"Light Table" is a fond allusion to the back-lighted, glass-topped
tables used by yesterday's relay engineers to coordinate protection
devices. Sheets of paper containing the time vs. current curves of
relays, fuses, etc., were stacked on the light table, and then
shifted around until a satisfactory combination of operating times was
obtained. The light from the table and the thinness of the paper
permitted the curves to be viewed simultaneously. Today, the light
tables are gone, replaced by a variety of graphics-oriented computer
programs. These programs allow the user to specify
the parameters of each device (such as relay pickup, time-dial, etc.),
and then the resulting curves are drawn on the screen along with the
corresponding operating times.
The Light Table program, conversely, allows each of the curves
to be simply "moved around", one at a time, in any order,
until a satisfactory
coordination is achieved, and the device parameters are then obtained
as a result. This creates a very user friendly atmosphere, since there
is no constant "back and forth" cycle that the user must navigate
between the drawing and various parameter input edit boxes, and there
is no annoying flicker caused by complete screen erasures followed by
re-draws of the entire collection of devices.
Relays, Fuses, and Reclosers may be easily added to a study from
corresponding pull down menu item list boxes. Cooper microprocessor
reclosers are also available, which can have operating time curves
that seem quite spectacular to anyone who has not seen them
before. Existing devices in a study may also be replaced from the
menu bar, or deleted. Entire "cases" (combinations of devices
comprising a particular coordination) may be saved and recalled at any
time. Complete operating directions and an overview of the program
may be obtained from the Help pull down menu.
The Light Table program runs under Windows 95/98.