On ships, drilling rigs and many other applications emergency generators can automatically be synchronised to line and loaded up. Automatic load shedding or power limiting (e.g. - variable speed drives) systems then matched the load to the generator power available. This was common practice in the back in 1970. The emergency generator can then be shutdown by shedding load to the main supply bus.It is virtually glitch free and if there is large motor load or capacitor bank that can regenerate onto the bus while other loads can automatically ride through several seconds until the power recovers ( though not long enough for the generator to start and sync).

The problem is very often power recovery to the main bus may be shortly be followed by another outage, so the generator can be programmed to load shed but only disconnect a few minutes later.

 The UPS can be used to maintain power during initial outage, but clearly only if the load shed system is programmed to rapidly shed loads to match the UPS capacity. This is not truly glitch free unless you have an oversized UPS. The downside is that the system requires large batteries which continually have to be charged and ideally cycled on a regular basis.

The best solution is a combinations of automatic load shedding / load recovery,  automatic synchronisation, emergency generator and UPS ( to maintain essential power until the generator syncs to line) . Some of the systems use a DC bus configuration, which is almost glitch free.

As stated previously emergency generators can easily be tested by synchronisation to line. You do not have to shutdown the main propulsion to test a generator.

As stated previously emergency generators can easily be tested by synchronisation to line. You do not have to shutdown the main propulsion to test a generator.

That does have complications where the main line is fed from the public supply - DNOs (understandably) aren't keen on the possibility of local generators back feeding onto a grid circuit they've just isolated (or been subject to ADS). It is doable, generally you somehow need to ensure that your generators are disconnected from the grid if the grid supply fails for any reason - and the rules get even more complicated if generators are rated at over 16A/phase (regardless if you're system is configured to export that much or not).

   - Andy.

As stated previously emergency generators can easily be tested by synchronisation to line. You do not have to shutdown the main propulsion to test a generator.

That does have complications where the main line is fed from the public supply - DNOs (understandably) aren't keen on the possibility of local generators back feeding onto a grid circuit they've just isolated (or been subject to ADS). It is doable, generally you somehow need to ensure that your generators are disconnected from the grid if the grid supply fails for any reason - and the rules get even more complicated if generators are rated at over 16A/phase (regardless if you're system is configured to export that much or not).

   - Andy.

Some UK customers may opt to follow NFPA 110 for their emergency and standby power systems depending on their needs and preferences.