Understanding the fundamentals of how electricity is transmitted

Understanding the fundamentals of how electricity is transmitted

Subject: Science and Tech

Section: Msc

About

Energy  exists in many forms, like light, sound, heat, etc., power and power transmission also exist in many forms. However, electric power transmission is more complicated because of the multiple phases of electric current, and factors like voltage, impedance, frequency, etc.

Basics of Power supply

• Any power supply system has three broad components: generation, transmission, and distribution.
• Electricity is generated at power plants as well as at smaller renewable-energy installations.
• Then it is transmitted using a distributed network of stations, substations, switches, overhead and underground cables, and transformers, among other elements.
• Finally, it is distributed to consumers in a standardized way, befitting the needs of various machines and applications.

How electricity is transmitted?

• First, in any conductor that transports electric current, the transmission efficiency is higher at lower current and higher voltage.
• This is because the energy loss during transmission increases as the square of the current, whereas the amount of voltage increase corresponds on a 1:1 basis with the amount of current decreased.
•  That is, if voltage is increased by five units, the amount of current will drop by five units, but the amount of energy lost will be reduced by 25 units.
• This is the purpose of transformers: they increase the voltage and reduce the current before feeding into transmission lines, and the reverse when receiving current to be supplied to consumers.
• Second, the cables that move the current still have some resistance, which results in some energy loss.
• The amount of loss can be controlled by adjusting the cable’s thickness: the thicker it is, the less energy is lost, but the cost increases. So when the cost of the cable’s material is high, the cables are thinner.
• Third, the longer the distance of transmission, the lower the transmission cost.
• All these factors are further complicated by the use of alternating current (AC).
• AC can be modified more easily in transformers than direct currents (DC) and also has higher transmission efficiency.
• But when the AC frequency is higher, the amount of resistance the current encounters in the material increases.
• Engineers model all these factors for a given network to understand how much electrical energy will be lost between generation and consumption.

Power transmission

• In a three-phase AC circuit, each wire transmits an AC current in a different phase.
• From a power station, the wires are routed to transformers that step-up their voltage.
• Then, they are suspended from transmission towers, which must be stable and properly wired, as they travel long distances.
• Insulators in contact with the wires draw away some current if there is a surge in the line; circuit-breakers ‘break’ the circuit if there is too much.
•  The towers are also grounded and equipped with arresters that prevent sudden increases in voltage — such as due to a lightning strike — from affecting the wires.
• Similarly, dampers prevent vibrations in the wires from affecting the towers’ stability. Switches are used to control the availability of current and to move currents between different lines.

Operation of grids

• As mentioned earlier, transmission is situated between production and distribution.
•  A national grid includes all three components, and as a result transmission also has to account for the particulars of power production at different types of sources, at various locations, and how and where that power is consumed.
• For example, some sources — like coal-fired or nuclear reactors — can produce energy continuously, whereas renewable energy sources are intermittent.
•  So grids also have storage facilities that store electrical energy when there’s a surplus supply and release it in times of deficit.
• Grids also need to respond to failure in different parts of the network and prevent them from carrying over to other parts, adjust voltages in response to demand, control the AC frequency, improve the power factor etc.

Conclusion

A grid becomes a wide-area synchronous grid if all the generators connected to it are producing an AC current at the same frequency. India’s national grid is also a wide-area synchronous grid. Such grids result in lower power cost but also require measures to prevent cascading power-supply failures.