International Journal of Engineering and Technical Research (IJETR) ISSN: 2321-0869, Volume-3, Issue-6, June 2015 232 www.erpublication.org Abstract— These days power quality is becoming increasingly essential in industrial electricity consumers point of view. This paper proposes a control strategy of DVR which interrupts fault current in a radial distribution line using dynamic voltage restorer (DVR). Under the conditions of linear and non-linear loads the DVR detects and compensates voltage sags effectively. This control scheme can interrupt fault current within few seconds. The magnitude and phase of measured voltages is estimated using digital filters which adequately mitigates the impacts of harmonics, disturbances and noise on the phasor parameters. The results of the simulation studies are performed in the MATLAB SIMULINK software. For this control scheme, phase locked loop is not required so that for each phase, the injected voltages of which magnitude and phase angle can be controlled independently. By using Matlab/Simulink software, these simulation studies give results: 1) Under different fault conditions, the proposed control system performs satisfactorily. 2) The point of common coupling voltage is also restored by using this control scheme of DVR. Index Terms— Dynamic voltage restorer (DVR), fault current interrupting, voltage sag and voltage swell. I. INTRODUCTION Custom power device (CPD) is a powerful tool to protect sensitive loads if there is any disturbance from power line and it is based on semiconductor switches concept. There are many custom power devices; one such is Dynamic Voltage Restorer (DVR) which is used to prevent voltage sags [1], [2]. To enhance voltage quality, three phase ac voltages are injected in series with the supply voltage by DVR which also adjusts the wave shape, phase angle and voltage magnitude. The main components of a DVR are a series transformer, a harmonic filter, a voltage- source converter (VSC), a dc-side capacitor and an energy storage device [5], [6] ) as shown in Fig. 1. The line-side harmonic filter [4] comprises of the filter capacitor and the leakage inductance of the series transformer. To increase energy efficiency and productivity, control devices, sensitive power electronic equipments and non-linear loads are employed by modern industries as part of automated processes. Industrial systems use large number of M.Prasanthi, , Dept. Electrical and Electronics Engineering, AITAM, Tekkali, India, Ph: 8179984969. Dr.D.Vijaya Kumar, Prof., Dept. Electrical and Electronics Engineering, AITAM, Tekkali, India. practiced and sensitive electronic equipment which results in voltage disturbances, the most common power quality problem. DVR is a series compensation device, which is introduced recently to protect sensitive electric load from power quality problems such as voltage sags, swells, unbalance and distortion by means of power electronic controllers that use voltage source converters (VSC). Voltage sags is defined as a sudden reduction of supply voltage from 90% to 10%of nominal with a recovery in short period of time. It is examined as the most serious problem of power quality that can occur at any time with amplitude ranging from 10%-90% for a duration lasts for half a cycle to one minute. Voltage sags is caused either by starting of large induction motor or fault in power system which can interrupt any electrical or electronic equipment that is load sensitive. There will be huge loss if the voltage sag is at customer load end. On the other hand an increase in rms voltage or current at the power frequency is defined as voltage swell with duration ranges from 0.5 cycles to 1 min, typical magnitude is between 1.1 and 1.8 up and swells magnitude is greater than 1.0 in this case. Fig. 1. Schematic diagram of a DVR with a line-side harmonic filter. In distribution systems voltage swells are less common compared to voltage sags, thus they are of not much importance. Both voltage sag and swell can cause failure or shutdown of sensitive equipment such as found in semiconductor or chemical plants and a large current unbalance is created that could blow fuses or trip breakers. The effects ranging from minor quality variations to production downtime and for the customer the equipment damage are very expensive. Different methods were introduced to reduce voltage sags and swells but the most efficient method is the use of Control Strategy for Fault Current Interruption in a Radial Distribution Line using Dynamic Voltage Restorer M. Prasanthi, Dr. D. Vijaya Kumar