Energy Storage System (ESS) is a system capable of storing electrical energy and supplying power, featuring functions such as smooth transition, peak shaving and valley filling, frequency and voltage regulation. It consists of the Battery Energy Storage System (BESS), Power Conversion System (PCS), Battery Management System, and other control devices. Well-known power fuses and switch devices are mainly applied in the battery system and PCS of the energy storage system.
The Battery Energy Storage System (BESS) is composed of several battery cells (Cell), battery modules (Module, also called battery packs or battery modules), and battery racks (Rack, also called battery cabinets), connected in series (S) and parallel (P) to form a battery "container" with system capacities of 500kW, 1MW, 2MW, 2.5MW, or 3MW.
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Controls the charging and discharging of the battery system and performs AC/DC conversion; converts electrical energy stored in the battery to AC load power (discharging), and may also convert AC power to DC to charge the battery system; therefore, the PCS may be a bidirectional DC/AC converter.
Fuse Selection Method - Voltage
The nominal rated voltage of the fuse should not be less than the rated voltage of the system.
☆ DC fuse F0 rated voltage > battery module voltage Un
☆ DC fuses F1, F2, F3 rated voltage > DC side system voltage Un
☆ AC fuse F4 rated voltage > AC side system rated voltage Un
Fuse Rated Current Selection
Based on the derating factors of fuse operating current conditions and installation conditions, the factors are decomposed as follows:
○ Ambient temperature derating factor: Kc
○ Current density derating factor of busbar (cable) connected at both ends of the fuse: Ke
○ Altitude derating factor (if any): Ka
○ Cyclic load derating factor: G. In practical applications, the operating current flowing through the fuse usually varies, often accompanied by overloads, surge impacts, or periodic load interruptions; this condition is commonly referred to as "cyclic load."
Effect of high altitude on fuse usage (Ka): According to IEC standards, fuse performance is unaffected at altitudes up to 2000 meters; above 2000 meters, for every 100 meters increase in altitude, the fuse's rated current decreases by 0.5%.
Selective Coordination Between Upstream and Downstream Fuses
Fuses F0 and F1 are connected in series in the circuit, carrying the same operating current; select the specification of F1 first based on the circuit's operating current and system voltage, then select F0 according to the "Fuse Selective Coordination" requirements. The voltage rating can be selected referring to the battery module voltage or system voltage. F0 and F1 are "upstream and downstream" fuses and require selective coordination during selection; the pre-arcing I2t of F0 > total I2t of F1: complies with the selective coordination requirements between upstream and downstream fuses in Chapter 9 of GB/T 13539.5.
This application selects fuse specifications for the battery rack: the rack consists of 208 series-connected 280Ah battery cells.
Rated operating current 140A;
Maximum operating voltage V = 208 * 3.6 = 748VDC;
Application ambient temperature is 45°C, altitude < 2000m;
1. Selection of fuse rated voltage (Un)
The fuse rated voltage should not be less than the maximum operating voltage of the application circuit, i.e., Un ≥ 748VDC; select fuse nominal rated voltage of 748VDC or above to meet the requirement.
2. Selection of fuse rated current (In)
Consider the ambient temperature derating factor Kc = 0.88 @ 45°C
Consider the derating factor Ke = 0.85 due to installation conditions affecting fuse heat dissipation.
According to the calculation formula:
Select fuse nominal rated current of 250A or above to meet the requirement.
