Scope of Work_Short Circuit Study.pdf

Scope of Work

Short-Circuit, Coordination, and Arc Flash Hazard Analysis Studies - Power System

U.S. Embassy Islamabad

1. Project Overview:

The U.S. Embassy in Islamabad requires electrical services from the manufacturer of Eaton MV/LV switchgear and equipment to perform comprehensive electrical system studies. The scope of work includes evaluating the electrical infrastructure of the Embassy compound and producing a Short-Circuit Analysis, Protective Device Coordination, and Arc Flash Hazard Analysis. The contractor will also review and update one-line diagrams, perform a system review, prepare recommendations, and generate arc flash labels.

The studies will be conducted in accordance with the latest industry standards, including IEEE Std 1584-2018, NFPA 70E-2021, ANSI, and NEC requirements.

2. Data Collection and System Modeling:

1) The Offerors will provide standardized forms and instructions to facilitate efficient data gathering from Embassy personnel.

2) The Offerors will develop a detailed system model using SKM Systems Analysis software, representing the electrical distribution from utility connections to all major equipment (panelboards, MCCs, switchboards, switchgear) as depicted in the provided one-line diagrams.

3) The model will include all relevant impedance data, sources of short-circuit contribution, and overcurrent protection characteristics.

3. One-Line Diagram:

The Offerors will prepare and provide updated one-line diagrams of the electrical distribution system, identifying all equipment included in the study (transformers, cables, motors, circuit breakers, relays, fuses, etc.).

4. Short-Circuit Study:

The study input data shall include the utility short circuit contribution, resistance, and reactance components of the branch impedances, the X/R ratios, motor and generator contributions, base quantities selected, and other source impedances down to and including all equipment listed in the scope of work.

The Offerors will calculate maximum available fault current at each significant location throughout the system. The short circuit tabulations shall include symmetrical fault currents and X/R ratios, for both momentary and interrupting conditions. For each fault location, the total duty on the bus, as well as the individual contribution from each connected branch, shall be included with its respective X/R ratio.

All short circuit calculations will be made in accordance with the latest standards adopted by the American National Standards Institute (ANSI) and the National Electrical Code (NEC). Each interrupting protective device in the scope of work will be analyzed to determine if its interrupting and momentary ratings can withstand the calculated interrupting and momentary duties. If the study reveals problem areas, the study will recommend changes to improve system performance.

Results of Short Circuit Study:

At the conclusion of the Short Circuit Study, the Manufacturer will submit the following for each circuit condition analyzed:

1) Fault current calculation summary listing momentary and interrupting duties with their respective X/R ratios.

2) Tabulated summaries listing circuit breakers, fuse and other protective device interrupting and momentary duties in percentage of their respective ratings.

3) Complete fault current magnitudes, including individual branch current contributions, for each bus in the electrical distribution system.

4) Complete tabulation of circuit breakers, fuse and other protective device momentary and interrupting ratings versus calculated short circuit duties for every protective device in the scope of the Short Circuit Analysis.

5) Recommendations for replacement or retrofit of over-dutied protective devices.

5. Protective Device Coordination Study:

The Offerors power system engineers will use the SKM Systems Analysis computer program to evaluate protective device coordination. Revised time-current coordination curves, showing the recommended phase and ground-fault protective device time-current characteristics, will be plotted. Time-current curves for protective devices that do not require changes will also be included. These curves will illustrate the coordination among devices as shown on the system one-line diagram.

1) The coordination curves will include, at a minimum, the following information:

Applicable NEC and ANSI protection criteria for equipment.

2) Magnetizing inrush points of transformers.

3) A simplified one-line diagram identifying the devices plotted.

4) Short-circuit current levels used for coordination.

5) Motor starting characteristics, where applicable.

Results of Protective Device Coordination Study:

1) Detailed recommendations for new and replacement protective devices when the study determines those existing devices do not provide proper protection or coordination.

2) Time-current coordination curves with the information described above,

3) Tabulations of recommended protective device settings identified by location, equipment number, function number and adjustable range.

6. Arc Flash Hazard Analysis:

1) The Offerors will perform arc flash hazard calculations in accordance with NFPA 70E- 2021 and IEEE Std 1584-2018, considering multiple operating scenarios (minimum and maximum fault current contributions).

2) The analysis will determine incident energy levels, arc flash boundaries, and required PPE ratings for each work location.

3) Locations with incident energy above 40 cal/cm² will be identified as “dangerous” per customer request.

4) Deliverables will include detailed incident energy calculations, arc flash boundaries, and recommendations for risk mitigation.

Results of Arc Flash Hazard Analysis:

At the conclusion of the Arc Flash Hazard Study, Manufacturer will submit the following for each circuit condition and work location analyzed:

1) Arcing fault magnitude

2) Device clearing time

3) Duration of arc

4) Arc flash boundary

5) Working distance

6) Incident energy

Arc Flash Labels:

Arc flash warning labels will be provided in the following manner.

1) For each low voltage panelboard, one arc flash label will be provided.

2) For each motor control center, one arc flash label will be provided.

3) For each low voltage switchboard, one arc flash label will be provided.

4) For each low and/or medium voltage switchgear, one flash label will be provided.

5) For medium voltage switches one arc flash label will be provided

6) Additional labels will be provided if required.

All labels will be based on recommended overcurrent device settings and will be provided after the results of the analysis have been presented to the customer and after any system changes, upgrades or modifications have been incorporated in the system.

Labels will be 4 in. x 4 in. thermal transfer type label of high adhesion polyester for each work location analyzed and will be machine printed, with no field markings. The label shall have an orange header with the wording, “WARNING, SHOCK & ARC FLASH HAZARD”, and shall include the following information in compliance with NFPA 70E-2021, Article 130.5(H) (see example label on following page).

1) Location Designation

2) Nominal Voltage

3) Arc Flash Boundary

4) Incident Energy

5) Working Distance

6) Shock Boundaries

7) Engineering report number, revision number and issue date.

7. Reporting and Recommendations:

1) The Offerors will issue a comprehensive electronic report within 6-8 weeks of receiving all necessary data.

2) The report will include all study results, recommendations for system improvements, and guidelines for interpretation.

3) The Offerors will provide recommendations for system upgrades, modifications, or operational changes to enhance safety and reliability.

8. Schedule:

1) Data request forms will be issued within 2-3 weeks of order receipt.

2) Final report and deliverables will be provided within 6-8 weeks after all required information is received.

9. Standards and Compliance:

All work will be performed in accordance with the latest applicable standards:

• IEEE Std 1584-2018

• NFPA 70E-2021

• ANSI

• NEC

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