how to design changeover control circuit 2

[vitzwaters]

help design a change over control circuit for LV from utility line contactor to genset contactor in event of power cut. also want to remove load before switching off genset, when power is back.

 

[waross]

Use mechanically and electrically interlocked contactors to switch the load current.
Relay #L (line)
This is a time delay on energization relay. It is connected to the line (grid) It energizes the "Line" contactor.
When the grid fails and this relay drops out, N/C contacts pull in relay #S which seals through normally closed contacts on the line contactor. Relay #S sends a "Start" signal to the gen set. This may be time delay on de-energization to provide "Cool down time"
Relay #G (Gen set)
This relay detects power from the gen set through normally closed contacts on Relay #L. This may be time delay on energization to prevent fast re-transfers. This relay energizes the Generator contactor.
When grid power returns, Relay #L times out and then pulls in. It interupts the power to the generator contactor coil with N/C contacts.
When the generator contactor drops out the N/C interlock contacts pull in the Line contactor.
Draw a diagram and post it for comments.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[vitzwaters]

warros, it sounds easy but not easy. my boss has said i must use less relays, at most 2, is a chicky boss. Am a junior engineer so only theoretical, plz help with a drawing

 

[Skogsgurra]

He may actually be testing you to see what kind of engineer you are (or will develop into).

If you can't figure this simple one out, then just say so to your boss. If he is any good, he will give you a hint. Like Bill just did. Then just sit down and start drawing a diagram, thinking about each and every function and detail. You may not get it right first time. But when you think it is right, then go to you boss and show it to him.

You will never be any good if you make other people do your work.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[vitzwaters]

Thanx guys, i am simulating the circuit, then go and mount the panel, i will let you know any development or prob.

 

[waross]

Hi vitzwaters;
Post your diagram and we will make comments.
See:
This is how to post pictures in your post.
faq238-1161
for instructions on posting pictures and diagrams.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

I'd think about using a Telemecanique Zelio or Moeller Easy or Siemens LOGO! smart relay. You program them in a simple ladder logic format.

 

[waross]

Good call LionelHutz.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[vitzwaters]

Bill,

I did not put the circuit for any test yet, but analyse the attachment.

 

[waross]

Hello vitzwaters;
Now we are making some progress. Unfortunately I am on the way out the door this morning. I will be on the road for a couple of days but I will get back to you as soon as I am able. A couple of challenges for you;- I don't see any Normally Closed contacts. Am I reading your drawing convention wrongly? Two things to add to your drawing;
1. A set of DRY, contacts to start the gen set.
2. Cross connected Normally Closed contacts in the coil circuits of the contactors.
A couple of questions;
How do you want to detect the mains voltage and what do you want to happen electrically when it fails and when it returns.
How do you want to detect the generator voltage and what do you want to happen electrically when it is present.
It would be much easier to just post a drawing for you, but I am willing to take a little extra time to help you develop some general control skills, and guide you towards developing your own drawing. I hope that his approach will be more valuable to you in the long run.
You got me on a good day, I don't always have this much patience. Feel free to help Skogs. I suspect that our student may be up against a time constraint and I may not be available until Sunday. I may be able to get on a borrowed computer tomorrow but no guarantees.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[slavag]

Hi.
Bill, good trip to you.
Vitzwaters. Welcome to the club.
Small additionals,it's some expand of Bill's.
Please pay attention.
1. If you have voltages U and G, both of relays are closed.
It's wrong situation.
That mens you must cross with NC closed contacts K1(NC) in series with K2 coil, K2(NC) in series with K1 coil.
In practical with some type of breakers used mechanikal interlock. Don't remeber now, but I think mechnical interloccks is used for the contactors too.
BTW, smart relay, what LionelHutz mentonied is best practic today.
2. What is a L4/L3 S1/S2/S4, etc.
3. Next point, you need start from somewthing, that means
you need start and stop pushbuttons for every contactor, but of course via cross NC contacts.
4. Now, next options, your customer would like two options:
4.1. manual control only,
4.2. auotomatic changeover between main and genset source.
You need some rotated switch with 3-position manual-off-auto.
5. Please pay attention push buttons will feeded from suitble control voltages. PB;s of K1 from U voltages, PB's
of K2 from G voltages.
Nice start of design with EPLAN SW according IEC standards.
Good Luck.
Best Regards.
Slava.
Bill, sorry for my small remarks

 

[Skogsgurra]

We love your "small remarks" Slava!

Yes. There is a lot to add to the drawing. As Slava says, there should be input signals, and interlock signals so that the two contactors cannot be activated at same time (that is what Slava calls cross NC contacts).

A little tip re. terminology and conventions: All circuit elements shall be drawn in non-activated state (no voltage on coils, switches in off or neutral position etc). NC contacts shall therefore be drawn as closed contacts (they open when activated) and NO contacts shall be drawn as open contacts.

Get used to these little factoids and try to use them to redraw your schematics to get the function you need.

