Analysis of Underfrequency Load Shedding Using a Frequency Gradient

Abstract

Underfrequency load shedding is one of the most important protection systems, as in many cases it represents the last chance to prevent a system blackout after a serious disturbance occurs in a power system. In order to improve traditional schemes, many efforts have been concentrated on attempts to use the frequency gradient as an indicator for determining the lack of active power in a system. This paper concentrates on analyzing the factors that influence the gradient. Analyses have shown that the gradient can give misleading information about the active-power deficit, as long as certain factors are ignored or assumed to be constant. A draft of a gradient-based underfrequency load-shedding scheme is presented, which also highlights the problems associated with the use of gradient. On the one hand, a frequency gradient alone does not appear to be sufficient for the active-power deficit estimation. Nevertheless, for the actual load-shedding procedure it is found to be very useful.Index Terms-Active-power deficit, frequency gradient, power system analysis, underfrequency load shedding.

Improving the performance of power system protection using wide area monitoring systems

“…However, accurately measuring the RoCoF quickly is a challenge and [48] identifies a number of potential threats to its successful use in adaptive load shedding. Other work addresses load shedding as an optimisation problem that can be solved using genetic algorithms [49] and neural networks [50].…”

Development of Smart Underfrequency Load Shedding System

“…A lot of papers describe the possibility to create centralized control systems. These systems have different types of construction and functionality [5]. Such systems integrate smart grid base technology, known as the smart metering system [8,9].…”

“…The frequency decay rate in such situations gives the turbine governor enough time to react accordingly. But when imbalances reach higher levels ("high-level imbalances") governor action cannot activate spinning reserve quickly enough to restore the system to its normal operating frequency, frequency actuated automatic load shedding (UFLS) serves as a last-resort tool to prevent the system from collapse [5]. UFLS system can be categorized into three groups [5]: -the traditional UFLS system; -the semi-adaptive UFLS system; -the adaptive UFLS system.…”

“…But when imbalances reach higher levels ("high-level imbalances") governor action cannot activate spinning reserve quickly enough to restore the system to its normal operating frequency, frequency actuated automatic load shedding (UFLS) serves as a last-resort tool to prevent the system from collapse [5]. UFLS system can be categorized into three groups [5]: -the traditional UFLS system; -the semi-adaptive UFLS system; -the adaptive UFLS system. Up-to-date traditional automatic load shedding system practically in the most power systems foresees disconnection without time delay or with small delay part of the load on underfrequency.…”

Load shedding scheme based on frequency and voltage stability for an islanding operation of a distribution network connected to mini-hydro generation

“…In [2], the authors presented an analysis of the frequency gradient in the load-shedding process. In addition, an interest in obtaining the optimal load-shedding value was highlighted in [1,10].…”