BRPL distributes power to over 12.2 lakh customers across 19 districts in South and West Delhi. Power is generated at medium voltages and stepped up to high or extra high voltages for transmission, then stepped down at distribution stations to 415/240V for customers. The Saket D-block substation has 2 transformers with a capacity of 1250kVA each that step down 11kV power from feeders to 416/240V. Ring Main Units are used at the high voltage side for feeding and protection, with 3 switches for 2 inputs and 1 output. Power is distributed through overhead or underground lines, with underground being more expensive. Faults can be transient from temporary contacts or persistent from cable damage, and can

1. Electricity Distribution System Jasjit Singh Jolly EEE-7thsem 0311324908

2. BSES Rajdhani power ltd BSES: Bombay suburban electricity supply BRPL distrbutes power to an area spread over 750 km serving over 12.2 lakh customers spread over 19 districts across south and west zones of Delhi including Alaknanda, khanpur, saket, nehru place, vasant vihar etc bses has invested rs 3500cr in Delhi.

3. Distribution system layout

4. The generation generally takes place at voltages around 3.3kV to around 22kV which is medium voltage. The voltage is then stepped up to a level of 110kV or 220 kV (high voltage) or even 400kV (extra high voltage) depending on the amount of power to be transmitted .

7. RMU: Ring Main Unit RMU panel generally forms ring system in which distributor is supplied from more than 1 feeders as input to RMU so that in case of failure from any one feeder, power can be fed uninterruptedly from other feeders at the same point. Now a days it is of SF6 gas insulated type.

8. Contd… RMU is used for HT side and it has a total number of 3 switches (Circuit Breakers or Isolators), it is used for two inputs and one outgoing to the load or one input with two outgoings. Primarily used for feeding purposes . Also protects secondary side transformer from the occasional transient currents.

9. Electricity supply to consumers The secondary winding of the transformer is mostly of wye connection type. This supply system with a neutral wire is termed as 4 wire 3 phase supply. 4 wire supplies are normally used to distribute domestic supplies since they can provide an earthed neutral.

11. Three single phase supplies are available between each phase line and the neutral wire.

13. Faults in distribution lines Transient Faults: A transient fault is a fault that is no longer present if power is disconnected for a short time. For eg - momentary tree or bird contact. Persistent Faults: A persistent fault does not disappear when power is disconnected. Faults in underground power cables are often persistent. These occur due to some external damage.

14. Contd… Faults can further be classified as symmetric or asymmetric faults. Symmetric faults: Equal fault currents in line with 120 deg displacement. Rare in nature. Eg - (L-L-L) or (L-L-L-G) faults. Asymmetric faults: Unequal fault currents with unequal phase displacement. Most likely to occur. Eg – (L-L) or (L-L-G) or (L-G) faults.

15. Fault detection To detect the exact location of a high resistance fault in underground transmission lines Arc Reflection Method (ARM) is used. LSG 300 surge generator manufactured by sebaKMT is use to testing purposes.

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