What is Arc Flash Study?
An arc flash study and assessment is engineering studies that identifies and analysis the specific arc flash hazard and risk for an electrical equipment within a facility. These studies involve meticulous procedures to determine the incident energy levels at various electrical devices, which in turn determine the amount of incident energy at an electrical facility or device and the necessary personal protective equipment (PPE) and warning label required for safe work practices. —Omazaki Consulant is a consultant provides comprehensive new or renew arc flash hazard studies and risk assessment consulting services. It is included renew arc flash label. Contact us if you are looking for consultants who provide both for new and arc flash renewal hazard program study, assessment, audit, evaluation and analysis consulting services for your electrical systems in Indonesia and South East Asia by sending an email to cs@omazaki.co.id or by filling in the form in contact. Our arc flash analysis study mostly using ETAP software.
Introduction
Arc flash study provides estimated calculation of short circuit currents, tripping times and incident energy (arc flash energy). Arc flash assessment also reviews coordination to mitigate arc flash energy levels while focusing on eliminating nuisance tripping, both during a ground fault and/or phase fault condition.
The objectives of the arc flash risk assessment are to:
- Identify arc flash hazards
- Estimate the likelihood of occurrence and potential severity of injury or damage to health
- Determine whether additional protective measures are required.
The arc flash study will calculate the short circuit current and the tripping time (opening or breaking of the electrical safety). Arc flash assessment is also carried out by reviewing coordination to reduce incident energy levels while focusing on eliminating disturbances, both during ground faults and/or inter-phase fault conditions.
Currently the majority of studies and assessments of arc flash hazard risk refer to IEEE 1584 and NFPA 70E. According to the NFPA 70E, arc flash studies must be carried out every 5 (five) years or whenever major modifications are made to the facility.
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Why Need to Conduct Arc Flash Assessment?
The main reason why we need to do arc flash studies or assessments is for the safety of personnel. Short circuit and arc flash fault are very dangerous and potentially fatal phonemes for personnel. Arc flash exposure often results in a variety of serious injuries such as severe burns. In addition, it can cause visual impairment, ruptured eardrums, damaged lungs, psychological trauma and even death.
Arc flash hazard analysis is required to determine the arc flash risk to personnel and to alert personnel or workers to what types of personal protective equipment they should wear when working on live electrical equipment.
The second reason why it is necessary to conduct an arc study or assessment is that there are obligations and government regulations.
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Scope of Study
In general, the scope of work in an arc flash study or assessment is as follows:
- Short circuit current analysis (worst case short circuit current)
- Evaluation and coordination analysis of electrical protective devices
- Arc flash hazard analysis
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Practical Steps for the Arc Flash Hazard Study
Step 1: Identify all sites and equipment to be assessed
Arc flash studies or assessments are required only for locations where workers are exposed to arc flash risk. Therefore, studies need not be carried out on every piece of equipment in the power system. Panels and switchboards with a value less than 208 volts can be ignored when fed by a transformer with a capacity of less than 125kVA. This is because the arc will not be sustainable at a lower voltage and the available fault current is smaller. This comes from the IEEE 1584-2002 recommendations. All panels with breakers and fuses should be included in the study if there is a significant potential for arc flash injury. Incidents can occur when a fused disconnect is operated, even with the door closed.
Step 2: Data Collection and Verification
The greatest single attempt at conducting an arc-flash study is in data collection. For systems with the most recent single-line diagrams, data collection can take up 25-40 percent of the research effort.
Details of the electrical distribution system are required to accurately calculate the hazard level. Here is a list of information that is usually required:
- Data for short circuit analysis: voltage, size (MVA/kVA), impedance, X/R ratio, etc.
- Data for protective device characteristics: device type, existing settings for relays, breakers and trip units, amp rating, current vs time curve, and total clearing time.
- Data for arc flash studies: type of equipment, type of enclosure (open air, box, etc.), gap between conductors, type of grounding, number of phases and approximate working distance for equipment.
The data collection approach could also include:
- Utility data, list or log of tampering and protection settings
- One Line Diagram showing major electrical equipment
- When a one-line diagram does not show a complete distribution, an additional list should be obtained from all three-phase power distribution panels. This is the location that will be labeled (and counted). Single-phase loads and distributions do not apply.
- List of cables by size & length
- Schedule of relay settings and circuit breakers.
Step 3: Updating One Line Diagram and System Modelling
After data collection and verification is carried out, it is usually necessary to update the single-line diagram It is to makes sure that the drawings match those installed in the field.
After the one-line diagram is confirmed to be the latest diagram, then the electrical installation system modeling is carried out. System modeling is carried out in application software such as ETAP, EasyPower, SKM, EDSA, and so on.
