SECTION SHORT CIRCUIT, COMPONENT PROTECTION, FLASH HAZARD AND SELECTIVE COORDINATION STUDY

Transcription

1 SECTION SHORT CIRCUIT, COMPONENT PROTECTION, FLASH HAZARD AND SELECTIVE COORDINATION STUDY PART 1 GENERAL 1.1 SUMMARY A. Section Includes: 1. Provide a short-circuit, component protection, flash hazard analysis, and selective coordination study for the electrical distribution system from all power sources (normal and emergency) down to the branch circuit overcurrent protective device and equipment. The short circuit, selective coordination and flash hazard study shall be performed by the manufacturer supplying the equipment. Series rated systems are not approved. 2. The Engineer has conducted a preliminary study based on Cutler-Hammer equipment. Prior to submission of any shop drawings, the study specified herein shall be submitted. Shop drawings will not be reviewed or approved without this study. 1.2 PURPOSE A. The study shall calculate the available short-circuit current at each point in the electrical distribution system. The overcurrent protective devices shall have an interrupting rating equal to or greater than the available short-circuit current at the point of application. B. The study shall examine proper protection of electrical system components and utilization equipment such that the equipment has a sufficient short-circuit current rating. If a specific type of overcurrent protective device is required for proper protection of equipment, it shall be noted in the report and reflected in the design of the system. C. The study shall include a flash hazard analysis for electrical distribution equipment where required per codes and standards. The analysis shall determine the flash protection boundary, incident energy, and required level of personal protective equipment (PPE) for workers at the electrical distribution equipment. The flash protection boundary and incident energy shall be determined based upon a working distance of 18 inches. The electrical distribution equipment shall be field marked with this information in accordance with codes and standards. D. The overcurrent protective devices shall be analyzed for selective coordination. This analysis shall identify any potential selective coordination problems up the available short-circuit current. Any areas where the overcurrent protective devices are not selectively coordinated shall be explicitly noted and recommendations shall be made to achieve selective coordination if desired. E. The studies shall be submitted to the Design Engineer prior to receiving final approval of the distribution equipment shop drawings and/or prior to release of equipment for manufacturing. If formal completion of the studies may cause delay in equipment manufacturing, approval from the Engineer may be obtained for a preliminary submittal of sufficient study data to ensure that the selection of device ratings and characteristics will be satisfactory. F. The studies shall include all portions of the electrical distribution system from the normal power source or sources down to and including the smallest adjustable trip circuit breaker in the distribution system. Normal system connections and those which result in maximum fault conditions shall be adequately covered in the study. G. The firm should be currently involved in high and low-voltage power system evaluation. The study shall be performed, stamped and signed by a registered professional engineer. Credentials of the individual performing the study and background of the firm shall be submitted to the Engineer for approval prior to start of the work. A minimum of five (5) Proj. No Short Circuit, Component Protection, Flash Hazard

2 years experience in power system analysis is required for the individual in charge of the project. H. The firm performing the study should demonstrate capability and experience to provide assistance during start up as required. 1.3 REFERENCES A. The study shall be completed in accordance with the latest edition of IEEE Standard 242 Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems. B. The flash hazard analysis shall be completed in accordance with latest editions of NFPA 70E Standard for Electrical Safety Requirements for Employee Workplaces and IEEE Standard 1584 Guide for Performing Arc-Flash Hazard Calculations. 1.4 DATA COLLECTION FOR THE STUDY A. The Contractor shall provide the required data for preparation of the studies. The Engineer performing the system studies shall furnish the Contractor with a listing of the required data immediately after award of the contract. B. The Contractor shall expedite collection of the data to assure completion of the studies as required for final approval of the distribution equipment shop drawings and/or prior to release of the equipment for manufacturing. 1.5 SHORT-CIRCUIT AND PROTECTIVE DEVICE EVALUATION AND COORDINATION STUDY A. The short-circuit study shall be performed with the aid of a digital computer program and shall be in accordance with the latest applicable IEEE and ANSI standards. B. In the short-circuit study, provide calculation methods and assumptions, the base per unit quantities selected, one-line diagrams, source impedance data including power company system characteristics, typical calculations, tabulations of calculation quantities and results, conclusions, and recommendations. Calculate short-circuit interrupting and momentary (when applicable) duties for an assumed 3-phase bolted fault at each supply switchgear lineup, unit substation primary and secondary terminals, low-voltage switchgear lineup, switchboard, motor control center, distribution panelboard, pertinent branch circuit panelboard, and other significant overcurrent protective device locations throughout the system. Provide a ground fault current study for the same system areas, including the associated zero sequence impedance data. Include in tabulations fault impedance, X to R ratios, asymmetry factors, motor fault contribution, short circuit kva, and symmetrical and asymmetrical fault currents. C. In the protective device coordination study, provide time-current curves graphically indicating the coordination proposed for the system, centered on conventional, full-size, log-log forms. Include with each curve sheet a complete title and one-line diagram with legend identifying the specific portion of the system covered by that particular curve sheet. Include a detailed description of each protective device identifying its type, function, manufacturer, and time-current characteristics. Tabulate recommended device tap, time dial, pickup, instantaneous, and time delay settings. D. Include on the curve sheets power company relay and fuse characteristics, mediumvoltage equipment protective relay and fuse characteristics, low-voltage equipment circuit breaker trip device characteristics, pertinent transformer characteristics, pertinent motor and generator characteristics, and characteristics of other system load protective devices. In addition, include all devices down to the largest branch circuit and largest feeder circuit breaker in each motor control center, and main breaker in branch panelboards. Include all adjustable settings for ground fault protective devices. Include manufacturing tolerance and damage bands in plotted fuse characteristics. Show transformer full load currents, transformer magnetizing inrush, ANSI transformer withstand parameters, and Proj. No Short Circuit, Component Protection, Flash Hazard

