The batteries, the grid/generator-supplied power supplies, and the telephone switch equipment are all connected in parallel -- as if the entire DC power infrastructure consists of only two wires, and everything involved with it connects only to those two wires.
1. In normal operation, the batteries are kept at a constant state of charge. The switches are powered from the same DC bus that keeps the batteries charged.
2. When the power grid goes down, the batteries slowly discharge and keep things running like nothing ever happened (for hours/days/weeks). There is no switchover for this; it's just the normal state, minus the ability to juice-up the batteries. (Remember: It's just one DC bus.)
3. When the grid comes back up (or the generators kick in), the batteries get recharged. There is no switchover for this either; nothing important even notices. (Still just one DC bus.)
4. If the grid stays up long enough, go to 1. Repeat as the external environment dictates. (And as you might guess, it's still one DC bus and there's also no switchover here. Things just continue to work.)
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You can play with this at home with a capacitor (which loosely acts like a battery does), an LED+resistor combo (which acts as a load), and a small power supply that is appropriate for LED+resistor you've chosen (which acts as the AC-DC converting grid input).
Wire them all 3 parts up in parallel and the light comes on.
Disconnect the power supply, and the light stays on for a bit -- it successfully runs from power stored in the capacitor.
Reconnect the power supply, and the light comes on and the capacitor ("battery") recharges -- concurrently.
Improve staying power by adding more parallel capacitance. Reduce or eliminate it by reducing or eliminating capacitance. Goof around with it; it's fun. (Just don't wire the capacitor backwards. That's less fun.)
The batteries, the grid/generator-supplied power supplies, and the telephone switch equipment are all connected in parallel -- as if the entire DC power infrastructure consists of only two wires, and everything involved with it connects only to those two wires.
1. In normal operation, the batteries are kept at a constant state of charge. The switches are powered from the same DC bus that keeps the batteries charged.
2. When the power grid goes down, the batteries slowly discharge and keep things running like nothing ever happened (for hours/days/weeks). There is no switchover for this; it's just the normal state, minus the ability to juice-up the batteries. (Remember: It's just one DC bus.)
3. When the grid comes back up (or the generators kick in), the batteries get recharged. There is no switchover for this either; nothing important even notices. (Still just one DC bus.)
4. If the grid stays up long enough, go to 1. Repeat as the external environment dictates. (And as you might guess, it's still one DC bus and there's also no switchover here. Things just continue to work.)
--
You can play with this at home with a capacitor (which loosely acts like a battery does), an LED+resistor combo (which acts as a load), and a small power supply that is appropriate for LED+resistor you've chosen (which acts as the AC-DC converting grid input).
Wire them all 3 parts up in parallel and the light comes on.
Disconnect the power supply, and the light stays on for a bit -- it successfully runs from power stored in the capacitor.
Reconnect the power supply, and the light comes on and the capacitor ("battery") recharges -- concurrently.
Improve staying power by adding more parallel capacitance. Reduce or eliminate it by reducing or eliminating capacitance. Goof around with it; it's fun. (Just don't wire the capacitor backwards. That's less fun.)