Tuesday, July 24, 2007

How to Repair Live High Voltage Transmission Lines(!)

Generally voltages above 110kV are used for transmission lines. While voltages can be as high as 1200kV, the bulk of energy transmission occurs between 138kV and 765kVac. So, repairing live transmission lines is a bit difficult, to say the least!

Here's an excellent video on how high voltage power lines are inspected prior to repair:

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Friday, July 13, 2007

What is Medium Voltage?

Various definitions exist. In general, medium voltage is a term used by the electrical power distribution industry. Here are a few ways medium voltage is defined:

ANSI/IEEE 1585-2002 refers to: Medium Voltage (1 - 35 kV). [It is assumed that this is ac.]

IEEE Std 1623-2004 refers to: Devices rated to medium voltage (1 kV-35 kV). [It is assumed that this is ac.]

NECA/NEMA 600-2003 refers to "medium voltage cables rated from 600 volts to 69,000 volts AC"

Littlefuse says: "The terms “Medium Voltage” and “High Voltage” have been used interchangeably by many people to describe fuses operating above 600 volts. Technically speaking, “medium voltage” fuses are those intended for the voltage range from 2,400 to 38,000 VAC."

Siemens says, "Medium voltage metal-clad switchgear (above 1000Vac up to 38kVac)"
This last one covers most of the definitions. Thus, probably a good working definition of medium voltage is from 1kVac to 38kVac.

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