###### Abstract  
When a fault occurs on the transmission line, the relay should send the faulty signal to the circuit breaker to trip or isolate the line. Timely detection is integral to fault protection and the management of transmission lines in power systems. This paper focuses on using the threshold current and voltage to reduce the time of delay and trip time of the instantaneous overcurrent relay protection for a 330 kV transmission line. The wavelet transforms toolbox from MATLAB and a Simulink model were used to design the model to detect the threshold value and the coordination time for the backup relay to trip if the primary relay did not operate or clear the fault on time. The difference between the proposed model and the model without the threshold value was analysed. The simulated result shows that the trip time of the two relays demonstrates a fast and precise trip time of 60% to 99.87% compared to other techniques used without the threshold values. The proposed model can eliminate the trial-and-error in programming the instantaneous overcurrent relay setting for optimal performance. circuit breaker; overcurrent relay; faults; threshold current; threshold voltage; transmission line +
Footnote †: journal:  
0000-0002-4400-333-2222][PERSON]  
1 Department of Electrical and Electronic Engineering, James Watt School of Engineering, University of Glasgow, Glasgow G12 8 QQ, UK
Some literature has recently proposed tools to aid transmission and distribution system protection based on overcurrent relay settings. In [5], an approach for fault calculation in imbalanced distribution systems was disclosed where the primary protective devices and functions employed in distribution systems have mathematical models. This method makes complete three-phase representations possible, and the solution is achieved directly in phase coordinates. In [6], an integrated optimising model for current relay coordination with tough, practical limitations based on a gradient-based optimiser was analysed, and the model was used to enhance the protection coordination of the transmission and distribution network with some constraints such as false tripping actions. In [7; 8], this study describes a computational tool that was created to automatically calculate the adjustments of all distribution network protection devices to acquire the best technological application, optimise its performance, and make protection studies easier. Ref. [9] presents a straightforward method in which two-phase faults were diagnosed based on the negative sequence current value, and the operating conditions of the suggested criteria arising from negative and zero sequence currents were automatically selected based on the three-phase short-circuit criterion. However, the paper fails to introduce the controller operation of the circuit breaker for adequate tripping of the transmission line. In another paper [10], based on a real-time estimation of the Thevenin equivalent circuit (TEC), the methodology determines the protection setting settings. The estimation process used the voltage and current values in the positive sequence and a system of nonlinear equations that were solved repeatedly using the Gauss-Newton method. Additionally, in [11], the implementation of a new adaptive protection method to set online overcurrent relays in distribution networks was implemented for miscoordination of the overcurrent relay. The connecting and disconnecting of transmission lines and their components are critical to changing fault currents' magnitude and flow direction. Change in the network configuration also leads to a disturbance in the overcurrent relay functionality. The fault current signal affects the power transformer and other components when a fault occurs in the transmission line. Therefore, the circuit breaker needs to open immediately to prevent damage to the installation. The fault current magnitude is greater than the standard load current, so the relay should be signed to operate and trip the circuit breaker for all currents above the relay settings.