A circuit breaker is a device that is used to protect electrical systems from damage caused by faults, such as short circuits and over currents. It works by interrupting the flow of current when a fault is detected, preventing further damage to the system.
The main function of a circuit breaker is to extinguish the arc that is produced when the contacts of the breaker are separated during the interruption of the current flow. This arc can cause damage to the equipment being protected and can also be a source of fire or explosion if not properly extinguished.
To achieve this, circuit breakers use different methods to extinguish the arc, such as using a high-pressure gas to cool and extinguish the arc, using a magnetic field to force the arc to collapse, or using a vacuum to create a high-pressure differential that extinguishes the arc.
The following terms are commonly used in the analysis of circuit breakers:
- Interrupting rating: the current that a circuit breaker is rated to interrupt without causing damage to itself or the system.
- Trip time: the time it takes for a circuit breaker to detect a fault and interrupt the current flow.
- Response time: the time it takes for a circuit breaker to trip or open its contacts after a fault is detected.
- Voltage rating: the maximum voltage that a circuit breaker is rated to handle.
- Dielectric strength: the ability of a circuit breaker to withstand voltage without breaking down or arcing.
- Thermal rating: the ability of a circuit breaker to dissipate heat generated during the interruption of current flow.
Overall, circuit breakers are critical components in any electrical system, as they protect the equipment and people from damage or harm by quickly and safely interrupting power when a fault is detected.
What is Arc Voltage?
When a circuit breaker interrupts the flow of current, an arc is formed between the contacts as they are separated. This arc is caused by the ionization of the medium surrounding the contacts, such as air or a gas. The ionization occurs because of the high-energy electrons that are present in the medium, which are generated by the high current flow in the circuit.
The arc voltage is the voltage that is responsible for maintaining the arc between the contacts of the circuit breaker. It is the small potential difference that exists between the contacts, which creates an electrical field that ionizes the medium and sustains the arc. This voltage is typically in the range of a few hundred volts to a few thousand volts, depending on the type of circuit breaker and the medium used.
Arc voltage is an important factor to consider when designing a circuit breaker. If the arc voltage is too high, it can cause damage to the contacts or the surrounding equipment. On the other hand, if the arc voltage is too low, the arc may not be able to sustain itself, resulting in an unreliable interruption of the current.
To reduce the arc voltage and improve the reliability of the interruption, different techniques are used such as using arc chutes, shields, and magnetic fields. These techniques help to contain and control the arc, making it more stable and reducing the potential for damage. Additionally, using a high-pressure gas or vacuum inside the breaker can also help to reduce the arc voltage.
In summary, the arc voltage is the voltage that is responsible for maintaining the arc between the contacts of a circuit breaker. It is a small potential difference that is created by the ionization of the medium surrounding the contacts. It is important to consider the arc voltage when designing a circuit breaker to ensure that it can reliably interrupt the current without causing damage to itself or the surrounding equipment.
What is Restriking Voltage?
Restriking Voltage, also known as Transient Recovery Voltage, is the voltage that appears across the contacts of a circuit breaker immediately after the arc is extinguished, or at current zero during the arcing period. This voltage is transient in nature, meaning that it is only present for a short period of time.
The restriking voltage is so named because the arc can only restrike, or reignite, during the existence of this transient voltage. If the arc does not restrike during this period, it will not restrike later, and the interruption of the current will be successful.
When the circuit breaker interrupts the current flow, it causes the voltage across the circuit breaker gap to suddenly rise from zero to a very high value. This high voltage is caused by the rapid change in the current and the energy stored in the inductance of the system.
The restriking voltage is a critical factor in the performance of a circuit breaker. If the restriking voltage is too high, it can cause the arc to restrike and interrupt the current again, which can cause damage to the contacts and surrounding equipment. On the other hand, if the restriking voltage is too low, the arc may not be able to restrike, and the interruption of the current may not be successful.
What is Recovery Voltage?
Recovery voltage, also known as final recovery voltage, is the voltage that appears across the contacts of a circuit breaker after the final arc extinction and after all the transients have died out. The frequency of recovery voltage is the same as the supply frequency.
When a circuit breaker interrupts the current flow, an arc is formed between the contacts as they are separated. This arc is caused by the ionization of the medium surrounding the contacts, such as air or a gas. The ionization occurs because of the high-energy electrons that are present in the medium, which are generated by the high current flow in the circuit.
