Help with two generators

[mbrooke]

Two independent generators.


Upon loss of utility power do let both generators start simultaneously, or do I let ATS #1 start generator #1 and if ATS #2 does not sense power after 10 seconds ATS #2 starts generator # 2 with transferring takes place? If so what type of time delay? Or do I need an electrical interlock between the ATS?



Second can a generator serve only equipment loads without any resistive or lighting loads? I only heard that a generator needs some restive loads due to the power factor and regenerative kickback of motors but no idea if its true.


Single line:

 

[iceworm]

This looks like an Architect's bad dream. (yuck)

Let's see if I understand:
Loads on the left side are Crit 1, Crit 2, Life Safety

Feed is:​

Normal first
On Normal failure, ATS-1x switches to Gen 1
On Gen 1 failure, ATS-2x switches to Gen 2
​

Loads on right side are Equip 1, Equip 2, Equip 3

Feed is:​

Normal first
On Normal failure, Equip ATS #x switches to Gen 2
​

This is where you get out the Detailed Design Document - The one where the Principal Engineer discussed critical operation with the Owner's Agent. This is sufficiently complex there should be one. Don't have it, get writing. I usually start talking to the users of the power:

What exactly is mandated by law?
What exactly do they need?
What would they like to have?​

I'm sure you already know all this. But if you don't have the design document, then next week when the power goes out for the first time, the top management is wondering why the alien containment field went out. And now they are spending $100K/day to field the agents rounding them up. Yep, you should have asked.

Upon loss of utility power do let both generators start simultaneously, or do I let ATS #1 start generator #1 and if ATS #2 does not sense power after 10 seconds ATS #2 starts generator # 2 with transferring takes place? If so what type of time delay? Or do I need an electrical interlock between the ATS? ....

Assuming I understood the power plan:

• Equipment circuits: If these are needed, then immediately start Gen 2 and switch the Equip-ATS #x. There is no other source for power for these.
• Critical and Life Safety:

Start Gen 1 immediately (of course)
As for switching to gen 2,​

How long does it take for gen 1 to start and come up to speed?
Are there any regulatory time limits of bringing up power to Critical/LS circuits?

Meet these two, then switch - Gen 2 is already running.
​

• Note on Gen 2 capability:

Is Gen 2 capable of powering both Crit/LS and Equip circuits?
If not, you will need to work in some load shed​

These are all question you will have to answer.

Or do I need an electrical interlock between the ATS? ...

I don't know where you are going with this one.

Second can a generator serve only equipment loads without any resistive or lighting loads? I only heard that a generator needs some restive loads due to the power factor and regenerative kickback of motors ...

I have no idea what a "regenerative kickback of motors" is (are?). Sounds like a quote from Robin, "Holy regenerative kickback, Batman. The motors are going to swap magnetic polarity."

Seriously, unless the motor loads are strange stuff, the gen will be just fine. And unless it is a strange gen, it will be rated for full load KVA and .8pf lagging. And unless the gen was sized wrong, it will be fine.

As for strange loads, unless you have heavy leading reactive loads, the gen will be fine. Examples of leading reactive loads are un-switched power factor correction caps, large capacitive front end VFDs

Good luck. Let us know how it comes out. It is an interesting project

worm
​

 

[mbrooke]

This looks like an Architect's bad dream. (yuck)

You want to be on life support when one of the generators or ATSs fail?

Let's see if I understand:
Loads on the left side are Crit 1, Crit 2, Life Safety

Feed is:
​

Normal first
On Normal failure, ATS-1x switches to Gen 1
On Gen 1 failure, ATS-2x switches to Gen 2
​

Yes

Loads on right side are Equip 1, Equip 2, Equip 3

Feed is:​

Normal first
On Normal failure, Equip ATS #x switches to Gen 2
​

Yes, spot on

This is where you get out the Detailed Design Document - The one where the Principal Engineer discussed critical operation with the Owner's Agent. This is sufficiently complex there should be one. Don't have it, get writing. I usually start talking to the users of the power:

What exactly is mandated by law?
What exactly do they need?
What would they like to have?​

Law requires 1 gene-set and 1 ATS for the critical branch. C- can get you to pass a course. Bare minimum rarely impresses, progresses or survives through unforeseen contingencies. Remember that it was 2 Manhattan hospitals in NY that blacked during Sandy while Goldman Sachs was lit up like a Christmas tree.

