The Line Protection for Outgoing Lines of New Energy Power Stations Based on the Equivalent Parameter of Line-to-Ground Admittance

Abstract

The present study finds that the existing line protection struggles to address the problem of amplitude-limited and phase-controlled fault currents for new energy outgoing lines. The paper defines the concept of the equivalent parameter of line-to-ground admittance and proposes a protection based on the parameter. The theoretical expressions of the equivalent parameters of line-to-ground admittances are analysed for various fault types on and outside the line. The line-to-ground admittance parameters reflect the line capacitance during normal operation or out-of-zone faults, with a very small amplitude and capacitive phase. Conversely, during in-zone faults, with a very large amplitude and inductive or resistive phase, they reflect the reciprocal of the transition resistance. The admittance protection relies on the detection of significant changes in the amplitude and phase characteristics of equivalent line-to-ground admittance parameters before and after a fault. This principle is not affected by any alterations in the power supply characteristics, making it highly appropriate for identifying faults in the outgoing lines of new energy power stations. The application of this principle can be extended to various voltage levels and system operation modes of conventional power systems. It has the potential to considerably enhance the performances of line protection and ensure both the safety and stability of the new-type power system.