Other requirements exist for continued operation for a limited time, eventually at a reduced power rate, for a broader range of voltage and frequency conditions (up to ±5% in frequency and ±10% in voltage) that are supposed to occur only on a few occasions per year. All generating units should be able to provide a specific range on reactive power to assist control of the system voltage. Finally, it should be noted that extremes of grid voltage could occur at the same time as extremes of grid frequency (in particular low voltage together with low frequency), generating plants should be designed to meet these extremes simultaneously.