Friday, July 4, 2014
The ac power supply scheme can be broadly divided into two functional systems
1.transmission system
2.distribution system
1.transmission system :
At the generating station bulk electrical power is generated by 3 phase synchronous generator operating in parallel. The usual generating voltage is 11kv.it may be 6.6kv or even33kv in certain areas. In order to reduce line losses the generated voltage is stepped up upto 430kv and the power is transmitted with the help of 3phase transformers at the generating station itself. The transmission system can be divided into two sub systems.
PRIMARY TRANSMISSION
The electrical power of generating station at 230kva is transmitted by 3phase 3wire over head line system to the out skirts of the city. This forms the primary transmission. In India extra high voltage and lines(above 220kv upto 760kv ac) were introduced in India during 1974 and the primary transmission is now well established in our country.
SECONDARY TRANSMISSION :
the primary transmission line terminates at the receiving station which is usually situated at the outer parts of the city. At the receiving station. Eat the voltage is reduced to 110kv by step down transformer. From this receiving station electrical power is transmitted at 110kv phase 3wire over head system to various substation located at different points in the city. This forms the secondary transmission.
DISTRIBUTION SYSTEM :
It is a system through which power is distributed to various consumer for utilization.
The entire power distribution system can be divided into two sub systems 1.primary distribution
2.secondary distribution
Primary distribution
The secondary transmission line ends at the distribution substation where voltage is reduced from 110kv to 11kv 3phase 3wire the 11kv lines run along the importance road side of the city this forms the primary distribution. The bulk consumer (having demand more than 150kw) are generally supplied power at 11 know for further handing with their own substations.
SECONDARY DISTRIBUTION :
the electrical power from primary distribution line 11kv is delivered to distribution substation. These substation are located near the consumer localities and step down the voltage to 400v 3phase 4wire for secondary distribution. The Voltages between any two phases is for 400v and between any phase and neutral is 230v.the single phase residential lighting load is connected between any one phase and neutral whereas 3 phase loads connected across 3 phase lines directly. The secondary distribution system consists of feeder, distributor, service mains.
