Design of Modular Battery Energy Storage System (BESS)

Electrical Short Circuit Study and UL9540 Arc Flash Assessment

MPR’s novel approach for short circuit analysis and arc flash assessment streamlines component selection and UL 9540 certification of modular BESS systems.

The Challenge

Short Circuit and Arc Flash Analysis of Modular BESS

Short circuit duration, peak short circuit current and arc flash incident energy are important design considerations of a BESS. Fault current duration and magnitude inform the design and selection of protection devices, and bounding arc flash incident energy is needed to select appropriate PPE for maintenance of energized equipment. The number of BESS modules, and the fault location, impact all three considerations such that a fault location may be bounding for one design consideration but not the others. Consideration of BESS fuse behavior during a fault is essential. BESS fuses are sized to selectively and rapidly clear faults to lower the short circuit duration, peak current and arc flash incident energy. Commercial DC analysis software generally does not support dynamic DC fault analysis or dynamic fuse clearing analysis.

The Solution

A first-of-a-kind BESS analysis tool

MPR’s first-of-a-kind transient DC short circuit tool can quickly analyze thousands of modular BESS fault scenarios. Our tool accounts for the circuit time constants and integrates fuse i2t to model fuse melting time. Short circuit time series data is post processed to calculate arc flash incident energy, working distance, and required personal protection equipment (PPE) associated for each short circuit scenario. Incident energy calculations include the Paukert and Stokes & Oppenlander methods for both open air and DC arc-in-a-box arc flash scenarios.

The Results

BESS design improvements

MPR revealed the modular BESS short circuit fault behavior and identified appropriate design constraints for those faults. Arc flash incident energies and peak short circuit currents were identified for all modular BESS configurations, supporting UL 9540 certification and informing future BESS design improvements.

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