During the interruption of current, the arc voltage, restriking voltage and recovery voltage will appear across the circuit breaker contacts.
The arc voltage is the voltage that is responsible for maintaining the arc between the contacts of a circuit breaker. It is a small potential difference that is created by the ionization of the medium surrounding the contacts.
The restriking voltage is the voltage that appears across the contacts of a circuit breaker immediately after the arc is extinguished, or at current zero during the arcing period. This voltage is transient in nature, meaning that it is only present for a short period of time.
The recovery voltage is the voltage that appears across the contacts of a circuit breaker after the final arc extinction and after all the transients have died out. The frequency of recovery voltage is the same as the supply frequency.
The recovery voltage is the final voltage that appears across the circuit breaker contacts after the final arc extinction. The circuit current is interrupted and no ions are present in the gap between the contacts. At this condition, the dielectric strength of the medium (air or oil) between the contacts will be high, which is strong enough to avoid the breakdown by the restriking voltage. As a result, the final arc extinction takes place and circuit current is interrupted.
What is Fault Clearing Time in circuit breaker?
Fault Clearing Time is the amount of time it takes for a circuit breaker to detect and interrupt a fault, such as a short circuit. It is the sum of three different time periods: relaying time, breaker operating time, and arcing time.
Relaying time is the time it takes for the relays, which are connected to the secondary of CTs and PTs, to detect the fault and send a signal to close the trip circuit of the circuit breaker. This time period is influenced by the sensitivity and response time of the relays, as well as the distance between the relays and the circuit breaker.
Breaker operating time is the time it takes for the circuit breaker to receive the signal from the relays and open its contacts. This time period is influenced by the design and construction of the circuit breaker, as well as the mechanical and electrical characteristics of the breaker.
Arcing time is the time it takes for the arc to be extinguished after the contacts of the circuit breaker have been separated. This time period is influenced by the medium used in the circuit breaker, the design of the circuit breaker and the techniques used to extinguish the arc.
The fault clearing time is the total time from the initiation of the fault to the final extinction of the arc. It is the sum of the relaying time, breaker operating time, and arcing time. It is an important parameter to consider when designing a circuit breaker, as it indicates the speed at which a fault can be detected and cleared, which is important to minimize the damage to the equipment and the power system.
In summary, Fault Clearing Time is the time it takes for a circuit breaker to detect and interrupt a fault, it is the sum of three different time periods: relaying time, breaker operating time, and arcing time. It is an important parameter to consider when designing a circuit breaker, as it indicates the speed at which a fault can be detected and cleared, which is important to minimize the damage to the equipment and the power system.
The formula for Fault Clearing Time is:
Fault Clearing Time = Relaying Time + Breaker Operating Time + Arcing Time.
This means that the total time it takes for a circuit breaker to detect and interrupt a fault is the sum of the time it takes for the relays to detect the fault and send a signal to the circuit breaker, the time it takes for the circuit breaker to open its contacts, and the time it takes for the arc to be extinguished after the contacts have been separated.
Difference among Arc Voltage, Restriking Voltage and Recovery Voltage:
The main difference among Arc Voltage, Restriking Voltage, and Recovery Voltage is the timing of when they appear across the circuit breaker contacts during the interruption of current.
Arc Voltage is the voltage that is responsible for maintaining the arc between the contacts of a circuit breaker. It is a small potential difference that is created by the ionization of the medium surrounding the contacts. It appears across the contacts while the current is flowing and the arc is sustained.
Restriking Voltage, also known as Transient Recovery Voltage, is the voltage that appears across the contacts of a circuit breaker immediately after the arc is extinguished, or at current zero during the arcing period. This voltage is transient in nature, meaning that it is only present for a short period of time. It has potential to restrike the arc if it is not controlled.
Recovery Voltage, also known as final recovery voltage, is the voltage that appears across the contacts of a circuit breaker after the final arc extinction and after all the transients have died out. The frequency of recovery voltage is the same as the supply frequency. It appears once the final arc extinction takes place and the circuit current is interrupted, it is of normal frequency RMS voltage which is approximately equal to the system voltage.
In summary, Arc Voltage is the voltage that maintains the arc during the current flow, Restriking Voltage is the voltage that appears immediately after the arc is extinguished, with potential to restrike the arc, Recovery Voltage is the final voltage that appears after the final arc extinction, after all transients have died out.