Additional time must be added if a time delay function is installed and operating. This can be broken down as follows: actual breaker time (approximately 2 cycles), plus relay operating time of approximately 1.74 cycles, plus an additional safety margin of 2 cycles, giving a total time of approximately 6 cycles. The clearing time of a 5-kV and 15-kV circuit breaker is approximately 0.1 second or 6 cycles if the instantaneous function is installed and operating. The clearing time for a current-limiting fuse is approximately ¼cycle or 0.004 second if the arcing fault current is in the fuse’s current-limiting range. For transformers with MVAratings below 0.75 MVA, multiply the transformer MVA rating by 1.25. MVAbf=bolted fault MVA at point involved. Where:Dc=distance in feet of person from arc source for a just curable burn (that is, skin temperature remains less than 80☌). The arc flash boundary distance is calculated in accordance with the following formulae: The short-circuit symmetrical ampacity, Isc, from a bolted three-phase fault at the transformer terminals is calculated with the following formula:Į70e-100_2012.png where Isc is in amperes, V is in volts, and %Z is based on the transformer MVA.Ī typical value for the maximum power, P (in MW) in a three-phase arc can be calculated using the following formula: 1584Ĝalculates incident energy and arc flash boundary for:Ģ08 V to 15 kV three-phase 50 Hz to 60 Hz 700 A to 106,000 A short-circuit current and 13 mm to 152 mm conductor gapsĭ.8ĚNSI/IEEE C2 NESC, Section 410, Table 410-1 and Table 410-2Ĝalculates incident energy for open air phase-to-ground arcs 1 kV to 500 kV for live-line workĭ.2 Basic Equations for Calculating Arc Flash BoundaryDistances. Table D.1 Limitation of Calculation Methodsĭ.2, D.3, D.4 Ralph Lee paperĜalculates arc flash boundary for arc in open air conservative over 600 V and becomes more conservative as voltage increasesĭ.5ĝoughty/Neal paperĜalculates incident energy for three-phase arc on systems rated 600 V and below applies to short-circuit currents between 16 kA and 50 kAĭ.6 Ralph Lee paperĜalculates incident energy for three-phase arc in open air on systems rated above 600 V becomes more conservative as voltage increasesĭ.7 IEEE Std. The limitations of methods summarized in Annex D are described in Table D.1. It is important to investigate the limitations of any methods to be used. This informative annex is not a part of the requirements of this NFPA document but is included for informational purposes only.Īnnex D summarizes calculation methods available for calculating arc flash boundary and incident energy. It does not store any personal data.Informative Annex D Incident Energy and Arc Flash Boundary Calculation Methods The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. The cookie is used to store the user consent for the cookies in the category "Performance". This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other. The cookies is used to store the user consent for the cookies in the category "Necessary". The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". The cookie is used to store the user consent for the cookies in the category "Analytics". These cookies ensure basic functionalities and security features of the website, anonymously. Necessary cookies are absolutely essential for the website to function properly.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |