Electricity Forum Electricity Today Magazine Arc Flash Training

Protective Relays


Switchgear


Gas-Insulated Switchgear (GIS)

Improving Grid Resilience

In today's world, reliable and resilient power grids are crucial for supporting critical infrastructure, businesses, and everyday life. Extreme weather events, cyber threats, and equipment failures can disrupt power delivery, causing significant economic and societal impacts. Gas Insulated...

Overvoltage Protection


Fuses


High Voltage Fuses

High Voltage Fuses in Industrial Applications

High voltage fuses are vital components within industrial electrical systems, safeguarding equipment and personnel from the damaging effects of overcurrents and short circuits. Selecting and sizing the appropriate high voltage fuse for a specific industrial application requires careful...

Protection Coordination


Circuit Breakers


Air Circuit Breakers

A Deep Dive into Air Circuit Breakers

In the intricate world of power distribution, a silent sentinel stands guard - the air circuit breaker (ACB). Often overshadowed by its flashier counterparts like transformers and generators, ACBs play a critical role in ensuring the smooth flow of electricity. These workhorses function as...

Protection

Selective Coordination in MCCB Design

Selective coordination in molded case circuit breakers (MCCBs) is crucial for ensuring that only the circuit breaker closest to the fault operates, leaving other circuits unaffected and maintaining system integrity. Achieving true selectivity under both overload and short-circuit conditions presents various challenges, necessitating a careful analysis of time-current curves, advanced trip units, and zone selective interlocking.

In power distribution systems, particularly multi-level architectures utilizing MCCBs, selective coordination is essential. The goal is to isolate a fault as close to its source as possible, minimizing disruption to the wider system. This presents challenges across the wide range of potential short circuit and overload conditions.

The Foundation: Time-Current Curves (TCCs)

TCCs visually depict the tripping behavior of circuit breakers. The horizontal axis represents fault current magnitude, while the vertical axis indicates the time required for the breaker to trip. Achieving selectivity involves analyzing the overlapping TCCs of upstream and downstream MCCBs.

Challenges in MCCB Coordination

  • Wide Range of Fault Currents: MCCB protective zones must coordinate under everything from minor overloads to maximum available short circuit currents. This makes achieving selectivity across the entire range complex.
  • Thermal-Magnetic vs. Electronic Trip Units: Thermal-magnetic trip units have inherent limitations in adjustability, particularly in the instantaneous region of...

Protection Articles