Analytical Approach to Study the Impacts of Mutual Coupling on Transmission Lines Protection Systems

Abstract

While there are numerous literatures that have addressed the impact of mutual coupling on the reliability and security of protection schemes and have provided possible mitigation solutions, there has not been adequate research and documentation presenting a comprehensive analytical approach to 1) estimate the magnitude of mutual coupling and 2) quantify the adverse impact of mutual coupling in real-life scenarios under several system faults across various types of protective elements. This should be considered as the first stage of any mutual coupling related study preceding the second stage in which the mitigation against mutual coupling is to be developed. The proposed methodology can be used to study the impact of mutual coupling on ground overcurrent relays, ground and phase distance as well as pilot protection schemes. As part of the proposed approach, EMT simulation is utilized to quantify the extent of sub-transient overshoot and current reversal that may have adverse impact on the performance of studied relays. A real-life case study within the ERCOT network has been used to demonstrate the proposed study approach.

A new methodology for the analysis and optimal setting of directional polarisation methods for overcurrent elements in line protection applications

“…As shown in Figure 5, it is possible that ground units are not sensitive enough to detect all expected internal faults. In this situation, polarization voltages are so low as to not exceed a fixed threshold voltage (predefined in modern relays) for some short-FIGURE 6 Unit protection scheme performance cases using different polarisation methods at sending and receiving ends circuits [8]. It leads to the use of specific methods that usually employs patented algorithms available only in relays of a unique manufacturer [11].…”

“…Figure 11 illustrates the extreme angles for forward faults 𝜃 max−F and 𝜃 min−F and the extreme angles for reverse faults 𝜃 max−R and 𝜃 min−R . Considering these angles, the limit values of the constraint are given by Equations ( 5) and (6).…”

“…Conventional methods and settings work successfully in basic topological configurations. However, their use in more diverse cases has shown critical reliability protection problems [4][5][6]. For this reason, there is the interest in developing detailed studies on directional overcurrent protection and specifically its polarisation methods.…”

“…For ground protection, the analysis of how mutual coupling affects ground directional elements were presented in [6,7,14], where some practical advice is offered for identifying situations where mutual coupling must be considered in using the zerosequence polarisation method. However, a general methodology is required to study completely this method.…”