Application of new directional logic to improve DC side fault discrimination for high resistance faults in HVDC grids

Abstract

This paper proposes a simple and fast way to determine the direction of a fault in a multi-terminal high voltage direct current (HVDC) grid by comparing the rate of change of voltage (ROCOV) values at either side of the di/dt limiting inductors at the line terminals. A local measurement based secure and fast protection method is implemented by supervising a basic ROCOV relay with a directional element. This directional information is also used to develop a slower communication based DC line protection scheme for detecting high resistance faults. The proposed protection scheme is applied to a multi-level modular converter based three-terminal HVDC grid and its security and sensitivity are evaluated through electromagnetic transient simulations. A methodology to set the protection thresholds considering the constraints imposed by the breaker technology and communication delays is also presented. With properly designed di/dt limiting inductors, the ability of clearing any DC transmission system fault before fault currents exceeds a given breaker capacity is demonstrated.

Enhanced Fault Current-Limiting Circuit Design for a DC Fault in a Modular Multilevel Converter-Based High-Voltage Direct Current System

“…The fault current at 1.201 s is consistently 4 kA given the unchanged fault circuit parameter. Therefore, Figure 17 presents that 4kA − ∆I 1 + ∆I 2 < 9kA (44) In comparison with the blue dashed-dotted line illustrated in Figure 17, two current curves share nearly the same part during ∆t 2 . Thus, ∆I 1 can be obtained with a difference between the current values of the two discharging conditions.…”

“…Moreover, Equations (44) and (38) can be simplified as Equation 46, because the two current curves depicted in Figure 17 have nearly the same value at 1.203 s.…”

“…In order to cooperate with protection relaying, the proposed FCL circuit is installed at the ends of transmission line so that communication delay among DCCB, measure point and protection relay could be reduced. Moreover, big smoothing reactor (200 mH) in [42][43][44] would influence the dynamic response speed and proposed FCL circuit could help reduce value of smoothing reactor for better performance of dynamic response. However, it requires further investigation on economic efficiency of proposed method, considering previous FCL methods, such as superconductor based fault current limiter, FCL circuit and converter topology based approach.…”

A Fast DC Fault Detection Method for Multi-Terminal AC/DC Hybrid Distribution Network Based on Voltage Change Rate of DC Current-Limiting Inductor

“…where, dU clis /dt and dU clif /dt are the voltage change rates of the CLIs on two ends of the DC lines respectively. The faulty line of the high-resistance fault can be identified according to (13). This method is not affected by the fault resistance and is suitable for the high-resistance fault.…”

Analysis of Local Measurement-Based Algorithms for Fault Detection in a Multi-Terminal HVDC Grid

“…Finally, the ROCOV algorithm protects a nine-terminal VSC based grid in [33] and a three-terminal bipole VSC based grid in [34]. Alternatively, a comparison of the ROCOV at both sides of the limiting inductor is used in [35] for fault detection. Similarly, the ratio between the ROCOV at both sides of the limiting inductor is employed in [36].…”