How Nexamp Energy uses ETAP for higher quality and accuracy DC Arc Flash Analysis in BESS

The various types of battery chemistries used have significantly different short-circuit current behavior. To determine the clearing time results for the Fuse C-areas, it's key to decide on the key parameters on which DC Arc Flash calculation methodologies are based.

Terry McKinch, Electrical Safety Manager at Nexamp Energy Inc.

This case study evaluated the modeling of a DC Battery Energy Storage System for a project in California. BESS systems are crucial for managing energy supply and demand, particularly when combined with renewable energy sources such as solar and wind, which can be intermittent. The study emphasized that large grid-scale BESS installations require careful modeling to ensure efficiency while maintaining safety for maintenance purposes.

Nexamp Energy is a clean energy company founded in 2007 that deploys and operates solar energy assets throughout the United States. It offers community solar programs, energy storage solutions, and power purchase agreements to provide savings and sustainable energy options for businesses and homeowners, with a portfolio of over 1.5 gigawatts of generating and in-construction capacity. Nexamp primarily serves the renewable energy sector, developing large-scale solar projects and energy storage systems.

Location: Boston, Massachusetts, USA

Year: 2024

Conducting feasibility studies on different scenarios to predict high incident arc flash energy events

Challenges

Lack of accurate electrical calculation methods for DC Arc Flash Incident Energy that avoid both overly conservative results and underestimation
Lack of analysis methods that considers the highly-variant nature of battery short circuit current
How to include specific properties of different battery types (lithium-ion, lead-acid, nickel-based, flow, etc.) in modeling to consider their unique characteristics in the analysis
How to integrate the various conductor and cell arrangements such as series, parallel, and bus systems into the simulation

Products used

ETAP software, featuring:

DC Load Flow - Calculate bus voltages, branch power flows and currents in a direct current (DC) system and compares calculated values against bus voltage limits, cable ampacities, and source capacities
DC Short Circuit - Analyzes system fault conditions and assesses protective device ratings in DC systems to determine fault currents and compare them against protective device ratings
DC Arc Flash - Calculates the incident energy for different types of direct current applications, including BESS and PV Array modeling
ETAP Digital Twin - Active blueprint of the electrical power system, enabling modeling simulation and real-time analysis and optimization under various operating conditions, data revisions and time scales

What we delivered

Digital modeling of the actual battery storage with conductors, busbars, and locations
Simulate various battery configurations and conductor arrangements
Simplified evaluation of multiple scenarios by swapping out equipment in the model
Model-driven DC short circuit, arc flash, and arc duration analysis - all from within one workspace
Specialized analysis that considers compliance with required standards, such as ETAP’s Transient DC AF for Battery Energy Storage Systems with IEC 61660

Outcomes

Ensuring the safe and efficient operation of battery energy storage systems

Improved accuracy of compliance-based estimates of incident energy
Proactive risk management
Design optimization

The biggest challenge is the lack of accurate methods. Engineers had relied on the Max Power method for many years, which could yield overly conservative and even under-conservative results. In this simulated test, conducted using ETAP software, a lithium-ion battery bank was simulated as having a fault, and the DC Arc current was plotted as a function of time. As shown here, the rise time constant of lithium-ion batteries is significantly shorter than that of other battery types, such as lead-acid.
Albert Marroquin, Chief Innovation Officer at ETAP

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