I'm sure you already know all this. But if you don't have the design document, then next week when the power goes out for the first time, the top management is wondering why the alien containment field went out. And now they are spending $100K/day to field the agents rounding them up. Yep, you should have asked.

I want to figure out and set the logic for myself

Assuming I understood the power plan:Equipment circuits: If these are needed, then immediately start Gen 2 and switch the Equip-ATS #x. There is no other source for power for these.

• Easy and doable.
  
  
  
  
  
  

  [*]Critical and Life Safety:

Start Gen 1 immediately (of course)

As for switching to gen 2,​

How long does it take for gen 1 to start and come up to speed?
Are there any regulatory time limits of bringing up power to Critical/LS circuits?​

Gen 1 takes a few seconds. If I remember right NEC requires both branches to come online within 10 seconds. I have to see if that applies to always. But it would be a good idea to treat it that way regardless.

Meet these two, then switch - Gen 2 is already running.

• Note on Gen 2 capability:

Is Gen 2 capable of powering both Crit/LS and Equip circuits?
If not, you will need to work in some load shed
​

So basically I start both generators- and if there is no need for Gen #2, I shut it down after 10 minutes?

For the discussion (and what will end up happening) is Gen 2 can run 100% of the load on life safety, 100% of both critical branches and 100% load on all 3 equipment branches.

I don't know where you are going with this one.



​

I have no idea what a "regenerative kickback of motors" is (are?). Sounds like a quote from Robin, "Holy regenerative kickback, Batman. The motors are going to swap magnetic polarity."

Basically an elevator motor can act as a generator when slowing down, putting power back on the generator. No idea, but its what I've heard over and over.

Seriously, unless the motor loads are strange stuff, the gen will be just fine. And unless it is a strange gen, it will be rated for full load KVA and .8pf lagging. And unless the gen was sized wrong, it will be fine.

Even if its 100% motor? The way this is set up gen 2 can end up taking 100% of the motor, while gen 1 takes all the resistive.

As for strange loads, unless you have heavy leading reactive loads, the gen will be fine. Examples of leading reactive loads are un-switched power factor correction caps, large capacitive front end VFDs

Good luck. Let us know how it comes out. It is an interesting project

worm
​

Noted and in agreement.


No, thank you

 

[iceworm]

This looks like an Architect's bad dream. (yuck)[/quote

You want to be on life support when one of the generators or ATSs fail? ...

This is when you check the Detailed Design Document. Maybe the system needs a few dual, fail-over UPS systems for the iron lungs. And if it is my iron lung, I suggest a triple fail-over UPS and a hand crank with two well paid orderlys, that like to play poker (and hopefully bring a couple of six-packs)

So basically I start both generators- and if there is no need for Gen #2, I shut it down after 10 minutes? ...

Why shut down gen 2?
You want the Crit/LS backup if gen 1 fails.
The equip circuits need power
Leave it run
Only issue I can see is if it is too lightly loaded and wet stacks.

... regenerative kickback of motors

Basically an elevator motor can act as a generator when slowing down, putting power back on the generator. No idea, but its what I've heard over and over.

Okay. Overhauling loads on induction motors can over-speed the motor, turning it into an Induction Alternator. Yes, that will pump power back into the line. If you have any of those, that would be considered "strange stuff".

Nothing really to worry about, just have to account for it.

For example:
As long as the power developed by the overhauling load is less than the rest of the generator load, the gen just backs down the throttle during the overhauling load periods. Power is absorbed by the rest of the generator load. Having resistive load won't help any, other than having sufficient load to absorb the power.

addition to example:

Gen load is 200 hp (yep, hp. If you like kw, multiply by .746)
Overhauling load is 50 Hp.
Elevator goes from full power up to overhaul down
Gen output goes from 200hp (elevator up) to 100hp (elevator down) to 150Hp (elevator stop)
All is good
​

Alternate:

Gen load is only 50 hp elevator

Elevator goes from full power up to overhaul down
Gen output goes from 50hp (elevator up) to -50hp (elevator down)
All is not good
During overhaul down period, the motor is pumping 50 hp into the generator.
Speeds up generator
Throttle pulls clear back
Gen still speeds up, turning it into a synchronous motor
Eventually gen over speeds and goes out on over-freq
Hopefully the elevator brakes lock up, the containment field holds, and the ups on my iron lung kicks in
​

So, yes, if there are strange stuff loads, they will need to be considered.

