Recommended Specifications for Arc Flash, Short Circuit and Selective Coordination Studies:
A. The Independent Engineering Firm shall provide an arc flash hazard analysis, short circuit and protective coordination study for the electrical distribution system shown on the one line drawings provided. The intent of the Arc Flash Hazard Analysis Study is to determine the arc flash and voltage hazards that exist at each piece of electrical equipment shown on the one line drawing. This will include switchgear, switchboards, panelboards, motor control centers, PDU’s, UPS, ATS’s and transformers. The study will include the creation of Arc Flash Hazard Warning labels specific to each individually identified piece of equipment. These labels serve as a guide to technicians and others in the selection of proper Personal Protective Equipment (PPE) when working near exposed energized equipment. The Independent Engineering Firm will install the labels.
B. The arc flash hazard analysis, short circuit and protective coordination study shall include the electrical distribution system equipment shown on the one line drawing(s). The Independent Engineering Firm shall verify the accuracy of the provided one line drawings and gather the required necessary data to complete the study. A maintenance person familiar with the electrical distribution system will be provided to assist in the acquisition of data and only this maintenance person will be authorized to open any of the electrical equipment. The latest short circuit coordination study (if available) will be provided to the Independent Engineering Firm. The arc flash hazard analysis study shall consider operation during normal conditions, alternate operations, emergency power conditions and any other operating condition that could result in maximum arc flash hazard conditions. The arc flash hazard analysis study shall analyze the Flash Boundary Distance and the range of incident energy based on the calculated available fault current range at each device.
The Independent Engineering Firm shall furnish the following:
A. Arc Flash Hazard Warning labels for all electrical equipment identified on the one line drawings.
B. Three copies of the Power Systems Study shall be submitted.
C. Hot work permits for all electrical equipment identified on the one line drawings.
A. The contractor shall have the coordination study prepared by qualified engineers of an independent consultant. The consultant shall be a Registered Professional Engineer who specializes in studies for protective device coordination, fault current calculations, and arc flash analysis, withal least (10) years of experience specializing in power systems studies. The Contractor is responsible for providing all pertinent information required by the preparers to complete the study.
B. The arc flash analysis, short circuit and coordination study shall be performed using the latest version of SKM system analysis power tools for Windows software, which meets the calculation requirements of IEEE Std 1584a, NFPA 70E, ANSI C.37 and IEEE Std. 399.
C. The personnel from the Independent Electrical Firm used to gather data shall be licensed electricians familiar with the hazards associated with industrial facilities.
D. Pre-approved: Power Analysis Associates, Inc.
A. The complete study shall include a system one-line diagram, short circuit and ground fault analysis, protective coordination plots, arc flash analysis and summary tables, arc flash hazard labels for all electrical equipment, and engineering analysis recommendations.
B. One-line Diagram (s):
1. Show, on the one-line diagram, all electrical equipment and wiring to be protected by the overcurrent devices including both breakers and fuses. Multiple one-line diagrams may be used if required to clearly present all of the required data.
2. Also show on the one line diagram the following specific information:
- Calculated fault impedance, X/R ratios, and short circuit values at all connected buses on the one line diagram.
- Breaker and fuse ratings.
- Transformer kVA and voltage ratings, percent impedance, X/R ratios, and wiring connections.
- Voltage at each bus.
- Identification of each bus.
- Conductors per phase, conductor’s size, length, and ampacity.
- Arc flash boundary.
- Incident energy in cal/cm²
C. Short Circuit Study:
1. The short circuit and associated coordination study shall includes the utility system feed data as well as the following sections of the distribution system. (Describe the scope of work, i.e. medium voltage, main SWB to 10 kAIR level, etc.)
2. If actual utility contributions are unavailable use an infinite primary source and systematically calculate the fault impedance to determine the available short circuit and ground fault currents at each bus. Incorporate the motor contribution in determining the momentary and interrupting ratings of the protective devices.
3. The study shall be calculated by means of a digital computer, with the latest version of SKM analysis software. Pertinent data and the rationale employed in developing the calculations shall be incorporated in the introductory remarks of the study. Calculation methods shall meet the requirements of IEEE Std 399 and ANSI C37.
