Abstract—Hidden failure in a protection system has been recognized as one of the main reasons which may cause to a power system instability leading to a system cascading collapse. This paper presents a computationally systematic approach used to obtain the estimated average probability of a system cascading collapse by considering the effect of probability hidden failure in a protection system. The estimated average probability of a system cascading collapse is then used to determine the severe loading condition contributing to the higher risk of critical system cascading collapse. This information is essential to the system utility since it will assist the operator to determine the highest point of increased system loading condition prior to the event of critical system cascading collapse. Keywords—Critical system cascading collapse, protection system hidden failure, severe loading condition. I. INTRODUCTION OWER system is a complex interconnected system with the aim of supplying electric power to the consumer. In a large-scale networked systems, the electric power system has become increasingly automated in the past few decades as a result of technological advancement [1]. Due to this situation, an unintentional failure of one equipment due to the misoperation of a relay will produce significant destruction to the interconnected system. The disastrous disturbance is often triggered causing to a system cascading collapse while the grid is generally operating close to critical loading [2]. A number of severe blackouts that had happened around the world recently have resulted severe consequences to the national economy and social life [3]. The most current blackout had happened in India on the 30 th and 31 st July 2012, where over 620 million citizens all over the country were affected [4], which is equal to 9% of the world’s overall population. The historical information on some other major blackouts afflicted by the system cascading collapse can be found in [5]-[7]. Since the effect of blackout could be This work was supported in part by Research Management Institute (RMI) and Ministry of Higher Education, Malaysia (MOHE) under 600-RMI/ERGS 5/3 (18/2012). N. A. Salim is with the Faculty of Electrical Engineering, Universiti Teknologi MARA, 13500 Pulau Pinang, Malaysia. (e-mail: ashida_amani@yahoo.com) M. M. Othman and I. Musirin are with the Faculty of Electrical Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Malaysia. (e- mail: mamat505my@yahoo.com) M. S. Serwan is with the Advanced Power Solution Sdn. Bhd., Worldwide Business Centre, Jalan Tinju 13/50, 40000 Shah Alam, Malaysia. catastrophic to the power system, therefore innovative approach is required in order to investigate the challenges in security planning to avert any turbulence which may occur to a large grid system. There are various models used to study the impact of cascading collapse in a complex network system. The OPA model studied in [8-11] is a blackout model in power system that represents probabilistic cascading line outages and overloads. Its initial outage is generated by random selection of line outages and load variation. Meanwhile, CASCADE model explored in [12-14] is a probabilistic model of a system cascading collapse which depends on the system loading condition. Even though this model can analyze major blackouts, it assumes all transmission lines are identical. According to [15], more than 70% of power system major disturbances are caused by the hidden failure of a protection system. Many researchers [16-18] have studied its significant impact to a catastrophic power system condition. Therefore, it is essential to investigate the consequence of cascading collapse as its impact to a power system is significant. In view of that, this paper put forward a computational useful technique of system cascading collapse considering the effect of protection system hidden failure. The study is performed in order to investigate the impact of different value of hidden failure probability to the average probability of cascading collapse and critical system loading condition. In this analysis, the determination of critical system loading condition is conducted according to the criticality of the system cascading collapse. The IEEE RTS-96 is used as a test system to confirm the effectiveness of the proposed technique considered in the assessment of system cascading collapse. Since the impact of system cascading collapse is catastrophic, therefore the assessment of cascading collapse should be done in the power system operation and planning in order to identify the critical loading condition which may cause critical system cascading collapse. II. DETERMINATION OF SEVERE TOTAL LOADING CONDITION DERIVED FROM THE CRITICAL CASCADING COLLAPSE This section will discuss on the methods used to estimate the probability of cascading collapse considering different case studies of hidden failure probability which are p HF = 8×10 -7 [15], p HF = 1×10 -12 and p HF = 1×10 -2 [19]. The results of average probability of cascading collapse, ߤ൫ ෠ ஼ ೗ ൯ for each N. A. Salim, M. M. Othman, I. Musirin, and M. S. Serwan Determination of Severe Loading Condition at Critical System Cascading Collapse Considering the Effect of Protection System Hidden Failure P World Academy of Science, Engineering and Technology Vol:77 2013-05-24 309 International Science Index 77, 2013 waset.org/publications/11077