Publisher's Synopsis
Excerpt from Instructions for Testing Electrical Apparatus
Each of the principal testing sections is equipped with a number of small direct current generators capable of giving a variable voltage for testing work which are known as exciters, because they are used frequently for field excitation. These generators are direct motor driven, steam turbine driven, engine driven, or belted sets. Turbine driven sets consist of a Curtis turbine driving one or two generators. When the turbine drives two generators, the switchboard is arranged so that the two armatures can be connected in series or multiple Belted sets are considered as temporary testing sets and are only used in emergency, since their use requires greater care and attention. Their operation is also a possible source of danger, in consequence of the possibility of slipping or breaking belts, etc.
When an exciter runs in series with a power circuit in order to boost or buck the voltage the following points require careful consideration. Under no circumstances must the source of driving power be disconnected while the exciter carries load. Therefore, no machine must ever be used in such cases unless it is equipped with a speed limiting device in good working order, which will automatically open the circuit-breaker of its armature circuit, should the machine begin to operate at excessive speed. Particular care should always be taken to see that all safety devices, in operation with such machines, are in good working condition before using them. All permanently installed motor generator sets have a speed limiting device and low voltage release installed on the motors and generators. These are wired in series, so that in case the speed rises suddenly, both motor and generator circuit breakers will be automatically opened and the set shut down. For the same reason, if the power supply from which the sets are driven fails all breakers will be Opened automatically. On direct current turbine driven' sets the circuit breaker tripping coils are wired so that, when the emergency governor operates, their circuits are broken and the breakers in the generator armature circuit are opened.
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