[jimmygrapes]

That is a good way to test the generator without interruption, but at some point you still need to test the ATS under real world circumstances: unstable or suddenly missing utility power. Throwing the main covers one of those, and the other requires a little more planning and resources.

[generatorguy]

Honestly I am struggling to remember an instance where we purposefully plunged an operating hospital in to darkness.

You can test the system’s ability to detect loss of power or poor quality power by lifting sensing wires or injecting out of frequency or voltage range power with a test set, and load pickup and load testing we used a load bank. The actual hospital load is fed through bypass breakers during these tests so if the utility went out we would have to manually operate breakers to disconnect the load bank and swing the vital loads over to the generators.

If I am setting up electrical protection on a generator I don’t put a short circuit on the generator, I show the protection relay what it would see by injecting current and voltage with a relay test set and make sure the relay gives the signal to open the breaker when it should.

Greenfield hospital generation sites are straightforward to open the utility feeds since the vital loads are still fed through the old power system.

[bluGill]

You can (and should) do all that. However until you actually disconnect from the utility power you don't know for sure that the systems all work. The generator powers a load, but turns out your hospital is more load than you thought. Or the generator starts but the switch to connect the hospital to the generator is broke and you didn't test that...

In the end you WILL test what happens when the hospital plunges into darkness. Would you prefer the first test to be a a bright sunny day when all the staff is ready for something (and you can turn the utility power back on quickly if something fails), or when someone with a backhoe/chainsaw has an accident with your power feed. The latter will happen, I don't know how or when, but at some point in your future trees will take down power lines, backhoes will cut something, major weather events will take out power for days, maybe a large blackout...

You should have course test everything separately often. However if you wouldn't let a random electrician (electrician only because they will know how to not kill themselves) turn off your utility connection with only a day of warning, your system isn't trusted to handle real events which are typically much worse than a clean turn off the switch.

[generatorguy]

I remember some complication with the elevators not working or homing properly at one place so we must have had an outage. it was probably at 3am, scheduled, and with incoming patients diverted. All our tests are and I’m in the electrical room so they all looks the same to me. An actual outage to vital loads would be done once and then you shut the door and walk away as there was never any question that it was going to work.

FYI where I’ve worked the tiers of loads are metered individually and picked up in order of priority and with a check to verify the combined capacity of the generators which are online is great enough to pick up the load. Likewise loads are shed in order if there isn’t enough generation such as one generator tripping.

I don’t really see that much difference between opening a breaker and bad quality power. It is the same sensing and logic in both cases: is the magnitude and frequency of the phase to phase voltages in the acceptable range or not?

[bluGill]

The important part is that whatever bad happens to mains power, the backup systems detect it and properly take over. Bad frequency or power out are both bad situations that the backups need to handle. You need to have confidence that your systems will handle both. If you only pull power and never test bad frequency, one phase missing, brown outs, over voltage, (list not complete because I don't know everything) then you have not done your job. If engineering determines that your test also covers another bad scenario then I'm fine with not testing it.

[brudgers]

Electric utilities provide appropriately higher levels of service and communication to hospitals. Hence there are protocols insuring hospitals don’t lose power in the way you are imagining. The people involved are serious competent professionals with extensive relevant experience, training, and education focused on safety and in touch with the specific facts of actual hospitals and utility grids.

[bluGill]

There isn't much that they can do about storms knocking down wires, squirrels chewing a wire and knocking out a phase (other than taking down all phases). Which is why hospitals have several backup systems.