Two gensets, three transfer switches

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sparky 134

Senior Member
Location
Joliet, IL
I'm preparing a proposal for a nursing home that has an existing natural gas genset that is somewhat dated. The customer wants me to:

A: Install a temporary diesel genset to backup the existing gas genset
B: Order two new gensets, one gas, the other diesel

The customer wants the gas genset to come online first. If that fails, the diesel genset will need to come online. The existing genset feeds a 400amp 208volt 4wire transfer switch and a 60amp 208volt 4wire transfer switch.

My plan so far is to install a third ATS outside and connect the gas genset to the normal power lugs, the diesel genset will connect to the EM lugs and the load side will then feed the two existing transfer switches. There will be a fault relay installed in the gas genset to monitor a no-start condition and send a start signal to the diesel genset if need be.

Any problems with the way I'm building this project ?
 

steve66

Senior Member
I watched a webinar where someone advocated using two transfer switches with two generators for redundancy (similar to what you are proposing). The counter arguement was to use two paralleled generators with paralleling gear.

With one gas and one diesel, I'm assuming you can't parallel your two generators.

I think the setup I saw had the normal power going through both transfer switches. Then you would tie the gas genset to the emergency lugs of the upstream switch.

The diesel genset would tie to the emergency lugs of the downstream switch. Then you would set the delay on that switch for longer than 10 sec to give the gas generator a chance to start. Then the diesel generator would start based on the standard wiring from its transfer swtich. No "fail to start" monitoring of the gas generator is needed.

With your setup - the upstream transfer switch won't have any control voltage unless one generator is running. Not sure if that will be a problem or not.
 

Hameedulla-Ekhlas

Senior Member
Location
AFG
I'm preparing a proposal for a nursing home that has an existing natural gas genset that is somewhat dated. The customer wants me to:

A: Install a temporary diesel genset to backup the existing gas genset
B: Order two new gensets, one gas, the other diesel

The customer wants the gas genset to come online first. If that fails, the diesel genset will need to come online. The existing genset feeds a 400amp 208volt 4wire transfer switch and a 60amp 208volt 4wire transfer switch.

My plan so far is to install a third ATS outside and connect the gas genset to the normal power lugs, the diesel genset will connect to the EM lugs and the load side will then feed the two existing transfer switches. There will be a fault relay installed in the gas genset to monitor a no-start condition and send a start signal to the diesel genset if need be.

Any problems with the way I'm building this project ?
Can you please post a single line diagram what you have done and what you want.
 

sparky 134

Senior Member
Location
Joliet, IL
With your setup - the upstream transfer switch won't have any control voltage unless one generator is running. Not sure if that will be a problem or not.
There will be a circuit monitoring the utility power and sending the start signal to the first genset upon utility failure. The fault relay will start the second genset if the first fails to start.
 

yucan2

Senior Member
There will be a circuit monitoring the utility power and sending the start signal to the first genset upon utility failure. The fault relay will start the second genset if the first fails to start.
That being the case, it would appear that you will be bypassing the ATS monitoring of the available normal power with your circuit monitoring arrangement.

Just wondering, as the ATS normally controls items such as exercising and the like, will these options still be available? Just curious.
 

steve66

Senior Member
I'd much rather have the ATS monitor the voltage and start the generator. It will monitor all three phases for over and under voltage, and frequency. And it will send a start signal to the generator. All this in one box that is listed for emergency service.

I still suggest you try putting the normal power into the 1st ATS, then connect the diesel to the two emergency inputs on the two downstream ATS's. At least draw it out and think about it.

Steve
 

Cold Fusion

Senior Member
Location
way north
Here is the one line drawing.
Where does the utility connect? Both the 400A and 60A transfer switches?

What is the plan to switch back to the utility?

Do yu have anybody for controls integration?

Why 4W transfer switches? I do a lot of multiple gen setup and never use 4W.

cf
 
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yucan2

Senior Member
Those are existing ATS's. He just didn't show their respective feeder and load entry and exits. They're there.

I'm just very hesitant, in fact reluctant, no adamant about relinquishing control of the gensets from the ATS. Really not a good way to go.
 
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Cold Fusion

Senior Member
Location
way north
...I'm just very hesitant, in fact reluctant, no adamant about relinquishing control of the gensets from the ATS. Really not a good way to go.
I rarely ever use an ATS. Only one I can think of. It's a little 60kw autostart comm backup.

All the rest are electric operated CBs in a switchboard - one per source. The utility has it's CB, each gen has it's CB. Controls are by small PLC - or in the OPs case, maybe a small relay panel with hardwired interlocks on the CB auxiliary contacts. Since there is no parallel operation, this one should be simple.

Unless it is a 700 or 701 in which case you are dealing with the AHJ for "identified for emergency (or standby) use and approved by the AHJ"

The few times I have dealt with the AHJ on these issues, they just roll up into a wilted ball if they can't find the little bug on the transfer switch design docs. Pointing out the definition of "identified" just got me a blank look.

Of course, they (the AHJ) may have an apolexy fit if this is the Ops case (700/701) and he is contemplating stacking up 3 ATS to get to the required loads.

However, if it is a 702, then I would look into the cost of something like this:

cf
 
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yucan2

Senior Member
I rarely ever use an ATS. Only one I can think of. It's a little 60kw autostart comm backup.

All the rest are electric operated CBs in a switchboard - one per source. The utility has it's CB, each gen has it's CB. Controls are by small PLC - or in the OPs case, maybe a small relay panel with hardwired interlocks on the CB auxiliary contacts. Since there is no parallel operation, this one should be simple.

