A. Capacitor Element Short Circuit Each capacitor element is an insulated foil capacitor which is insulated with a solid insulation film and insulating liquid. The failure mode of the capacitor element is an insulation film failure across the element foil capacitors and shorting the foil.
Capacitors in Small-Signal Analysis: Since we're now analyzing the behavior under AC conditions (albeit small signals), capacitors no longer behave as open circuits. They have a reactance given by XC = 1 jωC X C = 1 j ω C, where ω ω is the angular frequency of the signal.
In fact, that's exactly what you do. Capacitors are only short circuits when you consider the "small signal" component after you found the DC linearized point. So capacitors are open when considering the DC component, then shorts (or at least small negative imaginary impedance) when solving for the non-DC small signal response.
Capacitors used in firing sets and other high discharge current applications are discharge tested to verify performance of the capacitor against the application requirements.
The DC-link capacitor discharge is unique to the DC fault. Taking advantage of this phenomenon, the proposed fault detection method is designed such that it examines if the fault current has any trace of current originated from DC-link capacitor.
By having their shorted terminals, the voltage thereof is zero (more precisely, the potential difference between them), so that this element is not operational in the circuit, and can be removed for analysis. The other two capacitors are in series, hence that: