New Industry Products

Littelfuse High-Speed Fuses Protect Battery Storage System

April 01, 2024 by Mike Falter

The PSX series of high-speed fuses from Littelfuse respond quickly to high-voltage faults, providing circuit protection for battery energy storage systems and other high-voltage applications.

The Littelfuse PSX series of high-speed fuses can quickly interrupt fault currents up to 250 kA (DC interrupting rating) at voltages as high as 1500 VDC. 

Their quick response time, compact size, and high-power capability make these fuses ideal for circuit protection applications in large battery energy storage systems (BESS) and other high-voltage power conversion circuits.

The family of fuses supports nominal operating currents ranging from 80 A to 1400 A and is available in a space-efficient NH XL housing (1XL, 3XL) that optimizes power density.


PSX series fuses from Littelfuse

PSX series fuses from Littelfuse. Image used courtesy of Littelfuse


The fuses comply with UL248-13 safety and IEC 60269-7 battery protection standards, making them suitable for hybrid photovoltaic energy storage inverters and other high-voltage DC conversion circuits.

Littelfuse’s PSX series is now available through Rutronik.


Battery Energy Storage Systems 

Battery energy storage systems are constructed from large numbers of smaller battery cells configured into a larger system with grid-scale energy storage capabilities. Due to their high energy densities, lithium-ion cells are commonly used, but other battery chemistries can be applied, depending on the application’s priorities, such as cost, size, and capacity. 

BESS platforms are commonly used for long-duration energy storage in intermittent renewable power generation systems to assist with load balancing.


Battery energy storage for a solar farm in California.

Battery energy storage for a solar farm in California. Image used courtesy of Wikimedia Commons


Protecting BESS Circuits and Equipment

Within the BESS, modules are constructed from individual battery cells. Modules are stacked in series to form racks to store and deliver power at the BESS’s rated voltage. The number of racks within the BESS defines the system’s total energy storage capability. 

A BESS must be protected from short circuit conditions at the module and rack levels. With battery operating voltages up to 1500 V, fault conditions can lead to circuit shorts capable of producing very high currents. These high currents can damage the BESS modules or racks, creating potential safety hazards for equipment and personnel. 

At the rack level, the BPU (battery protection unit) found at the top of the rack provides protection. Littelfuse’s PSX series of fuses are well suited to rack protection due to their high DC-breaking capacity of 250 kA, 1500 V rating, and fast response time. 

For an RMS current of 50,000 A, the 1,400 A-rated fuse will have a virtual melting (pre-arcing) time of just 3 ms. This is the time span between initiation of the overcurrent condition and when instant arcing begins within the fuse and generally represents the fuse's response time to the fault condition.  


PSX series fuse response times.

PSX series fuse response times. Image used courtesy of Littelfuse


During normal operation, the PSX series fuses are designed to pass nominal load currents with minimal power losses to maintain system efficiency. The PSX3XLFL1400 (1400 A) has a watt loss of 361.9 W at 100% of rated current. Since most fuses typically operate between 60% and 80% of rated current, a watt loss correction factor curve can be used to de-rate losses based on actual fuse loading.  


PSX series watt loss correction factor

PSX series watt loss correction factor. Image used courtesy of Littelfuse


Fuses, a Good Investment

In addition to BESS rack protection, the PSX series is useful for protecting the DC conversion and inverter circuits that interface between the BESS, grid, and renewable energy source. Fuses are also a good investment since they are relatively cheap compared to the expense of repairing or replacing damaged capital equipment.  

The PSX series fuses are larger than board-mounted ones, given the power levels. The 3XL package used for the higher-rated fuses has a body size of roughly 5.1” x 2.9” x 2.9” and can be mounted flush, bolted, or DIN-mounted.  

When a fuse blows, the package provides a visual indication and a micro-switch indication that can relay fuse status to the rest of the system.