3 significant symmetrical fault currents. Terminate device characteristic curves at a point reflecting the maximum symmetrical fault current to which the device is exposed. E. Select each primary protective device required for a delta-wye connected transformer so that its characteristic or operating band is within the transformer characteristics, including a point equal to 58 percent of the ANSI withstand point to provide secondary line-toground fault protection. Separate transformer primary protective device characteristic curves from associated secondary device characteristics by a 16 percent current margin to provide proper coordination and protection in the event of secondary line-to-line faults. Separate medium-voltage relay characteristics curves from curves for other devices by at least a 0.4-second time margin F. Include complete fault calculations as specified herein based on contract documents. G. Submit qualifications of individual(s) who will perform the work for approval prior to commencement of the studies. Provide studies in conjunction with equipment submittals to verify equipment ratings required. Submit the study to Engineer for review prior to delivery of the study to the Owner. Make all additions or changes as required by the reviewer. H. Contractor shall furnish all data as required by the short-circuit/coordination study vendor. Utilize data for the study obtained by the Contractor from contract documents, including contract addendums issued prior to bid openings. I. Notify the Engineer in writing of circuit protective devices not properly rated for fault conditions. J. Mechanical Contractor to provide settings for the packaged chiller and/or motor starters. K. When emergency generator is provided, include phase and ground coordination of the generator protective devices. Show the generator decrement curve and damage curve along with the operating characteristic of the protective devices. Contractor shall obtain the information from the generator manufacturer and include the generator actual impedance value, time constants and current boost data in the study. Do not use typical values for the generator. 1.6 SUBMITTALS A. The results of the study shall be summarized in report form. Submit 6 copies for review and approval by the design engineer. B. The results of the study shall include the following: 1. Descriptions, purpose, basis, and scope of study. 2. Fault current calculations including definition of terms and guide for interpretation of computer printout. 3. Tabulations of protective device and equipment ratings versus calculated shortcircuit duties, and commentary regarding same. 4. Flash hazard analysis report for electrical distribution equipment. 5. Time versus current curves or fuse selectivity ratio analysis, with tabulations of overcurrent protective device settings, and selective coordination analysis and commentary regarding same. C. If power company review and approval is required, the results of the study shall be submitted to the power company for review and approval. Approved copies from the power company shall be forwarded to the design engineer. 1.7 SUBMITTALS CLOSEOUT A. Submit 6 copies of the final approved study to the electrical design engineer. PART 2 PRODUCTS Proj. No Short Circuit, Component Protection, Flash Hazard

4 2.1 REQUIREMENTS A. The short circuit and flash hazard analysis study shall be completed with the aid of a computer software program where possible. B. The available short-circuit current, corresponding required interrupting or short-circuit current ratings of components, and flash hazard analysis data, shall be calculated based upon the 3-phase bolted short-circuit, current and phase to ground/neutral short-circuit current at each of the following (if applicable): 1. Utility Service Point. 2. Low-voltage switchboards. 3. Distribution panelboards. 4. Branch circuit panelboards. 5. Other significant equipment or utilization equipment. C. The study shall include the following: 1. Calculation methods and assumptions. 2. One-line diagram (with available short-circuit current and flash hazard data identified). 3. Calculations shall identify: a. Available short-circuit currents from all power sources (kva). b. Motor fault contribution. c. Component impedance data. d. X to R ratio. e. Symmetrical and asymmetrical fault current characteristics. f. Flash hazard analysis data. 4. Tabulation of all calculation quantities and results. 5. Detailed description of each protective device identifying its type, function, manufacturer, interrupting rating, ampere rating, selected settings, and timecurrent characteristics. 6. System component characteristic curves or short-circuit current ratings identified and/or plotted up to the maximum symmetrical fault current to which the component is exposed. Include the following where applicable: a. Medium voltage equipment characteristics. b. Low voltage equipment characteristics. c. ICEA conductor damage characteristics. d. Transformer characteristics. e. Motor and motor circuit equipment characteristics. f. Generator and transfer switch (manual or automatic) characteristics. g. Other system equipment characteristics. 7. Time-current curves prepared graphically on full size, log-log forms with title, one-line diagram, and specific system components analyzed. 8. Conclusions regarding interrupting rating for overcurrent protective devices, flash hazard analysis, protection of components, selective coordination, and recommendations and requirements on the same. 2.2 LABELS A. Arc flash and shock hazard labels shall be provided and installed on all equipment in the report noting the appropriate PPE required. Submit sample label for approval. A sample label format is available from the Engineer. PART 3 EXECUTION 3.1 EXAMINATION Proj. No Short Circuit, Component Protection, Flash Hazard

5 A. The Contractor shall perform field adjustments of the protective devices as required to place the equipment in final operating condition. The settings shall be in accordance with the approved short-circuit study, protective device evaluation study, and protective device coordination study. B. Necessary field settings of devices, adjustments, and minor modifications to equipment to accomplish conformance with the approved short-circuit and protective device coordination study shall be carried out by the Contractor at no additional cost to the Owner. END OF SECTION Proj. No Short Circuit, Component Protection, Flash Hazard