Question about star-delta control circuit diagram

[Pandiani]

Hello guys,

I'm studing one control circuit diagram and need your help. It's star-delta changeover control circuit and I need one clarification. I know how this circuit works. K1T is special electronic timer that has adjustable starting time and fixed transition time (about 50 ms) for the transition between astar and delta contactor connection. I'm not 100% sure about right K1 contact (13-14) and don't know why is important to be in paralel with K2 contact (13-14). One explanation is that "I" contact (start contact 13-14) is just push button (momentary), and in order to energize K2, K1 NO (13-14 is needed), because, K1 is energized when "I" is pressed, and after "I" is released, K2 is energized through K1 NO (13-14). I wonder if that is real explanation, because, when "I" is pressed, almost immediately K1 is energized, and K2 can be energized through path (K2 NC 21-22, K1 NO 43-44, K1T) before operater release start button ("I"), since this action performs very quickly. When K2 is energized, K2 NO (13-14) is closed and thus coil K2 remain energized through its 13-14 contact.

Please can you give me more information?



I hope you understand my dilemma.

Thanks.

[moggie]

The control circuit is such that the Mains contactor must be de-energised (or not "stuck on") befor the Star contactor can be energised via the push button -S2, the star contactor then energises -K2 (the mains contactor.

It is a "simple" form of self check.

[rsdoran]

What you will have is Wye connection when first started; which usually is k1 and k2 and basically initiated together. This page will show NEMA and wiring configurations for Wye start Delta run wiring: http://www.patchn.com/motor_connections.htm

As an example for a 6 lead IEC motor K1 will connect to combine U2, V2, &W2 without power at those connections (K3 off), while K2 is connected to U1, V1, &W1 this creats your WYE start.

Delta Run is created by disengaging K1 and engaging K3 with K2 which combines U1 with U2 to Line1 , V1 with V2 to Line 2, and W1 with W2 to Line2.

Using starter interlocks should not allow K1 and K3 to ever be energized at same time, if using a safety relay it will know if one of the contactors is stuck on or does not engage and prevent problems. In the diagram I do not see a safety relay being used.

[Kidblue]

Delta Run is created by disengaging K1 and engaging K3 with K2 which combines U1 with U2 to Line1 , V1 with V2 to Line 2, and W1 with W2 to Line2.

Seriously not being picky Ron (would hate some young impresionable apprentice to get all confused! )

Usual Delta i've seen is:

U1 - W2 Line 1
V1 - U2 Line 2
W1 - V2 Line 3

Hope this helps.... (somebody!)

[rsdoran]

Originally Posted by Kidblue

Seriously not being picky Ron (would hate some young impresionable apprentice to get all confused! )

Usual Delta i've seen is:

U1 - W2 Line 1
V1 - U2 Line 2
W1 - V2 Line 3

Hope this helps.... (somebody!)

OOOOPPPPPSSS, CORRECT, my page even shows that: http://www.patchn.com/motor_connections.htm

I have been looking at this drawing for a while now, something is seriously wrong here. You have to energize K3 to de-energize K1 but I do not see how that can happen using the connections in this diagram. I will have to look more, in the meantime I am taking a post PLucas made over at IE&M and using it here.

Ok, I will see if I can explain a bit more with the aid of a picture, which was taken from our schematics.



Using the image above, you can see that when the start button is pressed, K1 is energised which connects the motor leads in star formation, T1 is also energised and starts timing. K1 N/O interlock closes and energises K2, (K1 N/C interlock electrically prevents K3 being energised when K1 is energised) K2 connects the motor to the supply(and retains itself via its N/O interlock), the motor runs up and after T1 has timed out, K1 is de-energided and via K2 interlock K3 is energised thus connecting the motor in delta formation. K1 and K3 are electrically interlocked and usually they are also mechanically interlocked.

The timer T1 will usually be adjustable up to 60 seconds, the time the motor runs in star would depend on the application, I don't think that there is any hard and fast rule regarding this time, perhaps someone else knows of one!

You can get dedicated star/delta switch timers that have a built in delay when switching from start to delta. This delay is usually about 80ms, that is they de-energise the star contactor and 80ms later they energise the delta contactor.

[rsdoran]

I thought I figured out my confusion too but from what I see K2 NC 21/22 will open and when K1T times out K1T 15/16 NC will open; which will not allow K3 to have a path to energize.

Maybe I looked at it too long but everytime I try to write about the operation that is the point where it fails.

