A low-current ground fault line selection device is the substation unit that identifies which outgoing feeder carries the earth fault in a 6–35 kV network where the fault current is only tens to hundreds of amperes. It watches every feeder…

Directional overcurrent relay protection is the ANSI 67 function that adds a direction check to a 50/51 overcurrent stage. The relay compares fault current phase angle against a polarising voltage reference, so it trips only for faults flowing into the…

Protection relay setting calculation turns a fault study into trip numbers: for every relay you fix the pickup current, the time delay and the zone it covers, then prove those numbers clear faults selectively. Four inputs drive the result —…

Power transformer protection is the coordinated set of electrical, mechanical and thermal functions that detect internal faults, abnormal operating conditions and external faults. Most schemes pair 87T differential with overcurrent and earth-fault backup, then add Buchholz, winding temperature and pressure devices…

Generator transformer unit protection is a unit protection scheme designed for generator-transformer blocks in power plants. It protects the generator, step-up transformer and connection equipment against internal faults, abnormal operating conditions and external system disturbances. Written by Leon Zhang, Protection…

Transformer fault types refer to the electrical, thermal, mechanical and insulation faults that can occur inside a transformer or in its external connections during operation. Common transformer faults include winding short circuits, inter-turn faults, earth faults, bushing faults, core faults,…

Types of transformer protection split into electrical relays and mechanical devices, each aimed at a different fault mode. Written by Leon Zhang, Protection Application Engineer · Technical review by Li Ming, Electrical Engineer · Last reviewed September 2026. Transformer Faults and…