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Fuses and Relay Circuits
Published in Dorin O. Neacşu, Automotive Power Systems, 2020
The main parameters for a fuse are as follows. The I2t rating represents the amount of energy let through by the fuse element when it clears the electrical fault.The breaking capacity is the maximum current that can safely be interrupted by the fuse.The voltage rating of the fuse must be equal to, or greater than, the open-circuit voltage.The manufacturer may specify the voltage drop across the fuse at a rated current.
Fault Analysis and Protection Systems
Published in Antonio Gómez-Expósito, Antonio J. Conejo, Claudio A. Cañizares, Electric Energy Systems, 2018
José Cidrás, José F. Miñambres, Fernando L. Alvarado
From the point of view of the relay, independently of the technology used for its construction, the two main characteristics that the circuit breaker must meet are Rapid separation of the main contacts, to minimize the time need to carry out the opening operation. When the relay gives the order to perform the opening to insulate the fault, the trip circuit is activated and, therefore, the contacts begin to separate. However, the initial separation of the contacts does not imply the immediate opening of the circuit, as an arc is initially established that maintains the current circulation between the two contacts. The circuit break occurs in the first cross zero current, but, if the separation of the contacts is not sufficient at that time, the voltage between them means that the arc is established again. The definitive circuit break, and therefore the opening of the circuit, occurs in the subsequent cross zero current, as the contacts have then had time to sufficiently separate to prevent the arc from linking up. The faster it takes for the contacts to separate, the less time will be needed to reach the distance that guarantees the opening of the circuit. Usually, the definitive circuit break in general occurs during the second or third cross zero current.Sufficient breaking capacity to guarantee the interruption of the maximum short-circuit current that may occur at the point where the circuit breaker is installed. The breaking capacity is closely linked to the capacity of the dielectric medium to also undertake the function of cooling medium, as it must be capable of channeling outside the energy released in the arc extinction process. It is common practice to use various arc extinction chambers in series, whose contacts must be operated in a synchronized manner, to increase the breaking capacity on HV lines. This fact does not introduce any modification from the relay point of view, as it is a single tripping order in any case and it is the circuit breaker that must incorporate the necessary mechanisms to ensure the synchronization.
Fault Analysis and Protection Systems
Published in Antonio Gómez-Expósito, Antonio J. Conejo, Claudio Cañizares, Electric Energy Systems, 2017
José Cidrás, José F. Miñambres, Fernando L. Alvarado
From the point of view of the relay, independently of the technology used for its construction, the two main characteristics that the circuit breaker must meet are Rapid separation of the main contacts, to minimize the time need to carry out the opening operation. When the relay gives the order to perform the opening to insulate the fault, the trip circuit is activated and, therefore, the contacts begin to separate. However, the initial separation of the contacts does not imply the immediate opening of the circuit, as an arc is initially established that maintains the current circulation between the two contacts. The circuit break occurs in the first cross zero current, but, if the separation of the contacts is not sufficient at that time, the voltage between them means that the arc is established again. The definitive circuit break, and therefore the opening of the circuit, occurs in the subsequent cross zero current, as the contacts have then had time to sufficiently separate to prevent the arc from linking up. The faster it takes for the contacts to separate, the less time will be needed to reach the distance that guarantees the opening of the circuit. Usually, the definitive circuit break in general occurs during the second or third cross zero current.Sufficient breaking capacity to guarantee the interruption of the maximum short-circuit current that may occur at the point where the circuit breaker is installed. The breaking capacity is closely linked to the capacity of the dielectric medium to also undertake the function of cooling medium, as it must be capable of channeling outside the energy released in the arc extinction process. It is common practice to use various arc extinction chambers in series, whose contacts must be operated in a synchronized manner, to increase the breaking capacity on HV lines. This fact does not introduce any modification from the relay point of view, as it is a single tripping order in any case and it is the circuit breaker that must incorporate the necessary mechanisms to ensure the synchronization.
A Millman based alternate to symmetric component methods for fault level calculations in marine power systems
Published in Journal of Marine Engineering & Technology, 2022
The RMS Symmetric and peak fault levels are of importance when selecting the circuit breaker used to protect a circuit. The circuit breaker has to be rated to break the RMS Symmetric fault current at the point in time at which its contacts open. This parameter is termed the circuit breaker’s ultimate breaking capacity (Icu). Further to this the circuit breaker has to be rated to withstand the peak fault current that would instantaneously flow if it was closed onto a circuit that was in fault. This parameter is termed the circuit breaker’s rated making capacity (Icm).