Volume I Issue VI 2012 September-2012 ISSN 2278 - 2540 5 A 24-pulse STATCOM Simulation model to improve voltage sag due to starting of 100 HP Induction-Motor Mr. Ajay Kumar Bansal 1 Mr. Govind Lal Suthar 2 Mr. Rohan Sharma 3 1 Associate Professor, Department of Electrical Engineering, Poornima College of Engineering, Sitapura Jaipur (Rajasthan)-302022. 2 M.Tech POWER SYSTEM(pursuing), Department of Electrical Engineering, Poornima College of Engineering, Sitapura Jaipur (Rajasthan)-302022. 3 M.Tech POWER SYSTEM(pursuing), Department of Electrical Engineering, Government Engineering College, Bikaner (Rajasthan)-334001 Abstract A simulation model of static compensator (24-p STATCOM) has been constructed on matlab/simulink software to examine its capability for voltage sag mitigation This paper describes the performance of a Flexible Alternating Current Transmission Systems (FACTS) device, namely, STATic synchronous COMpensator (STATCOM) based on 24-pulse Voltage Source Converter (VSC), for the mitigation of voltage-dip caused by the starting of a 100 HP high power induction motor. It improves the voltage profile feeding to a high power induction motor at starting by injecting a controllable current to the supply line. Its capability to compensate reactive power to the system when the voltage dip occurs due to starting of 100 HP power induction motor load is described. 24-pulse VSC- based STATCOM and implemented it into a power-system consist a 100 HP power induction motor in MATLAB Simulink environment. The results show that the fast response and the STATCOM capability to for mitigate voltage sag. Keywords Voltage-dip mitigation, Static Synchronous Compensator, multiple-pulse Voltage Source Converter, Voltage Injection Capability, Reactive Power Compensation, Harmonic Analysis I INTRODUCTION Power quality is a quite broad concept, summarizing different electrical power characteristics. Ideally, the delivered power should have perfect current and voltage wave shapes and hundred percent reliable. Over the last decade the power quality issue has become a matter of growing concern. There are several causes that have initiated and later stimulated this concern however one other most important cause is the growing sensitive loads, (eg. Industrial plants) that use power electronics as a means of modernizing their manufacturing processes [1]. As the sensitivity of the load increases the costs associated with the damage caused by voltage sags increase too. One of the most important voltage-related problems is voltage sag. Voltage sag is an rms reduction in the ac voltage at the power frequency, for duration from a half- cycle to a few seconds [2]. Magnitude and duration are its two most important characteristics. There are two causes of voltage sag, normally line to ground faults and motor starting. Line to ground faults result in voltage sags that are shorter (from approximately 10 ms) and have magnitudes down to 10%. Motor starting produces sags having smaller magnitudes but they last longer up to 600ms. This paper focused on voltage sag caused by starting of induction motor. The induction motor is subjected to the voltage sag slow down but usually do not stop operating, if not tripped by contactors. Problems can occur due to torque oscillations that can be associated with very deep sags or to tripping of over current relays, due to the high current drawn by the motor. Voltage dips are huge problem for many industries and they have been found especially troublesome because they are random events lasting only a few cycles. However, they are probably the most pressing power quality problem facing many industrial customers today [5]. The concern for mitigation of voltage dip has been gradually increasing due to the huge usage of sensitive electronic equipment in modern industries. When heavy loads are started, such as large induction motor drives, the starting current is typically 600% to 700% of the full load current drawn by the motor. This high current cause dips in the voltage during starting intervals, because there is a lot of voltage drop across the distribution conductor. Since the supply and the cabling of the installation are dimensioned for normal running current and the high initial current causes a voltage dip. This voltage dips are short duration reductions in rms input voltage as shown in Fig.1 [4]. It is specified in terms of duration and retained voltage, usually expressed as the percentage of nominal rms voltage remaining at the lowest point during the dip. Another reason for high starting current is the inertia of