New compact cooled fuses from Mersen protect electrical energy storage and distribution systems against short circuits
Figure 1: The completely new compact fuse can be welded directly to a cold plate
The energy transition is giving birth to numerous new DC applications that require protection against overloads and short circuits. These news applications are challenging for current fuse design. Furthermore, clearing a fault current in a DC circuit is harder than clearing a fault current in an AC circuit. To address these challenging DC applications, Mersen has developed and patented a completely new fuse design thus down to the fuse element pattern, especially developed for DC applications. Mersen PowerPack fuse is the latest development from Mersen featuring fast clearing, low I2t and high cycling performance to prevent damage and availability of the equipment been protected.
In the coming years, thousands of new charging stations, electrical energy storage systems and DC distribution systems will be put into service. These systems are, so to speak, the backbone of the energy transition. However, the expansion of charging and storage capacities involves numerous challenges. One of these is effective protection of the infrastructure against damage from short circuits. This is essential to guarantee constant availability of systems and equipment.
Currently infrastructures are protected by standard fuses. They are usually installed in an external circuit and therefore require a certain amount of installation space, as well as their own electrical connections. On top of electrical characteristics new emerging DC applications are requiring compact and lighter fuse, ease of connection as well as minimized heat generated in the cabinet where the fuses are installed.
A Specialist for Fault Current Protection
Mersen has released and is currently developing new ranges of DC fuses up to 1500 V and 2000 V DC. The latest developments are addressing new electrical as well as mechanical requirements expected by these emerging DC applications. The very last development focuses on compact DC fuse concept, product name PowerPack fuse, for applications up to 1000 V DC, followed by 1500 V DC rated fuse as a second step.
In a standard fuse, the heat from the fuse-link is dissipated for the most part via its connections, bars and cables, as well as fuse body. However, these thermal conduction paths are away from the zone with ohmic resistance. To gain in fuse current rating still maintaining low I2t a new cooling approach was investigated.
New Cooling Concept
Mersen therefore developed a completely new type of thermal management for the new fuses. The company relies on its cooling knowledge that is used for power semiconductor modules. The fuse elements are positioned as close as possible to a heat sink thru a DCB and base plate layer, allowing an efficient heat transfer. Since heat generated by the PowerPack fuse elements are efficiently managed versus a standard fuse, more current can be carried by this new design keeping a much lower I2t. The gain is estimated at 30% in current rating, 50% in peak let thru current, 10 times less in I2t vs a standard fuse. The PowerPack current ratings of the compact cooled fuses ranged from 330 A to 1000 A with a 65 °C cooling plate. The innovative fuse cooling concept is important especially with a view toward the increasing power density of electronic components.
Compact Design Enables Fast Clearing
The innovative PowerPack thermal management design is not the only advantage of the new fuses from Mersen. As a result, better thermal management of fuse elements help reduce their size, leading to a faster melting in the event of a short circuit. Consequently, a fault current is interrupted much faster. Another striking feature is its compact size, which is three times smaller than standard fuses. Fast triggering of the new compact fuses from Mersen means that the current flow is interrupted, thus protecting downstream components. This principle offers excellent protection against short circuits down to overload current.
The PowerPack fuse original design permits to eliminate the heat generated into a cabinet. Like semiconductor module designs, SiC or Si, PowerPack fuse module design allows the heat generated by the fuse elements to be extracted thru the fuse module base plate to a heat sink, thus eliminating the heat generated in a cabinet. In addition to saving space, this design offers other advantages like better cycling.
Standardized Dimensions for Easy Installation
For fast integration of the fuses in power distribution and storage systems, Mersen designed the fuses with dimensions like conventional semiconductor modules. Installation is also facilitated thanks to the fuse module design. Connection to a laminated bus bar becomes easier, resulting as well in a lower stray inductance. Fuse module design is three times lighter than standard fuse catalog. This makes it easy for manufacturers to integrate the compact fuses in their applications.
Innovative Simulation Process
The development process for the new fuse concept took a little more than one year. The experts at Mersen used innovative numeric tools for the development that were modeled using multi-physical simulation processes. It was shown that a compact fuse design with a cooling function not only results in a lower l2t value, but also a lower peak flow than standard fuses.
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Figure 2: The graph shows the current and voltage range of the cooled compact fuse during a short-circuit test at 3660 A and 1000 A respectively
The thermal simulation also showed that the new concept increases the conductivity rating of the fuse by at least 30 percent compared to an uncooled fuse if it is mounted on a cooling plate having a temperature of 65 °C. In addition, short circuit tests confirm the excellent performance of the cooled compact fuse in accordance with DC fuse standards. For a voltage rating of 1000 A, for example, a minimum breaking capacity of 3600 A was measured – which corresponds to 3.6 times the rated current. The maximum breaking capacity of the compact fuse was tested up to 30 kA, not representing the max IR of this fuse.
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Figure 3: Simulation of the thermal management of the cooled compact fuse at 1000 A on a cooling plate with a temperature of 65 °C
Continued Development
The new cooled compact fuses represent a high-performance electrical protection concept for DC on-board applications like charging box dedicated to MegaWatt Charging as well as for stationary applications like Charging Station or EES containers applications with L/R ≤ 3 mS. Featuring low I2t, ease of connection, no heat generated in the cabinet, smaller size, lower weight, offering a clear advantage versus standard fuses. The Mersen R&D team is continuing to improve the design of the compact fuses. The next version will also be suitable for DC applications up to 1500 V.
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Figure 4: Charging points for electric cars can be easily damaged by short circuits or overloads
