Current-Only Directional Overcurrent Protection for Distribution Automation: Challenges and Solutions

Under the ‘Smart Grid’ initiative, future medium and low voltage distribution grids would incorporate renewable sources like rooftop solar, etc. This would require bi-directional power flow between the generation and the loads. For optimal fault isolation and distribution automation, directional protection would be of great advantage. However, traditional directional overcurrent relays utilize the reference voltage phasor for estimating the direction of the fault, requiring measurement of both current and voltage using respective sensors. This makes the directional overcurrent relays prohibitively costly than the non-directional type for distribution side utilizations. Novel current-only directional protection algorithms have been proposed and demonstrated. However, as the current-only approach relies on the prefault current direction as the polarizing quantity, if the direction of the prefault current changes during normal condition, the direction definitions (forward or reverse) would be vice versa. This is a problem for the current-only approach. In this paper, a signal processing-based solution is proposed, leveraging the fact that change in direction in prefault condition is associated with a phase angle change of 180°.

Directional overcurrent and earth-fault protections for a biomass microgrid system in Malaysia

This paper presents the evaluation of a line protection scheme for interconnected power subtransmission systems by comparison of the feasibility of relay time coordination, under different criteria. The protection scheme consists of distance relays as primary protection and directional overcurrent relays as back-up relays at 69 kV. A coordination computer program that uses linear programming and goal programming techniques is employed to determine the relay settings. Three cases are considered: (1) independent coordination of inverse-time relays and distance relays; (2) combined coordination of inverse-time directional overcurrent relays considering distance relays; and (3) combined coordination of definite-time-high-current setting directional overcurrent relays. The test case consists of a system located in the Eastern zone of Venezuela with 108 buses, 86 lines, 61 transformers and 97 directional overcurrent relays. It is shown that all three cases have advantages and disadvantages regarding the feasibility and viability of relay coordination, however the case with definite-time-high-current setting directional overcurrent relays is simpler for time coordination achievement.

Due to the concerns for reduction of system losses, providing back-up power during loss of the grid, mitigation of energy security risks and conspicuous perturbation of power outages triggered by severe environmental constraints; the modernized distribution grids elicited grid resiliency and reliability enhancement through pragmatic enforcement of the Microgrid (MG) concept with distributed generation. With the proliferating power ultimatum, several intricate factors prone to MG operation modes, bidirectional power flow complexities, management and control of power transfer, varying fault current contribution, and high impedance faults (HIF) customized the network configuration and imperiled the protection system operation and system stability. The propitious utility framework persuaded the prerequisites to embrace the integration of state-of-the-art affiliated Distributed Energy Resources (DERs), which requires assimilated and coordinated studies to emphasize the outcomes of an efficient, reliable, and fast protection scheme for both the grid-connected and islanded modes of operation. Operating modes of distributed generation (DG) will affect the magnitude and direction of fault currents resulting in failure of protection coordination between directional overcurrent relays (DOCRs). In this paper, the negative-sequence based adaptive directional overcurrent relay (NSADOCR) stratagem is proposed. Protection coordination is accomplished by a new adaptive approach, which alters time dial setting (TDS) of negative-sequence overcurrent relay based on the ratio of the normal mode to operating mode of plug setting multiplier function. Furthermore, the direction of fault is attained using phase change in between the pre-fault and superimposed negative-sequence current components. Performance of the NSADOCR is evaluated on the dSPACE controller board, which is interfaced with Real- Time Digital Simulator (RTDSTM) to perform the hardware-in-the-loop (HIL) tests. Extensive simulation studies and hardware results on DG systems exemplify and indicate that the new adaptive technique results in effective protection coordination over the conventional approach, considering various distribution network (DN) modes of operation.

Microgrids are the localized grids which consists of number of distributed generators (DGs) with the distribution system. Introduction of DGs into distribution system cause changes in the fault current levels & directions, thus results in inaccurate operation of the existing protection system. Fault currents in the system also varies significantly following the transition of grid-connected and islanded operational modes of microgrid. Procuring a coordinated protection system which operates accurately in DGs integrated scenario is still a challenging aspect for the planners. In this paper, protection system has been proposed which is suitable for both grid-connected and islanded operational modes of microgrid. Differential evolution (DE) algorithm has been used for achieving the proper coordination of directional overcurrent relays (DOCR) in the distribution systems. IEEE-9-bus distribution system integrated with four DGs have been analysed in this paper. Discrete plug setting (PS) and time multiplier setting (TMS) has been obtained which are feasible for numerical relays. Obtained optimized relay settings provide efficient and accurate operation of relays with minimum operating time.

