Multiple ATS configuration for generator

[katwalatapan]

Hello,

I have a query concerning multiple ATS configuration for single, SG050, 50kW, 3-phase, 120/208V, generator.

I'm considering a scenario, where a 200A, 3-Pole, HTS series ATS is connected to the SG050 generator. The 200A, ATS feeds a 200A, 3-phase, 120/208V, emergency panel. Nine (9), 50A, 2-Pole, RTG series ATS with load center would be installed in the apartment units, which would be connected to the emergency panel during a power outage. As per the product spec sheets the utility sensing and load transfer could be configured from the SG050 generator controller and the 200A, HTS series ATS. The RTG series uses utility sensing and timing functions from the generator as per the spec sheet. Based on the above scenario, I have the following queries:

1. With both the SG050 and the HTS series ATS providing utility sensing and load transfer, should the generator or the ATS be configured for voltage sensing and transfer?

2. Is control wiring required from the Nine (9), 50A, RTG series ATSs to the generator for operation i.e. transfer load from utility to generator and vice versa? If so, then would we have to home run the control wiring from the ATSs to the generator OR could we combine the control wiring from all the nine (9), ATSs and send one (1) control wire to the generator for transfering load from utility to generator and vice-versa?

I'd appreciate your assistance on this matter.

Thank you.

 

[waross]

I did some similar installations. Two were apartments, the other was a department store with two independent services both fed from the same standby generator. Two transfer switches in different locations.
In my situation, the main ATS at the generator was configured normally. The main ATS detected power failure and sent a start signal to the generator control panel.
The remote ATSs may be configured normally with the exception of the start signal. It is provided by the main ATS and is not needed.
When the generator voltage stabilizes, the main ATS will connect generator power to the outgoing feeders.
The remote ATSs will already be aware of the loss of power. When the remote ATSs see the power available on the standby feeders, they will connect to the available standby power.
You may want to consider staggered closures. Block loading may stall the gen-set. I have had issues with block loading on gen sets up from 8 KVA up to 1500 KVA.
You could put a series of timers in the main panel and run conductors to the remote ATSs. You could use a PLC or smart relay and run conductors.
Myself, I would by a handful of economy priced two wire timers, set at different times and connect one in each remote ATS standby circuit.
Much cheaper, a failure affects only one apartment, easy trouble shooting, easy to install, no cable to run, have I missed any advantages?

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

 

[katwalatapan]

Thank you very much Bill for your insights.

The generators nowadays send the switching signals to the ATS (other way round) via their on-board controllers. The controller also does utility voltage sensing and timing functions as well. Most ATS does the voltage sensing and timing functions.

The remote ATSs, which could sense voltage on utility line or generator line and switch accordingly w/o signal from the main ATS or generator, would those be electrically operated with mechanically held contactor OR electrically operated with electrically held contactor?

 

[waross]

From another thread:
"Warum einfach, wenn mann es so schön komplizieren kann" (Why keep it simple when it can be so beautifully complicated)

The remote ATSs, which could sense voltage on utility line or generator line and switch accordingly w/o signal from the main ATS or generator, would those be electrically operated with mechanically held contactor OR electrically operated with electrically held contactor?

Electrically held, single solenoid, mechanically held, electrically operated circuit breakers,- All the ATSs I have seen were capable of sensing the mains voltage and switching by themselves. Closed transition and very fast open transition will have a synch check circuit to inhibit out of sync switching.


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

 

[wayne440]

Bill,

The subject switches are not "two wire start", a (sometimes not so well thought of) manufacturer of small generators introduced that wonderful complication to the market many years ago.

 

[waross]

