Flexibility in certain types of loads could be exploited to provide fast and controllable power reserve if the supply voltage/frequency is controlled using existing power electronic interfaces (e.g., motor drives) or additional ones like recently proposed electric springs. Such a load together with its power electronic interface forms a so called smart load. Effectiveness of static smart loads for primary frequency response provision has been shown in the previous papers through case studies on a segment of the low voltage/medium voltage (LV/MV) distribution network. In this paper, collective contribution of both static and motor type smart loads to rapid frequency response provision is demonstrated through a case study on the Great Britain (GB) transmission system. The active power reserve available from such smart loads are quantified and aggregated at each node at the transmission level (275/400 kV). The study shows that the smart loads collectively offer a short-term power reserve which is comparable to the spinning reserve in the GB system, and thus can ensure acceptable frequency deviation and its rate of change following a large infeed loss.

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Abstract-Flexibility in certain types of loads could be exploited to provide fast and controllable power reserve if the supply voltage/frequency is controlled using existing power electronic interfaces (e.g., motor drives) or additional ones like recently proposed electric springs. Such a load together with its power electronic interface forms a so called smart load. Effectiveness of static smart loads for primary frequency response provision has been shown in the previous papers through case studies on a segment of the low voltage/medium voltage (LV/MV) distribution network. In this paper, collective contribution of both static and motor type smart loads to rapid frequency response provision is demonstrated through a case study on the Great Britain (GB) transmission system. The active power reserve available from such smart loads are quantified and aggregated at each node at the transmission level (275/400 kV). The study shows that the smart loads collectively offer a short-term power reserve which is comparable to the spinning reserve in the GB system, and thus can ensure acceptable frequency deviation and its rate of change following a large infeed loss.Index Terms-Demand response, electric spring, primary reserve, rapid frequency response, smart load. NOMENCLATURE Acronyms

Abstract--Network harmonic impedance forms the link between harmonic currents emitted by individual devices and the harmonic voltage levels in the grid. It is essential for the definition of current emission limits in order to ensure Electromagnetic Compatibility between all equipment connected to the grid. Among all electrical equipment in future smart grid electronic devices, like PV inverters, EV chargers or lamps with electronic ballast, will have a dominating share. This is expected to have a considerable impact on the network harmonic impedance characteristic.The paper discusses the frequency-dependent input impedance of different types of modern electronic equipment and its potential impact on the network harmonic impedance. It is shown that the semiconductor switching results in a variation of the impedance within the fundamental cycle. This is not considered by the presently used assessment methods as they assume only passive network elements. Beside a method to measure these variations, several indices are introduced to quantify the level of its impact. The paper aims to provide some impulses for further discussions, particularly about the definition of network harmonic impedance in presence of electronic devices, the necessity to include these variations in realistic harmonic studies and if this has to be considered in the standardization.