Modeling a voltage source converter assisted resonant current DC breaker for real time studies

Abstract

In order to test protection performance of future multi-terminal HVDC grids where DC circuit breakers (DC CBs) play an important role, a DC CB model in real time test environment should be developed. It is well known that a DC CB needs to interrupt DC faults very quickly in order to avoid converter damages and to ensure security of supply. The total current interruption time consists of a fault detection time, which is needed for the DC protection to provide a trip command to the DC CB, and a DC CB interruption time. Thus, it is necessary to demonstrate the performance of associated protective devices through real time simulations, before these devices can be implemented and commissioned in practice. This paper presents a detailed modeling of the voltage source converter assisted resonant current DC circuit breaker (VARC DC CB) in real time simulation environment based on RTDS. The proposed model provides sufficient representation of the circuit breaker for system level studies. External current-voltage characteristics of the proposed VARC DC CB models replicate the ones of the device in the real world. The proposed model of the breaker is tested in a simple test circuit including a DC voltage source and a T-scheme HVDC cable. Additionally, a case study has been presented by making use of a protection algorithm in a multi-terminal HVDC grid with frequency dependent parameters of the HVDC cables to show both protection performance and current interruption.