IEC 62305-1 pdf download

IEC 62305-1 pdf download.Protection against lightning – Part 1: General principles
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply. 3.1 lightning flash to earth electrical discharge of atmospheric origin between cloud and earth consisting of one or more strokes 3.2 downward flash lightning flash initiated by a downward leader from cloud to earth NOTE A downward flash consists of a first impulse, which can be followed by subsequent impulses. One or more impulses may be followed by a long stroke. 3.3 upward flash lightning flash initiated by an upward leader from an earthed structure to cloud NOTE An upward flash consists of a first long stroke with or without multiple superimposed impulses. One or more impulses may be followed by a long stroke. 3.4 lightning stroke single electrical discharge in a lightning flash to earth 3.5 short stroke part of the lightning flash which corresponds to an impulse current NOTE This current has a time T 2 to the half peak value on the tail typically less than 2 ms (see Figure A.1 ). 3.6 long stroke part of the lightning flash which corresponds to a continuing current NOTE The duration time T LONG (time from the 1 0 % value on the front to the 1 0 % value on the tail) of this continuing current is typically more than 2 ms and less than 1 s (see Figure A.2). 3.7 multiple strokes lightning flash consisting on average of 3-4 strokes, with typical time interval between them of about 50 ms NOTE Events having up to a few dozen strokes with intervals between them ranging from 1 0 ms to 250 ms have been reported. 3.8 point of strike point where a lightning flash strikes the earth, or protruding structure (e.g. structure, LPS, line, tree, etc.) NOTE A lightning flash may have more than one point of strike. 3.9 lightning current i current flowing at the point of strike 3.1 0 current peak value I maximum value of the lightning current 3.1 1 average steepness of the front of impulse current average rate of change of current within a time interval Δt = t 2 – t 1 NOTE It is expressed by the difference Δi = i(t 2 ) – i(t 1 ) of the values of the current at the start and at the end of this interval, divided by the time interval Δt = t 2 – t 1 (see Figure A.1 ). 3.1 2 front time of impulse current T 1 virtual parameter defined as 1 ,25 times the time interval between the instants when the 1 0 % and 90 % of the peak value are reached (see Figure A.1 )3.1 3 virtual origin of impulse current O 1 point of intersection with time axis of a straight line drawn through the 1 0 % and the 90 % reference points on the stroke current front (see Figure A.1 ); it precedes by 0,1 T 1 that instant at which the current attains 1 0 % of its peak value 3.1 4 time to half value on the tail of impulse current T 2 virtual parameter defined as the time interval between the virtual origin O 1 and the instant at which the current has decreased to half the peak value on the tail (see Figure A.1 ) 3.1 5 flash duration T time for which the lightning current flows at the point of strike 3.1 6 duration of long stroke current T LONG time duration during which the current in a long stroke is between 1 0 % of the peak value during the increase of the continuing current and 1 0 % of the peak value during the decrease of the continuing current (see Figure A.2) 3.1 7 flash charge Q FLASH value resulting from the time integral of the lightning current for the entire lightning flash duration 3.1 8 impulse charge Q SHORT value resulting from the time integral of the lightning current in an impulse 3.1 9 long stroke charge Q LONG value resulting from the time integral of the lightning current in a long stroke 3.20 specific energy W/R value resulting from the time integral of the square of the lightning current for the entire flash duration NOTE It represents the energy dissipated by the lightning current in a unit resistance. 3.21 specific energy of impulse current value resulting from the time integral of the square of the lightning current for the duration of the impulse NOTE The specific energy in a long stroke current is negligible.