[Electric engineering.] . the electromagnetreleases its armature, thus opening the switch and discon-necting the cells from the machine. 66. Automatic Overload-and-TJnderload Switch.— Fig. 53 shows a special automatic switch designed to protectthe dynamo from any backwardrush of current and, also, to pro-tect the battery from coils a and^ are connectedin series between the battery anddynamo, as indicated at A, Fig. the current becomes excessive,coil b pulls up a core that releasesa trip and causes the arm to flyout, thus breaking the circuitat d, d. When the battery ischarg
[Electric engineering.] . the electromagnetreleases its armature, thus opening the switch and discon-necting the cells from the machine. 66. Automatic Overload-and-TJnderload Switch.— Fig. 53 shows a special automatic switch designed to protectthe dynamo from any backwardrush of current and, also, to pro-tect the battery from coils a and^ are connectedin series between the battery anddynamo, as indicated at A, Fig. the current becomes excessive,coil b pulls up a core that releasesa trip and causes the arm to flyout, thus breaking the circuitat d, d. When the battery ischarging, coil a holds its armature,but if the current becomes verysmall, as it must do before itbegins to reverse and flow backfrom the batteries, the armatureis released, which action releasesthe catch and allows c to fly instrument is, therefore, a FlG-53- protection against both underloads and overloads. For example, a battery might be charging and the speedof the dynamo might drop or the belt fly off. In either. 56 ELECTRIC TRANSMISSION. 15 case, the voltage of the dynamo would drop and the charg-ing current fall to zero. If the circuit were not opened, acurrent would flow from the battery through the dynamoand run it as a motor. Another instance in which damagemight result if an underload switch were not used is in casethe field circuit of the dynamo should happen to become
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