Modeling and Implementation of Percentage Bias Differential Relay with Dual-Slope Characteristic

The transformer's protection against internal faults like phase to phase faults, phase to ground faults, and inter-turn faults are provided using the percentage bias differential protection scheme. The paper introduced dual-slope implementation in percentage bias differential relay by considering mal-operation of the percentage bias differential relay against high external fault current and inrush current harmonics. The paper's beginning shows the modeling and analysis of a percentage bias differential protection scheme to protect the 132KV/33KV primary distribution transformer. The issues of a percentage bias differential protection scheme are explained in the middle of the paper. The dual slop algorithm is designed and implemented on a radial distribution system using MATLAB software environment. The results show that the through fault stability of the transformer is improved due to dual-slope implementation. The risk of maloperation of bias differential scheme due to high external fault current and harmonic inrush current is considerably reduced after implementing dual-slope characteristics. The proposed algorithm is practical for deploying in the digital signal controller (DSC) for protection engineers.