ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
dsk 13
doc 3
Admin 3
Recent Posts
Bathroom electrical
by doc. 08/19/17 06:53 AM
electircal ageing test on IPC
by SIAME. 08/15/17 02:43 AM
electrical aging test on IPC
by gfretwell. 08/15/17 12:27 AM
"Line level" audio on Cat 5?
by gfretwell. 08/08/17 10:39 PM
Fire alarm phone lines and color coding
by gfretwell. 08/08/17 10:26 PM
New in the Gallery:
Housebilding DIY wiring
Popular Topics(Views)
239,939 Are you busy
175,526 Re: Forum
167,790 Need opinion
Who's Online Now
0 registered members (), 60 guests, and 8 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#130435 - 05/03/06 07:03 PM Y-Y starter  
Dnkldorf  Offline
Joined: Dec 2004
Posts: 1,064
nowhere usa
Are these nothing more than a 2 speed motor starter?

In a y-d, the voltage is reduced on the start, and the current is reduced also, then full voltage and full current is applied when delta is run...

If a Y-Y does the same in the start, what happens in the run? Does the current stay voltage and current stay lower?


Tools for Electricians:

#130436 - 05/05/06 07:04 AM Re: Y-Y starter  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,217
SI,New Zealand
Where did you hear of one of them?.
My experience tells me either Star-Delta (where the motor starts in Star and runs in Delta).
But a Star-Star starter?.
The reason behind the Star-Delta start is the lower current upon start-up, hence a lower voltage drop on the supply lines.
And Star-Delta requires 3 contactors.
Having said that, I can find no advantage in starting a motor in Star and also running it in Star.

Let's face it, these days if you're not young, you're old - Red Green grin

#130437 - 05/05/06 08:24 AM Re: Y-Y starter  
winnie  Offline
Joined: Sep 2003
Posts: 649
boston, ma
There are enough different names for the same concept that I won't claim to know what a Y-Y starter actually _is_. Here is a guess [Linked Image]

In a star-delta starter, you don't actually reduce the voltage supplied to the motor at start. Rather you change the way the motor windings are connected together so that the current drawn by the motor is reduced. The voltage 'seen' by each winding _is_ reduced because of the different connection. The supply voltage remains constant, but there is a 1/root(3) change in coil voltage in star versus delta.

As an analogy, consider a lamp 'dimmer' made with switches. You have two lamps; in one switch configuration the lamps are in parallel across the supply, seeing the full supply voltage; in the other the lamps are in series. The supply voltage remains constant, but each lamp now 'sees' half the supply voltage.

Given this, there is no theoretical reason why a motor starter could not incorporate some different switching arrangement than star/delta, one that (say) reconnects a motor between 2 series star and 2 parallel star. This would give you a 1/2 change in coil voltage. With a complex enough switching arrangement, one could step through different connections and 'sneak up' on full voltage.

I've never seen such switching arrangements used. A 'soft start' probably makes more sense [Linked Image]


#130438 - 05/05/06 09:02 AM Re: Y-Y starter  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Star-delta starters are the norm here for such things: 240V to each winding during star/wye start-up then 415V across each winding after switching to delta.

Given that North American motors are perhaps more likely to have windings in some sort of 2:1 ratio to provide for 120/240/480V operation, maybe Jon's idea about running series and parallel wye is correct.

#130439 - 05/05/06 06:44 PM Re: Y-Y starter  
Dnkldorf  Offline
Joined: Dec 2004
Posts: 1,064
nowhere usa
Thanks guys, I've seen star-delta starters, and I thought all of them were mechanically interlocked so both contactors can not be energized at the same time? And the Y (star) contactor had jumpers across each phase..

The thing I'm dealing with right now, is a 300 hp motor, 480V 6 lead type. It has two starters, not interlocked together and the second starter is pulled in after the timer times out, just like a y-d..

I assumed they called this a star-star..

FYI, I'm putting in some new soft starter/optimizers.


#130440 - 05/06/06 05:40 AM Re: Y-Y starter  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
If there are only 6 leads from motor to starter, then I guess the series/parallel idea is out the window.

Are you absolutely certain it's not switching to delta configuration? I thought 480V was only a phase-to-phase voltage (either 480V delta or 480Y/277V) in the U.S.? [Linked Image]

#130441 - 05/07/06 04:49 AM Re: Y-Y starter  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA

Is this Schematic anything close to your 300 HP 480VAC 6 Lead Motor?

[Linked Image]

This drawing + others in the similar design categories of Wye connected Squirrel Cage Induction Motors, may be found in the Technical Reference area.

Here is a link to the page with the Wye connected Motors:

3 Phase Wye Motor Drawings # 1


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#130442 - 05/09/06 04:08 PM Re: Y-Y starter  
Dnkldorf  Offline
Joined: Dec 2004
Posts: 1,064
nowhere usa
Scott, I don't know the answer to that question...

I can't see the motors, nor can I get to them. The engineers did all the prelim work. I was hired to just intstall the soft starters/optimizers at the MCC locations.

This was done at a huge brick manufacturer. If anyone has seen how a brick gets made, it is very interesting indeed....

Thanks for the help fellows as usual....


Member Spotlight
California ,Long Beach
Posts: 28
Joined: May 2007
Show All Member Profiles 

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman


Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.019s Queries: 14 (0.004s) Memory: 0.7956 MB (Peak: 0.9551 MB) Zlib enabled. Server Time: 2017-08-19 14:56:22 UTC