Reactive power provision from distribution systems to support transmission systems’ voltages has been identified in the literature as viable alternative in cases where access to transmission-connected reactive power resources, such as synchronous generators, is diminished. Distribution systems’ potential to provide reactive power is usually described through capability charts at DSO/TSO interface giving feasible values of active and reactive power exchange at the interface for different operating conditions of the distribution system. This paper discusses that such description should be complemented with information on short- to medium-term reactive power response of the distribution system to the voltage changes at the DSO/TSO interface. For this purpose, a quantity called voltage regulation strength at DSO/TSO interface is introduced. A method on how it can be calculated is presented and its application is illustrated on case studies of Swedish distribution systems.

The energy transition is placing increased strain on power systems and making it challenging for Transmission System Operators (TSOs) to securely operate power systems. System Integrity Protection Schemes (SIPSs) are one of the solutions to address these challenges. SIPSs are a type of over-arching power system control; their goals are to increase the secure utilization of power system assets and to limit the impact of large disturbances on the system. Due to societal developments, the interest in utilizing SIPSs is increasing internationally, highlighting the importance of the standardization of terms and definitions to support collaboration between internationally interconnected power systems. This paper addresses the issue of increasing SIPS literature and the efficient exchange of knowledge about SIPSs by providing a new, up-to-date literature review and proposal for the standardization of SIPS terminology. The need for standardized terminology is highlighted by gathering various terms used to describe SIPSs and proposing a standardization of definitions, terms, and SIPS operational execution steps. The goal of the proposed standardization is to provide clarity and to decrease the sources of misinterpretation in an international collaborative environment. The analyzed literature is further classified according to the SIPS features it addresses, and conclusions about well-established and interesting future research areas are drawn. For example, it has been observed that the most commonly considered SIPS action is load shedding, while more sophisticated actions, e.g., using HVDC (High Voltage Direct Current) and FACTS (Flexible AC Transmission System) installations, controlled together with var rescheduling, are more in the realm of future research that may provide additional benefits to TSOs.