Circuit Breaker
How Power Factor Affects the Transient Recovery Voltage (TRV)
After a circuit breaker interrupts a fault at current zero, the voltage across its opening contacts does not return gently to normal — it os...
Circuit Breaker
Circuit Breaker Ratings and Specifications Explained
A circuit breaker's nameplate carries a set of ratings — voltage, current, breaking capacity, making capacity, short-time current and du...
Circuit Breaker
Vacuum Circuit Breaker: Advantages and Disadvantages
The vacuum circuit breaker (VCB) is the standard medium-voltage breaker today — quiet, compact and almost maintenance-free. Its strength com...
Circuit Breaker
Oil Circuit Breaker vs Vacuum Circuit Breaker: A Complete Comparison
Oil and vacuum were the two great interrupting media of the twentieth century — oil came first, vacuum replaced it at medium voltage. They e...
Arc Interruption
High-Resistance vs Low-Resistance Arc Interruption
When a circuit breaker's contacts separate, an arc burns between them, and the breaker's whole job is to kill that arc. There are tw...
Circuit Breaker
How an MCB Works: Thermal-Magnetic Tripping Explained
The miniature circuit breaker (MCB) in every home distribution board protects a circuit against two different dangers: a sustained overload ...
Circuit Breaker
Circuit Breaker vs Isolator: Differences and Why Isolators Sit on Both Sides
A circuit breaker and an isolator (disconnector) both open a circuit, so beginners often confuse them. In reality they do opposite jobs: the...
Circuit Breaker
Impedance Relay: R–X Characteristic and Its Disadvantages
The impedance relay is the simplest member of the distance relay family. Instead of comparing a current against a fixed setting, it measures...
Circuit Breaker
The 90° Quadrature Connection and the Compensating Resistor R
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...
Circuit Breaker
Directional Overcurrent Relay: How It Detects Fault Current Direction
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...
Circuit Breaker
Shaded-Pole Induction Relay: Operating Principle and the IDMT Characteristic
The shaded-pole induction relay is the classic overcurrent relay: a simple, rugged device that has protected power systems for decades. Its ...
Circuit Breaker
Why a Power System Is Divided into Protection Zones
A power system is not protected as one big whole. It is divided into separate protection zones — one for each generator, each transformer, ...
Circuit Breaker
Restriking Voltage Derivation and Proof That RRRV Is Proportional to Natural Frequency
When a circuit breaker interrupts a fault, the voltage that appears across its contacts immediately after the arc goes out is called the res...
Circuit Breaker
Resistance Switching: Sequence of Operation and Why ABCBs Need It
When a circuit breaker interrupts a small inductive current — for example, switching off an unloaded transformer or a shunt reactor — the cu...
Circuit Breaker
Circuit Breaker Selection by Voltage Level and the Dielectric Curve
Not every circuit breaker suits every voltage. A breaker that works perfectly at 400 V would fail catastrophically at 132 kV, and a breaker ...
Circuit Breaker
Air Blast Circuit Breaker (ABCB): Working Principle and the Series Isolator
An Air Blast Circuit Breaker does something no oil breaker can: it uses the same blast of compressed air twice — once to move the contacts a...
Circuit Breaker
Minimum Oil Circuit Breaker (MOCB): Advantages and Disadvantages
The Minimum Oil Circuit Breaker (MOCB) was the answer to one simple complaint about the older Bulk Oil Circuit Breaker (BOCB): it used far t...
Circuit Breaker
MCCB Explained: Thermal and Magnetic Operation and the TCC Curve
A Molded Case Circuit Breaker (MCCB) is the workhorse of low-voltage protection. Inside one rugged moulded housing it carries two completely...
Circuit Breaker
Parallel Feeder Protection: How Directional (67) and Non-Directional (51) Relays Work Together
Two feeders in parallel between the same two substations look like a simple reliability upgrade — if one feeder trips, the other carries the...
Circuit Breaker
What Is a Switchyard? Definition and the 7 Switchgear Elements Inside It
A switchyard is one of those places every electrical engineering student hears about but rarely sees from the inside. In simple words, it is...