In the event of a bolted fault, a large amount of thermal
energy and magnetic force can be produced. In accordance
with various standards, protective devices and current
carrying components are to be properly rated to withstand
and interrupt the fault.
As seen in Figure 8.1, fault current can “flow” down or up
a circuit when a short is created. The current flowing from
the utility (the larger amount) is represented by the arrows
pointing in the direction of the motor, and the contribution
returning from the motor (the smaller amount) can been
seen in the arrows pointing back toward the utility. The
reason for this back contribution is the spinning rotor of
the motor will not instantaneously stop, and the magnetic
field will remain for a short number of cycles. This occurs
even though voltage in the event of a bolted fault would
theoretically equal zero (0).
The danger is that if equipment is not properly rated
for the available fault current, catastrophic failure can
occur. Through the use of specialized software and the
associated equipment libraries, Electrical Power and
Safety Company can help advise if your existing electrical
infrastructure is rated to handle a worst-case scenario
bolt fault. Please keep in mind that with an ever-changing
electrical grid and utility power supply, the worst-case
bolted fault can vary over time.
