13-01-2012, 10:42 AM
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