Capacity of capacitor installed in PDCs for voltage variation suppression during short circuits in HVDC power feeding systems

Abstract

This paper describes a molded-cased circuit breaker (MCCB) for higher voltage direct current (HVDC) power feeding systems. To protect circuits from fault current, such as an overcurrent or a short circuit current, an overcurrent circuit breaker is installed in power feeding systems. When a large-scale overcurrent circuit breaker is required, the case which uses MCCBs in HVDC power feeding system can be considered. However, the interrupting time of MCCBs is generally longer than that of semiconductors and fuses. Therefore, a short circuit current continues flowing for about several milliseconds until it is intercepted, and the voltage of the power feeding system continues to drop. This results in a large voltage variation of the power feeding system after a short circuit occurs when using MCCBs. We evaluated the degree of the power feeding system voltage after a short circuit occurs when using a commercial MCCB as an overcurrent circuit breaker in an HVDC power feeding system. We confirmed through experiments that the capacity of capacitor was the main factor in the voltage variation during a short circuit. We clarified the key factors concerning of the configuration of the cable condition and power distribution cabinet (PDC) for the voltage suppression when a short circuit occurs in HVDC power feeding systems equipped with MCCBs. I. INTRODUCTIONWith the rapid spread of information and communication technology (ICT) services, power consumption of telecommunication buildings and datacenters inevitably increases. The increase in power consumption is related to the increase in CO2 emissions and employment costs. Therefore, loss reduction of electric power is required in power feeding systems.Direct current (DC) power feeding systems provide electric power to ICT equipment more efficiently than alternative current (AC) power feeding systems because DC systems have fewer conversion stages than AC systems [1]. DC power feeding systems are also more reliable than AC systems because the DC systems have a direct connection to the batteries. Schematics of AC and DC power feeding systems are shown in Fig. 1 (a) and (b), respectively.