the3DUtility #6 - Substation Lightning Protection from the IEEE Std 998 Rolling Sphere Method.

Application of IEEE Std 998 - Guide for Direct Lightning Stroke Shielding of Substations. This video presents a method for applying the equations of the Rolling Sphere method of protection design utilizing plain vanilla AutoCAD or BricsCAD. This application utilizes standard AutoCAD/BricsCAD commands. The following AutoLisp routine is used to overcome AutoCAD's and BricsCAD's inability to construct an Arc from a point tangent to a line.

For more information on 3D substation design and more videos in this series please go to https://www.the3dutility.com

(I recently discovered an error in the lisp program. I have modified it below. It was caused by a difference in the Arc command between BricsCAD and AutoCAD. If you tried it and it failed, you might want to copy it again and give it another try.)

; Constants
(setq END 1) ;ENDpoint
(setq NOD 8) ;NODe
(setq NEA 512) ;NEArest

;Degrees to radians conversion
(defun dtr(y)
(* pi (/ y 180.0))
)
;Radians to degrees conversion
(defun rtd(y)
(* 180.0 (/ y pi))
)

(defun c:aptr() ;Arc, Point, Tangent, Radius
;Construct an arc given a starting point, a line in the X-plane tangent to the arc
;and the radius of the arc. The UCS must be in the normal X-Y plane.
(setq osm (getvar "Osmode"))
(setvar "Osmode" (+ END NEA NOD))
(if (= rad nil)(setq rad 0))
(setq pt1 (getpoint "Get first point of arc:")
pt2 (getpoint pt1 "Get point on tangent of arc:")
rr (distof (getstring (strcat "Enter Radius of Arc #" (rtos rad) "%:")))
)
(if (/= rr nil)(setq rad rr))
(if (= rad 0)(exit)) ;must have a value for the Radius
(setq y1 (cadr pt1)
y2 (cadr pt2)
yy (- y2 (- y1 rad))
d1 (sqrt(- (* rad rad)(* yy yy)))
d2 (- y1 y2)
chord (sqrt (+ (* d1 d1)(* d2 d2)))
an (dtr (- 0 (rtd(atan d2 d1))))
pt3 (polar pt1 an chord))
(setvar "Osmode" 0)
(command "arc" pt1 "e" pt3 "r" rad)
(if (# (car pt2)(car pt1)) ;picked point on negative side of X-axis
(command "mirror" "l" "" pt1 (polar pt1 (dtr 90) 100) "y"))
(setvar "Osmode" osm)
)
Note: Substitute left angle bracket (less than) for # and right angle bracket (greater than) for %. The angle bracket chars are not allowed by YouTube.

You can download the spreadsheet in the video with this link - https://www.the3dutility.com/Rolling%.... However, you should be very familiar with IEEE 998 before applying it. I suggest you use it to work through the example calculations in the Annex before applying it to your work. The Spreadsheet also contains a macro required to find the value of Rc through Goal Seeking. You may have to adjust your security level to use this.