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The Derry Collard Co.

Figure 60

Single phase synchronizer. proper relation to each other to be connected. With continuous current generators all we have to look after in connecting them in parallel is the voltages of the machines, which must be the same; but with alternating current generators, we must also make sure that they are running at velocities that will make the frequencies the same, and, further, that the currents are in phase with each other; in other words, the machines must be synchronized as to frequency, and the currents must be brought into phase before they can be connected in parallel. The apparatus required to accomplish this, and the way in which it is used, can be clearly explained in connection with the diagrams, Figs. 60 to 62.

Fig. 60 illustrates the synchronizing apparatus for a single phase system. I and 2 represent two single phase generators arranged to be connected in parallel with the two bus bars shown. H and H' are transformers whose primaries are connected with the two machines in the manner shown. If the e. m. f, of the formers are not required, as their only office is to furnish generators is one hundred volts, or thereabout, the trans

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secondary currents of low voltage. At a a and b b incandescent lamps are connected in the circuit of the secondary coils of the transformers in the manner shown. Suppose generator i is connected with the bus bars, then the current from it at the instant when it flows upward in the left side line will traverse the primary coil of H in the

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Synchronizers.

direction indicated by the arrows, and the current induced in the secondary will flow downward through the left side a lamp, causing it to light up. Let the main switch of generator 2 be open and the switch connecting H' closed in the direction indicated, then current will pass from the bus bars through the primary coil of Il' in the direction indicated by the arrows, and this will induce a current in the secondary of H' in the direction of the solid arrows, causing the right side o lamp to light up. With the current flowing in the two secondary coils in the direction of the solid arrows, there will be no current passing through the b b lamps. If, however, the connections of the primary of H' are reversed, the current in its secondary will flow in the direction of the dotted arrows and then the lamps b b will light up as well as lamps a a. Suppose that we now swing over the switch in the circuit of H' so as to connect with the generator 2 below the main switch, then if at a given instant the two generators are generating currents that flow in the same direction, the current of: generator 2 will flow through H' in the same direction it would if it came from generator 1, as is clearly indicated by the arrows; hence, if the connection of the primary coil of H' is such that the b b lamps will remain dark when both transformers are traversed by current from generator 1, they will remain dark when the current comes from generator 2, providing the two machines are generating currents that are in phase. If the connections of H' are reversed, so that b b will light up when the current comes from 1, then they will light up if it comes from 2, providing the two machines are in phase. This is what will occur if the two generators are

Synchronizers.

running in synchronism. If generator 2 is running faster or slower than 1, the lamps b V will light up and go out periodically, as often as the current of 2 comes into phase with 1. If generator 2 is running slower than i the lamp a on the right will not be as bright as the one on the left. If 2 is running faster than i the right side a lamp will be brighter than the other. As the velocities of the two generators approach equality, the fluctuations in the b b lamps will come at longer intervals, and when both machines reach the same speed the fluctuations will stop and the lamps will remain dark or bright continuously, according to how the primary of H' is connected, providing the currents are in phase or nearly so. When this stage is reached, the main switch of 2 can be closed, and thus the generator is connected with the bus bars in parallel with 1. After the two generators are connected the switches of their transformers can be opened, or they can be turned so as to connect with the generators below the main switches.

Fig. 61 shows the synchronizing arrangement for two two-phase generators. As will be noticed, it is simply a duplicate of Fig. 73. The arrangement of lamps, however, is different, the a a lamps being omitted. As will be seen, these last-named lamps are not actually necessary, for if generator 1 is running and the switches of H' K' are open, the currents passing through the primaries of H and K will generate currents in the secondaries that will light up the lamps LL L'L', and if the switches of H' K' are now closed, the currents generated in the secondaries of these transformers will be either in phase or in opposition with the currents from the secondaries of H K, so that they will either help to light Synchronizers.

up the lamps, and make them brighter by doubling the e. m. f. or they will extinguish the lamps by neutralizing the e. m. f.

Fig. 62 shows the synchronizing arrangements for two three-phase generators, and as the principle of action is the same as in the previous diagrams, an extended explanation will not be necessary. In this diagram it will be noticed that the primaries of the transformers can be connected with the generators below the main switches only. It is not necessary to provide a switch that will connect on either side of the main switch, because the upper connections are only required to ascertain the direction in which the transformer primaries are connected, and this has only to be found out when the switchboard is first tried, or when through some circuit changes doubt may arise as to the actual connection. In all such cases, however, if the upper connection with double throw switches are not provided, temporary connections can be made in any convenient manner.

The generators shown in Figs. 57 to 59 are separately excited only, but in almost every case alternators are made so that the field is magnetized in part by a current derived from an independent source and in part by a current derived from the armature, this current being rectified by means of a commutator. The object of this arrangement is to provide means whereby the magnetism of the field may increase as the current increases, so as to maintain the e. m. f. as nearly constant as possible. There are many ways in which the armature and independent currents utilized for magnetizing the field are adjusted, and also in the way in which the armature current is obtained. In some cases it is taken directly from

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