Deployment Logic Of Vertical Fuse Isolating Switches In Photovoltaic Inverters

DC-side power distribution protection for photovoltaic inverters has always been an unavoidable technical issue in power plant design. With the widespread adoption of high-power components and the increase in the number of series and parallel connections, the risk of DC-side short circuits has risen accordingly. Against this backdrop, vertical fuse switch disconnector equipment has gradually become one of the mainstream configuration options.

Why deploy two types of devices on the DC side simultaneously?

Fuses and disconnectors have fundamentally different functional roles. Fuses are passive overcurrent protection devices, relying on the thermal melting characteristics of the fusible element to disconnect the fault circuit without relying on any external control circuits; disconnectors, on the other hand, are centered on the physical disconnection point, primarily serving maintenance and repair scenarios, providing maintenance personnel with a clear electrical isolation status. Their functions are complementary, not substitutive.

nhrt40 vertical fuse switch disconnector integrates these two functions into one, adopts a vertical breaking method in structure, and makes the contact travel visible and the disconnection status intuitive, meeting the technical requirements of IEC 60269-6 for photovoltaic-specific fuses, while also taking into account the specification requirements of isolation devices for obvious disconnection points. This integrated solution is widely used between the combiner box and the inverter's DC input terminal.

Typical Deployment Methods in Photovoltaic Inverter Scenarios

In string inverter configurations, vertical fuse disconnect switches are typically installed in each MPPT input circuit. The specific deployment logic is as follows:

• For single MPPTs connected to 2 or fewer strings: During a short circuit, the backflow current does not exceed one times the module short-circuit current. The vertical fuse disconnect switch can simultaneously perform overcurrent protection and isolation functions.

• For single MPPTs connected to 3 or more strings: According to the IEC 62548 standard, each string must be independently configured with an overcurrent protection device. In this case, the vertical fuse disconnect switches are connected in series, forming a complete multi-level protection architecture.

• In centralized inverter combiner boxes: Vertical fuse disconnect switches are typically centrally arranged at the DC bus input end, working in conjunction with the string detection function of the intelligent combiner box to achieve a linked response of fault location and physical disconnection.

Compared to deploying fuses or disconnect switches separately, the integrated structure of vertical fuse disconnect switches is more rational in terms of both space occupation and maintenance operations, and is one of the DC-side protection configuration solutions recommended by mainstream inverter manufacturers at home and abroad.