Abstract
To cater the consumers with high quality electricity, a reliable Power System (PS) is a must. Recently several major changes have been taken place in the PS of Sri Lanka. Today the PS of Sri Lanka, that operates under Ceylon Electricity Board (CEB) is comprised with 3 numbers of coal Power Plants (PPs), each having a generation capacity of 300 MW, a combined cycle PP (Yugadanavi) and considerably extended transmission network [1], [2]. To maintain the stability of a PS, the balance between power generation and consumption (demand) is a must. In any event, the first few seconds of frequency degradation and recovery after a major generator trip is essentially be accomplished by governor control. When the PS‟s self-regulation is insufficient to establish a stable state, the system frequency (SF) will continue to drop until it is arrested by automatic under-frequency load shedding (UFLS) to re-establish the load-generation balance within the time constraints necessary to avoid system collapse [3], [4]. Therefore it has become necessary to review the performance of the present CEB LS Scheme (LSS) and suggest amendments where necessary. This paper proposes two LSSs which can address the recent changes taken place in the Sri Lanka PS while maintaining stability. Having simulated the PS of Sri Lanka, performance comparison of the CEB LSS which is being implemented in Sri Lanka and the proposed LSSs (PLSSs) are presented. Results show that the LSS should exclusively be specific for a particular PS. It depends on factors such as electrical PS practice, regulations, largest generator capacity, electricity consumption pattern etc.
Highlights
Reliable and secure operation of electrical Power System (PS) is of great importance and it has always been a primary goal for PS operators
The problem of optimal LS has been extensively investigated and many publications on the utility implementation are presented in the literature over the past[5], [9][11].Selection of a suitable LS strategy depends on the application scenario
This helps in determining the perturbation location so that the area affected by the power deficiency can be addressed by implementing a LS action confined to that particular area[6], [9], [12]
Summary
Reliable and secure operation of electrical PSs is of great importance and it has always been a primary goal for PS operators. In large scale and wide area PSs, typically the adopted methods are based on voltage measurement This helps in determining the perturbation location so that the area affected by the power deficiency can be addressed by implementing a LS action confined to that particular area[6], [9], [12]. The most initiative method of checking the level of danger is measuring the average frequency of the grid: when the frequency falls below a certain threshold it is possible to obtain an indication on the risk for the system and to shed a certain amount of load This approach is effective in preventing unintended LS in response to small disturbances with relatively longer time delays and low frequency thresholds, it is not capable of distinguishing the difference between normal oscillations and large disturbances in the power system. It has been showed through simulations that the proposed scheme is more effective compared to the prevailing one
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