Recommended Study Specifications: New Construction
Recommended Specifications for Arc Flash, Short Circuit and Selective Coordination Studies:
1.1 DESCRIPTION
A. The Contractor shall have an arc flash analysis, short circuit and coordination study prepared for the electrical overcurrent devices to be installed under this project ( or as defined herein) to verify that the specified and supplied equipment is properly rated, will function correctly, and that the electrical system and personnel are properly protected.
B. The study shall present an organized time-current analysis of each protective device analyzed in series with upstream devices. The short circuit and coordination study shall reflect the operation of each device over the determined worse case available fault current range. The arc flash study shall analyze the Flash Boundary Distance and the range of incident energy based on the calculated available fault current range at each device.
1.2 SUBMITTALS
The Contractor shall furnish the following:
A. Submit protective equipment shop drawings simultaneously with or after the protective device study. Equipment submittals will not be approved without the completion and review of the power systems study.
B. Arc Flash Hazard Warning labels for all electrical equipment identified on the one line drawings.
C. Three copies of the Power Systems Study shall be submitted.
D. Certification: Two weeks prior to final inspection, deliver to the Resident Engineer four copies of the following certifications:
- Certification by the contractor that the protective devices have been adjusted and set in accordance with the approved protective device study.
1.3 QUALIFICATIONS
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. Pre-approved: Power Analysis Associates, Inc.
1.4 REQUIREMENTS
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):
- 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.
- Also show on the one line diagram the following specific information:
a. Calculated fault impedance, X/R ratios, and short circuit values at all connected buses on the one line diagram.
b. Breaker and fuse ratings.
c. Transformer kVA and voltage ratings, percent impedance, X/R ratios, and wiring connections.
d. Voltage at each bus.
e. Identification of each bus.
f. Conductors per phase, conductor’s size, length, and ampacity.
g. Arc flash boundary.
h. Incident energy in cal/cm²
C. Short Circuit Study:
- 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.)
- 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.
- 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.
- Present the data determined by the short circuit study in a table format as an equipment evaluation. Include the following:
a. Device identification and type
b. Device description
c. Bus and device voltages
d. Associated bus
e. Device AIC rating
f. Calculated short circuit current
g. Calculated X/R
h. Equipment evaluation comments
D. Coordination Curves:
- 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.
- The following specific information shall also be shown on the coordination curves:
a. Device identification
b. Voltage and current ratios for curves
c. 3-phase and 1-phase ANSI damage points for transformer directly fed from the switchgear
d. Minimum melt and total clearing curves for fuses
e. Cable damage curves
f. Transformer inrush points including total connected kVA inrush for feeder circuits
g. Maximum short circuit cutoff point
h. Corresponding one line diagram
- Develop a table to summarize the settings selected for each protective device. Include in the table the following:
a. Device identification and breaker or load controlled
b. Relay CT ratios and electronic set point equivalents for relay tap, time dial, and instantaneous pickup points
c. Circuit breaker sensor rating
d. Fuse rating and type
e. Ground fault pickup and time delay
E. Arc Flash Analysis:
- 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.
- 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.
- Determine the following for each bus analyzed:
a. Flash Hazard Protection Boundary
b. Incident Energy Level
c. Required Personal Protective Equipment Category
d. Type of Fire Rated Clothing
e. Limited Approach Boundary
f. Restricted Approach Boundary
g. Prohibited Approach Boundary
- 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.
- Present the data determined by the Arc Flash Analysis Study in a tabular format summary sheet. Include the following for each bus analyzed:
a. Flash Bus Name
b. Protective Device Name
c. Bus Operating Voltage
d. Bus Bolted Fault Current
e. Protective Device Bolted Fault Current
f. Protective Device Arcing Fault Current
g. Trip/Delay Time (Sec)
h. Breaker Opening Time (Sec)
i. Ground
j. Equipment Type
k. Gap (mm)
l. Arc Flash Boundary (in)
m. Working Distance (in)
n. Incident Energy (cal/cm²)
o. Required Protective FR Clothing Category1.5 ANALYSIS
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.
1.6 FINAL WRITTEN REPORT
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.