Unless it is a 700 or 701 in which case you are dealing with the AHJ for "identified for emergency (or standby) use and approved by the AHJ"

The few times I have dealt with the AHJ on these issues, they just roll up into a wilted ball if they can't find the little bug on the transfer switch design docs. Pointing out the definition of "identified" just got me a blank look.

Of course, they (the AHJ) may have an apolexy fit if this is the Ops case (700/701) and he is contemplating stacking up 3 ATS to get to the required loads.

However, if it is a 702, then I would look into the cost of something like this:

cf
Oh no, I wasn't or am not concerned from a code standpoint, I'm purely hesitant because of the potential damage to loads or the equipment.

The ATS aside from having numerous features such as frequency and voltage monitoring, also has other safe guards and options such as delay on neutral, delay on transfer, delay on return to normal, the list goes on and on, depending upon the manufacturer of the transfer switch.

By removing the ATS's ability to start the unit, once again that doesn't really bother me either. They (the owner), can always exercise the unit manually with or without load, themselves. It's the ability or rather the inability of the ATS to stop the unit, especially the larger gensets, that gives me grave concern.
 

Hameedulla-Ekhlas

Senior Member
Location
AFG
I'm preparing a proposal for a nursing home that has an existing natural gas genset that is somewhat dated. The customer wants me to:

A: Install a temporary diesel genset to backup the existing gas genset
B: Order two new gensets, one gas, the other diesel

The customer wants the gas genset to come online first. If that fails, the diesel genset will need to come online. The existing genset feeds a 400amp 208volt 4wire transfer switch and a 60amp 208volt 4wire transfer switch.

My plan so far is to install a third ATS outside and connect the gas genset to the normal power lugs, the diesel genset will connect to the EM lugs and the load side will then feed the two existing transfer switches. There will be a fault relay installed in the gas genset to monitor a no-start condition and send a start signal to the diesel genset if need be.

Any problems with the way I'm building this project ?
there are three ATS have been used which economically it cost too much.

What is the distance between 400 ampere ATS and 600 amp ATS
what is purpose of 400 amp ATS and does it have any connection from local power too.
what is purpose of 60 amp ATS and how far it is from 600 amp.

The connecion you have shown is ok.

Try to minize the number of ATS, if it is possible. I dont know the distance and 400 Amp, 60 amp ATS usage purpose.

my suggestion is

Minimize the number of ATS and make one ATS and one Main Distribution panel and feed all sub panel from main.
 

dbuckley

Senior Member
I'm with Cold Fusion on this: stand-alone ATS are fine for simple jobs, but this one is non-simple, and getting quite ugly, and thus one mechanically interlocked, electrically operated CB per source onto a main bus is the neatest solution, driven by a PLC (only need to be a tiddler micro-PLC with a porogramming LCD on the front, nothing heavy).

The only annoyance is the need to provide 24VDC for the PLC and CB motors from batteries.

To do the mains sensing and pretty display functions, I would use the DeepSea Electronics DSE500 ATS controller, (check the datasheet for wiring diagram) which in spite of being an (excellent) UK made product, has distributorship in the USA, and (like all the DeepSea stuff) is really a rather nice component.
 

Cold Fusion

Senior Member
Location
way north
... and thus one mechanically interlocked, electrically operated CB per source onto a main bus is the neatest solution, ...

...The only annoyance is the need to provide 24VDC for the PLC and CB motors from batteries. ...
I wouldn't do mechanically interlocked, rather electric interlock from the CB aux contacts. I don't think I have ever seen a mechanical interlock for this size CB. (Note to the contrarians: Yes, I'm sure that somewhere, some goof has or does make one)

And this setup, might not even need batteries. Closing power will be from the line side of the source CB. Then, select CBs with self-powered trip mechanisms. All that is left is powering the PLC. Maybe it can do with an inexpensive UPS - one step above a plug-in. Yes, I know this is batteries, but sometines a package unit is less maintenance.

Just some thoughts. Which may not matter if the OP never returns.

cf
 

hillbilly1

Senior Member
Location
Atlanta,Ga
I wouldn't do mechanically interlocked, rather electric interlock from the CB aux contacts. I don't think I have ever seen a mechanical interlock for this size CB. (Note to the contrarians: Yes, I'm sure that somewhere, some goof has or does make one)

I think there is a requirement that the interlock cannot be electrically only, on manual transfer switchs of large size, "Kirk" key mechanisms are used to prevent both sources to be energized at the same time,The switch that has the Kirk key has to be turned off before the key mechanism can be removed, and the other cannot be closed until the key is moved to it. On the 1200 amp transfer switches that Cutler Hammer makes, they have mechanical cables that run between the two motorized breakers, along with electrical interlocks.
 

dbuckley

Senior Member
I have seen what happens when both the utility and the generator thinks its supplying the load. Well, I waw it once the "discussion" had. The switchgear was the loser in this discussion. Arc F'd. But not arc flash. A big mess.

Having said that, I too cannot think (top of head) of a motorized breaker in the small hundreds of amps range that has mechanical interlocks, maybe the Schneider / Square D / whatever the heck they're called these days MasterPact range?

For PLC and stuff power, if it were me I'd be tempted to steal the power from the cranking batteries of the two gensets, and use a DC/DC inverter to go from 12V to 24V, but most folks would think thats too much trouble. A 24V battery backed power supply is available as an off the shelf item, just screw it on the wall and wire her in; the 12V variants are widely used in security alarms.
 
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