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Ferrenti effect

Jithu

Ferranti Effect in HV Cable Systems Zap 
When a long high voltage cable is energized with little or no load the voltage at the receiving end can become higher than the voltage at the sending end.

This is known as the Ferranti Effect.

The reason is that HV cables have high capacitance, which generates charging current and reactive power along the cable route.

If not controlled this voltage rise can:
Heavy check mark Cause overvoltage in the network
Heavy check mark Increase stress on equipment insulation
Heavy check mark Affect system stability and reliability

To reduce this effect, utilities install shunt reactors.

A shunt reactor absorbs excess reactive power generated by the cable and helps keep the system voltage within safe limits.

In many long HV cable circuits, the shunt reactor is not just an option it is an important part of the system design.

Understanding cable systems is not only about carrying power but also about controlling the electrical effects that come with long cable routes.

  • +1
    Jithu said:
    To reduce this effect, utilities install shunt reactors.

    We can thank Heaviside for the work behind some of that transmission line analysis.

    Worth looking up Preece vs Heaviside and "The British Debate" about practical men.. (and also 'we have telegraph boys').

    There's more too it than just wires;-)

  • 0

    Thanks for the information and was was insightfull

  • 0 in reply to Philip Oakley

    Its also worth noting that it is really the same physics as the impedance matching that we do for RF or how the L-C network in a traditional, now near obsolete,  florescent lamps  formed by the series choke and the PFC cap that we do to changes the voltage down, in the lamp case, from 230 to about 100 on the tube. 
    The lines that are short compared to a full wave at the frequency of interest, can be seen as essentially lumped L-C, and while longer than perhaps 0.1 wavelength, is worth allowing for the fact that the voltage at one end of the line is someway behind the other.

    Mostly at 50Hz the assumption that the propagation delay can be neglected holds for all but the longest cables.  At the other extreme a length of network cable on a modern network has much of the data in flight - the voltage wiggles that represent the data have left the transmission end, have not yet arrived at the destination, and yet already the next packet of data is on the way out of the transmitter.

    Mike.

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