Following large disturbances, the conventional under frequency load shedding (UFLS) relays may not operate properly, as they are designed to merely preserve the frequency stability of the system, independent of its voltage stability. In this study, an adaptive load shedding scheme is proposed to maintain the power system stability when the conventional scheme fails. In doing so, the frequency and its falling rate along with a properly defined voltage falling rate are exploited to determine closeness to the disturbance area and its severity. Accordingly, a proper amount of load is shed from the locations with the highest influence on the system stability. The proposed scheme exclusively utilises locally measured quantities and does not require a communication link. The associated logic is practical and can be easily appended to the existing UFLS relays to enhance their performance. To demonstrate the efficiency of the proposed UFLS scheme, it is applied to two large-scale power systems where the exact load model is taken into account. The obtained results verify that a large number of blackouts because of inappropriate operation of conventional UFLS relays can be prevented using the proposed scheme.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-gtd.2013.0937

Adaptive load shedding scheme to preserve the power system stability following large disturbances

Predictive underfrequency load shedding scheme for islanded power systems with renewable generation

Applications of artificial intelligence in power systems

This paper presents an overview of the key issues in the use of frequency rate change (df/dt) in power system emergency control schemes. The role of df/dt in designing effective under frequency load shedding (UFLS) plan is discussed. The impact of new variable renewable sources (such as wind and solar units) on system frequency gradient is analyzed, and the need for the revising of frequency performance standards, re-tuning of automatic UFLS relays, and use of Δf/Δt rather than df/dt are emphasized.

On the use of df/dt in power system emergency control

In this paper several Under Frequency Load Shedding (UFLS) schemes are designed as special protection schemes to preserve the integrity of islands, formed following the outage of tie lines connecting two areas in a double area power system. For the purpose of analysis, the Iranian interconnected grid is simulated in a suitable power system analysis software. The grid is connected to the Khorasan province network, the greatest province of the country, through a double circuit tie line. Following the outage of tie lines in a double area power system the area with great import of power may face large deficiency of energy and consequently blackout may occur in the island. The purpose of this research work is to propose a special protection scheme, being capable of preserving the balance of generation and consumption in order to prevent major outage. Special types of adaptive UFLS scheme are proposed in this work.

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Design of New Load Shedding Special Protection Schemes for a Double Area Power System

Several practical intelligent setting schemes that consider the effect of df/dt are suggested and simulated for a power system operating in an underfrequency situation. Considerations for df/dt relay setting are discussed. These intelligent setting schemes have made a positive improvement in the underfrequency condition. As an extension of these new intelligent control schemes, a microcontroller based intelligent under/over frequency relay is introduced. With its advanced hardware and intelligent software, this microcontroller has the advantages of high flexibility, less cost, and high communication ability. >

J.C. Gu

Papers

Application of df/dt in power system protection and its implementation in microcontroller based intelligent load shedding relay