Electrical Schematic

[Marxman99]

Hi, I am doing course on electrical engineering. I have an electrical schematic. The scheme uses 1000kva transformer, 500kva back-up gen, 2nr 160kva ups (parallel operation).

I have 3 questions:
1. The schematic shows a main 800A fuse and a separate neutral 400A fuse, why cant the fuse 800A switch all phases and neutral together e.g 4pole?

2. The fuses I refer to in 1 above are in the switchpanel, should there be a fuse at the beginning of the incoming cable (cable from the transformer) to protect the cable?

3. In books 3 switches are shown for the wrap-around bypass, why can’t 2 switches be used.

I would very much appreciate answers in layman terms as I have only just started the course.

 

[Marxman99]

Would like to first say that the project was implemented by an electrical building services company, it is now in operation. There are many occasions where the main supply was to be paralleled with the gen. If you google G59 relay you’ll see that the manufacturers make reference to paralleling the mains with another source. I have no control schematic, in building services we do not usually produce these.

So, here’s how the system is supposed to work:

• The loads connected to the top busbar = non-essential load. Loads connected to the bottom one are called essential loads. The essential loads are always feed via the online UPS, always – no matter the status of Tx and gen!

• Upon mains (Tx) failure the gen activates and runs. All loads are supplied.

• When the mains is up again, both mains and gen will be running momentarily but synchronised by G59 relay.

• Gen is made to shut down.

• System now back in normal operation i.e loads supplied by mains (via online UPS for essential loads)

At the time when the gen comes on, of course it will have to sych with the UPS, but the control to allow that is either part of the UPS integral control or the gen control panel, not sure which.

Re. Mains/ gen synchronising, I have googled the wording:

“The synchronization process can be done automatically by an auto-synchronizer module. The auto-synchronizer will read the voltage, frequency and phase parameters from the generator and bus-bar voltages, while regulating the speed through the engine governor or ECM (Engine Control Module).”

‘auto-synchronizer module’ – more commonly known as G59 relay.

The more I think about it, the use of the G59 relay is not needed because the online UPS will ensure that there is no momentary break to the essential loads. Hmmmm.

Fyi the 1000kva Tx was purposely oversized, maybe for future load increase.

What I missed of the drawing (don’t have a scanner so had to draw it for you guys) was 2 earth rods adjacent to the Tx, why is 2 needed as oppose to only 1?

Did you guys understand all the modules / equipment in the switchpanel that I uploaded?

 

[Engineer54]

As it's getting late here, i'll ask one simple question before commenting further later....

If this switchboard and system is now in operation, how the dickens can you maintain or fault-find problems on this set-up without a control schematic drawing(s)?? There should and would normally be such a necessary drawing, located in the control cabinet in this switchboard.... And it wouldn't be the only copy!!!!

As for the un-shown Earth rods, what and where are they connected too, ...the star point of the TX secondary or direct to the switchboard?? If to the TX secondary star point then that is normal. Usually as a minimum, two deep driven earth rods located at diagonally opposed corners of TX, exothermically weld connected together by a substantially sized bare buried copper conductor ring, (usually with one end of the ring conductor being a bolted connection to one of the rods for testing purposes) and an exothermic weld connection from the ground ring conductor or rod, to the TX star(neutral) point.

 

[Marxman99]

What you say makes sense, there should be a control schematic. I'll make enquires.

Thanks

 

[Engineer54]

Marxman,

The more i look over your essential/non-essential system, the more confused i am as to why, a relatively perfectly simple system has been made so complicated. In essence, with the UPS units permanently in service to supply the essential loads of this installation, there really is no need to parallel the two main power sources.

As i see it, based on your mode of operation, TX power fails and opens TX ACB, ...UPS battery power takes up the load, ...Generator gets signal to start, and comes upto to speed, ...UPS senses stable power at it's input terminals and changes from battery to primary power.
TX power restored, ...signal sent to generator to open ACB, ...UPS battery power takes up load, ...TX ACB closes, ...UPS senses stable power at it's input terminals and changes from battery to primary power. ...Sequence complete!!!