I think you got it. Just have to plot out and account for all the weirdness.

The worm

 

[mbrooke]

This is when you check the Detailed Design Document. Maybe the system needs a few dual, fail-over UPS systems for the iron lungs. And if it is my iron lung, I suggest a triple fail-over UPS and a hand crank with two well paid orderlys, that like to play poker (and hopefully bring a couple of six-packs)

UPS can only go for so long on battery.

Why shut down gen 2?
You want the Crit/LS backup if gen 1 fails.
The equip circuits need power
Leave it run
Only issue I can see is if it is too lightly loaded and wet stacks.

Waste of fuel-unloaded running- but I get your point and it stands.

Okay. Overhauling loads on induction motors can over-speed the motor, turning it into an Induction Alternator. Yes, that will pump power back into the line. If you have any of those, that would be considered "strange stuff".

Nothing really to worry about, just have to account for it.

For example:
As long as the power developed by the overhauling load is less than the rest of the generator load, the gen just backs down the throttle during the overhauling load periods. Power is absorbed by the rest of the generator load. Having resistive load won't help any, other than having sufficient load to absorb the power.

Perhaps this what I've been hearing and it does make more sense now that I think about it.

addition to example:

Gen load is 200 hp (yep, hp. If you like kw, multiply by .746)
Overhauling load is 50 Hp.
Elevator goes from full power up to overhaul down
Gen output goes from 200hp (elevator up) to 100hp (elevator down) to 150Hp (elevator stop)
All is good
​

Alternate:

Gen load is only 50 hp elevator

Elevator goes from full power up to overhaul down
Gen output goes from 50hp (elevator up) to -50hp (elevator down)
All is not good
During overhaul down period, the motor is pumping 50 hp into the generator.
Speeds up generator
Throttle pulls clear back
Gen still speeds up, turning it into a synchronous motor
Eventually gen over speeds and goes out on over-freq
Hopefully the elevator brakes lock up, the containment field holds, and the ups on my iron lung kicks in
​

So, yes, if there are strange stuff loads, they will need to be considered.

Got it.

I think you got it. Just have to plot out and account for all the weirdness.

The worm

Any ideas on how to set the ATS? Or should I change the diagram at all, ie have gen 2 be the source for ATS 1 and gen 1 the source for ATS 2? Just thinking whats best.


BTW, are you getting a long gray box over most of the thread?

 

[mbrooke]

I can't see the pic on my end, so here is the single line:

 

[iceworm]

UPS can only go for so long on battery. ...

Yep. That's the reason two six-packs.
Then there is time to fix the gen before I run dry

... Any ideas on how to set the ATS? Or should I change the diagram at all, ie have gen 2 be the source for ATS 1 and gen 1 the source for ATS 2? Just thinking whats best. ....

Nope clueless (on this and several other issues)
Is there a difference between the generators? That might drive a change.

There are:
Physical constraints
Legal constraints
Operational constraints

Once you meet these, the system is likely boxed in tight.

... BTW, are you getting a long gray box over most of the thread?

yes

 

[mbrooke]

Yep. That's the reason two six-packs.
Then there is time to fix the gen before I run dry

Maintenance? Cost of new bats? What if the gen fails catastrophically?

Nope clueless (on this and several other issues)
Is there a difference between the generators? That might drive a change.

One is 400kw, the other 1,200kw

There are:
Physical constraints
Legal constraints
Operational constraints

Honest question, how would you do this? Someone said here, design to this, we just want redundant power.

yes

Thats good, thought I was going crazy from the long hours :lol::lol: Mods, can you wave your magic wand?

 

[iceworm]

Yep. That's the reason (for the) two six-packs.
Then there is time to fix the gen before I run dry ...

Maintenance? Cost of new bats? What if the gen fails catastrophically? ...

