TRANSMISSION LINES VOLTAGES

Transmission Lines Voltage Evolution and Selection

Electricity has been used as a major energy source since the late 19th century. The first three phase alternating current transmission started in 1891, a 175 km long line supplying electricity to an electrical engineering exhibition in Frankfurt and Main Germany. A power of about 200 kW was transmitted by this line operating at 40 Hz.

Since then, the selection of transmission voltage have evolved to facilitate the needs and requirements of the user. The evolution of voltage levels and other milestones can be seen below:

1891 - First three phase transmission in Germany

1911 - 110 kV transmission in Germany

1929 - 220 kV transmission in Germany

1932 - 287 kV transmission in USA

1952 - 380 kV transmission in Sweden

1965 - 725 kV transmission in Canada

1985 - 1200 kV transmission in former USSR, specifically Kazakhstan

The 1200 kV transmission voltage in Powerline Ekibastuz-Kokshetau, Kazakhstan remains the highest as of this writing.

Transmission Lines Classification

There have been no unified terms as far as classification on voltage levels in transmission lines. More often, it primarily depend and differs in each country or on what standards that governs their practice. Some common transmission voltage classifications are as follows:

IEEE (Institution of Electrical and Electronic Engineers)

Low Voltage: A class of nominal system voltages 1 kV or less

Medium Voltage: A class of nominal system voltages greater than 1 kV and less than 100 kV

High Voltage: A class of nominal system voltages equal to or greater than 100 kV or less than 230 kV

Extra High Voltage: A class of nominal system voltages equal to or greater than 230 kV

CENELEC (The European Electrotechnical Standardisation Committee)

Low Voltage:  A class of nominal system voltages 1 kV or less

Medium Voltage: A class of nominal system voltages greater than 1 kV and less than or equal to 35 kV

High Voltage: A class of nominal system voltages greater than 35kV

ANSI (American National Standards Institute)

Low Voltage: 120V to 600V

Medium Voltage: 2400V to 69000V

High Voltage: 115000V to 230000V

Extra High Voltage: 345000V to 785000V

Ultra High Voltage: 1100000V

IEC (International Electrotechnical Commission)

Low Voltage: A class of nominal system voltages 1 kV or less

High Voltage Range I:  A class of nominal system voltages greater than 1 kV and less than or equal to 245 kV.

High Voltage Range II:  A class of nominal system voltages greater than 245 kV.

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