The Tata Power Companies (TPC) and the Maharashtra State Electricity Board (MSEB) have their generating stations located in different parts of Maharashtra State and form an interconnected transmission system grid in the Mumbai-Pune region. Electric Power from this system is transmitted at 220/110kV through overhead conductors and underground cables amongst others to TPCís sub-stations at Carnac, Parel, Dharavi, Backbay & Mahalaxmi. From here power is made available to BEST at 110/33/22kV.
The BEST Undertaking on behalf of Brihan Mumbai Municipal Corporation
(who are the licensees for the distribution of electric power within the City Limits of Mumbai) receives power in bulk from the TPCs. At 110 / 33 / 22kV, 3 Phase, 50Hertz.
The 110 / 33 / 22 kV substations are completely indoor equipped with power transformers, switch-gears, control panels, reactors, capacitors, batteries and other auxiliary equipment.
Bulk power at 110 / 33 / 22 kV is transmitted from Tataís five sub-stations through underground cables to BESTís receiving sub-stations situated at different localities in Mumbai where the BEST Undertaking has installed 110 / 11 kV, 110 / 33 kV, 33 / 11-6.6 kV or 22 / 11-6.6 kV or 33/11 kV power transformers. The Power transformers have been provided with On load Tap Changing (OLTC) gear for regulating the voltage for giving stabilised supply to the consumers.
Each distribution substation comprises one or more incoming and outgoing feeders
and one or more transformers of 1600/1000/630 kVA. The outgoing feeders and primary of the transformers are controlled
and protected by 11 KV oil circuit breakers in conjunction with their associated trip coils and current transformers. The
distribution substations are normally equipped with 11 kV switch-gear, distribution transformers and Low Voltage Distribution
boards or pillars. 56 kVAr capacitor banks are connected on the L. V. side of transformers for power factor improvement.
Where the switchgear and the transformers are located inside a building.
Where the switchgear and the transformers are located in open land and directly subjected to outside atmosphere.
Where the switchgear is located inside a
building and the transformers are
located in an outdoor plot open to sky.
Underground 11kV cables radiate from the
BEST receiving sub-stations to supply
power to a large number of distribution
substations and to certain consumerís
substations. These feeders form a radial
network under which each feeder supplies
on an average four to five substations
Power at 6.6 kV or 11 kV is stepped down to 415 / 240 V at the distribution substations where the various sizes of 6.6kV / 415-240 V and/or 11-6.6 kV / 415-240 Volts delta/star transformers of vector group 41DY11 are installed. The star point of these transformer is solidly grounded and is also brought out to an insulated terminal for the 3 Phase, 4 wire distribution system.
The 415 / 240 V secondary distribution system comprises of a vast network of underground four core cables, suitably sectionalized by means of distribution pillars. The service cable lines are teed off, and taken into meter rooms, situated in the building premises, to supply power to medium and low voltage consumers.