- Electrical Supply System Definition: An electrical supply system is defined as the network delivering electricity from generating stations to consumers, including transmission and distribution.
- Components of Electrical Supply System: The system has three main components: generating stations, transmission lines, and distribution systems.
- Voltage Transformation: Power is generated at low voltage, then stepped up for efficient transmission and stepped down for safe distribution.
- AC and DC Usage: AC systems are used for most purposes, but DC systems are employed for ultra-high voltage transmission.
- Transmission and Distribution: These systems can be divided into primary and secondary stages, ensuring electricity reaches consumers effectively.
An electric supply system is the path that takes energy from generating stations to users. One small local machine used to be enough. Demand is now far larger, so utilities run many large power plants.
Those plants often sit near fuel, water or wind rather than next to the city. Urban combined-heat-and-power exists, but bulk generation is still usually remote from the load.
So the industry builds electrical network systems to carry that energy from the station to the user. The two big parts of that path are transmission and distribution.
The network that delivers electricity from the source to the user is the electrical supply system. It has three main parts: generating stations, transmission lines and distribution. Machines usually generate at a moderate voltage, often about 11 kV to 25 kV, because that suits the generator insulation.
step-up transformers at the sending end raise the voltage for the lines. The transmission system then carries that higher-voltage electrical power toward the load. Higher voltage cuts current for a given power, so I²R loss and conductor size fall. The lines use overhead or underground electrical conductors. step-down transformers at the receiving end of the transmission lines lower the voltage for distribution. Distribution then feeds customers at the levels they need.
Generation, transmission and distribution are usually AC. HVDC is used for long overhead or submarine links, for asynchronous ties and for some ultra-high voltage corridors. Lines can be overhead or underground. Overhead is usually cheaper where space and weather allow. AC transmission is typically three-phase three-wire. Low-voltage AC distribution is often three-phase four-wire, with a neutral.
Many textbooks split the path into primary transmission, secondary transmission, primary distribution and secondary distribution. Real networks skip stages. Some have no secondary transmission. A small local scheme may have no transmission at all, with generators feeding distribution directly.
The next diagram is one Indian-style example, not a worldwide voltage rule. Other grids use 110 kV, 220 kV, 400 kV or 765 kV on the backbone, and HVDC at ±500 kV or higher.
A worked electrical supply system example starts at 11 kV, three-phase, at the generator. An 11/132 kV step-up transformers bank at the station raises it to 132 kV. A transmission line takes that 132 kV power to a 132/33 kV substation with step-down transformers on the edge of town. That 11/132 kV to 132/33 kV stretch is primary transmission: a three-phase three-wire circuit with three phase conductors and no distribution neutral.
From there, 33 kV three-phase three-wire circuits feed 33/11 kV substations around the town. That stretch is secondary transmission. The 33 kV secondary of the 132/33 kV transformer is the sending end of those feeders.
11 kV three-phase three-wire feeders along the streets carry the output of those 33/11 kV substations. Those 11 kV feeders are the primary distribution.
Local 11/0.4 kV transformers step that down to 400 V line-to-line. These units are the distribution transformer and may be pole-mounted or pad-mounted. From there, a three-phase four-wire circuit feeds users: three phase conductors and a neutral.
A user may take three-phase or single-phase service. Three-phase service is 400 V phase to phase (line voltage). Single-phase service is 400 / √3, about 231 V to neutral. IEC 60038 and Indian IS 12360 now name that low-voltage pair as 230/400 V. The service terminals on the premises are the end of the electrical supply system. The stretch from the secondary of the distribution transformer to those terminals is secondary distribution.