By-Pass line is configured to close only for UPS failure and for maintenance purposes... This is virtually the basic set-up that i've had, on projects where large computer processing facilities have been present.

Now obviously there's a lot more to the above sequence of operation on the controls side of things, but i feel sure that there is far less to go wrong, and would be far easier to maintain, than the what seems convoluted system i'm looking at on your system. But that remains to be seen, .....if you can manage to get hold of that control schematic drawing(s)

Now all that remains is that neutral configuration on the TX output, that to be honest i still don't fully understand at this time. It is obviously something to do with the UPS earthing system, that we have as yet, no knowledge about!!!

What are the 2 input supplies to the UPS units about?? I see there is a BMS connection to the switchboard, ....doe's it include any over ride controls, or is it just monitoring points??

A question, ....have there been any problems with the this installation since being put into service?? I hope that this facility has some pretty decent maintenance technicians, if it has suffered any problems...lol!!!

 

[Marxman99]

Confused hey, I aint got much hair left to pull out!

I feel like I have advanced a little more in understanding this subject because my observation is exactly as yours, i.e no need to parallel the 2 main power sources because the essential loads are permanently being fed via UPS : -)

I disagree with your 2nd paragraph in explaining the operation of the UPS. The UPS is permanently online i.e the essential loads ALWAYS being fed via UPS. The load (data racks) will be given a more steady power using this method.

The 2 input breakers f or each UPS: 1 breaker for when the UPS is in normal operation (see paragraph above). Other breaker for when the UPS switches to mains power via internal bypass switch (switches automatically, but maybe have external switch to do manually. Note, to service the UPS this bypass is not as safe as the wrap-around external bypass method).

The below is someone else’s observation:

“Looking at the switchgear arrangement it would appear that the following has been utilised:

1. Non auto 800A ACB’s for generator and transformer with external relays. P141 for transformer & a P341 (G59) for the generator.

The P120 can be used for restricted earth fault or single pole/ circuit monitoring.

2. Single Maintenance Bypass MCCB in lieu of the 3No. noted in the schematic.

3. The ‘400A’ neutral MCCB is noted as a TP&N Non Auto (NA) UPS Earthing MCCB, connected to one of the external Areva relay P120 relays.

4. Maintenance bypass interlocked with UPS Breakers and a solenoid held key. It is unsure what is holding the electrically held solenoid key.

Overall, I would say that the bypass MCCB is reduced from 3No. to a single unit with a Castell key interlock.

Not sure why there is a key exchange for the bypass MCCB using keys from the output UPS MCCB’s in the switchboard.

Typically you use keys from the UPS MCCB’s in the UPS units themselves.

Looking at the arrangement you would have to turn the UPS output OFF (no UPS), to obtain the bypass key and then switch the bypass in. This creates a break….

This is not how you would want to do this…… you never want to switch off a UPS.

The solenoid held key….. maybe linked to the UPS units, so that when the UPS units are in static bypass (raw mains) the key is released. This would make sense……


The 400A TP&N MCCB noted as UPS Earthing is interesting…..

It would appear that the device is monitoring the Neutral Earth (via the P120) of the UPS.

What the device would do is something that only AF switchgear can advise.

You would need to obtain AF’s schematic to confirm how the device is connected…….

It may be that the 400A device is connected to an external delta zig zag isolation transformer…….”

I’ll have to read this in more detail when I have a clearer head. I’m sure I’ll have questions.

I’m not aware of any problems the system may have had. I was only told that the project is finished. I will try ask the question and try get hold of the control schematic.

Do you work as an electrical engineer, electrician????

 

[Engineer54]

Marxman,

Sorry if my sequence of operation was a little unclear to you, but it is utilising the UPS to feed the load at all times, only solely independent of either source of primary power, during primary power change overs. I think i did say battery power in my sequence operation!!!

OK, understand about the 2 UPS supply incomer breakers and confirms my initial thoughts...