I have been trying to find online a diagram of the subject switches.
I have installed dozens of ATSs and worked on many more. All two wire start.
Just when I think I think I've seen it all, something new.
I accept that this combination is not two wire start.
From online searches I believe that the gen-set is capable of using two wire start, but that's besides the point.
The point is: How to configure the remote transfer switches.
Over the years I have seen three price levels for Automatic Transfer Switches.
Cheapest; Bought as part of a package with the gen-set.
Reasonable; Build your own with an interlocked contactor and a phase and voltage monitoring relay.
Outrageous; Bought from the set supplier as an individual piece of equipment without the purchase of a gen-set.
I see several options here. I will make comments but the final choice is up to you. It may be a compromise considering; cost of installation, have the remote switches been ordered yet, warranty issues, customer preference, ease of use and trouble shooting and possibly other concerns. You have to make this call.
If the remote transfer switches are capable of working as stand alone units, then there should be no problems.
If the remote switches must have operating signals then there are two main choices;
1> Install voltage and phase monitoring relays in each remote ATS to make them function as stand alone units. This may have warranty issues if the relay is mounted in the ATS enclosure, but these issues may be avoided by mounting the relay in a separate enclosure adjacent to the ATS.
2> Run control wiring to each individual ATS.
Location of the ATSs. I have done this both ways. In one installation, the ATSs were mounted together adjacent to the revenue meters.
This kept the feeder short and one feeder daisy chained trough the ATSs. The ATSs were 4 pole devices and the services were single phase, so each ATS could do two apartments. The ATSs were bought together on the gen-set order.
Another apartment installation was done differently. The set had been bought without adding the transfer switches.
A set of standby feeders ran throughout the building and picked up a manual transfer switch at each apartment. The tenants were responsible for their own switching.
In a very poor country with weekly power failures, this was still one of the most advanced apartment buildings in the city.
Generally the cheapest installation will be with the transfer switches located near the metering stacks. This will mean no extra feeders to the individual apartments, no control wiring to the individual apartments.
You can go with one set of feeders from the gen-set to the ATS location and use either a splitter or a sub panel to feed the individual switches depending on protection and/or code requirements.
By the way, if you find an online wiring diagram, please share it.
Don't allow the remote an ATSs to send a generator start signal. If the control system of a remote switch develops trouble you don't want the generator starting.
Hope this rambling discourse helps you make your decisions confidently.
Bill




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

 

[katwalatapan]

Thank you very much Bill. You may think of it as rambling, but it surely exemplifies your experience in doing complex installations.

I'll run this idea by the engineer and check if AHJ or Generac may have any issues with the warranty and certifications.

Having the remote ATSs running as stand alone units using the phase and voltage monitoring relays, which could switch between the utility line and emergency panel line automatically, seems to be the best approach. The emergency panel would be energized anyways by the 200A, main ATS. We would only need the remote ATSs to switch back and forth between utility line and emergency panel line, based on the phase and voltage monitoring on each line.

 

[wayne440]

Bill,

https://www.norwall.com/product_pdfs/5909_rtg10eza1_om_2015.pdf

this is probably close enough for your purposes.

 

[waross]

I have found that the most economical location for remote transfer switches is often not really remote but grouped near the metering equipment. Long feeders are expensive and this generally gives the shortest feeders.
Generally you will have the service coming into the main panel with breakers feeding the individual meters for the individual apartments.
Installing the ATS past the meter lets you take advantage of the feeder protection to protect the ATS.

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

 

[waross]

Hi Wayne440. Thanks for the link. unfortunately that switch sends a two wire control signal to the generator and does not have provisions to be controlled by the generator panel.
I wasted some time looking for a model HTS without success.

katwalatapan For that size set, don't forget to consider staggered start.

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

 

[wayne440]

Hmm. I must be losing it- I read that diagram as the generator sending a transfer signal to the switch, energizing relay TR1 via wires 23/194.

HTS manual here

http://soa.generac.com/manuals/9959185/0H6470

 

[waross]

Sorry Wayne. I'm the one who lost it. I have seen the similar circuit so many times for two wire control that I didn't take the time to determine which were the coil terminals.
You are correct.

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

 

[katwalatapan]

Thank you very much Wayne and Bill.

The SG050 control panel does seem to send the switching signals to the ATS. So to make this system work, my option would be to run additional control wiring from the dry contacts at the generator control panel to the nine (9) remote ATSs for the switching to occur.

 

[waross]

Yes but don't forget staggered starting. Maybe a smart relay. Possibly individual two wire timers depending on the signal voltage.

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

 

[redlinej]

Try this solution. use the two wire from each ATS(engine start signal) to control 9 miniature relay at the generator,then series the n/c of the 9 relays and use this connection to breaker the main sensing of the genset. On the ATS stagger the transfer to genset timers.If genset settings are adjustable, set the setting the >U,<U,<F,<F higher and lower that ATS.

 

[katwalatapan]

Thank you very much everyone for your insights.