Metal Oxide Varistor Design Optimization and Main Breaker Branch Switch
Control of A Progressively Switched Hybrid DC Circuit Breaker
Abstract
In this work, metal oxide varistor (MOV) design optimization and
switching control in the main circuit breaker (MCB) branch of a
progressively switched hybrid DC circuit breaker (DCCB) is presented. A
progressively switched hybrid DCCB can achieve faster fault isolation
with reduced peak fault current magnitude and transient recovery voltage
compared to a regular hybrid DCCB due to its modified switching
strategy. Consequently, thermal stress on the semiconductor devices in
MCB is significantly reduced. Analytical model of the system dynamics
during fault isolation with progressive switching is derived to
demonstrate the switching scheme’s effect on the energy-absorbing
component, MOV, during turn-off process. Derived analytical model in
conjunction with the displacement curve of the fast mechanical switch of
the hybrid DCCB is utilized to optimize the components of the main
circuit breaker branch to reduce MOV degradation through asymmetric
energy dissipation. A model of the circuit breaker is built in PSCAD to
validate the performance of the proposed optimization method in a
10kV/250A system with four stage progressive switching. Additionally, a
low voltage system model at 380V is developed in PLECS for two stage
progressive switching that works as the basis of experimental
validation. This includes both look up table based MOV model and device
thermal model for junction temperature estimation. Experimental results
are provided for a 380V system to demonstrate reduced fault current peak
in a progressive switching and near uniform energy absorption in
optimally selected MOVs