Circuit Breakers: Introduction and Classification

Circuit Breakers: Introduction

• Circuit breakers (CBs) are switching devices used to protect and control electrical power systems from overloads or short circuits.
• Unlike fuses, which need replacement after activation, circuit breakers can be reset manually or automatically to resume normal operation once the issue is resolved.

Circuit Breaker Classification

• Circuit breakers (CBs) are categorized in various ways:
  • Arc interrupting medium: air, oil, vacuum, SF6 (for high voltage only)
  • Location: indoor or outdoor
  • Action: automatic or non-automatic
  • Control method: direct or remote operation
  • Mounting: panel-mounted or remote
  • External design: dead tank or live tank
  • Voltage: low, medium, or high

Low-Voltage Circuit Breakers Overview

• Low-voltage networks are a critical component in power systems.
• Essential loads like lighting, heating, ventilation, refrigeration, and air conditioning typically operate at voltages such as 230, 380, 400, 415, 480, 500, and 525 volts.
• Protection systems are crucial to ensure safety and protect equipment and people.
• Circuit breakers are needed at different levels in power distribution.
• Different types are used for residential, commercial, and industrial applications, catering to varying capacity needs.

Miniature Circuit Breaker (MCB)

• MCBs are compact circuit breakers used in low-voltage applications like homes, shops, and distribution boards.
• They are designed to trip automatically in case of excessive current.
• These breakers do not require replacement after a short circuit within their rated capacity.
• Available in various current ratings ranging from 10 amps to 125 amps.
• MCBs have thermal and magnetic protection against overload and short circuits, respectively.
• MCBs are classified into different types based on their tripping characteristics (B, C, and D curves).
  • B type trips at a rate of 3 to 5 times its rated current, suitable for resistive and small inductive loads. This is typically for residential and light commercial applications.
  • C type trips at a rate of 5 to 10 times its current, suitable for highly inductive applications like motors and fluorescent lighting.
  • D type trips at a rate of 10 to 20 times its rated current and is suitable for industrial and commercial applications with frequent high inrush currents, such as industrial motors and welding equipment.
• Specifications include rated current (maximum continuous current), short circuit capacity (maximum fault current it can carry).
• MCB tripping time is correlated with fault current (in multiples of rated current).

Molded Case Circuit Breaker (MCCB)

• MCCBs are larger than MCBs and more complex to provide higher short-circuit current ratings and more adaptable functionality than MCBs.
• MCCBs are applicable in residential and industrial distribution panels, main power feed panels, low-voltage motor starters, and other commercial applications.
• Current ratings typically vary from 15A to 125A.
• Frame size (ampere frame AF) is the maximum current for which the MCCB was designed.
• MCCBs have a wide range of short circuit capacities.

Air Circuit Breaker (ACB)

• ACBs are used for high voltage applications within the power systems.
• They are frequently used in industrial and commercial settings.
• Operate in three phase circuit configurations only.
• Current ratings are generally higher than those of MCBs and MCCBs.
• Rated current generally ranges from 630 to 6300 amps.
• ACB trip characteristics are electronically adjustable.
• Used as the initial protection in LV networks.

Residual Current Circuit Breaker (RCD)

• RCDs are specifically designed to identify and interrupt leakage currents, providing a safety function.
• RCDs are installed to protect against electrical shocks.
• They monitor current entering and leaving a circuit (in a circuit with no leakages, these currents should match), and cut power to a circuit if this difference exceeds the threshold of leakage.
• RCDs can be used as part of a switchgear.
• RCDs are available in various forms, including plug-in types, socket-outlet RCDs, and fixed types in consumer units.
• RCBOs combine RCD and overcurrent protection functions in a single device.

High Voltage Circuit Breakers (HVCB) Overview

• HVCBs, also known as power circuit breakers, commonly feature in substations.
• They are categorized based on the extinguishing medium used in the circuit breaker (such as oil, air, vacuum, or SF6).
• Relays trigger the circuit breaker upon detecting a fault or overload in high voltage systems.

Summary of Circuit Breaker Types

• MCBs: Best for homes, smaller shops, and similar installations; have three types (based on breaking characteristics).
• MCCBs: Can withstand higher fault currents and are more complex and adaptable than MCBs.
• ACBS: Used in medium to higher voltage systems.
• RCDs: Protect against electric shocks by sensing differential currents.

This quiz provides an overview of circuit breakers, their functionalities, and classifications. Gain insights into the various types of circuit breakers based on medium, location, and control methods. Perfect for students and professionals in electrical engineering.