How Does a Circuit Breaker Work?

Circuit breakers are indispensable in preventing overload, short circuit, and ground faults, among others. This article discusses the working principle of the circuit breaker and helps you understand why they are vital for keeping reliable operation and electrical safety in your commercial or industrial environments.

Pemutus Sirkuit

The main function of a pemutus sirkuit is to protect your electrical systems and equipment from damage caused by high currents, and to prevent fires or electric shocks and other dangers. Unlike fuses, circuit breakers can be reset and used over and over again.

Overall, in the electrical system, circuit breakers can protect equipment, reduce fire risks, improve safety and system reliability, and enable rapid circuit recovery.

The Working Principle of Circuit Breaker

Normal Operation

Under normal operating conditions, the circuit breaker remains in the ON position and current flows through the circuit. The contacts inside the circuit breaker remain closed; that is, the circuit is not interrupted.

Current flows from the power supply through the circuit and ultimately to the load without any problems. In this normal state, the circuit breaker acts as a regular conductor and does not cause any resistance to the current.

Fault Detection

The main function of a circuit breaker is to detect faults. It is used to detect the following conditions:

Overload: when the current exceeds the circuit’s rated capacity, this may be caused by the simultaneous use of too many devices.

Short Circuit: A surge of current occurs when a charged wire contacts a neutral or ground wire.

Ground Fault: When the current passes through an unexpected path, such as when a charged wire contacts the ground.

Detection of faults is done through the trip mechanism inside your circuit breaker. Depending on your circuit breaker design, there are different types of trip units:

Thermal tripping mechanism: This type of circuit breaker uses bimetallic strips, which are used for cutting off moderately high currents of longer duration. It bends when the current heats. The release mechanism is initiated when the bimetallic strip is bent to a predetermined limit.

Magnetic tripping mechanism: It mainly consists of a solenoid (electromagnet). When there is an overcurrent, excessive current increases the magnetic force of the electromagnet. If current exceeds a certain threshold, the magnet pulls on the lever or plunger, eventually tripping the circuit breaker.

Electronic trip mechanism: It mainly uses sensors and microprocessors to precisely measure the current level and compare it with the preset threshold. You can customize this system to meet advanced protection needs and implement functions such as time delay or selectivity.

Trip Mechanism Activation

The trip mechanism automatically activates once your circuit breaker detects a fault condition, such as an overload, short circuit, or ground fault. Then, upon reaching the fault condition, the operating mechanism is triggered, and the circuit is quickly disconnected by separating the contacts.

If your circuit is overloaded, a thermal or electronic trip unit will delay tripping and allow the circuit to be temporarily overloaded. This avoids the short surges caused by large equipment or motor start-ups and unnecessary downtime. A long overload can cause the circuit breaker to trip.

If a short circuit occurs, the magnetic trip unit will respond immediately. Typically, an electromagnetic circuit breaker is also equipped with a spring inside. When the magnetic force moves the lever, the spring tension is quickly released. The spring-loaded separate contacts operate without any delay, which can help you prevent catastrophic damage.

Arc Formation

When the contacts of the circuit breaker start to separate, an arc will form between the moving contact and the fixed contact. What causes this? It is because the current is seeking a path to continue flowing. Even if the contacts separate, the current can still cross the gap and form an arc.

You should note that the temperature of the arc can reach thousands of degrees Celsius. If you don’t control it properly, this arc can damage the circuit breaker, create a fire hazard, or damage surrounding components.

Arc Extinction

If you want good arc control, you can choose a circuit breaker with an arc extinguishing system. This helps you safely control and extinguish the arc. The control and extinguishing method used depends mainly on the type of circuit breaker you are using.

Air circuit breakers extinguish the arc primarily by blowing air when the contacts separate. The air pressure cools the arc, lowers its temperature, and stops the current.

If you are using a vacuum circuit breaker in high voltage applications, the arc will primarily extinguish in a vacuum environment. In an environment without gas or air, the arc cannot conduct electricity.

Besides, sulfur hexafluoride circuit breakers(SF₆ circuit breakers) use sulfur hexafluoride gas to extinguish the arc. This application is common in high-voltage applications such as substations. These circuit breakers can help you safely cut off current without damaging components inside the circuit breaker.

Circuit Isolation

After the arc is extinguished, the contacts inside the circuit breaker are fully open to effectively isolate the circuit. The rest of the system continues to operate, ensuring that only the faulty parts of the circuit are affected. This prevents widespread power outages from causing reduced downtime in your industrial or commercial environment.

Resetting the Circuit Breaker

After troubleshooting, you can reset the circuit breaker. Before resetting the circuit breaker, you need to reengage the trip mechanism and return the contacts to the closed position. A properly restored circuit breaker can operate normally and help you protect the system from the effects of future failures.

Tanya Jawab Umum

Can A Circuit Breaker Fail to Trip?

Yes. Circuit breaker tripping failure may be caused by mechanical wear, improper circuit breaker size, trip unit failure, etc. Therefore, you need to regularly inspect and test the circuit breaker to guarantee that its protection function is intact.

What Is the Difference Between A Circuit Breaker And A Fuse?

Both devices are used to protect the circuit from overcurrent, and the difference between them is the way they work. Circuit breakers can be reset after tripping, while fuses must be replaced. Circuit breakers provide more accurate protection and switching capability. Fuses have low initial cost but high long-term maintenance costs.

In commercial and industrial systems, reliable and reusable circuit breakers are your best bet.

How Do You Choose The Right Circuit Breaker for An Electrical System?

Selecting the right circuit breaker requires you to evaluate the rated current, rated voltage, breaking capacity, interface characteristics, installation environment, and many other parameters. In industrial applications, you also need to guarantee that the circuit breaker is compatible with other protection equipment.

How Long Do Circuit Breakers Typically Last?

Circuit breakers typically have a service life of 20 to 40 years, but this mainly depends on factors such as type, environmental conditions, and maintenance. For instance, MCBs and MCCBs can be used for 20 to 30 years with proper maintenance. Circuit breakers for high voltage, such as VCBs and SF₆ circuit breakers, can last for 30 to 40 years.

What Are the Main Types of Circuit Breakers Used in Industrial Systems?

MCCB is mainly used for medium current protection in industrial equipment, machinery, and distribution panels, providing adjustable overload and short-circuit protection settings. ACB is used in medium-voltage systems, for industrial factories and distribution systems, with high breaking capacity.

Besides, there are VCBs applied in industrial substations and power networks, as well as SF₆ circuit breakers for high-voltage transmission systems. You can make a choice based on voltage, current rating, and the specific protection requirements of the industrial system.

How Quickly Does A Circuit Breaker Respond to A Short Circuit?

Its response time is often related to the type of circuit breaker, the severity of the fault, and the fault detection mechanism. Typically, circuit breakers with electromagnetic trip mechanisms ( MCCBs) have a reaction time to short circuits within 1-3 milliseconds.

A circuit breaker (ACB) for a thermomagnetic trip mechanism unit combines thermal protection (for overload) and magnetic protection (for short circuit). It reacts slowly to overloads but very quickly to short circuits (within 1-5 milliseconds).

Circuit breakers (VCB) equipped with electronic trip units are equipped with microprocessors that respond to short circuits in less than a millisecond.

Final Thought

As a professional manufacturer of electrical enclosures, KDM can provide you with various types of circuit breaker enclosures according to your application. Depending on your specific needs, we also provide you with one-stop custom production services. We will promptly respond to your requirements and provide you with samples. Contact us to get your customized solution.