The pole rebalancing reactors (PRR) are installed at the AC converter side through an AC switch and are intended to be used to rebalance the healthy pole voltage after a pole to ground fault within less than 100ms. When a pole-to-ground fault takes place, and once the faulty line has been selectively isolated by means for example of line DCCB, the PRR are switched on. By this action, the high impedance grounding device (e.g. the star-point reactor) is by-passed, creating alow-impedance path that allows the flow of current between the AC and the DC grids. This current will flows through the stray capacitance of the cables and will discharge the healthy pole while charging the faulty pole. The PRR may be realized as an air core single-phase reactor and may have a value of few Henry. The use of series resistors can be considered in order to limit the discharge current.
What are the alternatives:
- natural rebalancing (sustained overvoltage)
- full discharge (need for DC discharging resistor)
- dynamic Braking System (very costly)
This solution is:
- simpler (AC technology)