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7/23/2019 Guidelines for Arc Flash Hazard Evaluation.pdf
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Vale Inco Engineering Standard
Design Guide
Page 1 of 4
Number: 5001-01.01.111
Rev. 0
Guidelines for Arc Flash Hazard Evaluation3 Phase A.C. Systems
Issued Revised Approved Reviewed
November 3, 2008 G. Saini J. Fuller
SCOPE
This specifications covers guidelines and requirements for carrying out Arc FlashHazard Evaluations of 3 phase AC electric power systems at any surface or
underground plant at Vale Inco Ontario Operations.
The calculations for arc hazard evaluation shall determine the following:
Incident energy in cal/cm2 at working distances
Flash Protection Boundary distance – distance at which incident energy is 1.2cal/cm2.
Personal Protective Equipment (PPE) required.
Identification of system conditions/equipment ratings that may precipitatehazardous conditions e.g. circuit breaker ratings, system configurations,protection scheme used etc.
Recommendations for mitigating the exposure for all locations designatedhazard/risk category 3 or higher.
1. CODES AND REGULATIONS
The latest issues, amendments and supplements of applicable standards fromthe following codes and regulations shall apply, unless stated otherwise.
CSA Canadian Standards AssociationIEEE Institute of Electrical & Electronics EngineersNFPA National Fire Protection Association
OESC Ontario Electrical Safety CodeOHSA Occupational Health & Safety Association
2. STANDARDS
The latest issues, amendments and supplements of the following standards shallapply, unless stated otherwise.
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Vale Inco Engineering Standard
Design Guide
Page 2 of 4
IEEE 1584-2004 Guide for Performing Arc-Flash Hazard Calculations.
NFPA 70 E-2004 Standard for Electrical Safety in the Workplace
3. DEFINITIONS
For the purpose of this specification the Terms and Definitions as in IEEE 1584shall apply. For any terms not defined in this standard, IEEE 100 ”The
Authoritative Dictionary of IEEE Standards Terms” shall be referred.
4. DEVIATIONS FROM SPECIFICATIONS
No deviations from these specifications shall be permitted without specific writtenpermission of Vale Inco General Engineering Department.
5. TOOLS
Acceptable software package is “Easy Power”. Longhand calculations performedby a professional engineer licensed by the Province of Ontario are acceptable forsmall systems or for cases for which the software package does not haveprovision/yields anomalous results.
6. ENGINEERING REQUIREMENTS
6.1 System model
The system fault level and the X/R ratio at the nearest upstream 69 KV bus bar
shall be furnished by Vale Inco. Vale Inco, where available, shall provide singleLine Diagrams and Protection Co-ordination settings for the applicable upstreampart of the electrical system, from the location to be evaluated.
It shall be the responsibility of the engineer carrying out the study to field verifyaccuracy of information on the Single Line Drawings/relay settings and to collectany additional information required for an accurate and complete model of thesystem under study.
The hazard evaluation study shall include all operating scenarios such asnormal operating switch positions, tie conditions if present or possible parallel
feeds from transformers. Arc hazard shall be calculated for both, themaximum available fault current and the minimum available fault current.
All motors rated 50 HP and above shall be included in the system model.
All three winding transformers shall be represented as a 4-bus model withappropriate base conversions.
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Vale Inco Engineering Standard
Design Guide
Page 3 of 4
6.2 Specific requirements
The following requirements must be ensured by proper option selections, whereapplicable, in the software package.
The locations for arc hazard evaluations will be specified in the P.O. for thestudy. If this is not the case the engineer shall discuss the requirements withVale Inco and all locations to be evaluated shall be decided beforecommencement of the study.
The clearing time of the fault-interrupting device upstream of the faulted busbar shall be based on the actual branch current flow through the device.
The arc current shall be calculated based on the total 3 phase bolted faultcurrent available at the faulted bus.
Fault clearing time shall include the operating time of the relay or sensingcircuit and interrupting time of the circuit-interrupting device.
Calculations shall be carried out as per IEEE 1584 and NFPA 70E standards.The PPE requirements as per each of the standards shall be included in thereport.
Protective device clearing times shall be arrived at by selection of short circuitcurrent duration in cycles commensurate with protective device operatingcharacteristics e.g. induction disc over-current relays do not respond to DC
offset current portion of short-circuit current.
Irrespective of the default values provided by the software tool employed, thetypical values for working distances and bus gaps as specified in IEEE 1584shall be used.
Working distances and bus gaps for voltages above 13.8KV shall be based ontask performed on live equipment and actual bus clearances.
All transformer secondaries 600 V and below having incident energy of 20cal/cm2 or below shall be rechecked for accuracy of result.
7.0 DELIVERABLES
On completion of the study an “Engineering Report” shall be delivered. This shallinclude the following:
Short circuit calculation report
Model generated Single Line Diagram
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Vale Inco Engineering Standard
Design Guide
Page 4 of 4
Protection device Time Current Curves
- Fault current to be labelled as symmetrical or asymmetrical. Includeduration in cycles from fault commencement on label of fault current value.
- For numbering all equipment (switches, breakers, relays etc.) the model
should show the same numbers used on the Single Line Drawings.
- The model single line, reports and TCC shall all show the relay modelnumbers
List of drawings used for reference
Arc flash evaluation report comprising the following information in excelspreadsheet
- Bus identification number as generated by software
- Bus designation as per single line diagram
- Description of bus (e.g. transformer T2 secondary)
- Nominal voltage
- 3 phase symmetrical fault current
- Arc current (100%) and it’s protective device branch current and totalclearing time
- Arc current (85%) and it’s protective device branch current and totalclearing time
- Incident energy and arc protection boundary (greater of 100% or 85%)
- Recommendations for required PPE, mitigation strategy for category 3 andabove locations and a list of any other hazards revealed by study.
System model in electronic format. Additional hard copies of report as requiredin P.O.
Marked –Up single line drawings, if found different from Vale Inco provideddocuments.
END OF STANDARD 5001-01.01.111