Mr Brooke - let this one go.
If it is my iron lung, I'm hiring two girls (forget the guys) to come in each day, with a deck of cards and two six-packs - oh yeah also a hand crank.

... What if the gen fails catastrophically? ...

I assume you mean "both generators". One failure would not do it.

Then I get them to break out the single-malt and toast my sorry butt off to the eather. Probably to the shade of Mick's Bar and Grill - Purveyors of decent Scotch, good IPA, and barbecue ribs.

No disrespect intended here. Some peoples' higher authority resides in alternate places.

... Thats good, thought I was going crazy from the long hours :lol::lol: ...

Okay, probably. What does that have to do with the long blank page?

Just curious

Worm

 

[iceworm]

... Is there a difference between the generators? ...

... One is 400kw, the other 1,200kw ...

And the 1200KW is on the equipment loads and 400kw is on the Crit/LS loads.

That sounds good

There are:
Physical constraints
Legal constraints
Operational constraints

Honest question, how would you do this? Someone said here, design to this, we just want redundant power.

Let's see:

Utility
two generators
nine transfer switches​

"Butch - I think we have enough dynamite here."

You have discussed with the owners' agent and are confident the you are meeting their needs/desires.
You have verified the installation meets any regulatory commitments. The equipment line-up looks fine.

Where to go from here:
Tweak the ATS settings to minimize the switchover time.

• Maybe set both gen start times to zero. Any detectable power blink starts gens.
• Allow 10 seconds for gens to stabilize. (Or longer if available - 15 seconds is good) Just meet the regulation.
• Don't transfer back until the utility is stable. Once the transfer happens, stay on generators until the utility is in spec for 15 minutes

Go spend money on a PM testing program that adequately verifies availability and doesn't PM unto death. As part of the PM verify the batteries are better than good.
Add any critical UPS systems to the PM program. Again verify the UPS batteries are better than good.

Get any test equipment needed to perform PMs.

If any money is left, consider a 1 MW load bank for gen testing. That is pretty expensive. I likely would not add that unless it was hard to get operations to allow switching the ATSs over to back up power for a periodic load test.

Hire mfg training for the maintenance crews on the gens and ATSs.

If you haven't already, start NFPA 70E training on the specific equipment. Make retraining a three year cycle.

I think you got this

The worm

 

[mbrooke]

And the 1200KW is on the equipment loads and 400kw is on the Crit/LS loads.

That sounds good








Let's see:

Utility
two generators
nine transfer switches​

"Butch - I think we have enough dynamite here."

You have discussed with the owners' agent and are confident the you are meeting their needs/desires.
You have verified the installation meets any regulatory commitments. The equipment line-up looks fine.

Where to go from here:
Tweak the ATS settings to minimize the switchover time.

• Maybe set both gen start times to zero. Any detectable power blink starts gens.
• Allow 10 seconds for gens to stabilize. (Or longer if available - 15 seconds is good) Just meet the regulation.
• Don't transfer back until the utility is stable. Once the transfer happens, stay on generators until the utility is in spec for 15 minutes

Go spend money on a PM testing program that adequately verifies availability and doesn't PM unto death. As part of the PM verify the batteries are better than good.
Add any critical UPS systems to the PM program. Again verify the UPS batteries are better than good.

Get any test equipment needed to perform PMs.

If any money is left, consider a 1 MW load bank for gen testing. That is pretty expensive. I likely would not add that unless it was hard to get operations to allow switching the ATSs over to back up power for a periodic load test.

Hire mfg training for the maintenance crews on the gens and ATSs.

If you haven't already, start NFPA 70E training on the specific equipment. Make retraining a three year cycle.

I think you got this

The worm

What do you think about bypass vs none bypass ATSs?

 

[mbrooke]

And the 1200KW is on the equipment loads and 400kw is on the Crit/LS loads.

