A suitable protective system is of highest importance for an interconnected system. It is
the duty of circuit breaker to remove a faulty section as quickly as possible from the
system and if desired it should be able to insert the removed section in the circuit. While
breaking the circuit, an arc appears across the circuit breaker contacts. Field emission
and subsequent thermal ionization are the causes for initiation and maintenance of the
arc. It is further observed that natural current zero is a favorable point for arc extinction.
At natural current zero, there is a transient phenomenon which gives rise to high frequency
transient voltage whose peak value may be at the most double the peak value of phase
voltage. At natural current zero for final arc extinction, the voltage buildup across the
circuit breaker contacts is important. The restriking voltage is defined as transient voltage
which appears across the circuit breaker contacts at the instant of arc being extinguished
(Ravindranath and Chander, 1977; and Ram and Vishwakarma, 1995). There are various
factors which affect the severity of restriking voltage. These factors include power factor,
circuit conditions, current asymmetry and armature reaction.
At the time of circuit breaker contact separation, the effect of these factors involves
uncertainty owing to the random nature of these parameters. Further, the Rate of Rise of
Restriking Voltage (RRRV) depends on circuit inductance and capacitance. Uncertainty
is also there in the values of inductance and capacitance. In view of this, maximum
RRRV is also a random variable. Hence, in this paper, a methodology has been presented
for statistical evaluation of peak value of Restriking Voltage (RV) and RRRV using Monte
Carlo Simulation (MCS). |
