This paper presents a computational method using the Monte-Carlo simulation approach for the calculation of the settings of load shedding underfrequency relays and the selection of appropriate spinning reserve policy in autonomous power systems. The method can be used for comparing alternative strategies by taking into account the amount of load to be shed and the corresponding risk for system stability. This method was applied on a system, that is based on the autonomous power system of the Greek island of Crete and the obtained results are presented and discussed.

A Monte-Carlo simulation method for setting the underfrequency load shedding relays and selecting the spinning reserve policy in autonomous power systems

This paper describes an efficient computational methodology that can be used for calculating the appropriate strategy for load shedding protection in autonomous power systems. It extends an existing method that is based on the sequential Monte Carlo simulation approach for comparing alternative strategies by taking into account the amount of load to be shed and the respective risk for the system stability. The extended methodology uses artificial neural networks (ANNs) for determining directly the parameters of the most appropriate load shedding protection strategy. For this purpose, the system inputs are the desirable probabilistic criteria concerning the system security or the amount of customer load interruptions. Using this methodology, the utility engineers can adopt a specific strategy that meets the respective utility criteria. The methodology was tested on a practical power system using a computer simulation for its operation, and the obtained results demonstrate its accuracy and the improved system performance

Method Combining ANNs and Monte Carlo Simulation for the Selection of the Load Shedding Protection Strategies in Autonomous Power Systems

Study on a system frequency response model for a large industrial area load shedding

An automatic load shedding scheme considering the pumped-storage units at Taiwan Power Company (Taipower) is proposed in this paper. Taipower owns ten pumped-storage units which can be shed with higher priority when operated in pumping mode in order to restore the system frequency. In this way, the amount of customer load required to be shed can be significantly decreased. The system reliability and stability can also be enhanced. In the paper, a load frequency control model is developed. An automatic load shedding scheme that is adaptable to Taipower operation is thus developed. The proposed method has been validated through the utility data and compared with the utility shedding scheme. Test results solidify the feasibility and effectiveness of the proposed method for the applications.

An automatic load shedding scheme including pumped-storage units

Under frequency load shedding (UFLS), which has been worldwidely adopted in modern power systems, is an effective method to stop rapid frequency decay and to restore power system stability following heavy loss of generation. The traditional UFLS scheme is proposed for determining the amount of load to be shed based on the observed frequency deviation (Deltaf) following the system disturbances, but it has some drawbacks of itself. Although it is attractive to use the variation rate of frequency (df/dt) as an additional signal for load shedding, but there is no practical scheme available today. The reason lies in the fact that the instant df/dt changes so violently that it cannot indicate the information of the severity of generation deficiency in power system directly. In this paper, the authors proposed a method to try to use the df/dt as auxiliary information for the UFLS scheme design. The integrating of dynamic frequency from one UFLS frequency step to the next step is assigned as the df/dt in the UFLS design, which is called integrating df/dt in this paper. The study results show that this new UFLS scheme has much more adaptability than the traditional ones

UFLS Design by Using f and Integrating df/dt

A typical application procedure for a coordinated load shedding scheme using both frequency trend relays and normal discrete underfrequency relays is described. By using such a combination of relays it is possible to develop comprehensive protection against frequency disturbances, both sudden and gradual. It is emphasized that in a system where the causes of frequency disturbances are quite varied and complex, a fully automatic scheme may not be the ideal solution and manual load shedding as a backup may be necessary. A typical procedure for a captive power plant system operating in parallel with the grid is described as applicable to a continuous process plant industry. The strategy for islanding such industrial power systems from the grid during grid disturbances is described. >

P.V. Subramanian

Papers

Frequency trend and discrete underfrequency relaying practices in India for utility and captive power applications