This document discusses fuse coordination in power systems. It explains that when multiple fuses are used in a system, they must be coordinated so that only the fuse closest to a fault operates while others remain unaffected. This coordination is achieved by using the time-current characteristic curves of the fuses. The document provides criteria for fuse-fuse coordination, stating that the maximum clearing time of the main fuse for all fault currents should be no greater than 75% of the minimum melting time of the backup fuse in order to ensure discrimination between fuses. Examples are given to demonstrate how to apply this criteria.

1. Dr. Ahmad Al-Subhi
SWITCHGEAR AND PROTECTION
Lecture 3
FUSE
Prepared by: Dr. Ahmad Al-Subhi

2. 3a. Introduction to Fuse.
3b. Fuses Coordination in Power System.
3c. Effect of Ambient Temperature on Fuse
…..Performance.
Outline:
Prepared by: Dr. Ahmad Al-Subhi

3. Dr. Ahmad Al-Subhi
SWITCHGEAR AND PROTECTION
Lecture 3b
FUSES COORDINATION IN POWER
SYSTEM
Prepared by: Dr. Ahmad Al-Subhi

4. Fuse-Fuse Coordination:
- When there are two or more fuses in the system, there should be
coordination between them.
- This is concerned with correct operation of correct fuse in such
a way that only the fuse nearest to the fault (main fuse) operates
while the other fuse remains unaffected (backup fuse).
- Thus, the coordination between fuses connected in series, can
be achieved by using the TCC curves of the fuses.
Prepared by: Dr. Ahmad Al-Subhi

5. Prepared by: Dr. Ahmad Al-Subhi
Criteria for fuse–fuse coordination: t1 < 0.75×t2
Criteria: (rule of thumb)
maximum clearing time for
the main fuse (downstream
fuse) should be no greater
than 75% of the minimum
melting time of the backup
fuse (upstream fuse) for all
currents up to the maximum
fault current that the pair
will experience.
discrimination
interval

6. Example 4: for a fault of 1000
A at the main fuse:
- maximum clearing time of
the main fuse is 0.0632s.
- This value should not exceed
75% of the minimum
melting time of the backup
fuse.
- 0.0632 < 0.75×0.0901
- 0.0632 < 0.067575 s.
Prepared by: Dr. Ahmad Al-Subhi

7. Example 5: How if the
minimum melting time of the
backup fuse is 0.08 s:
- maximum clearing time of
the main fuse is 0.0632s.
- This value should not exceed
75% of the minimum
melting time of the backup
fuse.
- 0.0632 < 0.75×0.08
- 0.0632 < 0.06 s.
Prepared by: Dr. Ahmad Al-Subhi