Voltage balancing of symmetric HVDC monopole transmission lines after earth faults

摘要

A voltage balancing unit for a symmetric monopole high voltage direct current (HVDC) transmission line interconnecting two voltage source converters (VSCs), the transmission line including first arresters having a first switching impulse protective level (SIPL) is provided. The voltage balancing unit includes a pair of second arresters having a second SIPL which is less than the first SIPL, and a switching device being arranged for temporarily connecting, in the event of a voltage unbalance on the transmission line, the first arresters between either pole and ground. A voltage unbalance on the transmission line may be removed by temporarily connecting second arresters, with a significantly lower SIPL than the first arresters, for limiting the pole voltage to a level close to the normal voltage. Further, a method of voltage balancing is provided. Voltage unbalances may arise as a consequence of lightning induced earth faults.

主权项

1. A voltage balancing unit for a symmetric monopole high voltage direct current, HVDC, transmission line being arranged for interconnecting a first voltage source converter, VSC, and a second VSC, the transmission line comprising:
a first pole and a second pole, and two pairs of first arresters, a first pair being arranged at a first end of the transmission line and a second pair being arranged at a second end of the transmission line, a first arrester of either pair being connected between the first pole and ground and a second arrester of either pair being connected between the second pole and ground, the first arresters having a first switching impulse protective level, SIPL, wherein the voltage balancing unit is arranged to perform voltage balancing for a voltage unbalance caused by an earth fault and comprises: a pair of second arresters having a second SIPL which is less than the first SIPL, and a switching device configured to:
connect, through being closed after the earth fault has been cleared and in response to determining that the voltage unbalance exists between the first pole and the second pole, a first arrester of the pair of second arresters between the first pole and ground, and a second arrester of the pair of second arresters between the second pole and ground, anddisconnect, in response to determining that the voltage unbalance is cleared, the second arresters.