Emergency supply and Ah vs Wh efficiency

Emergency supply system for an industrial plant

An emergency supply system is an independent, automatically started power source that supplies the essential loads of a plant when the normal supply fails, to protect life, equipment and critical processes.

Essential loads: escape and exit lighting, fire alarm, fire pumps, lifts, control and protection supplies, process loads needing safe shutdown (cooling, stirring, lubrication), communication and security.

Sources:

1. Battery systems – self-contained or central battery; supply is instant.
2. UPS – no-break supply for computers, PLCs and instruments.
3. Diesel generator with AMF panel – starts automatically in about 10–15 s; feeds large loads for long periods.
4. Second utility feeder with automatic transfer switch (ATS).

 Utility ─►[ATS]─► Essential bus ─► fire pump, lights
             ▲
 DG set ─────┘
 Battery/UPS ─────► PLC, alarm, control (no break)

Essential loads are kept on a separate bus, batteries are on float/trickle charge, and the system is tested regularly.

Ah efficiency vs Wh efficiency

η_Ah = Ah delivered on discharge / Ah supplied on charge
η_Wh = Wh delivered on discharge / Wh supplied on charge
     = η_Ah × (V_avg discharge / V_avg charge)

Example: discharge 4 A × 12 h at 2.2 V, charge 3 A × 20 h at 2.44 V → η_Ah = 48/60 = 80%, η_Wh = 105.6/146.4 = 72.13%.