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Electric power transmission

September 3, 2019
Electric power transmission

Electric power transmission

Electric power transmission is a major process in the electrical system. So, in simple definition, transmission is the process of movement of electricity from power plants to distribution grids in populated areas.

We use interconnected lines (transmission network) to facilitate this movement over long distances.  

Electric power transmission

Someone may come and ask why we don’t simply produce electricity where we need it!  This needs a back in time journey to discover why and how they transmit electricity by less cost and high efficiency.

History of transmission:

  • We can start from Menlo Park, New Jersey in the 1880s when Thomas Edison operated the Pearl Street station. The station distributed power over underground copper lines using 100 K W direct current (DC) to serve small networks that covered only a few city blocks.

Pearl Street station


To make this DC networks safe … it operated at low voltage, the initial cost of the station was high.

Most of the produced power lost as heat and at the same time power cannot be transmitted very far so it was so inefficient.

    • In 1896 the Westinghouse’s Niagara power plant constructed on the first commercial alternating current (Ac) power system designed by G. Westinghouse, Stanley and O. Shallenberger on 1886.
    • The inventions of Ac induction motor by N. Tesla in 1888  and the Tesla coil in 1891.

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Westinhouse’s Niagra power plant

All this by using new transformers to increase and decrease the voltage helped to transmit electricity over a long distance.

Actually, there was 37 MW output power which was powerful several hundred times than Edison’s station.

The station developed several times by many engineers till they built the hydroelectric power station. This station used transformers to increase the generated voltage from 2200 volt to 11000 volts before transmitting it.

  • As a result of the induction motor invention all industries revolutionized, power washing machine, vacuum cleaners, and refrigerators invented so demand and spread out of electricity became greater. At this time it was too important to make laws to facilitate regulation of electric utilities, protect the financial health of public utilities supplied out electricity and at the same time, retail natural gas;  The Public Utility Holding company allowed the following in 1935:
    • There is a limit of the geographic spread of utility holding companies.
    • They control the amount of debt and loans.
    • Cross-subsidies regulated of unregulated business to regulated business.
    • Common ownership of electricity and natural gas was limited.
    • The Concentration of economic power in just a few companies reduced and electricity became a regulated business.

How electricity transmission work?

To understand how electricity is transmitted, we must start from the steam generating plant where fuel is burned to drive a turbine which in turn produce electricity.

The electricity produced in generating stations is at low voltage so we use step-up transformers at generating plants to raise the voltage up to the transmission voltage (69, 115, 230, 500 or 765 Kv) to transmit it over high voltage transmission lines to long distances.

How electricity transmission work

Large industries need 2400 to 4160 V to run heavy machinery so there are step-down transformers in transmission substations to reduce electricity to 69 or 34 Kv to be suitable for usage.

At the same time homes, schools, small business and farms 120/240 or 120/208 V so we also use transformers to step down the electricity.

Components of transmission system:

Actually, we need many components to successfully deliver electricity from generating station to distribution. So we have primary components as:

  • Transmission towers:

They are the most visible component of the transmission system that carries the heavy transmission conductor at a sufficient, safe height and sustains all kinds of natural calamities.

  • Power lines (conductors):

From the name they are lines that carry the electric power from sending to receiving end. These conductors usually are copper, aluminum, and aluminum conductor steel reinforced.

Components of transmission system

  • Substations:

We use substation to transfer voltage to a higher or lower level of voltage so there would be various types and classifications of substations depending on the amount of voltage, equipment on site and transformation desired.

There are transformers to convert voltage levels, large amount of protection and control equipments, and circuit breakers.

Besides that, we use substations to provide the ties, switching, transformation, and protection for transmission and distribution systems


  • Switchyards:

It’s a substation that delivers generated power from the power source to the nearest transmission line.

The switchyard operates at a single  voltage level therefore it hasn’t  transformers and it’s used connections and interconnections.