ACO(ATS) made on PLC-s

[pisimatza]

Hello
I want to ask you about Auto chageover systems-ACO(called also auto transfer switches- ATS), made on PLC-s not on relays.
Power system:
400 V, 50 HZ, Europe
How many ACB-s(Air circuit breakers) can you pun in such a system?
For example if you have a system of 4 switchboards, 2 supplied from transformers, 2 from generators as per sketch attached: can we do a ACO system on PLC-s involving all 11 ACB-s.
The purpose of ACO system is to always have power supply.
If someone has an experience with such system, not with ACO made with 2 incomers, or 2 inc. +tie, please mention.
Thanks!

 

[ScottyUK]

We have a system with two incomers and a single generator with the option for a second generator. It is under PLC control, as are load shedding breakers feeding loads. So yes, it is certainly possible to use a PLC as an ATS controller.

Which is the load which always needs power - the two lower boards I assume? If you have critical loads then presumably they are on a UPS, so an open transfer scheme is acceptable?

Personally I think your sketch is a little more complex than necessary. Do you need to automate breakers 1, 6, 7, & 10, or can you manually reconfigure these once an ATS around breakers 2, 3, 9 & 11 secures the supply to the essential boards. Are the essential boards physically next to each other, if so why have two bus tie breakers 4 & 5? Do you need to synchronise generators to each other and / or to the utility bars?

This really needs a full design doing, and that is something you will pay good money for, not get done by a group of anonymous engineers you met on line.


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If we learn from our mistakes I'm getting a great education!

 

[slavag]

Hello.
I have expirience with such of application, but on MV.
On LV is more or less same.
1. For my pinion, no needed CB 5,7 , enough link or disconnector.
2. CB 8 for is not provide any benefit and only add problem to the scheme.

Now, about concept:
Yes, possible use PLC and it's standard solution.
But please take in account, you need in all cases NV relays on the buses and infeeds and synchrocheck relays on each optional synchronasing point.
In cases of load shedding:
1. possible use static logic of LS.
2. possible build some dinamic load shedding on the actuall load. For this you need some convertors 5A to 4-20mA to PLC.
If you will ask me "are work?" answer will "yes".
But I strongly recommend for this application used MV bay conrollers are included NV, SC and load shedding options.
Is more expensive, but for whole projects, once I calculated
it's same price( no need PLC cubicles, interposing relays for close open commands, additional NV relays, cables, etc..). Lot of swg. factories used PLC only, but is only seems cheaper.
Many, many faults with PLC and coordinations between parts of systems are problematic.
Just my opinion
Regards.
Slava

 

[pisimatza]

Thanks for replies.
95%of the loads are on main busbars(those from the top of sketch). And the switchboards are in the same room.
slavag : You said something about dynamic load shedding: this is something like : if a certain load exceeding a pre-defined value (by PLC logic), that load is shut down ?
Anyway, i am interested if maybe a PLC runned system can work with all 11 CB-s involved(inputs from all ACB-s and outputs to control all of them).
To be mentioned that i have very small Knowkedge on PLC-s.
Regards.

 

[slavag]

Hi.
Yes, you can running ATS with 11 ACB's on the PLC. No problem. Two important points.
1. Used good PLC, from high level: SIEMENS, AB, maybe Modicon, ABB AS800, etc.
2. Please see Scotty's recommendation:
"This really needs a full design doing, and that is something you will pay good money for, not get done by a group of anonymous engineers you met on line".
Yes, you understand exactly what is dynamic LS.
It's some table of loads and priorities in the PLC ( something like to 5-10 groups of load's).
PLC on line meas actuall power on the infeeds and save in the memory ( for example each 15min). According to the infeed load PLC decide what groups need shedding in case of ATS and send sedding before command close to alternative infeed.
Possible use simple static LS, that means: direct shedding
w/o groups and prorities ( commonly used in the LV).
Regards.
Slava

 

[ScottyUK]

The biggest problem with implementing full automation on such a complex scheme is making sure that the automation is able to handle all the contingencies gracefully: for example, if a breaker is isolated for maintenance work, or a breaker fails to operate. With 11 breakers there are a lot of contingency situations to consider. Minimise your breaker count, then work out your switching strategy to secure your critical loads, then factor in the contingencies.

For example: an incoming breaker to an essential bar is out of service so the automation must fall back to closing the bus tie IF the other essential bar can support the additional load AND the out of service breaker did not trip on fault (indicating a fault on the essential bar)....

Do this a few times and you will have a pretty complex PLC program. Can it be done? Yes. Is it the best solution? Probably not.

I would consider something simpler such as equipping each essential board with a three-way ATS able to draw supply from Main 1, Main 2, and a generator (or two), and then replicate this on the other essential board. If you think you need a disaster recovery capability I might consider a manually operated bus tie between the two essential boards.


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If we learn from our mistakes I'm getting a great education!

 

[slavag]

Scotty. Good and very important points.
Pisimatza. I fully agree with Scotty.
Possible ---> yes, good option---->NO.
Electrical system must be simple as possible.
Such sytems are have most chances for faults.
Regards.
Slava