An Improved Directional Relay Adapted to a Distribution Network with IIG Integration

Abstract

The integration of distributed generation (DG) into a distribution network changes the network's topology. Three-stage current protection for a radial distribution network cannot meet the requirements of relay protection for a distribution network with DG. A directional relay that is based on the positive sequence fault component (PSFC) can effectively identify faults in the positive and negative directions and can be used to solve the adaptability problem with three-stage current protection in a multi-source distribution network. However, DG and the traditional generators have different fault characteristics and are affected by different control strategies, which may lower the sensitivity of a directional relay based on the PSFC or even cause mal-operation. Focusing on this problem, this paper proposes an improved directional relay that is adapted to a distribution network with inverter-interfaced generation (IIG) integration. The improved scheme divides the operation zone of the directional relay based on the PSFC into sensitive and insensitive areas. If the result of a phase comparison is located in the insensitive area, further identification is needed according to a comparison of the current amplitudes. Simulation experiments are carried out based on PSCAD/EMTDC, and their results verify the correctness of the proposed scheme.Energies 2019, 12, 3345 2 of 14 in [11,12]. Unfortunately, [9-12] do not consider the low-voltage ride through (LVRT) requirement of DGs. The traditional DOP may mal-operate in the cases of a wind farm increasing the reactive power output [13]. Reference [13] uses a load encroachment function as a solution, but the function does not consider the effect of high transition resistance. To summarize, problems with directional overcurrent protection may arise in the following two situations:•A high-impedance ground fault, which may result in difficulties with identifying the direction of the fault; • A change in the reactive power output of inverter-interfaced generators (IIGs), which may cause the mal-operation of the traditional directional overcurrent relay.To improve the traditional directional overcurrent protection, the directional relay based on the positive sequence fault component (PSFC) has been widely used due to its ability to withstand transition resistance [14].However, the fault characteristics of DGs are affected by the control strategies, which are different from conventional generators. The directional relay based on the PSFC is not suitable for the distribution network with IIG integration. In [15], the influence of IIGs on the directional relay based on the PSFC was analyzed. The authors pointed out that the phase angle of the equivalent positive sequence abrupt impedance (PSAI) of the IIG will vary from 0 to 180 • , which may lower the sensitivity of the directional relay-or even cause its mal-operation. Unfortunately, no effective solution has been proposed yet.In view of the low sensitivity or mal-operation of the directional relay based on the PSFC for a distribution ...

A Survey on Power Grid Faults and Their Origins: A Contribution to Improving Power Grid Resilience

“…Baran et al [113] studied a protection method based on early overcurrent for DC relay protection. Zhu et al [114] proposed a directional relay solution that can identify faults in both the negative and positive directions and will help to solve the adaptability problem as well as to identify current faults on the EPG.…”

Alternative Methodology to Calculate the Directional Characteristic Settings of Directional Overcurrent Relays in Transmission and Distribution Networks

“…Other studies have been carried out proposing new methods for the direction determination algorithm in very specific cases, as the one proposed in [12], for its application in distribution networks with inverter-interfaced generation (IIG), but again, they do not provide specific means to calculate the relevant settings, and are limited to present the operation characteristic, with setting values not supported by a detailed analysis.…”