost time!!!
later
David
PS Nice job on the new  :patchn Eric!!!!
Logged
marke
Young Skywalker
*
Posts: 8


View Profile WWW
« Reply #27 on: December 29, 2005, 02:49:15 PM »

Quote
The stator of the motor is first connected in star configuration (wye), the voltage at start is then reduced to 1/ root 3 x line volts, because the voltage is reduced then the start current is also reduced by a ratio of root3:1, then when the motor is running the stator is switched to 'delta' configuration, the motor then receives full line voltage (per phase).
The voltage across the winding is certainly reduced by root 3, but because the motor is now star connected, the net effect is that the line current is reduced to one third of delta current. The torque is also reduced to one third of delta torque. - just a minor point!
Star delta (wye delta) starting is used as a means of reducing the start current, however if the motor does not get to full speed in star, switching to delta will stil result in close to Locked Rotor Current so there is no appreciable reduction in start current. The transition fro star to delta is usually an open transition which results in a "reclose" transient that is several time higher than LRC albeit for a few cycles only. The current and torque transient associated with the reclose transient does more damage than a full voltage start so little is achieved except for the maintenance boys! You can find more information on the star delta starters and other reduced voltage starters at http://www.LMPhotonics.com
The Dahlander starter (two speed) is similar to the star delta starter in that it has three contactors, but the motor does not have three diiscrete windings. The motor is hard wirded in Delta and has center taps from each of the delta windings. In low speed, the motor is connected in delta. In high speed, the motor is connected in "double star". The incoming three phase is connected to the three center taps and the delta points are connected together.

Best regards,
Logged

Wino
Jedi Knight
**
Posts: 155


View Profile
« Reply #28 on: December 31, 2005, 07:55:28 PM »

Marke, I don't know if I agree with your position.  I've been wrong before, so I might be wrong again.

I think that current is reduced to one divided by root three (star vs delta), as the winding impedance has not changed, and therefore the current  function is linear with applied stator voltage.

Torque is roughly equivalent to voltage squared, so you do get the one-third reduction there, as you stated.
Logged

_____________
Regards,
Don
marke
Young Skywalker
*
Posts: 8


View Profile WWW
« Reply #29 on: December 31, 2005, 08:35:52 PM »

Hi Wino

You are correct in that the voltage across each winding is reduced to one over root three. This will result in the current through each winding also being reduced to one over root three, however if you look at the current in the line, in the delta connection, yu have the combined current of two windings. This current is 60 degrees offset and the sum of these two currents is root three time the current in one winding. Hence the line current is infact three times the line current in star.

Best regards,
Logged

Pages: 1 [2]
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.2 | SMF © 2006-2007, Simple Machines LLC Valid XHTML 1.0! Valid CSS!