1. Not sure why the mains and generator ACBs are non automatic, i would want these breakers to be motorised, but then you have this parallel situation, that frankly i'm not keen on... I'm far more familiar with ANSI protective relay codes, so had to look these multi function relays up to see what they were doing... Thankfully they related to the ANSI code numbers in there data... I agree with the other guy, in his assessment of these relays.

Still not sure of this 400A neutral breaker. If used for the essential UPS output, why is it shown connected to the primary bus?? This could well be a drawing error. This is one area where you really do need that schematic drawing!!! It is very likely that it is connected to a zig zag isolation transformer, certainly makes more sense than how it's shown connected in the present drawing.

2. Also agree with a single By-pass breaker being used, although there are two 400A MCCBs shown on your panel drawing.

3. Still not sure of this 400A neutral breaker. If used for the essential UPS output, why is it shown connected to the primary bus?? This could well be a drawing error. This is one area where you really do need that schematic drawing!!! It is very likely that it is connected to a zig zag isolation transformer, certainly makes more sense than how it's shown connected in your drawing.

4. Yes the castell key interlocking arrangement is also confusing, why you would need to open the UPS output breakers to gain access to the key to close the By-Pass breaker?? Once again we need the schematic control drawing, to show what is ''actually'' happening and not to just to make assumptions on what maybe happening....

Without the ''As Built'' single line control drawings, and/or mode of operation, this system will always ask more questions, than can be answered, and will just continue to go around in circles without them!!

From where i've been working on projects over the years, (overseas) the emphasis has always been, on simplicity of specialised installations whenever possible!! Mainly due to a lack of skilled or adequately trained Engineers, technicians, etc... Your system is a far cry from being simple to understand, or in it's operation, ...lol!!!

In answer to your question, my work is as a Project teams Electrical Engineer, mainly on large overseas commercial projects and hospitals...

 

[Marxman99]

I just assumed that the ACBs were motorised. How else then would they be controlled to open and close???

Someone elses conclusion of the ACBs:
"The 2No. ACB’s act as the ATS or ‘flip flop’ between the 2 sources. In this case both ACB’s can close (not a typical ATS) if the G59 allows and the generator is in ‘generating’ mode, if not the generator will become a motor (reverse power) and initiate the opening of the generator ACB."

Dont really understand how and why the gen will become a motor though.

I spoke to AF Switchgear this afternoon and have just now sent an email to them to send me the control schematic. Hopefully should receive it by Wednesday afternoon. So stick in there, we’ll solve this mystery!

Seems like my main failing is the lack of understanding of transformers and earthing, so gonna have a long night now reading up on this.

 

[Marxman99]

Hmmmm, asked AF Switching for a control schematic for the switchpanel, they came back with the attached. It's not what i was expecting, and i guess you neither. Maybe something wrong with my wording????? Had a quick look, and with peoples previous explanations, the interlock switches makes more sense now.

 

[Engineer54]

Where is this attachment then ?? lol!!!

 

[Marxman99]

So sorry about that. I've attached it now. Tomorrow i'll ask again, this time saying wiring schematic.

 

[Knobhead]

OK I know you’re trying.

But for AF to send you that is beyond a joke. (I’ve had it happen to me, I wanted a scheduled wiring diagram for a furnace control panel. Got a great drawing of the front of the panel).

 

[Marxman99]

Good news and bad news:

I have the wiring schematics now. They were emailed to my work email but i didn't have time to convert the CAD drawings to pdfs. The CAD drawings is a big file so dont think can upload here. If you can wait until monday i can convert to pdf when i get back to work, or if you have CAD or a CAD viewer then i'll need your email address to send it.

 

[Engineer54]

That'll be fine Marxman, ...should make for some interesting reading!!! lol!!!

 

[Marxman99]

Sorry for the delay in responding, i haven't been at work too often to convert the drawings. I dont have the full pdf writer at work or at home, tried to upload the files now but the file is 10.4MB, so it will not upload. Not able to seperate the file with my pdf reader. Over the weekend will try to do at friends house.

 

[Engineer54]

Fine, ..whenever your ready, ...looking forward to looking over these controls