Power Loads in Data Centre

 As we all know, a Data Centre is a building with heavy Electrical machines, IT equipment, Mechanical machines, etc. To run this equipments/machines we need electric power either from Power station or Diesel generators.

The power which we get from the power station is of High Tension Or High Voltage (11KV, 33KV) which is feed into HT panel which consists mostly of VCB (Vacuum Circuit Breaker) because while make and break operation it creates huge spark due to high voltage and current here is low but the potential difference charges the molecules of air of surrounding and gets charged during switching operation which creates huge arc which needs to be extinguished. Since Vacuum has high arc quenching property than air so the VCB is used in quenching the arc instead of ACB (Air Circuit Breaker), which is used in quenching the arc in LT( Low Tension/Voltage) side.

HT panel is a metal enclosure with relays, circuit breaker, and energy meter used to receive high voltage power supply and distribute the power from its outgoing feeder. The number of feeder outgoing depends on the load of the building. These HT panels can either be indoor or outdoor which helps in controlling the flow of electricity as well as for the protection against faults.

HT Panel

The outgoing feeder from the HT panel will be the incoming feeder for the Transformer where the high voltages coming from the HT side are lowered to make it low voltages (as the transformer is step down transformer) and is feed to the LT panels. Now the power from the LT panels are distributed to various panels which goes to different machines UPS, Air Handling unit like PAHU or PAC, Purging system, etc, and also to Distribution Box where the MCB's are located for various lighting, workstation, comfort air conditioning, lifts, chillers, electric pump motors, etc. All the power from the LT panels to other panels except to the UPS panel (which leads towards UPS) when added, the total power is called the Facility power. 

The power from LT panel to UPS panel to UPS charges UPS for Power backup and also suppresses the power surges so they don't damage equipment. The outgoing feeder from the UPS goes to another LT panel as we cannot connect many outgoing feeders directly from the UPS and from where the power is sent to the Isolation transformer (to change the different mains grounding systems to what the data center IT equipment requires), from where the power is further sent to IPDU (Intelligent Power Distribution Unit) which is located in the server room inside the Racks where we directly connect the IT equipment like servers, routers, firewall, storage, etc. Now the power reaching to IPDU inside the server room is called the IT Power.

The meter reading of the load can be taken from the IPDU which is called 1st level of IT Power whereas the meter reading of the load taken from the Isolation Transformer is called the 2nd level of IT power and the meter reading taken from the UPS is called the 3rd level of IT power. All these 3 readings will never be the same as there are some losses as it moves forward and reaches its destination.

So, Hence we can say that power in a Data Center is broadly classified into two parts:

1. Facility Load.
2. IT Load.

Both these loads play a very important part in the Data Center Efficiency called PUE (Power Usage Effectiveness).

If there is a power failure from the main supply then the Diesel generator will have to be operated which directly feeds its output to the LT panels as the DG is designed to feed on the LT side and not on the HT side. It depends on the AVR( Automatic Voltage Regulator) settings. Now the power from the LT goes as described above.