Bill and Slava are nice guys. They will help you - just listen to them.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Hi guys, let's build this part by part so that our friend can follow the steps. I propose a basic circuit first and we cxan add manual controls later.
Contactors are available with mechanical interlocks. Some brands offer a mechanical interlock kit that may be added in the field. What brand are your contactors?
First step.
monitor the line voltage and connect the line contactor when line voltage is present.
You could just wire the contactor coil across the line.
Second, you have to start the generator. This circuit is generally included in the generator control panel. A remote contact closure is all that is reqired. This could be normally closed contacts on the contactor that close and start the generator when the line voltage is lost and the contactor drops out.
The generator contactor could likewise be connected ddirectly to the generator voltage.
The operation would be:
1> Line voltage present, contactor pulled in and feeding the loads.
2> Line voltage lost;
Contactor drops out.
Normally closed contacts start the generator.
The generator voltage comes up and pulls in the generator contactor.
The load is supplied by the generator.
Critique. The primary problem is that now the set will stay on the generator until it runs out of fuel.
We need to detect the return of the mains voltage in order to retransfer and go back to the mains.
Add a relay. This relay will detect the presence of line voltage. It will pull in the line contactor and interupt the generator contactor if the set is on the generator.
This basic circuit will work for a small set.
BUT
If you want to check the level of the line voltage rather than just assuming either voltage or no voltage, you may use an adjustable voltage monitoring relay in this position.
Like wise, you may use a voltage and/or frequency monitor relay to detect the generator output and control the generator contactor.
More useful is a time delay on retransfer. Use a time delay on energization relay to control the line contactor. When power returns the instantaneous contacts on the relay will drop out the generator contactor and stop the set. A few seconds later the line contactor closes.
To review, your component count count is:
1> Two contactors with a mechanical interlock and normally closed contacts.
2> One relay.
This is your rcok bottom basic circuit.
Now, suggested additions in suggested order of implementation:
1> Voltage monitoring. Use voltage monitoring relays for both the contactors. The basic is to use cheap plug in relays with series resistors so that the pull in voltage is higher than the pull in voltage of the contactors. Thjis protects the more expensive contactor coils from low voltage conditions.
2> Time delay on retransfer. This may be a seperate relay or a time delay relay may be used in place of the line relay. It will work but it is not a really good idea to try to combine a series resistor for voltage monitoring and a time delay in the same relay. Better to use a third relay if you want a delay on retransfer.
This scheme will be suitable up to about 15 KVA to 25 KVA. A larger set will need more protection.
A three position swith with one set of normally open contacts and one set of normally closed contacts can provide basic manual control.
The positions are:
1> run generator with load.
2> Normal automatic operation.
3> Run generator without load.
Please give us some feed back. Mark up your drawiong and repost it.
Remember Gunnars advice.
Thanks for the help, Slava.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Great! Bill.

I do not do these things very often. But I understand that you eat little gensets for breakfast.

I think that "our" pupil doesn't have acess to his work computer during holidays. I think that we shall wait for him to pick up and do his homework.


Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Hi Gunnar;
Thanks to you for filling in the EU wiring conventions.
It is nice to have a poster who is willing to do some of the work himself and post his diagrams.
I'll be off-line again soon. Yesterday, I drove about 1000 K
Through the Rocky mountains and a couple of other mountain ranges, and through two storms. About 14 hrs driving. I'll be on the bus all night tonight and drive about 400 K tomorrow. Back on-line tomorrow night if all goes well.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[slavag]

Bill!!!!
Without any comments.
Star.
Best Regards.
Slava

 

[vitzwaters]

thanx for comments, will work on each and every comment, i wanna be as good as possible, all comments welcome.

Vitzwaters

 

[vitzwaters]

Bill, 12/12/08,

I want the mains to be independent, but its effect on mains conductor is my concern on behaviour of mains contactor. when power cut is detected thru n/o or n/c of mains contactor, genset must switch on at no load, wait for few seconds and energise the genset contactor. if power is back, the genset contactor must be de-energised, mains contactor energised, and genset switch off. I was away. Vitzwaters SA

 

[vitzwaters]

i will do my homework whole heartedly, bt your advice i suggest should be long ways, ie, i want to wire the intelock not to use one component with interlock already.

I put my n/o and n/c as switches, not used to the sw for drawing so the S are seeing slava are contacts, goog explnation is undernearth,L are coils.

I was concerned of the control circuit first, the when its ready, can work out hw start/ stop buttons can be put in circuit.

The genset will have to be automatic, bt should be room for isolation for other reasons eg, maintenance.

nb: I did not pt proper contactor sympol, instead i made one fro n/o contacts for u1, u2, u3 and g1, g2, g3.

 

[vitzwaters]

warross,

The left ckt conected on u1 and u3 is to detect the mains supply as u sugested in first step.note my ckt was based on your 10/12/12 advice, maybe i did the wrong way, then you must rephrase that i may do it properly.

Ckt explanation:

if u1 and u3 have power, Line relay #L is energised and NO relay closes after some seconds and power is send to the load.

If power is off, n/o s1 and s2 close on 12v ckt, and start relay , generator coil energised.

G1 and G3 will have power, and after some seconds, #s n/o contactor closes and energises the generator coil and the power is delivered to the load.

I think L4 is not supposed to be there.

Vitzwaters