Challenges

1. Lack of confidence in legacy study results. The client’s previous arc-flash study (2009) produced incident energies exceeding available PPE, prompting delays to essential operations.

2. Outdated or incomplete system data. The earlier study relied on estimated short-circuit currents and assumed protection settings - two parameters that directly influence arcing current and clearing time.

3. Limited configuration analysis. Important operational scenarios such as transformer paralleling, motor contribution or alternate feeds were not evaluated.

4. Use of the older IEEE 1584-2002 method. The newer 2018 edition introduces major accuracy improvements based on thousands of additional laboratory tests.

The consultant set out to deliver study results that were valid in regards to updated equipment and standards. The study would help the client with decision-making regarding operations and maintenance, de-energization, and PPE updates to protect their workforce from high incident energy. The first step was determining the best approach for preparing an updated study result using visualizations and validations to compare with the existing study. 

Since the older study did not include the level of detail regarding the equipment, the consultant determined that by including cables, loads, additional overcurrent protection relay equipment and settings, and direct on-line motors (which include power and feeder sections of MCCs), the results of the new study would be more accurate. The new feasibility study involved verification of electrical system resilience according to the IEEE 1584-2018 standard, which includes additional tests, configurations, variances, and enclosure sizing. By comparing the older study with the new study, a number of issues were discovered with the way the older study results had been determined. 

The consultant was able to provide simulations using the model in ETAP to evaluate the improvements under consideration, including 'worst-case' scenarios, by applying the latest protection settings with as-built site information from the client.

Although the UK does not have an equivalent for NFPA 70E to revisit an arc flash study every 5 years, the consultant advises doing so as a good engineering practice using the latest standards, especially if system parameters are changing. 

ETAP software, featuring:

• ETAP Digital Twin – Active single-line diagram that is a blueprint of the electrical power system, including realistic equipment models and enclosures for ‘worst case’, enabling modeling simulation and real-time analysis and optimization under various operating conditions, data revisions and time scales
• ETAP Short Circuit - Analyze the effect of balanced and unbalanced faults and determine fault currents and automatically compare these values against manufacturer short circuit current ratings
• ETAP Star™ Auto-Evaluation - Automatic detection and evaluation of system protection and coordination / selectivity based on customized design criteria and industry guidelines
• ETAP Arc Flash - Arc flash analysis and automatic evaluation of incident energy (IE) and arc flash damage points at multiple locations by simulating and evaluating various mitigation methods in the study. Fine tune the analysis with the Enclosure Editor to analyze different switchboard configurations featuring typical-sized cubicles (1U, 2U, and 3U. Evaluate the impact of varying electrode configurations (VCB, VCBB, HCB). Select the compliance standard to the model, such as IEEE 1584, and relevant configuration data such as for the HCB electrode configuration capacity (Horizontal Conductor inside a metal box). 
• ETAP Arc Fault - To calculate the incident energy results for HV and MV switchboards, sources, feeders, and motors

• Detailed electrical model distribution based on customer’s data
• Simulation of various protection improvements to quickly quantify the impact of proposed changes
• Integrated up-to-date IEEE 1584 compliance standards applied to IE study results
• Visualization of arcing current directly on TCC curves
• Overall improved accuracy in study results
• A distribution model which can be revised and reused over time for new studies

One notable example reduced incident energy from 44 cal/cm² to just 3 cal/cm² by adjusting instantaneous pickup - verified instantly inside ETAP.

Realistic safety results for different operating scenarios 

• Safer Operating Environment - Accurate study results help ensure safety - such as arc flash severity depending on the location of activities on the switchboard.
• Standards Compliance - IEEE standards built into ETAP and used in the model simulations help to identify areas where there were increases and decreases in IE results, compared to the older study.
• Confidence and Clarity - The client can rely on the consultant’s study and has a much clearer understanding of the impact their decisions can make to their system.
• Future-Ready Preparedness - The development of the model in ETAP provided a better basis for the consultant to do further study work, such as time-current characteristic (TCC) charts.

With a detailed ETAP model in place, we can leverage the advantages of  the various modules offered by ETAP to run a suite of studies, including short-circuit analysis according to IEC 60909, and protection coordination checks in the model, before proceeding to run the arc flash analysis itself.
Nick Bramhall, Director and Electrical Engineering Consultant, Safe Arc Solutions