[Thomas Sullens]

I'm not 100% sure about right K1 contact (13-14) and don't know why is important to be in paralel with K2 contact (13-14).

Its also in parallel with the other K1 terminals 43&44 which might help with the inrush current from the K2 coil?
Like yours its just a thought.

[Kidblue]

Agree with Ron, that cct looks a little dubious!

Here's what i normally use (KA4 is the start from the PLC)





Hope this helps.....

[moggie]

-K1T when timed out will open contacts 15 & 16.
This in turn will de-energise contactor -K1 and the timer -K1T.
The contacts of the timer will now "re-close" (15 & 16) and as contactor -K2 is still energised (via its "hold on contact") this will now energise -K3 (via n-closed contact -K1T & n-closed contact -K1)
-K1 cannot re-energise because of the n-closed contact of -K2 being open (21 & 22).

[Sparkz]

The Star connection by K1 is made BEFORE the main contactor K2 is energized. This way, the main contacts of K1 can be chosen smaller (read: cheaper) since they're already closed at motor inrush.

After K1 kicks in, its 13-14 contact will energize K2 (Main), so only K2's main contacts will have to handle the inrush. The main contacts of Delta-K3 will still have to be of the same size as K2.

After time out, K1T opens its 15-16 contact for approx. 50..100ms, even while it's de-energized: This will de-energize both K1 and K1T. After the transition time, K1T's 15-16 contact will close again, but this time only K3 can be energized, since K1's 43-44 contact remains open, while K1's 21-22 contact is closed.

[silva.foxx]

-K1(13/14) is just the START button latch.

[Pandiani]

Guys,

thank you for all these replies.

Sparkz, I agree that connection to K1 is made before main contactor K2 is energized.

I'm thinking this: When start button is pushed, K1 will energize through the following path:

Start-S2-K2(21-22)-K3(21-22). At the same moment when K1 energize, K2 will also energize through two paths:

1. Start (I assume that start is momentary push button and it will be pressed much longer than it takes current to flow, so in my opinion K1 will energize before operator release Start button)-K2(s1-22)-K1(43-44)-K1T(15-16)-K2

2. S1-K1(13-14)-K2.

I think that short period when operator presses start button is sufficient to energize both K1 and K2 without need K2 to be energized with K1 (13-14), since there is another K1's contact (43-44).

This circuit is found in ABB's catalog, so it must be OK. K1T is special el. relay that has adjustable time (time in which motor runs in star config.) and fixed transition time (50 ms) which is needed to make transition between star and delta configuration.

[Thomas Sullens]

I think that short period when operator presses start button is sufficient to energize both K1 and K2 without need K2 to be energized with K1 (13-14), since there is another K1's contact (43-44).

That is true BUT if K2 contact 13 & 14 doesn`t come in when you release the start button the whole mess will drop out. K2 aux. seals in K2 & K3 after K1 times out.

[Sparkz]

Originally Posted by Pandiani

1. Start (I assume that start is momentary push button and it will be pressed much longer than it takes current to flow, so in my opinion K1 will energize before operator release Start button)-K2(s1-22)-K1(43-44)-K1T(15-16)-K2

One could easily think that, but it's not exactly true: K2(21-22) opens the very moment K2 starts to pull in! Therefore, the only path available to energize K2 is via S1-K1(13-14).

[shilpesh]

what i feel is there is no need of K2(21 21)and the timer contavt should be before the contactor K1so that it switchs off the star and there is no need for the contact K1 parallel with K2 contact.

Originally Posted by Pandiani

Hello guys,

I'm studing one control circuit diagram and need your help. It's star-delta changeover control circuit and I need one clarification. I know how this circuit works. K1T is special electronic timer that has adjustable starting time and fixed transition time (about 50 ms) for the transition between astar and delta contactor connection. I'm not 100% sure about right K1 contact (13-14) and don't know why is important to be in paralel with K2 contact (13-14). One explanation is that "I" contact (start contact 13-14) is just push button (momentary), and in order to energize K2, K1 NO (13-14 is needed), because, K1 is energized when "I" is pressed, and after "I" is released, K2 is energized through K1 NO (13-14). I wonder if that is real explanation, because, when "I" is pressed, almost immediately K1 is energized, and K2 can be energized through path (K2 NC 21-22, K1 NO 43-44, K1T) before operater release start button ("I"), since this action performs very quickly. When K2 is energized, K2 NO (13-14) is closed and thus coil K2 remain energized through its 13-14 contact.

Please can you give me more information?



I hope you understand my dilemma.

Thanks.