That sounds good

I know I asked this, but I just want you honest opinion. Would you leave this as is, or have it such that gen 2 feeds ATS 1 with gen 1 feeding ATS 2? That way gen 2 is the primary backup source for everything, but gen 1 is the "last resort"? Personally I like this setup, but always like to weigh all sides/options/what ifs just for the sake of it. I'd rather now then 10 years from now think 'I should've looked at it like this'

 

[iceworm]

I know I asked this, but I just want you honest opinion. Would you leave this as is, or have it such that gen 2 feeds ATS 1 with gen 1 feeding ATS 2? That way gen 2 is the primary backup source for everything, but gen 1 is the "last resort"? Personally I like this setup, but always like to weigh all sides/options/what ifs just for the sake of it. I'd rather now then 10 years from now think 'I should've looked at it like this'

Using best computer voice:

Working
I'll look at it tomorrow

 

[mbrooke]

Using best computer voice:

Working
I'll look at it tomorrow

It would mean the world to me.

Thank you in advance!

 

[iceworm]

It would mean the world to me. ...

I think you are screwing with me. But that is okay. Truly speaking, if one's causal internet acquaintance's can't screw with you occasionally, what the use of having them.

Bail out disclaimer 1:
The Eng-Tips discussion is pretty good. Those guys are generally pretty informed - although they get stuck sometimes (not me though - nope, never)

Bail out disclaimer 2:
You have been staring at this for weeks? I have spent a total on maybe 30 minutes. You have discussed this with the owners agents - and certainly should have a clear idea of the expectations. Hard for me to believe that I would have any better ideas that you do.

Now that I am by that, next post will have some random thoughts

 

[mbrooke]

I think you are screwing with me. But that is okay. Truly speaking, if one's causal internet acquaintance's can't screw with you occasionally, what the use of having them.

:roll::roll:

The only mistake is not asking. People see things that I don't all the time. Don't sell yourself short.

Bail out disclaimer 1:
The Eng-Tips discussion is pretty good. Those guys are generally pretty informed - although they get stuck sometimes (not me though - nope, never)

But sometimes they get stuck on the right stuff. Love an in depth discussion on a particular concern/solution/product.

Bail out disclaimer 2:
You have been staring at this for weeks? I have spent a total on maybe 30 minutes. You have discussed this with the owners agents - and certainly should have a clear idea of the expectations. Hard for me to believe that I would have any better ideas that you do.

Now that I am by that, next post will have some random thoughts[/QUOTE]

Where did I say weeks? :huh:

Expectations- but its me on how to go about putting any particular expectation into practice.

Don't sell your self short

 

[iceworm]

Now that I am by the disclaimers, a couple ofquestions:
Do any of the following apply?
1. Article 708 Critical Operations Power Systems
2. Article 700 Emergency Systems
1. If so, is there provision for 700.3.F, Temporary Source of Power forMaintenance
2. 700.5 Transfer equipment listed for emergency use
3. 700.5.B Transfer Switch Bypass Isolation Switches (You had asked aboutthis)
4. NFPA 110, Standard for Emergency and Standby Power Systems
4. Article 701 Legally Required Standby Systems
1. 701.5 Transfer Equipment Listings
5. Article 702 Optional Standby Systems (Note: Life Safety does not depend onthe operation of this system.)
6. Article 695 Fire Pumps
7. Article 517, Health Care Facilities

I'm guessing COPS is not a requirement

You did make a comment about "Life Support" and one of the feeds is listed as "Life Safety". So, if Article 700 applies. If not, remove the reference to "Life Safety", "Emergency", and none of the rest applies.

Assumptions:

• The 1200KW is enough to feed the L/S, 2-Crit, 3-Equip.
• The 400KW is sufficient to feed the L/S, 2-Crit, but not the 3-Equp.
• Each of the two utility feeds is sufficient to supply all loads.
• Each service entrance transformer is sufficient to supply all loads (Not necessary, but nice)
• I don't know how much of the equipment is existing and this design may not fit

Going from here:
Use the 1200 KW gen as primary, with 6 ATS feeding all the loads.

1 - L/S (Listed Emergency)
2 - Crit (Maybe Legally Required Standby)
3 - Equip (Legally required Standby? Optional Standby?)

• Drop one of the Emergency buses
• Connect the 400KW to the same Emergency bus as the 1200KW using a non-Automatic DPDT 3 phase Switch
• Interlock the 400KW Gen SW with the CB from the 1200KW Gen, mechanical or electrical.
• Load shed the Equipment Feeds if the 400KW is brought on-line.

