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To: File From: Jon Hagen Date: 10-21-99 Subject: Lightning protection references Lightning Protection Code 1980 ANSI/NFPA 78 AO Library, TH9057.N3 1980 p41 height h 50 ft cone of p42 height 50 ft:
ZO N ES O F PR O TEC TO N I

M A S T T A L L ER T H A N 5 0 F T .

M A S T SHOR T ER T H AN 5 0 F T .

1 0 0 FT RAD US I

4 5 .0 0 0 °

excerpts: Mast with not exceeding protects radius h. Mast with greater than protection determined

by volume not accessible to an imaginary sphere with a 100 ft radius.

p3-15: No bend of a conductor shall form an included angle of less than 90 degrees nor shall have a radius of bend less than 8 inches. Lightning and Lightning Protection, Wm. C. Hart and Edgar W. Malone, Don White Consultants, Inc. 1979 AO Library TH9061.H325 Includes interesting historical information. Lightning characteristics: A lightning stroke typically has several current pulses, all of the same polarity. Successive pulses have lower peak currents but last longer and transfer more charge. The median peak current for a first stroke is about 20,000A. A typical first stroke a rise time of 5 to 10 microseconds and a fall time of 10 to 20 microseconds. First stroke peak current greater than 2 to 8 kA: 90% probability greater than 10 to 25 kA: 50% probability 1


greater than 40 to 60 kA: 10% probability Maximum observed peak current: 230 kA More than 1 to 2 pulses in a stoke: 90% probability More than 2 to 4 pulses in a stoke: 50% probability More than 5 to 11 pulses in a stroke: 10% probability More than 5 to 10 ms between pulses: 90% probability More than 30-40 ms between pulses: 50% probability More than 80 to 130 ms between pulses: 10% probability Maximum observed time between pulses: 500 ms On page 3.16, four model strokes are given: low amplitude, typical, high amplitude, and extreme amplitude. The typical stroke has four pulses, separated by 42 ms. This model pulse is shown in three Mathcad plots of current (in Amperes): the leading edges of each pulse, the duration of each pulse, and the complete 4-stroke pulse.

2


a1

1
5 4.8 . 10

a2

1
4 4.2 . 10

b1

1 10
6

b2

1
6 4.5 . 10

A1

28000

A2 e

28000 Be e

A3

I1 ( t ) I3 ( t )

A1 e

a1 . . t b1 t a2 . . t b2 t . .

5. A2 6 I2 ( t ) I4 ( t )

A4

2. A2 3

B

115

a1 . . t b1 t a2 . . t b2 t A2 . e e B. e e a1 . . t b1 t a2 . . t b2 t A4 . e e B. e e

a1 . . t b1 t a2 . . t b2 t A3 . e e B. e e

t

6 6 6 .05 . 10 , . 10 . 10 10 4 3 10

t

6 6 6 .5 . 10 , 00 . 10 . 1 10 I1( t ) I2( t ) 4 3 10 I3( t ) I4( t ) I1( t ) I2( t ) I3( t ) I4( t ) 4 1 10 4 2 10 0 0 5 10 t 6 1 10 5 4 1 10 4 2 10

t
0 0 5 10 t 5 1 10 4

.00001 , . .00002 . .3

National

I( t)

I1 ( t )

( t> ) .042 ) . 42 I2 ( t .0

( ( t> . ( t> . 2 .3 ( t 2 .042 ) .042 ) . I 3 .4 ( t 3 .042 ) ) .042 ) . I

4 3 10

4 2 10 I( t ) 4 1 10

0

0

0.1 t

0.2

0.3

Association of Broadcasters Engineering Handbook 8th Ed. Section 2.2, Lightning Protection for Broadcast Facilities excerpts: Protecting equipment from the effects of lightning involves a combination of grounding, bonding, and surge suppression. Grounding provides a path to introduce lightning currents into the earth. Bonding serves to equalize lightning potential differences between various elements of the equipment to be protected. Surge suppression limits differences in 3


potential on active circuits which cannot be directly bonded.

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