~"Static" Interrupters.~--A static interrupter is a _combination of a choke coil and a condenser_, the two being mounted together and placed in a tank and oil insulated.
It is used on high pressure circuits and its function is to so delay the erroneously called "static" wave in its entry into the transformer coil, that a considerable portion of the latter will become charged before the terminal will have reached full pressure.
A choke coil alone sufficiently powerful to accomplish this would be too large and costly on very high pressure and would interfere with the operation of the system.
~Ques. How is the condenser and choke coil connected?~
Ans. The condenser is connected between the line and ground behind the choke coil near the apparatus to be protected as shown in fig. 2,413.
[Illustration: FIG. 2,413.--Diagram showing connections of static interrupter for protecting a transformer.]
~Ques. What is the effect of the condenser?~
Ans. The condenser, which has a very small electrostatic capacity, has no appreciable effect upon the normal operation, but a very powerful effect upon the static wave on account of its extremely high frequency.
~Regulation of Alternators.~--Practically all the methods employed for regulating the voltage of direct current dynamos and circuits, are applicable to alternators and alternating current circuits. For example: in order that they shall automatically maintain a constant or rising voltage with increase of load, alternators are provided with composite winding similar to the compound winding of direct current dynamos, but since the alternating current cannot be used directly for exciting the field magnets, an accessory apparatus is required to rectify it or change it into direct current before it is used for that purpose.
It is a fact, however, that composite wound alternators do not regulate properly for inductive as well as non-inductive loads.
In order to overcome this defect compensated field alternators have been designed which automatically adjust the voltage for all variations of load and lag. These machines have already been described.
~Alternating Current Feeder Regulation.~--With slight modification, the various methods of feeder regulation employed with direct current, may be applied to alternating current distribution circuits. For instance, if a non-inductive resistance be introduced in any electric circuit, the consequent drop in voltage will be equal to the current multiplied by the resistance. Therefore, feeder regulation by means of rheostats is practically the same in the case of alternating current as in that of direct current. In the case of the former, however, the effect of self-induction may also be utilized to produce a drop in voltage. In practice, this is accomplished by the use of self-induction coils which are commonly known as reactance coils.