What is a Circuit Breaker?

A circuit breaker is an essential device used in electrical systems to protect circuits and electrical equipment from damage caused by excessive current. It automatically interrupts the flow of current in a circuit when it detects a fault or overload condition. This helps prevent overheating, fire hazards, and damage to electrical devices.

Ionisation and Circuit Breakers

Ionisation is a process in which atoms or molecules gain or lose electrons, resulting in the formation of charged particles called ions. In the context of a circuit breaker, ionisation plays a crucial role in the operation of certain types of circuit breakers, such as air circuit breakers and vacuum circuit breakers.

When a fault occurs in a circuit, such as a short circuit or an overload, the current in the circuit increases significantly. This increase in current causes a corresponding increase in temperature, which can lead to the formation of an electric arc between the contacts of the circuit breaker. An electric arc is a luminous discharge of current through a gap in a circuit.

Factors Facilitating Ionisation in Circuit Breakers

Several factors contribute to the facilitation of ionisation in circuit breakers. Let's discuss each of these factors and their significance:

a) Material of Contacts
The material of the contacts in a circuit breaker significantly affects the ionisation process. The contacts need to be made of materials that can withstand the high temperatures generated during the arc interruption process. Materials with good electrical conductivity, such as copper or silver, are commonly used for this purpose.

b) Increase of Mean Path
Increasing the mean path refers to the elongation of the arc path between the contacts of the circuit breaker. By increasing the distance between the contacts, the arc is stretched, and its conductivity is reduced. This elongation allows for greater cooling and facilitates easier extinguishing of the arc.

c) Increase of Field Strength
The field strength in a circuit breaker refers to the electric field intensity between the contacts. Increasing the field strength helps in breaking down the insulating properties of the medium surrounding the contacts, allowing ionisation to occur. This can be achieved by using suitable insulation materials and optimizing the design of the circuit breaker.

d) High Temperature of Surrounding Medium
A high temperature of the surrounding medium can aid in the ionisation process. When the temperature is increased, the atoms or molecules in the medium gain energy, leading to a higher likelihood of ionisation. However, it is important to note that excessive temperature can also damage the circuit breaker or compromise its insulation properties.

Conclusion

In conclusion, ionisation in a circuit breaker is not facilitated by the material of contacts. Instead, it is facilitated by factors such as increasing the mean path, increasing the field strength, and having a high temperature of the surrounding medium. The material of contacts should be chosen based on its electrical conductivity and ability to withstand the high temperatures generated during arc interruption.