SHORT CIRCUITS

Effects of Short Circuits

Short circuits can cause damage to electrical installation by giving rise to

§              Thermal Stresses

§              Mechanical Stresses

§              Arcing

Thermal Stresses

   Heavy fault current causes temp. of cables and busbar rise enormously even            if  the circuit is interrupted in a few cycles.

§  ( Temp. rise is proportional to I*I*t where  I= Current flowing in the conductor and   t = the duration of the current flow)    

§  Frequent repetitions of these stresses will reduce the life of the insulation of cables, busbar supports etc. leading to a permanent damage to the installation

Mechanical Stresses

o   Heavy fault currents set up mutual forces between current-carrying conductors causing them to be mechanically stressed.

§  (This force is proportional to I*I/d where   I = Current I the conductor and d = Distance between the conductors )                  

§  These forces can cause conductors to bend or break and also mechanically damage the insulation of the cables, bus supports etc

ARCING

§  An arc, which occurs at the point of contact separation in a breaker, represents an enormous concentration of energy and can cause severe damage at the point of arcing by burning away the contact tips, and adjacent conductors and insulation.

§  Greater the distance of contact separation, higher are the effect of arcing

• With arcing, the time duration is extremely important because the feet of the arc tend to move towards the supply source, spreading the area of damage.