4. Present the data determined by the short circuit study in a table format as an equipment evaluation. Include the following:
- Device identification and type
- Device description
- Bus and device voltages
- Associated bus
- Device AIC rating
- Calculated short circuit current
- Calculated X/R
- Equipment evaluation comments
D. Coordination Curves:
1. Prepare the coordination curves to determine the required settings of protective devices to maximize selective coordination and minimize incident energy. Graphically illustrate on log-log paper that adequate time separation exists between series devices, including the utility company upstream device where applicable. Plot the specific time-current characteristics of each protective device in such a manner that all applicable upstream devices will be clearly depicted on one sheet with no more than six OCPD’s on a single plot.
2. The following specific information shall also be shown on the coordination curves:
- Device identification
- Voltage and current ratios for curves
- 3-phase and 1-phase ANSI damage points for transformer directly fed from the switchgear
- Minimum melt and total clearing curves for fuses
- Cable damage curves
- Transformer inrush points including total connected kVA inrush for feeder circuits
- Maximum short circuit cutoff point
- Corresponding one line diagram
3. Develop a table to summarize the settings selected for each protective device. Include in the table the following:
- Device identification and breaker or load controlled
- Relay CT ratios and electronic set point equivalents for relay tap, time dial, and instantaneous pickup points
- Circuit breaker sensor rating
- Fuse rating and type
- Ground fault pickup and time delay
E. Arc Flash Analysis:
1. Perform an arc flash analysis study in conjunction with the previous specified short circuit and protective device coordination study. This arc flash analysis study to be performed in accordance with IEEE Std 1584a.
2. The study shall be calculated by means of a digital computer, with the latest version of SKM Analysis Software. Pertinent data and the rational employed in developing the calculations shall be incorporated in the introductory remarks of the study.
3. Determine the following for each bus analyzed:
- Flash Hazard Protection Boundary
- Incident Energy Level
- Required Personal Protective Equipment Category
- Type of Fire Rated Clothing
- Limited Approach Boundary
- Restricted Approach Boundary
- Prohibited Approach Boundary
4. Produce an Arc Flash Warning label for each piece of electrical equipment with a specific equipment ID and the previous items a-g listed. Also include the system operating voltage and date of issue. Labels shall be printed in color on adhesive backed nylon labels.
5. Present the data determined by the Arc Flash Analysis Study in a tabular format summary sheet. Include the following for each bus analyzed:
- Flash Bus Name
- Protective Device Name
- Bus Operating Voltage
- Bus Bolted Fault Current
- Protective Device Bolted Fault Current
- Protective Device Arcing Fault Current
- Trip/Delay Time (Sec)
- Breaker Opening Time (Sec)
- Ground
- Equipment Type
- Gap (mm)
- Arc Flash Boundary (in)
- Working Distance (in)
- Incident Energy (cal/cm²)
- Required Protective FR Clothing Category
Analyze the short circuit calculations, protective device coordination, and arc flash calculations and highlight any equipment that is determined to be underrated as specified or cause abnormally high incident energy levels. Propose approaches to effectively protect the underrated equipment and to reduce the energy levels. Provide minor modifications to conform with the study (Examples of minor modifications are trip sizes within the same frame, the time curve characteristics of induction relays, CT ranges, etc.). After developing the coordination curves, highlight areas lacking coordination. Present a technical evaluation with a discussion of the logical compromises for best coordination. Proposed major corrective modifications will be taken under advisement by the Engineer, and the Contractor will be given further instructions.
The results of the power system study shall be summarized in a final written report. The report shall include the following sections.
A. Introduction, executive summary, recommendations and assumptions.
B. Electrical One-Line(s) with previously identified specific data values.
C. Tabulations of equipment ratings versus calculated short circuit values and X/R ratios, arc flash values.
D. Protective device time versus coordination curves, tabulations of relay and circuit breaker trip settings and fuse selection with commentary.
E. Engineering analysis, commentary and recommendations.
F. The report is to be stamped by a professional engineer.