Algorithm for Islanding Detection in Distributed Generation System

Abstract

Power industry has been emphasizing more importance on distributed generation because there are new technology like fuel cell, wind turbine and power electronic use for advancement of power system has been evolved so much which cannot be possible without distributed generation. Hence distributed generation (DG) has become an inseparable part in power system and gained so much importance because of economical and environmental purpose. Islanding is a situation where a part of the distributed generation system containing a distributed generator gets electrically isolated from the remainder of the power system still continues to energise the network where the situation has occurred. Thus it has become important that the portion where islanding has occurred must detect this situation immediately for safety purpose. If tripping doesn’t occur in time there can be various and critical problem. Currently in industry practice we disconnect all distributed generators after islanding has occurred. Generally a distributed generator should be disconnected within 0.1s to 0.3s after loss of grid/main supply. To achieve this, each distributed generator must be supplied with an anti-islanding device which detect islanding like vector surge relay and ROCOF relay.
In this thesis we have discussed about current practices and development of power system through distributed generation, Islanding and other problems in distributed generation system, importance of islanding detection , islanding detection techniques which are used in common, Wavelet transform and hybrid technology developed in islanding detection, New method based on negative sequence component’s like voltage and current for islanding detection of wind turbines using the wavelet transform, Usage of both active and passive method and how it eliminates most of the non-detective zone, The coefficient at d-1 separation through daubechies wavelet transform localizes the corresponding islanding events and the change in energy and standard deviation at d-1 levelfor one cycle gives the threshold comparing which we conclude about the islanding condition , The usage of positive feedback and continuous feedback method and the implementation of DQ model of electrical machine for hybrid detection technology, simulation on islanding detection based these two techniques using SIMULINK and MATLAB is done. Finally a case-study of distributed Generation System containing 9 MW wind farms, 500 kW resistive loads and ,9MVAR filters, are considered for wavelet transform method and results are shown on islanding detection using those data and for hybrid method the same is done using feedback method and dq implementation for active method and checking the parameter through passive method with and without the controller. For islanding and nonislanding condition different conditions are checked so that islanding conditions can be clearly distinguished from the non-islanding condition. Sudden load change, line trip, islanding and normal condition for wavelet transform and detection of islanding with and without controller in hybrid method found to be highly effective in islanding detection. These two methods are then compared according to their stability and importance in different condition of power syste.