Ground Overcurrent Protection Research Articles

Optimizing TOC and IOC units of directional overcurrent relays in mutually coupled circuits using evolutionary PSO: Requirements and modeling

The efficient coordination of directional overcurrent relays is a challenging problem. Recent papers in the literature have focused on developing efficient algorithms to solve this issue. However, there is a lack of reporting practical procedures that affects the mathematical formulation to ensure accurate outputs by any optimization algorithm. In this paper, we show a comprehensive procedure that considers mutually coupled circuits via Graph Theory, the requirements of short-circuit current calculation, contingencies to be considered as well as the setting of Instantaneous Overcurrent (IOC) and Time Overcurrent (TOC) units, both for phase and ground protection. The simulation has been carried out by using a real electric network and C++ language programming. Computational simulation has shown the performance of the method, which provides high-quality solutions, with adequate coordination of the selected protective devices that increase the efficiency in setting this type of protection with safety. Evolutionary Particle Swarm Optimization (EPSO) outperformed conventional Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) as the best metaheuristic for optimally minimizing the proposed problem, achieving faster convergence times for the phase overcurrent protection scenario (16.36 s vs. 22.27 s and 17.03 s, respectively), and also for the ground overcurrent protection scenario (19.87 s vs. 20.44 s and 20.11 s, respectively).

Practical Charts for Sizing Neutral Grounding Elements for Machine-Based Distributed Energy Source Step-Up Transformers

One of the challenges resulting from the adoption of machine-based distributed energy resources lies within the intersection of protection and performance grounding. These are strongly interrelated and conflicting subjects that dictate the occurrence of ground fault overvoltage and the effectiveness of ground overcurrent protection. Currently, there remains a gap in the distribution planning of most jurisdictions in formulating these aspects and adopting simple and practical measures to balance these subjects. This letter introduces a simulation-based method to develop a set of practical charts intended to be used as a sizing guideline for neutral grounding elements, which are to be employed in the associated step-up transformers. This solution became pivotal to the electrical utility conducting the research and has allowed planning engineers to simplify design and streamline cooperation between the utility and large-scale DER developers.

Podešavanje usmerenih zemljospojnih zaštita u prenosnoj mreži korišćenjem unapređene metode diferencijalne evolucije

The paper presents the procedure of directional ground overcurrent protection setting calculation in the transmission network by using classical calculation procedure and by using an advanced algorithm of differential evolution. To meet the basic requirements of relay protection systems such as speed, selectivity, coordination and sensitivity, the conditions that need to be considered when setting directional ground overcurrent protection are defined. By using the optimization method, the problem was solved in two ways. In the first case, the settings are designed to minimize the total response time of directional ground overcurrent protection to remote-end high-resistance faults, whereas in the second case the settings are designed so that the maximum response time to remote-end high-resistance fault is minimal. The results obtained using the classical approach are compared with the results obtained using the optimization method and the advantages and disadvantages of both approaches are highlighted.

Wildfire Trips De-Energized Line Shunt Reactor

Dense smoke from wildfires within a 500-kV line corridor led to several line protection trips over a three-day period. A switchable line-connected reactor, provided to control Ferranti voltages, tripped and locked out twice by its protection shortly after the line was de-energized. Lockout operation prevented quick reactor reinsertion and impeded operational flexibility until visual inspections of the reactor were conducted on both occasions. Forensic investigation of the event concluded that the smoke increased the line capacitances. This created a near 60-Hz zero sequence resonant circuit when the line tripped and became de-energized along with the reactor. The resonant circuit amplified the capacitively coupled zero sequence 60-Hz voltage induced from circuits which run adjacent to the line for a short distance. The voltage amplification drove enough current through the reactor to trip the sensitive ground overcurrent protection. A holistic mitigation is designed to avoid reoccurrence of the incident and improve overall line reliability. The intent of this paper is to share lessons learned from the event investigation with peer utilities because this problem of unexpected operation of line shunt reactor protection has not previously been reported.

Proposal of a New Sensitive Ground Overcurrent Protection for High-Impedance Faults

This paper presents the development of a sensitive ground overcurrent protection algorithm. The proposed algorithm is able to detect high-impedance faults produced by downed conductors in solidly grounded primary distribution networks. It presents a higher level of accuracy when compared to conventional overcurrent protection functions. The algorithm is based only on current measurements and uses additional conditions to generate the trip signal, in order to prevent false tripping due to its high level of sensitivity. This paper presents a detailed description of the proposed algorithm, the hardware prototype developed during the research and its performance in laboratory tests.

Static relays permit enhanced protection

Multi-function multi-phase static overcurrent relays, using digital technology available today, provide basic time, (51) (51G) (51N) and instantaneous (50) (50G) (50N) three phase and ground overcurrent protection, and may offer some or all of the following additional functions: undervoltage (27); overvoltage (59); reverse phase sequence (47); negative phase sequence voltage (47N); directional overcurrent (67) (67N); frequency (81O/U); reverse interlocking trip coil monitoring; and battery monitoring. This article describes two applications that use some of the additional functions in such a relay: reverse interlocking, also using the directional overcurrent (67) function; and ground fault detection for systems utilizing high resistance grounding. The first application was installed on a 4160 volt power system which was supplied by two 5000 kVA transformers.