Arc Initiating for Low Voltage Circuit Breakers:
Introduction
Low voltage circuit breakers are used to protect electrical systems and equipment from being overloaded or short circuited. The function of the breaker is to detect an over current, open the circuit, then to withstand and extinguish an arc that forms when contacts separate. This process requires the circulation of a hot current and the creation of an arc. The arc is created through the arc initiating process, known as arc initiating.
Principles of ArcInitiation
Arc initiating is a complex process that occurs in the gap between the two main contacts of a circuit breaker. The physical phenomenon begins when a large pneumatic energy force is triggered by a rapid movement of the contacts. While the rapid movement of contacts and the presence of a gap between them gives rise to an arc, additional energy is needed for the arc to bridge the gap and to continue over the contacts.
Once the initial arc is formed, it is very difficult to extinguish it on its own and, as a result, the development of reliable arc initiating systems is essential for a successful operation of a circuit breaker. The integrity of the arc initiating system is determined mainly by the dc voltage level and the current it is capable of producing. The arc needs to be initiated at the right voltage level and with enough current to form and sustain an arc.
Ways to Improve SuccessfulArc Initiation
The following are some of the measures circuit breaker designers use to ensure successful arc initiation in low voltage circuit breakers.
1.Choose the Appropriate Contact Material: Arc initiation performance is significantly affected by the material used for the contacts. Generally, contacts with higher rates of electrical conduction and thermal conductivity are preferred for arc initiation. Contacts made from materials such as silver oxide, graphite, copper, and aluminum oxide are generally used for successful arc initiation.
2.Select the Optimal Contact Configuration: The overall performance of an arc initiation system is highly dependent on the contact configuration. For example, the distance between the two contacts and the number of contact points can significantly affect arc initiation. Generally, a low resistance gap between the two main contacts is preferred.
3.Use Arc Interrupters: Arc interrupters are devices that work by quickly cutting off the current flow when an arc is detected. These devices work by sensing the pressure of the arc and can quickly cut off the flow of current, thus preventing further damage to the contacts.
4.Choose the Correct Limiting Circuit Breaker: Limiting circuit breakers are designed to detect over current conditions and quickly cut off the circuit breaker’s power supply before further damage can occur. These circuit breakers are designed to limit the amount of power flowing through the contacts so that the arc is extinguished quickly.
5.Optimize the Surge Protection System: A surge protection system is designed to prevent the circuit breaker from being damaged due to sudden voltage surges. The system works by blocking the flow of current if the voltage exceeds a preset threshold level.
Conclusion
Arc initiating is an essential part of the operation of low voltage circuit breakers and is a complex physical phenomenon. Reliable arc initiation depends on a combination of appropriate contact materials and configurations, arc interrupters, limiting circuit breakers, and optimized surge protection systems. By carefully selecting and optimizing these components, successful arc initiation can be achieved.
