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Module 4 : Overcurrent Protection

Lecture 14 : Fuse Protection

14.6	Physics of Fuse Interruption

		Fig 14.9 and fig 14.10 shows the function of expulsion type and current limiting fuses. Notice that in expulsion type fuses, arc voltage is low, the peak first cycle current is not limited and current is interrupted after one or two loops at near nominal current zero. In contrast, in current limiting fuse, high arc voltage resulting in substantial current limiting capacity with advanced current zero. This condition is achieved at time t_i, when
14.7	Power class and Distribution class fuses :
	Fuses can also be classified by their domain of application. Based on this approach they are classified into following types:
	Power class.
	Distribution class type.
	Power fuses are tested to TRVs and X/R ratio values more likely to be encountered in or near the generating station or substation for three phase circuits. Distribution fuses have specifications more closely matched to distribution system which is further away from source or substation on a single phase or three phase system.