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GRID
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 TPC’s 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 BrihanMumbai
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.
BEST SYSTEM
110 / 33 / 22 kV Distribution System:
 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
Tata’s five sub-stations through underground cables to
BEST’s 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.
 11/6.6
kV distribution system:
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.
The distribution substations in the city are of the
following three types :
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Indoor Type – Where the switchgear and
the transformers are located inside a building. |
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Outdoor Type – Where the switchgear and
the transformers are located in open land and
directly subjected to outside atmosphere. |
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Indoor/Outdoor Type – Where the
switchgear is located inside a building and the
transformers are located in an outdoor plot open to
sky. |
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11 / 6.6 kV Cable Network:
Underground 11kV cables radiate from the BEST receiving
sub-stations to supply power to a large number of
distribution substations and to certain consumer’s
substations. These feeders form a radial network under
which each feeder supplies on an average four to five
substations in series.
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.
 415
/ 240 Volts distribution system:
The 415 / 240 V secondary distribution system
comprises of a vast network of underground four core
cables, suitably sectionalised 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.
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