Abstract
In contemporary power systems, the load shedding schemes are typically based on disconnecting a pre-specified amount of load after the frequency drops below a predetermined value. The actual conditions at the time of disturbance may largely differ from the assumptions, which can lead to non-optimal or ineffective operation of the load shedding scheme. For many years, increasing the effectiveness of the underfrequency load shedding (UFLS) schemes has been the subject of research around the world. Unfortunately, the proposed solutions often require costly technical resources and/or large amounts of real-time data monitoring. This paper puts forth an UFLS scheme characterized by increased effectiveness in the case of large disturbances and reduced disconnected power in the case of small and medium disturbances compared to the conventional load-shedding solutions. These advantages are achieved by replacing time-consuming consecutive load dropping with the simultaneous load dropping mechanism and by replacing ineffective fixed-frequency activation thresholds independent of the state of the system with implicit adaptive thresholds based on fuzzy logic computations. The proposed algorithm does not require complex and costly technical solutions. The performance of the proposed scheme was validated using multivariate computer simulations. Selected test results are included in this paper.
Highlights
The algorithms of underfrequency load shedding (UFLS) operating in power systems were adopted more than half a century ago
The operating range of UFLS is delimited by f max and f min, where the former denotes the frequency at which the load shedding process is initiated and the latter is the safety threshold defined by steam turbines
The other indicator is given by Equation (12) and expresses the relative difference between f minNsh, which is the lowest frequency that occurred during the load shedding for the given number of thresholds Nsh, and f minRef that denote the minimum frequency of the reference variant; the difference is related to the maximum permissible distance between the rated frequency and the actual frequency
Summary
The algorithms of underfrequency load shedding (UFLS) operating in power systems were adopted more than half a century ago. New solutions for the UFLS should limit, as much as possible, the role and responsibility of dispatcher control services To this end, an algorithm was sought that would be capable of effective and reliable load shedding while using a limited number of decision thresholds (frequency values) and values of power to be disconnected.
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