How emergency power line work?

[Pawelk198604]

For exemple in Poland and most of countries in the world the Hospitals had it's own power generator in case of black out i wonder how it activated does it activate after system detect power lose, does it automatic switch when when Power is off. 

 

I always wonder how it work that if we disconnect laptop or mobile phone from power line it's automatic switch to internal power without any disturbance   

Edited December 21, 2015 by Pawelk198604

[AngelLestat]

About hospitals or other services, is not an instant switch unless they had some batteries to backup the change.  It takes some time.

On cellphones this is the circuit.

D1 to D4 are diodes, current just follow one direction (this is because the power transformer works with AC and needs to be DC.

The C1 or C2 are capacitors, they are needed to convert the power wave into something more linear.

 

But all that should be included in the same charged, not in the cellphone, so in resume, we can said that the cellphone is always (in some way) taking power from the battery, that is why we dont notice the switch.

Edited December 21, 2015 by AngelLestat

[magnemoe]

Most systems activates automatically. You tend to have two lines, one is for critical stuff who have an uninterrupted power supply.
Like you disconnect your laptop this takes over power without any interrupt. 

Two effects, first you are charging your battery and the laptop run off the battery. Second you might have noticed that an tower pc, tv and other stuff can survive short blip in the power as the power supply hold some power so the electronic has time to switch to battery.

After switching to battery the system start the generator who not only power the critical systems but also the rest. 
Most systems switch back automaticly too but they tend to have an delay as power might be unstable just after restarting it. 

[Shpaget]

Air traffic controll I worked at has redundant lines, not just power, but telephone lines, internet, radio, radar...

Power is run through a giant UPS where batteries are located. They provide a few minutes of power, enough for the diesel generators to power up. Once the generators are running, the facility has enough power for vital functions and can be run for as long as tanker truck keep bringing the fuel.

[cantab]

There are various ways to build a UPS, with different cost, efficiency, and quality of supply.

https://en.wikipedia.org/wiki/Uninterruptible_power_supply#Technologies