Numerical Modeling of High Voltage Circuit Breaker Arcs And Their Interaction With The Power System
ABSTRACT: In this work, the interaction between series
connected gas and vacuum circuit breaker arcs has been studied.
The breakdown phenomena in vacuum interrupters during the post arc
current period have been of special interest.
Numerical models of gas and vacuum arcs were developed in the
form of black box models. Especially, the vacuum post arc model was
implemented by combining the existing transition model with an ion
density function and expressions for the breakdown mechanisms. The test
series studied reflect that for electric fields on the order of 100MV/m over
the anode, the breakdown of the vacuum gap can result from a combination of
both thermal and electrical stresses. For a particular vacuum device,
the vacuum model helps to find the interruption limits of the electric field
and power density over the anode.
The series connection of gas and vacuum interrupters always performs
better than the single gas device. Moreover, to take advantage of the good
characteristics of both devices, the time between the current zero crossing
in each interrupter can be changed. This current zero synchronization is
controlled by changing the capacitance in parallel to the gas device. This
gas/vacuum interrupter is suitable for interruption of very stressful short
circuits in which the product of the dI/dt before current zero and the dV/dt
after current zero is very high. Also, a single SF6 interrupter can be
replaced by an air circuit breaker of the same voltage rating in series with
a vacuum device without compromising the good performance of the SF6 device.
Conceptually, a series connected vacuum device can be used for high
voltage applications with equal distribution of electrical stresses between
the individual interrupters. The equalization can be made by a sequential
opening of the individual contact pairs, beginning with the interrupters that
are closer to ground potential. This could eliminate the use of grading
capacitors.
Copyright 1997
by
Lionel R. Orama
All Rights Reserved
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