Why Use VCB Circuit Breakers in HV Transmission, & Not ACB?

Electrical Technology

Why are VCB Circuit Breakers Preferred in High Voltage Transmission Systems Instead of ACB?

Table of Contents

What is an Air Circuit Breaker (ACB)?

An Air Circuit Breaker (ACB) is a type of circuit breaker that operates in air as an arc extinguishing medium. It is used to protect electrical circuits from overloads, short circuits, and other types of faults. ACBs are commonly used in low and high voltage applications and are known for their reliable performance and ease of maintenance.

What is Vacuum Circuit Breaker (VCB)?

A Vacuum Circuit Breaker (VCB) is a type of circuit breaker that uses a vacuum as an arc extinguishing medium. It is designed to protect electrical circuits from overloads, short circuits, and other types of faults. VCBs are known for their high breaking capacity, compact size, and maintenance-free operation. They are commonly used in medium voltage applications.

Comparison Between VCBs and ACBs

Comparison table between Air Circuit Breaker (ACB) and Vacuum Circuit Breaker (VCB) based on their key characteristics:

Characteristic	Air Circuit Breaker (ACB)	Vacuum Circuit Breaker (VCB)
Arc Quenching Medium	Air	Vacuum
Breaking Capacity	Typically up to 10,000 A	Higher, up to 50,000 A or more
Insulation	Requires regular maintenance to ensure insulation integrity	Maintenance-free insulation due to vacuum technology
Life Expectancy	Generally lower compared to VCB	Longer life expectancy due to vacuum technology
Operating Mechanism	Typically uses spring mechanism for operation	Can use various mechanisms, including spring or magnetic
Maintenance	Requires periodic maintenance for contacts and insulation	Generally maintenance-free except for occasional checks
Environmental Impact	More environmentally impactful due to the use of air	More environmentally friendly due to the absence of air
Size and Weight	Larger and heavier compared to VCB	Smaller and lighter compared to ACB
Cost	Generally lower cost compared to VCB	Higher cost compared to ACB

Why are VCBs Mostly Used in HV Transmission Systems Instead of ACBs?

VCB (Vacuum Circuit Breaker) is preferred over ACB (Air Circuit Breaker) in high voltage transmission lines, power plant, substation and typical power systems for several reasons:

High Dielectric Strength:

VCBs have higher dielectric strength compared to ACBs, allowing them to interrupt fault currents more effectively without arcing and breaking-down, especially in high voltage systems and applications.

Low Maintenance & Longer Service Life:

VCBs require minimal maintenance compared to ACBs, as they have fewer moving parts and do not use arc-chutes that need regular cleaning and replacement.

As compared to the ACB, they don’t need refiling of oil and gas etc. The main parts are safe from wear and tear and corrosion due to the non-exposure to moisture and air. This helps to increase the overall service life of the VCB.

Faster Operation:

VCBs have faster operating times, which is crucial for quickly isolating faults in high transmission systems to prevent damage to equipment and ensure system stability.

Compact Size with Lower Cost:

VCBs are more compact than ACBs, making them suitable for installation in high voltage switchgear where space is limited. Due to its compact size and lower material requirements, the operational cost of a VCB is less than that of an ACB.

Due to its lower energy consumption, reduced heat and noise generation, compact size, and lower material requirements, the operational cost of a VCB is less than that of an ACB.

Reliability & Environment Friendly:

VCBs are safer and more reliable than ACBs. They don’t cause fire hazards like ACBs can because they don’t produce flames or sparks during the opening and closing of contacts. VCBs are also less prone to mechanical failures, and they are less likely to break down and last longer.

During arc quenching, VCBs do not produce pollution or emit harmful gases into the atmosphere.

That’s why, the superior performance, reliability, and lower maintenance requirements make VCBs a preferred choice for high transmission systems.