High-voltage circuit breakers have been extensively used in
electrical power systems in order to make, carry, and break the
current within specified times, in normal and abnormal operating
conditions. Degradation is caused by several types of stress
and aging. In order to implement an economical monitoring
system for large circuit breakers in transmission and distribution
networks, selection of the monitoring parameters is critical.
These parameters, grouped according to importance, are listed
in Table 2.
During circuit breaker operation, switching arcs erode and
oxidize the contact surfaces, creating a high resistance layer that
can generate high temperatures at the contacts. Contact resistance,
voltage drop, and temperature rise are all related to contact
arc erosion and the formation of oxidized products such as
tungsten oxides and silver tungstate. Fifty consecutive contact
resistance values, obtained after various numbers of cycles,
are plotted in Figure 6. Figure 7 is the corresponding Weibull
probability plot. The data show that contact resistance increases
rapidly with increasing number of cycles, and there is a significant
probability that the increase of resistance will result in a
temperature rise exceeding the allowed maximum. Traditional
contact resistance, as a function of number of switching cycles,
has always varied widely, especially in Ag/W contacts. This is
because the arc erosion products are formed dynamically, and
contact is made with considerable force.
Unfortunately these static resistances, measured when the
breaker remains in a closed position, do not give any indication
of the condition of the arcing contacts. To evaluate the latter
without dismantling the circuit breaker, a dynamic contact