DC Fault Protection Strategy for Medium Voltage Integrated Power System: Development and Assessment

In medium voltage direct current (MVDC)-based power distribution scheme DC faults can cause instant disruption in service continuity to various connected loads. Many integrated power systems (IPS) found MVDC as a better replacement of MVAC for detection, isolation as well as protection against DC faults. DC fault protection strategy for developed MVDC-IPS system (which is accompanied by LVDC subsystem), is proposed here by introducing a modified series Z-source breaker circuitry which minimize fault or transient current that reflects back at the DC source by keeping its common ground return path and to re-energize the DC load after fault clearance. The versatility of the proposed idea also include to energize the loads after the fault clearance. The main problem is that a large value of fault/transient current 0 that reflects back at the source and SCR (when it stops commutation). This large reflective current value is much greater than the value of the SCR peak cycle surge value and can damage the SCR permanently. To overcome this problem in the developed technique, an addition of series resistance is made with capacitors which minimize the effect of transient level on SCR and source. Furthermore, due to this resistance the other component size or value is decreased which helps in minimizing the effect of transient current at SCR and source. Another aim is to build the breaker structure in such an optimize way so that to minimize dissipation and weight as compared to its classic structure along with enhancement of efficiency. The proposed strategy of DC fault for IPS is validated through two case studies done in PSCAD simulations.