Bi-directional DC Circuit Protection Technology for Photovoltaic Applications

The demand and challenge for DC circuit protection products continue to grow as renewable energy installations further expand with increasing system voltages such as photovoltaic systems. This drives the need for cost effective and compact DC circuit protection devices. Most of the products on the market for DC circuit protection and isolation disconnect are based on traditional AC products with poles connected in series to meet the DC interruption performance requirement for photovoltaic systems. A few of them do utilize permanent magnets design to achieve effective DC interruption performance required by DC electrical systems. However, they typically have only unidirectional switching capability. In this paper, a DC arc interruption technology has been developed to achieve bidirectional interruption capability at 600VDC per pole of a molded case circuit breaker. Unique arc chamber structure was implemented employing permanent magnets to allow effective arc motion and arc splitting with minimum change of existing AC switching devices. Arc motion gas dynamics during switching operation was investigated by both numerical simulation and experimentation. Tests were carried out to verify the feasibility of the technology. Test results show that this technology enables the DC single-pole molded case circuit breaker to not only be able to interrupt over current fault, but also be able to switch low level current such as a few Amperes.