The aim of the relay coordination is that protection systems detect and isolate the faulted part as fast and selective as possible. On the other hand, in order to reduce the fault clearing time, distance protection relays are usually equipped with pilot protection schemes. Such schemes can be considered in the Distance and Directional Over-Current Relays (D&DOCRs) coordination to achieve faster protection systems, while the selectivity is maintained. Therefore, in this paper, a new formulation is presented for the relay coordination problem considering pilot protection. In the proposed formulation, the selectivity constraints for the primary distance and backup overcurrent relays are defined based on the fault at the end of the transmission lines, rather than those at the end of the first zone of the primary distance relay. To solve this nonlinear optimization problem, a combination of Genetic Algorithm (GA) and Linear Programming (LP) is used as a Hybrid Genetic Algorithm (HGA). The proposed approach is tested on an 8-bus, the IEEE 14-bus and the IEEE 39-bus test systems. Simulation results indicate that considering the pilot protection in the D&DOCRS coordination, not only obtains feasible and effective solutions for the relay settings, but also reduces the overall operating time of the protection system.

Directional overcurrent protection is used when it is necessary to protect the system against fault currents that could circulate in both directions through a system element, and when bidirectional overcurrent protection could produce unnecessary disconnection of circuits. This can happen in ring or mesh-type systems and in systems with a number of infeed points.

A new and effective directional overcurrent relay coordination approach for IIDG-based distribution networks using different setting groups for peak and off-peak demand periods

A pilot-based distance protection scheme for meshed distribution systems with distributed generation

Enhanced real time coordination of distance and user defined over current relays

This research focuses on the study of the directional phase overcurrent relaying concept that can be briefly explained by the relay tripping whenever the faulted current exceeds a pre-determined pick up value in a specific predefined direction, in order to isolate only the faulted part of the network. The Directional Phase Overcurrent Protection appears more important in the distribution system when the Overcurrent protection is the main protection. Any glitch in its setting can lead to opening the circuit in the non-faulty area or can perform non-trip in the faulty area. As an example in Algeria, this problem happens repeatedly in the plurality distribution substations. This reliable and selective protection is generally used in multisource networks, parallel transmission lines and mesh distribution networks. It is mainly characterized by its Maximum Torque Angle and Relay Characteristic Angle (RCA), also known as the directional angle as it decides the direction of the tripping zone. The variation of the RCA setting has a direct impact on the sensitivity operation of the relay (45 degrees' maximum sensitivity operation for any type of fault). Tests have been performed on The Four Step Directional Phase Overcurrent Protection Function of the Line Distance Protection REL670 ABB IED numerical relay. On one hand, the 51/67 ANSI protection has been tested and results were discussed. On the other hand, different cases of RCA settings were evaluated under fault to showcase that the 45-degree angle is the best applicable value for a maximum sensitivity.

This paper introduces a deterministic method to address coordination challenges between distance relays (DS) and directional overcurrent relays (DOR) by employing quadratic programming with quadratic constraints (QCQP). The conventional nonlinear coordination problem associated with DORs is reformulated as a QCQP, incorporating quadratic constraints, and the zone-II setting of the DS relay is included as a variable. To optimize relay settings that adhere to coordination constraints, the approach eliminates redundant constraints, proposing a minimal coordination constraint set (MCS) to prevent miscoordination issues. Furthermore, the MCS is divided into subsets suited to specific network topologies, thereby reducing programming complexity and execution times. Implementing QCQP with MCS and the SCIP optimizer (a global optimization tool) led to significant reductions in operating times as 86.4%, 10.77%, and 72.4% for the 8-bus, 14-bus, and IEEE-39 bus system models, respectively. These results highlight the QCQP approach’s superiority over previous solutions, demonstrating its effectiveness in optimizing power system protection operations while substantially reducing computation times compared to existing methods.

With increase of distributed generators (DG) in power system, there arise the potential for operation of power system during islanding mode as well. Along with its advantages, there come challenges with protection system due to change in short circuit current (which is the primary factor for overcurrent relay setting). In this paper, investigation of impact of Distributed Generators (DG) in protection system of the distribution network has been carried out. Simulation based study regarding protection issue during islanding condition has been carried out for distribution network in mid Himmerland (Denmark). Use of definite time overcurrent relay along with directional overcurrent relays has been proposed for the reliable protection scheme. Simulation in ‘DIgSILENT Power Factory’ shows the proper selectivity and coordination of overcurrent relays for 3 phase faults during various cases, such as islanding or shutdown of some DG.

Protection of transmission lines is essential to ensure a correct operation of power systems. In this paper a pilot protection scheme, known as permissive overreaching transfer trip, is used. This structure combine two different protection relays: directional overcurrent relay, a backup protection for phase-earth faults, and distance relay for phase-phase faults. An intelligent method was developed to the optimal coordination of protection relays in meshed networks like transmission networks. The proposed method employs the genetic algorithm as optimization procedure that considers network characteristics (maximum load current and minimum fault current) and adjustment parameters of overcurrent and distance relays. Two testing networks, one of 8-bus and other of 39-bus, were used to evaluate the proposed method that obtained feasible and good solutions for the coordination problem.

Chapter 4 - Design of nonconventional time curves for overcurrent relays