It should be noted that the study results will only be as good as the system model. Every effort should be made to model actual equipment as found in the field.
Step 4: Defining Possible Operation Scenarios
Record all possible connections (system operation mode) using diagrams and tables. The status of the circuit breaker, switch, or fuse may change during abnormal operation. Parallel feeders can greatly increase the fault current and produce an arc hazard. The motor also contributes to the disturbance and increases the danger. Arc flash studies or assessments should cover normal operating conditions as well as worst-case scenarios. In general, the higher the fault current present, the greater the arc energy. Since arc energy is a function of arc duration and current, it cannot automatically be assumed that the highest fault current will always be the worst arc flash risk. From the various established operating scenarios, the arc flash study must find the worst hazard conditions.
Operation Scenarios
For example, the following scenario could be created:
- Maximum Utility – full contribution from all sources, including the motor
- Minimum Utilities – the minimum contribution of utilities and all rotating equipment out of service
- Emergency – with an emergency generator supplying part of the system
A calculation needs to be done for all applicable scenarios, the evaluation must be based on the worst case results. Which scenario produces the worst case outcome is determined for each location separately.
For installations with a simple radial service from the utility, there is usually only one mode of operation – normal. However, for larger installations, there may be several modes of operation. Other scenarios that could be developed include:
- Multiple source utilities that are enabled or removed.
- Multiple generator sources are operated in parallel or isolated depending on system configuration.
- Emergency operating conditions. This is possible only with a small backup generator.
- Maintenance conditions where the short circuit current is low and the travel time is high.
- Source operating in parallel for toast switchgear or MCC.
- The operable tie breaker is open or closed.
- Large motor or process part is not operating
What is important to realize is that each of these conditions can change the level of short circuit current, which in turn changes the clearing time of the protective device. These changes can have a significant impact on arc flash hazard and PPE requirements for individual equipment.
Step 5: Short-Circuit Current Analysis
In this step, the short circuit fault current will be calculated. The bolted short-circuit current for each apparatus will be calculated and compared with the equipment short-circuit rating. The short circuit analysis aims to check whether the design capacity of the switchgear and the electrical protection device is adequate to cut short circuit current calculated or simulated.
The analysis is carried out at this stage:
- Calculation of the maximum 3-phase fault current (bolted short-circuit current)
- Calculation of short-circuit current for each branch and contributing load.
The above calculations are carried out for each of the operating scenarios defined in Step 4. If there is insufficient design capacity of protective equipment, it should be reported immediately, as it can create unsafe working conditions.
Bolted Short-Circuit Current Calculation
Bolted fault is a short circuit that occurs without any resistance or zero resistance. While the bolted short-circuit current is the maximum short-circuit current that may be generated at a specified location or system configuration. This current is often used to select withstand and interrupt ratings as well as for setting protection relays.
The scenario for calculating the bolted short-circuit is carried out by considering the following conditions:
- Power sources where it is scenarioed that each source is OFF or ON serving the load
- Parallel operated or isolated generation generator depending on system configuration
- During emergency operating conditions
- A maintenance condition where the short circuit current is low but the arc duration may be long
- Parallel feeder to switchgear or MCC
- Bus-tie in a closed or open position
- Large motors or non-operating process parts.
Step 6: Evaluation and Coordination of Electrical Protection Devices
Is performed to ensure selection and arrangement of protective devices limits the effects of an over-current situation to the smallest area. We perform this study in accordance with IEEE Std. 242-2001 (Buff Book)
Step 7: Arc Flash Analysis
Is based on available short circuit current, protective device clearing time and distance from the arc. Calculations of incident energy levels and flash protection boundaries are completed for all relevant equipment locations. The magnitude of arc hazards are determined using the ‘Incident Energy Analysis Method’, per NFPA 70E-2015, IEEE Std. 1584 or NESC Tables.
Step 8: Reporting
Upon completion of the calculations, final report will be prepared as an Arc Flash Hazard Assessment Report and full size one-line drawings. The report will be certified by a Licensed Engineer (PE).
Arc flash consultant who provide arc flash consulting services will provide them above.
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Contact Omazaki Consultant if you are looking for new and renewal arc flash hazard program study and risk assessment consultants who provide consulting service to analyze your electrical system in Indonesia and South East Asia, both existing and planning systems.
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Related Articles
- Arc Flash: Definition, Hazards and Risks
- Arc Flash Causes & Location
- Arc Flash Calculation Methods
- Arc Flash Boundary and Requirements of Personal Protective Equipment (PPE)
- Electric Shock Protection Study
- Power System Study and Analysis
- Short Circuit Study and Analysis
Reference
- NFPA 70E – Standard for Electrical Safety in the Workplace
- IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations
- Book of Practical Solution Guide to Arc Flash Hazards by EasyPower
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