Fuse have two strategies to protect the distribution system. One is fuse saving
ID: 2079652 • Letter: F
Question
Fuse have two strategies to protect the distribution system. One is fuse saving and another is fuse blowing. Briefly describe fuse blowing, fuse saving strategies and specify each one's pros/cons Which one improves SAIDI? Which one improves MAIFI? If we improve one of the reliability indices (SAIDI or MAIFI), what happens to the other? If a 40 kA lightning stroke with a rise time of 12 ms strikes a building with a grounding inductance of 15 mH, find the largest allowable grounding resistance that will limit the voltage rise to 95 kV.Explanation / Answer
(a). In fuse breaking strategy, whenever the current flowing in the circuit exceeds a specific limit, the fuse wire breaks and the entire facility which was protected by the fuse gets disconneced from the power suppy. By discinnecting the system from the power supply, this scheme actually protects the devices from getting burned in the excessive electric current.
Fuse saving scheme on the other hand, there are multiple parallel paths present. Some of the paths are connected to some of the appliances of the hosehold and one path is connected to the ground. Whenever the incoming electric current increases, it divides the current in various branches and sends the excessive amount to the ground. In this way it does the job of saving the various household electrical appliances. This type of fuse is used in modern day fuse boxes.
(b) Saidi- System Average Interruption Frequency Index: SAIDI=Total No of sustained Interruptions a year/ Total No of consumers.
Maifi-Momentary Average Interruption Frequency Index: Maifi=Total no of momentary interruptions a year/Total no of consumers.
Using fuse blowing improves MAIFI and fuse saving improves SAIDI
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