The Arc Flash Study determines the incident energy and arc flash boundary for each location in a power system. The short-circuit study results provide input data to calculate the arcing fault current. Based on the protective device settings and clearing time, the Incident energy and arc flash boundaries are calculated in accordance with the NFPA 70E and IEEE 1584 standards
Custom Labels that display the Incident energy, Flash Protection Boundary, and PPE Clothing Category are provided for switchgear and panelboards throughout the system. These labels are generated from the SKM Power Tools for Windows Software and can be customized to include additional items featured in the client’s electrical safety requirements. For accurate results, the data collection survey must reflect the as-built conditions as close as possible. The arc flash study should also consider all operating scenarios including normal utility power and backup power from generators, open and closed transition switching modes, and with or without motor contribution to simulate maintenance conditions.
In some cases, the Arc Flash Mitigation is employed to lower the PPE Category Level. . This may include lowering the instantaneous setting for a protective device to reduce the fault clearing time and the accumulation of incident energy. Other mitigating solution may include photo-sensing devices, differential protection relays, with zone-interlocking schemes, and arc reduction mechanisms to override the normal trip settings and switch to a fast-mode instantaneous setting.
Why an Arc Flash Study?
An arcing fault can release a tremendous amount of energy that can result in extremely high temperatures and an enormous blast pressure in a fraction of second. The blast can project shrapnel and vaporized metals from equipment at a high velocity. The arc flash can cause serious injury or death to a worker.
OSHA enforces Electrical Safety Requirements for Employee Workplaces. Employers are required to provide a workplace assessment to determine if hazards are present, and must select the proper personal protective equipment (PPE) for personnel working on or near energized equipment. This requirement is intended to reduce the occurrence of serious injury or death due to arcing faults.
Arc Flash Study Benefits
• Design Safer Power Systems
• Customized Arc Flash Labels
• Flash Protection Boundary
• Calculate Incident Energy
• PPE & Clothing Requirements
• Provide Worst Case Scenarios
• Arc Flash Labels Based on Recommended PD Settings
• Technical Training & Assistance
Arc Flash Case Studies
The electrical 1-line drawing is used to develop a power system model. The component study data is supplied by data collection in the field or by equipment submittals and drawing documents for new construction. The field data entered into the model, is matched to the same types of components in the reference libraries of the study software. Each component is selected from the library and is based on the identical type, style, size and ratings of the manufacturers’ equipment that is installed on the power system. After a load flow solution is generated the study model can be further developed by setting the criteria for the short-circuit study, the equipment evaluation and additional studies to be considered. Then the Time Current Characteristic Curves and related reference drawings are developed and used to coordinate the protective devices to sequentially interrupt fault currents and to provide system protection against potentially damaging fault currents. Case Study Scenarios are developed for systems that have multiple sources of power. Each case is used to simulate the fault conditions under various switching states and modes of operation. The worst case results are used to determine if the equipment will pass or fail the equipment evaluation in any case, and the highest incident energy and HRC levels to report in the Arc Flash Study results. The system model can then be used for additional types of studies and archived for future reference and updates. The primary components for the Arc Flash Study include:
• Develop Study Model using Component Data
• Provide Short Circuit Analysis and Equipment Evaluation
• Provide Protective Device Coordination
• Develop TCC Curves with Detail 1-line Drawing Sections
• Developed Operational Scenarios and Case Studies
• Provide Arc Flash Hazard Analysis and Worst Case Results
• Provide Arc Flash Labels and Online Training Webinar
JP Morgan Chase Data Center 1
The Arc Flash Study for this power system included a 35kV dual feed service entrance to two 15MVA Transformers at 13kV, including eight 2.0MVA generators. Use Maintenance Operation Procedures (MOP) to develop 16 operational scenarios. These case studies were used to determine the worst case results for the short circuit analysis and the arc flash results. Provided load flow analysis, short-circuit and coordination, equipment evaluation, arc flash and protective device settings. Provided recommendations to improve the coordination between protective devices and arc flash mitigation to lower the HRC level for the PDU’s and review working distances to customize AF Labels for the mechanical substations. Similar Studies include JP Morgan Chase Data Center 2, Countrywide Data Center, Bank of New York, and The Center for Disease Control.
JP Morgan Chase Data Center 1 (Solar Power Unit)
Provide Load Flow Analysis and update previous study model to add 750 kVA Photo-Voltaic Solar Power Unit and Inverter to supplement the normal power to a 4000Amp Mechanical Bus. This included scenarios for the normal utility power and the closed-transition between the utility and generator power sources. Provided a short-circuit analysis to confirm the maximum fault contribution, an equipment evaluation, protective device coordination and update to the arc flash analysis. Provided recommendation to adjust the protective device settings and update the associated arc flash hazard labels.
The Home Depot Store Data Center
Short Circuit Coordination Study included: Two utility feeder circuits to 2-10MVA transformers at 20kV-to-4.16kV Grounded-Wye. Each transformer supplies a main switchgear unit that contains a main breaker (i.e. SR750 Relays), tie-breaker (i.e. DT-DRLXS01 Relays), and breaker to transfer the data center and mission critical loads to the generator paralleling switchgear that consists of 4-2.5MVA medium-voltage generators with high-resistance grounded. The GPS supplies stand-by power to the main switchgear (in building backup mode). The feeder breakers in the main switchgears (i.e. DT-DRLXS01 Relays) each supply power to an ATS, that feeds a unit substation rated at 2.5MVA, at 4.16kV Delta-to-480Y/277. The power for the emergency side of each ATS is from a feeder in the GPS (in ATS Mode). The main switchgears feeders also power 12 UPS modules with static switch tie to the companion units. Provided recommendations to improve the coordination, system protection, and to eliminate a potential ground fault hazard during return from generators (in island mode) to normal utility power. Provided Arc Flash Hazard Analysis and recommendations to lower the Hazard Risk Category for select buses. Developed procedures supervised and install the recommended setting changes for the protective relays and static trip breakers.