delhi metro rail corporation

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POWER SUPPLY CLASSIFICATION
Power supplies are classified into 5 categories:


A Emergency
B Essential
C Semi-essential
D1 Normal-dual supply
D2 Normal-single supply



A Emergency
Emergency services are provided with duplicated supplies to the power input of the local distribution boards and are also supplied from the UPS systems. Changeover of supplies is automatic on the event of loss of normal supply. The UPS systems prevent these services from seeing any disturbances in supply on change over or loss of supplies. Emergency services include:

 Emergency lightning (station and tunnels), signs and exits
 Fire detection, protection and alarm system
 Automatic gaseous fire suppression system
 Station Control Rooms
 Station Operations Computer
 Automatic Fare Collection
 Control Circuits of main LV switchboard


B Essential
Essential services are also provided with duplicated supplies, but are connected to the Diesel Generator system. Changeover of supplies is automatic in event of loss of normal supply. Changeover to the DGs is automatic in the event of loss pf both supplies. Essential
Services include:

 Fire fighting pumps
 Station ventilation plant and smoke extraction fans
 Under Platform Exhaust fans
 Air conditioning for equipment rooms
 Lifts
 Emergency station exhaust fans
 Sewage and seepage pumps
 Tunnel lightning
 Emergency services
 Tunnel Ventilation Fans and booster fans

C Semi-essential
These services are provided with duplicated supplies, but are not connected to a DG system or to a UPS system in the event of loss of both supplies. Changeover of supplies is automatic. Semi-essential services include:

 Escalators
 Station and tunnel drainage plant




D1 Normal-Dual supply
These supplies are split between the two 33KV/415V transformers (ASS1 &ASS2) to minimise the effect of a single transformer or switchboard failure. Normal services are provided with dual normal supplies from both main switchboards A & B. in the event of loss of one or both normal supplies, there will be no backup. Normal dual services include:


 ECS system- chillers and cooling plant associated pumps and controls
 Station normal lighting
 Station normal small power
 Condensate sump pumps
 Ventilation systems not used for fire safety


D2 Normal-Single supply
These services are split between the two 33KV/415V transformers (ASS1 & ASS2) to minimise the effect of a single transformer or switchboard failure. Normal services are only provided with a single supply from either main switchboard A or B. in the event of loss of normal supply, there is no backup.
Normal single supply services include:

 Water heaters
 Water pumps


MAIN DISTRIBUTION BOARDS
Each station is equipped with 2 main LV switchboards (MDB1 & MDB2) in the ASS rooms with remote switching from the Station Control Room. Normal power is taken from the 2 transformer supplies on the basis of 1 as the main supply and the other as live standby. The A & B supplies is physically segregated in the 2 separate ASS at each end of the station to ensure that a single fault or incident will not affect more than one supply.


SUB MAIN DISTRIBUTION BOARDS
These distribution boards receive power from the MDBs.These SMDBs are divided as per the load category as under:

 DB-1A & DB-2A Feeding Emergency Loads
 DB-E1 &DB-E2 Feeding Tunnel Lighting and station Lighting
 DB-1B & DB-2B Feeding mechanical equipment under essential supplies
 DB-1C & DB-2C Feeding all normal escalators under normal category
 DB-ESC-1 & DB-ESC-2 Feeding escalators under emergency supply
 DB-1D & DB-2D Feeding normal lights, sockets, other equipment in normal category