Category Archives: Protection

This article focuses specifically on directional earth fault protection (ANSI 67N) for electrical networks with an impedance-grounded neutral. We’ll be releasing more articles soon that explore how directional earth protection behaves in other grounding systems. The goal is to give you a complete, system-by-system view of how earth fault protection works. Stay tuned—there’s much more coming. In this… Read More »

Distance protection schemes play a vital role in ensuring reliable and speedy fault clearance on transmission lines. The fundamental idea behind distance protection is to measure the impedance between the relay location and the fault point, enabling the relay to detect faults within set zones. Conventional time-stepped distance protection, for instance, sets an instantaneous Zone 1 reach to about… Read More »

An interposing relay (sometimes called an interface relay or isolation relay) is essentially a relay used to interface two circuits that have different electrical characteristics (e.g. different voltages, current levels, or common references). It “interposes” itself between a control circuit (e.g. PLC, sensor output) and a load or another circuit that may not be directly compatible. Key roles… Read More »

Magnetising inrush is a transient electrical phenomenon that primarily occurs when a power transformer is energized. It is not indicative of a fault but rather a normal response of the transformer’s magnetic core to sudden application of voltage. However, it poses significant challenges for transformer protection systems, which must distinguish this temporary surge from actual faults to avoid… Read More »

The transmission of electrical energy is a fundamental element of global power grids, and one of the main distinctions between systems lies in the frequency used: 50 Hz or 60 Hz. Most countries in Europe and Asia adopt a voltage of 220 V at 50 Hz, while nations like the United States, certain regions of Japan, and Saudi… Read More »

Vector algebra is a fundamental tool in electrical engineering, particularly in the analysis of circuits and protection systems. It allows for the representation of physical quantities, such as current or voltage, not only by their magnitude but also by their direction. This article highlights the importance of vector representation in simplifying calculations involving complex quantities, while providing a… Read More »

Directional earth fault protection, identified by the ANSI code 67N, is a specialized protection function used in electrical networks with a compensated neutral, typically employing a Petersen coil earthing system. This protection is designed to detect and isolate earth faults (single-phase-to-ground faults) in such networks by distinguishing the fault current in a faulty feeder from the capacitive currents… Read More »