Backup protection for a Delta–Wye (Δ–Yg) transformer looks straightforward — put overcurrent relays on both sides and be done — but the tran...
A power transformer is the most expensive single item in a substation, and it can fail in more ways than almost any other apparatus: slowly ...
The impedance relay is the simplest member of the distance relay family. Instead of comparing a current against a fixed setting, it measures...
A directional relay needs two inputs that are roughly 90° apart: a current and a voltage. The standard way to get them is the 90° quadrature...
Most relays watch one current and trip when it gets too big. A differential relay watches two currents — the current entering a protected a...
An ordinary overcurrent relay trips whenever the current is too big — but it cannot tell which way the current is flowing. On a radial feede...
The shaded-pole induction relay is the classic overcurrent relay: a simple, rugged device that has protected power systems for decades. Its ...
A power system is not protected as one big whole. It is divided into separate protection zones — one for each generator, each transformer, ...
An induction motor draws six to eight times its full-load current every time it starts — yet the overload relay must not trip during a healt...
Two feeders in parallel between the same two substations look like a simple reliability upgrade — if one feeder trips, the other carries the...