System integrity protection schemes for future power systems

An interconnected power system must be capable of delivering electricity economically and reliably to the customers. Maintenance of all power system parameters (voltage, frequency, real and reactive power flows, etc.) within specified limits is imperative for the effective and reliable operation of an interconnected system. A disturbance at any location, if not tackled quickly and appropriately, can aggravate a challenging situation further and may initiate cascading events, which could eventually lead to major wide-scale disruption to the power supply, as has happened several times in the past [1,2]. The rapid growth of converter-interfaced renewable generation to meet ambitious decarbonisation targets has significantly increased the complexity and uncertainty associated with future power systems, and there are growing risks and concerns relating to blackouts and system-wide disturbances, which present compelling needs to re-evaluate solutions and arrangements in place for maintaining power system integrity. Wide-area synchrophasor data provides a promising opportunity to system operators to identify vulnerable regions in a power system by identifying and predicting system risks/operational issues (e.g. instability), analysing system security and safety margins (e.g. overload limit), and enable effective actions to reduce the risk, and ideally avoid, a wide-spread event, thereby maintaining overall system integrity. Typically, protection relay settings may need to be adaptive to the system conditions to provide maximum security without compromising dependability. Corrective actions (such as load shedding (LS), generation rejection, reactive power control, etc.) may be performed to bring back the system to a desired and stable state, which could also be followed by isolating the unsynchronised areas. Individual and/or hierarchical operation of such detection and correction methods are known collectively as 'System Integrity Protection Schemes (SIPS)'. SIPS are also sometimes referred to differently, with terms such as special protection schemes (SPS) or remedial action schemes (RAS) [3]. Such schemes are installed to protect the integrity of a power system or a strategic portion of the system and are different from conventional protection schemes, which are dedicated to protecting specific power system elements (e.g. power lines, transformers, generators, busbars, etc.) typically against electrical faults. SIPS provide a effective countermeasure to impede and/or diminish cascading outages resulting from extreme contingencies. For this purpose, the schemes typically obtain both local and remote synchrophasor data from multiple locations using communication systems and links. Network complexity and increasing power demand, coupled with limited power transfer corridors, and minimum redundancy are the major challenges for SIPS operation [4]. Furthermore, significant changes in system dynamics and fault levels due to renewable energy integration introduce new challenges to the power system monitoring, control, and protection methods that are often incorporated within, and/or operate in parallel with, SIPS. This chapter reviews the fundamental concepts and operating principles of SIPS with different monitoring, protection, and control methods. Classification, architecture, and design considerations in SIPS are discussed in detail in Section 8.1. Different monitoring, protection and control methods applied widely in SIPS are discussed in Section 8.2 with a hierarchical overview for SIPS implementation. Section 8.3 provides an overview of the practical implementation and operational experience of different SIPS applications in different countries. Challenges and advances in various monitoring, protection, and control methods as part of synchrophasor-based SIPS for future power systems with high penetration of renewable energy sources are discussed in Section 8.4. In Section 8.5, a number of reliability and testing requirements for SIPS are presented, along with views on current trends relating to the development of synchrophasor-based SIPS to support secure and reliable future power system operation.