What are Circuit Breakers?

Brief Overview Of Circuit Breakers

A circuit breaker is an electrical device that works under normal and abnormal conditions. A circuit breaker is used manually and automatically to protect the system. A circuit breaker performs different works including

To Disjoint the system if we need maintenance or Extension
To Disjoint the system from faulty part to healthy part.

The simple switch does not protect from the arc because there are no methods to extinguish the arc so that's why we need a circuit breaker to protect the system from faults.

A basic circuit breaker consists of fixed and moveable contacts connected to the quick-acting mechanism. if a circuit breaker consists of one set of fixed and moveable contacts is called a single-pole circuit breaker.

if a circuit breaker consists of three sets of fixed & moveable contact and each set is connected with the single-phase supply is called a Three-pole circuit breaker.

Each circuit breaker consists of an Arc Extinguishing Chamber for an Individual pole. Many Types of Circuit breakers are available in the market including air circuit breakers, Oil Circuit breakers, Gas Circuit breakers etc. Below you see the "On position" and "off positions" of the contacts

Normally Closed State

In a normally closed(NC)state, when its contacts are connected, their resistance is zero in the case of ideal and currents are easily flown in the contacts.

A Brief Overview Of Circuit Breakers ｜Arc Initiation in circuit breaker｜Arc Extinction Methods in circuit breaker｜Electronicsinfos

Normally open State

In a normally open(NO)state, when its connections are open their resistance is infinite and current is not flown in the contacts.

Working Principle of circuit breaker

When current-carrying contacts are separate from each other the arc is produced in between them. To minimize the arc effect we used an insulating Medium for example Dielectric Oil, Sulpher Hexa Flouride(SF6) Gas and vacuum.

In normal conditions, the Circuit breaker contacts are closed until the system becomes faulty. when a fault occurs in a system the Relay generates a Signal to the trip coil of the circuit breaker and energizes the trip coil. after that, we separate the contacts with the help of any mechanism.

The different parts of the Circuit breaker including

Parts of the circuit breaker

Relay
A trip coil of CB
Trip Circuit
Battery
Relay contacts
Potential Transformer(CT)
Current Transformer(PT)
Auxiliary Switches
Protected Lines

Arc Initiation Process

When Circuit Breaker contact is separate the Arc is produced across the connections. due to the separation of contacts, the I²R losses occurred in the form of heat, resulting in a temperature increase.

Due to an increase in temperature, the thermal emission effect starts in the system. which results in generating the arc

Arc Extinction Method

There are two methods of Extinction of the arc including

current Zero Method
High Resistance Method

Current Zero Method

The other name of the Current zero method is the Low resistance method. this method is used in high-power AC circuits. we know that Every half cycle of AC supply the current is zero because of alternating supply.

when the current is zero at this particular time the arc is also zero. we used this principle to avoid the arc, we used insulating material i.e. oil or gas in the contacts which resulted in the medium being deionised.

High Resistance method

The high resistance method is an Arc Extinction Method in which we increase the Arc Resistance until The arc current is minimised. When we increase arc resistance the flow of current is stopped in the electrode or ionized gasses.

The major disadvantage of this system is Energy loss in the form of heat. the heat is in direct relation to the I²R. This method is limited to the low AC circuit capacity and DC system. There are different methods To increase the Arc Resistance including

Lengthening The Arc
Cooling the cross-section Area
Splitting the Arc Arc

Lengthening The Arc

We know that according to the law of resistance, the resistance is directly proportional to the lenght. if we increase the distance between the contacts the length is increased. we also increase the length using arc runners or arc splitters.

To increase the length the resistance is increased and the current is minimized. The construction of arc runners is horn shapes that are connected to arching contacts and the tip of the arc runner is a V shape.

Cooling The Arc

To minimize the arc we use the cooling method in the circuit breaker to deionize the medium. due to cooling the arc resistance is increased and the arc current is decreased.

Reducing the X-section Area

If we decrease the arc cross-sectional area the arc resistance increases and the arc current decreases.

Splitting the Arc

Splitting the arc is another Method of reducing the arc currents. in this method, we split the arc into small arc sections so every small length provides a cooling effect and a long length minimises the arc effect. the other name is arc splitter. we set these plates as verticle side.

Magnitude of Arc

An electrical discharge consists of electrical charge carriers. the more charge carriers the less resistance of the arc. the charge carrier depends on the following things

Magnitude Depending Factors

The potential difference between the arc points
the dielectric strength of the insulating material
The physical properties of the insulating medium
The current flow due to the discharge
The temperature of the Arc
The Quantity of insulating medium between the arc
The Diameter of the Arc
The Length of the Arc

There are different Temperature zones in the Arc. The first temperature zone is the Core temperature a value between 6000 degrees to 25000 degrees.

The second zone is the ionized gasses zone which is a value between 2000 degrees to 6000 degrees. the other zone is the Hot gasses zone the temperature is 2000 degrees.

The Relationship between the steady-state arc current and Voltage is

Varc = A + Bd + (C+Dd)/Iarc

A, B, C, D is a constant value

d= Length of arc
Varc = Voltage drop in the arc
Iarc = Arc Current
Earc= Varc * Iarc*t

Where

E arc I the useable energy in the arc
t = time in ms

Conclusion

Circuit breakers are important components in the electrical power system. They provide safety and reliability by protecting circuits from overcurrent, short circuits, or overload conditions.

They operate by detecting fault conditions and interrupting the current flow. The choice of arc quenching medium in a circuit breaker, whether it be cooling, compressing, or replacing the ionized medium with fresh gas, is determined by the voltage level and current rating of the device.

Frequently Asked Questions – FAQs

How does a Circuit Breaker work?

A circuit breaker is an electrical device that works under normal and abnormal conditions. A circuit breaker is used manually and automatically to protect the system.

What are common Types of Circuit Breakers?

Common types include air, vacuum, oil, and SF6 circuit breakers

What is the difference between a fuse and a circuit breaker?

A fuse is a safety device designed to protect electrical circuits from overcurrent conditions.
A Circuit breaker automatically switches off the circuit when it detects overcurrent, short circuits, or faults.