Wind farms that are connected to the distribution grid (15 – 20kV) are equipped with electrical protection systems, which allow wind farms to disconnect themselves in the event of a malfunction. This provides protection to both the wind farm and the grid. There are three kinds of protection commonly used:
- C13-100: This device monitors any problems relating to current, short-circuit, or in-line problems. If such problems arise it is usually as a result of internal problems with the park, rather than anything to do with the grid. The device is made up of three current transformers connected to ammeter detection equipment of a maximum temporization of 0.2s. C13-100 faults are rare.
- PWH: Created with the neutral compensated grid, this form of protection monitors line-earth faults and aims to reduce leakage currents in case of problems. It detects if an issue is coming from the park’s internal grid and can disconnect the plant from the main grid if necessary, though this very rarely occurs.
- GTE: Also referred to as the ‘disconnection’ protection, this monitors the voltage and frequency of the grid. GTE is responsible for 99% of the cases where the disconnection of wind farms occurs. There are various thresholds for the voltage and frequency of a park which would trigger a disconnection. Depending on the duration of dips in voltage and frequency (>500 ms or <500ms) the plant may or may not reconnect automatically to the grid. This form of protection monitors the distribution grid and is available in five levels – from H1 to H5.
The performance of a wind farm can be greatly optimized through the choice of H5 protection, since this greatly reduces the number of grid disconnections likely to occur. Naturally, the choice of protection will depend on a number of factors such as grid topology, park power, and whether lines are aerial or buried – however, the level of protection can also be subject to negotiations with the grid operator.
Significantly, case studies have shown that switching from a H3 level to a H5 halves the number of grid disconnections that occur. This can result in a total saving of €5000 to €10,000 a year.
Greensolver would strongly advise asset owners to negotiate with grid operators to increase their GTE level as much as possible. H5 protection not only improves production, but also reduces HV maintenance costs.