Under-frequency load shedding (UFLS) is a classic and a commonly accepted measure used to mitigate the frequency disturbances in case of loss-of-generation incidents in AC power grids. Triggering of UFLS is classically done at frequency thresholds when system frequency collapse is already close to happening. The renewed interest for synchronous condensers due to the global trends on massive commissioning of non-synchronous renewable power generation leading to reduction of system inertia gives an opportunity to rethink the approach used to trigger load-shedding activation. This question is especially relevant for the Baltic states facing a desynchronization from Russian power grid and a necessity to operate in an isolated island mode. The main goal of this paper is to introduce a predictive load shedding (LS) method without usage of either frequency or ROCOF measurements based on the monitoring of active power injections of synchronous condensers and to prove the efficiency of the concept through several sets of case study simulations. The paper shows that the proposed approach can provide a greatly improved frequency stability of the power system. The results are analyzed and discussed, the way forward for the practical implementation of the concept is sketched.

From time to time a sequence of unexpected and overlapping contingencies may lead to power system angular instability and even blackouts if not addressed adequately by means of an out-of-step (OOS) protection system. The motivation of the paper is an attempt to develop a workable prototype of the OOS protection system. The deficiencies of the protection currently used in the Latvian Power System network are highlighted and a new protection structure is proposed. The protection system comprises of several strategically located terminals, exchanging information in real time by means of a communication network. The OOS condition detection method is based on system-wide generation sources, electromotive forces, vectors, and angle control. The network splitting decision is based on generator coherence evaluation. Protection terminals determine online the groups of coherent generators and choose the splitting boundary from a predefined transmission lines (TLs) cut sets list. The protection system structure, algorithm of operation, and possible IEC 61850 communication standard-based implementation are described.

In light of continuously growing penetration of nonsynchronous generation, the gas-fired plants along with hydro power will provide the major part of system inertia and frequency reserves. This article evaluates the resilience of the Baltic power grid in the event of outage of a major natural gas-fired power plant. An importance of such evaluation is justified by a set of additional challenges, the Baltic power grid will experience due to its disconnection from the unified power system of Russia and synchronization with the European Network of Transmission System Operators synchronous power system in 2025. A case study, highlighting the system resilience-related problems will be presented in the article. The results can be used in the planning activities of transmission system operators undergoing energy transition and preparing for operation in low-inertia grid modes.

The hybrid AC/DC grid, based on a significant share of renewable energy sources, is gradually becoming an essential aspect of the modern energy system. The integration of intermittent renewable generators into contemporary energy systems is accompanied by the decommissioning of power plants containing synchronous generators. Consequently, this leads to a reduction in system inertia and an increase in the risk of stability disruption. The abrupt disconnection of the primary generator or power line can result in an unanticipated mismatch between power generation and consumption. This discrepancy can trigger substantial and swiftly evolving alterations in power distribution, angular speed, load flow, and the frequency of generators. The risks of an energy system collapse can be mitigated through automation, enabling rapid adjustments to generation and load capacities, as well as power flows, in the electrical network. This article justifies the utilisation of a power control method for high-voltage power line interconnections. The technology of hydro storage power plants and measurements of voltage phasors are employed. The potential for easing power flow restrictions and realising substantial economic benefits is supported by the results obtained using simplified dynamic model of the Baltic power system and Nord Pool electricity market model.

This study explores the challenges posed by the transition to large-scale deployment of renewable energy sources, which lead to a significant reduction in the inertia of power systems. It focuses on enhancing resilience and frequency stability in response to sudden disturbances, such as generator failures or transmission line disconnections. The paper critically evaluates the limitations of conventional under-frequency load shedding (UFLS) methods and advances a novel Rapid Load Shedding (RLS) approach. The RLS method harnesses the active power response of synchronous condensers (SCs) to enable faster load shedding, thereby improving system stability and addressing operational constraints from a reliability perspective. The study demonstrates the feasibility of implementing new control systems using the proposed structure of a special protection scheme. It also examines the economic benefits of enhancing the allowable transfer capacity in the Baltic Power System (BPS) through this method. The findings highlight how the RLS approach can enable higher transfer capacities whilst maintaining system resilience. Additionally, the results indicate that the RLS method can significantly mitigate frequency deviations and enhance system stability, offering a promising solution for low-inertia power systems with high levels of renewable energy integration.

Stability of complex electrical power systems (EPS) is an important technical property, indicator of reliable and efficient operation of the EPS. The concept of stability can be divided into three types: the static, dynamic and resulting one. Static stability is the ability of the system to restore normal operation after minor perturbations, in its turn, dynamic and resulting stability is the ability of the system to restore normal operation after large disturbances. The most dangerous system condition is asynchronous operation, when the system loses resulting stability. This paper is devoted to the evaluation issues of static stability of operation mode on the example of the Latvian power system 330 kV. It is separately described the principle of operation of the elimination automatic device of asynchronous operation (AGNA, out of step protection), as a modern reliable means of emergency automation to preserve resulting stability.