Light Table For Relay Coordination Engineers

Icon "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.

Icon 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.

Icon 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.

Icon The Light Table program runs under Windows 95/98.