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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.
3 Electrical Transients
Published in C. Sankaran, Power Quality, 2017
During fault conditions, large currents are generated in an electrical system. The fault currents are interrupted by overcurrent devices such as circuit breakers or fuses. Figure 3.17 shows a simplified electrical circuit where an electrical fault is cleared by a circuit breaker. C represents the capacitance of the electrical system up to the point where the overcurrent device is present. Interruption of the fault current generates overvoltage impulse in the electrical system, and the magnitude of the voltage depends on the amount of fault current and the speed with which the fault is interrupted. Older air circuit breakers with slower speed of interruption produce lower impulse voltages than vacuum or SF6 breakers, which operate at much faster speeds during a fault. While using vacuum or SF6 technology to clear a fault quickly and thereby limit damage to equipment is an important advantage, a price is paid by the generation of higher level voltage transients. Once the fault is interrupted, the generated voltage impulse can interact with the inductance and capacitance of the electrical system and produce oscillation at a frequency much higher than the fundamental frequency. The oscillations are slowly damped out by the resistance associated with the system. The response of the system might appear somewhat like what is shown in Figure 3.18. The voltage can build up to levels equal to twice the peak value of the voltage waveform. The overvoltage and associated oscillations are harmful to electrical devices.
Transmission and Distribution Systems
Published in Amitava Sil, Saikat Maity, Industrial Power Systems, 2022
Advantages of per unit are (i) dealing with numeric near unity rather than over a wide range (ii) provides more meaningful comparison of parameters of machines with different ratings (iii) the avoidance of 3 factor in the calculation for a three-phase system (iv) enable the use of symmetrical components for electrical fault analysis (v) ideal transformers are eliminated as circuit elements. This results in a large saving in component representation and reduces computational burden.
DC-grid system for ships: a study of benefits and technical considerations
Published in Journal of International Maritime Safety, Environmental Affairs, and Shipping, 2018
Kyunghwa Kim, Kido Park, Gilltae Roh, Kangwoo Chun
Arc flash is a dangerous condition associated with the release of energy caused by an electrical fault. Therefore, it is recommended to minimize the dangerous effects of the arc flash on personnel in both AC and DC-grid. In this regard, IEEE standard 1584 (2002) provides techniques for designers and facility operators to apply in determining the AC arc flash hazard distance and the incident energy to which employees could be exposed during their work on or near electrical equipment. However, there are no unified standards or guidelines for the DC arc flash yet.