Training

The conveyance of knowledge relating to protection devices is one of the foremost objectives of PRO FUSE INTERNATIONAL. In this way, manufacturers and end users are given the opportunity of being able to make a responsible choice, based on objective criteria, between the various protection devices, the ultimate target being electrical switchgear with optimum operational reliability and maximum durability whatever the application may be.

Electrical Safety in fuses

Safety in fuses English
Safety in fuses German

Training advice on fuse links

Is the peak current (cut-off) current important?
Short circuits are dangerous for several reasons:

•  The destructive electrodynamics effects increase as the square of the peak current value, during the short circuit.
• The destructive thermal effects increase in proportion with the I²t reached during this short circuit.

Fuselinks are designed to drastically limit both these effects.
For the prospective short circuit current of 10,000 Amp rms with a totally asymmetrical current, the maximum value could reach 25,000 Amp peak. A 100A gG fuselink limits the first peak to 8,000 Amp, less than the third part of the prospective maximum value. The destructive electrodynamic effects are reduced by 90% (8,000/25,000)2.


Why is current limitation so important?
If a protective device cuts off a short circuit current in less than one half cycle, before it reaches its total available (and highly destructive) peak value, the device is "current limiting". It restricts fault currents to such low values that a high degree of protection is given to circuit components against even very high short circuit currents. This minimises the needs of other components to have high short circuit current "withstand" ratings.
If not limited, short circuit currents in industrial applications can reach tens of thousands of amperes in the first half cycle after the start of a fault. The heat that can be produced in circuit components by the immense energy of short circuit currents can cause severe insulation damage or even explosion. At the same time, huge magnetic forces developed between conductors can crack insulators and distort and destroy bracing structures. It is therefore important that a protective device limits fault currents before they reach their full potential level.
A fuse interrupts a short circuit current very quickly. Consequently the energy let-through is very low.
An example:-
A fuse 100A, 20kA rms, 400V reduces an initial, half cycle, fault current of 4,000,000A2s to 46,000 A2s. This ratio is indicated in the picture below.



Why is overcurrent protection required?

 There are many factors that contribute to the occurrence of overcurrents, such as general deterioration and accidental damage. The effect of overcurrent on electrical equipment can be dramatic if no appropriate protection is provided:
 

• Distortion of conductors or busbars.
• Vaporisation of metal.
• Ionisation of gases.
• Arcing, fire and explosion.
• Insulation damage.

Apart from being hazardous to personnel, significant economic losses can result from downtime and repairs required to restore damaged equipment. The most widely used and respected overcurrent protective device is the fuselink.
 

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