I J E E C E International Journal of Electrical, Electronics ISSN No. (Online) : 2277-2626 and Computer Engineering 2(2): 57-61(2013) Special Edition for Best Papers of Michael Faraday IET India Summit-2013, MFIIS-13 Assessment of CT Saturation Caused By Switching Transient Aveek Chattopadhyaya * , Harsha Banerjee ** , Surajit Chattopadhyay ** and Samarjit Sengupta *** * Supreme Knowledge Foundation Group of Institutions, Hooghly, WB, India. ** MCKV Institute of Engineering, Howrah, WB, India. *** Department of Applied Physics, University of Calcutta, India. (Received 15 October, 2013 Accepted 01 December, 2013) ABSTRACT: This paper presents an approach for assessment of effect of different switching transient on current transformer saturation. This has been achieved by wavelet transform. Secondary signal of current transformer is captured and decomposed wherefrom approximate and detail coefficients have been estimated. Then different useful parameter like Skewness of approximate and detail coefficients are determined. Simulated result shows significant changes of those values for different conditions, wherefrom, saturation of current transformer is detected and switching time corresponding to the switching transients at the primary side which causes the saturation is assessed. Keywords: CT Saturation, wavelet, approximate coefficient, detail coefficient, Skewness value. I. INTRODUCTION Current transformer (CT) is an important instrument transformer widely used in power system application. CT is an essential part in measuring, controlling and protection unit for which linear behavior is important. However due to various reasons, CT suffers from saturation early detection of which is essential. A lot of research work is going on this matter. An algorithm is introduced for compensating secondary current of current transformers [1]. Neural network has been used for current transformer saturation correction [2]. Current related relaying algorithm has been introduced to immune saturation of current transformer [3]. Over current protection has been done using signals derived from saturated measurement CTs [4]. Waveform reconstruction has been attempted from distorted (saturated) currents [5]. For these purposes some useful definitions and standard requirements for Instrument Transformers are presented in [6]. Impact of current transformer saturation has been assessed [7] on over current protection operation. Differential protection relay performance has been evaluated [8] during transformer inrush current & CT saturation period. A novel CT saturation detection algorithm has been introduced [9] for bus differential protection. CT based protection schemes are presented in [10]. Development and hardware implementation of a compensating algorithm were done [11] for the secondary current of current transformers. Correction of saturated current transformers secondary current is done [12] using ANNs. A method of compensating has been introduced [13] for distorted secondary current of current transformer. Method and device are introduced [14] for detecting saturation in current transformers. New standards are introduced in [15]. ANSI/IEEE C37.110 Standard for IEEE Guide for the application of current transformers used for protective relaying purposes. Differential relay with adaptation has been introduced [16] during saturation period of current transformers. An algorithm was made [17] for detecting CT saturation using the secondary current third-derivative function. Applications of ANN are made [18] [19] for instrument transformer performance correction in transmission line protection. Genetic Algorithm (GA) was used [20] for design and optimization of out-of-step protection of generator was done based on Neural Network [21]. ANN based detection of OS conditions is done [21] in power systems. A. Chattopadhyaya et al (2013) proposed a method of signal assessment for detection of CT saturation under switching transient condition by Wavelet transform based skewness and kurtosis analysis [22]. In this paper, assessment of effect of different switching transient on current transformer saturation has been done using wavelet transform based skewness values. II. MODELLING OF CURRENT TRANSFORMER Current transformer has been modelled as shown in Figure 1. Secondary of the transformer is connected with resistive burden wherefrom signal is captured and sent to sampler. Sampled signal is digitized and passed through DAS unit for assessment. Fig. 1. Modeling used for assessment of CT saturation for switching transients. III. SIMULATION Computer simulation is performed on the above model. Different switching transients are created by switch on/off at different time. In some cases current transformer remains normal; in other cases current transformer get saturated.