Article 700 gives some clues as how the interconnects shall work. And there are a bunch of words about Maintenance and Testing,

Operation:
Both utility feeds have failed
1200 KW immediately starts (no intentional delay)
Sequential closing of ATS:

L/S
Crit 1
Crit 2
Equip 1
Equip 2
Equip 3​

Reclose to utility after stable

1200KW gen fails
400KW immediately starts
Operator disables interlock (Kirk Keys?)
Equip Emergency feeders open
Operator closes 400KW to bus

Time is not an issue. There have been two failures. That would put most airline transports in the dirt. If there are loads that require rapid response on second failure, selected circuits shall have high reliable UPS, with Bypass.

No other ideas

the worm

 

[iceworm]

Well, one (okay 1-1/2)
No paralleling
No closed transition ATS

 

[mbrooke]

Now that I am by the disclaimers, a couple ofquestions:
Do any of the following apply?
1. Article 708 Critical Operations Power Systems
2. Article 700 Emergency Systems
1. If so, is there provision for 700.3.F, Temporary Source of Power forMaintenance
2. 700.5 Transfer equipment listed for emergency use
3. 700.5.B Transfer Switch Bypass Isolation Switches (You had asked aboutthis)
4. NFPA 110, Standard for Emergency and Standby Power Systems
4. Article 701 Legally Required Standby Systems
1. 701.5 Transfer Equipment Listings
5. Article 702 Optional Standby Systems (Note: Life Safety does not depend onthe operation of this system.)
6. Article 695 Fire Pumps
7. Article 517, Health Care Facilities

I'm guessing COPS is not a requirement

You did make a comment about "Life Support" and one of the feeds is listed as "Life Safety". So, if Article 700 applies. If not, remove the reference to "Life Safety", "Emergency", and none of the rest applies.

I will checkout 700.5 B

Yes, life support- 517 level 1 applies.

Assumptions:

• The 1200KW is enough to feed the L/S, 2-Crit, 3-Equip.
• The 400KW is sufficient to feed the L/S, 2-Crit, but not the 3-Equp.
• Each of the two utility feeds is sufficient to supply all loads.
• Each service entrance transformer is sufficient to supply all loads (Not necessary, but nice)
• I don't know how much of the equipment is existing and this design may not fit

Yes to all except there will be multiple service transformers and main-tie-mains.

Going from here:
Use the 1200 KW gen as primary, with 6 ATS feeding all the loads.

1 - L/S (Listed Emergency)
2 - Crit (Maybe Legally Required Standby)
3 - Equip (Legally required Standby? Optional Standby?)

• Drop one of the Emergency buses
• Connect the 400KW to the same Emergency bus as the 1200KW using a non-Automatic DPDT 3 phase Switch
• Interlock the 400KW Gen SW with the CB from the 1200KW Gen, mechanical or electrical.
• Load shed the Equipment Feeds if the 400KW is brought on-line.

Critical will carry medical equipment and ORs.

Article 700 gives some clues as how the interconnects shall work. And there are a bunch of words about Maintenance and Testing,

Operation:
Both utility feeds have failed
1200 KW immediately starts (no intentional delay)
Sequential closing of ATS:

L/S
Crit 1
Crit 2
Equip 1
Equip 2
Equip 3​

Reclose to utility after stable

Sounds good

1200KW gen fails
400KW immediately starts
Operator disables interlock (Kirk Keys?)
Equip Emergency feeders open
Operator closes 400KW to bus

But how do I prevent the 400kw from starting after all power is lost?

Time is not an issue. There have been two failures. That would put most airline transports in the dirt. If there are loads that require rapid response on second failure, selected circuits shall have high reliable UPS, with Bypass.

No other ideas

the worm

So code allowed the failure of the primary gen or ATS to result in an indefinite outage until operator action is taken? Just seems like code would want 10 seconds restoration even if two gens fail provided there are 3.

Its what the code exactly calls for that has me confused.

 

[mbrooke]

Well, one (okay 1-1/2)
No paralleling
No closed transition ATS

BTW, do you agree with this? Especially page 31 and onward?


https://www.slideshare.net/michaeljmack/standby-power-systems-for-hospitals