Figs. 2,654 and 2,655.—Diagrams illustrating a simple method of determining bus capacity as suggested by the General Electric Co. Fig. 2,654 relates to any panel; the method is as follows: 1. Make a rough plan of the entire board, regardless of the number of panels to be ordered. The order of panels shown is recommended, it being most economical of copper and best adapted to future extensions. 2. To avoid confusion keep on one side of board everything pertaining to exciter buses, and on other side everything pertaining to A. C. buses. 3. With single lines represent the exciter and A. C. buses across such panels as they actually extend and by means of arrows indicate that portion of each bus which is connected to feeders and that portion which is connected to generators. Remember that "Generator" and "Feeder" arrows must always point toward each other, otherwise the rules given below do not hold. Note also that the field circuits of alternator panels are treated as D. C. feeders for the exciter bus. 4. On each panel mark its ampere rating, that is, the maximum current it supplies to or takes from the bus. For A. C. alternator panels the D. C. rating is the excitation of the machines. 5. Apply the following rules consecutively, and note their application in fig. 2,654. (For the sake of clearness ampere ratings are shown in light face type and bus capacities in large type.) A. Always begin with the tail of the arrow and treat "generator" and "feeder" sections of the bus separately. B. Bus capacity for first panel = ampere rating of panel. C. Bus capacity for each succeeding panel = ampere rating of panel plus bus capacity for preceding panel. (See sums marked above the buses in fig. 2,654.) D. For a panel not connected to a bus extending across it, use the smaller value of the bus capacities already obtained for the two adjoining panels. (See exciter bus for panel C.) E. The bus capacity for any feeder panel need not exceed the maximum for the generator panels (see A. C. bus for panel G) and vice versa (see exciter bus for panel B). Hence the corrections made in values obtained by applying rules B and C. The arrangement of panels shown in fig. 2,654 is the one which is mostly used. The above method may, however, be applied to other arrangements, one of which is shown in fig. 2,655. Here the generators must feed both ways to the feeders at either end of the board so that in determining A. C. bus capacities it is necessary to first consider the generators with the feeders at one end, and then with the feeders at the other end as shown by the dotted A. C. buses. The required bus capacities are then obtained by taking the maximum values for the two cases.
Fig. 2,656.—End view showing general arrangement of switchboards for 240, 480, and 600 volt alternating current. The cut shows a single throw oil switch mounted on the panel.
In the case of a dynamo, a good representative panel would have mounted upon it a reverse current circuit breaker, an ammeter, a double pole main switch (or perhaps a single pole switch, since the circuit breaker could also be used as a switch) a double pole socket into which a plug could be inserted to make connection with a voltmeter mounted on a swinging bracket at the end of the board; a rheostat handle, the spindle of which operates the shunt rheostat of the machine, the rheostat being placed either directly behind the spindle, if of small size, or lower down with chain drive from the hand wheel spindle, if of larger size, a field discharge switch and resistance, a lamp near the top of the panel for illuminating purposes, a fuse for the voltmeter socket, and, if desired, a watthour meter. If the dynamo be compound wound, the equalizing switch will generally be mounted on the frame of the machine, and in some cases the field rheostat will be operated from a pillar mounted in front of the switchboard gallery. If the generator be for traction purposes, the circuit breaker is more often of the maximum current type, and a lightning arrester is often added, without a choke coil, the latter as well as further lightning arresters being mounted on the feeder panels.
Figs. 2,657 and 2,658.—Two views of a feeder panel, showing general arrangement of the devices assembled thereon. A, circuit breaker; B, ammeter; C, voltmeter; D, switches.