The main circuit after passing through the main switch is further protected on both sides by circuit breakers. Leaving these protective devices, the left hand side of the circuit includes the alternating current ammeter, and then connects with one of the bus bars. The right hand side of the circuit runs from the circuit breaker to the other bus bar. As many feeder circuits may be connected to the bus bars and supplied with current by the alternator as the capacity of this machine will permit. If, however, there be more than one feeder circuit, each must be wired through a double pole switch.
In alternating current work the pressures dealt with are much greater than those in direct current installations, so that proportionate care must be taken in the wiring to remove all possibility of grounds.
To locate such troubles, however, should they occur, a ground detector is provided. For this class of work the ground detector must be an instrument especially designed for high pressure circuits. Two of its terminals should be connected to the line wires and the third, to ground; in case of a leak on the line, a current will then flow through the detector and by the position of the pointer the location and seriousness of the leak may be judged.
A step down transformer is also rendered necessary for the voltmeter and the pilot lamps, owing to the high voltage in use. The primary winding of the transformer is connected across the main circuit of the alternator. This connection should never be made so that it will be cut out of circuit when the main switch is open, for it is always advisable to consult the voltmeter before throwing on the load by closing this switch.
Figs. 2,826 to 2,829.—General Electric diagrams of connections. A, ammeter; C.B, circuit breaker; C.P, candle power; C.T, current transformer; D.R, discharge resistance; F, fuse; F.S, field switch; L, lamp; O.C, overload coil; P.P, pressure plug; P.R, pressure receptacle; R.C, reactance; rheo, rheostat; R.P, synchronizing plug, running; R.S, resistance; S, switch; S.I, synchronous indicator: S.P, synchronizing plug, starting; S.R, synchronizing receptacle: V, voltmeter.
Ques. How does the switchboard wiring for a two phase system differ from the single phase arrangement shown in [fig. 2,820?]
Ans. It is practically the same, except for the introduction of an extra ammeter and a compensator in each of the outside wires, and in the use of a four pole switch in place of the two pole main switch.
The ammeters, of course, are for measuring the alternating currents in each of the two phases or legs of the system, and the compensators are two transformers with their primary coils in series with the outside wires and their secondary coils in series with each other across the outside wires. The transformers thus connected are known as compensators or pressure regulators, and as such compensate for the drop in pressure on either side of the system.