424 ELECTRICAL MACHINERY 



be two sets of coils in a power-factor meter, just as there are 

 two coils in a wattmeter. 



The stationary coils of a power-factor meter produce a 

 magnetic field which is in phase with the current in the 

 circuit. The movable coil, which is connected across the 

 load circuit (just as the potential coil of a wattmeter is 

 connected across the circuit), produces a magnetic field 

 the phase of which depends upon the phase of the line 

 voltage. The position which the movable coil takes under 

 the action of the two magnetic fields, depends upon the phase 

 relation of the voltage and current. The pointer which 

 the movable coils carry, moves over a scale calibrated 

 directly in the values of cos <j>. 



136. Switchboards. Originally the switchboard was a 

 very crude affair, a wooden rack on the front of which were 

 mounted the switches and fuses necessary for the operation 

 of the plant. To-day the switchboard is probably the 

 most important part of a generating plant; if an accident 

 happens at the switchboard, the whole plant may be 

 crippled. 



The switchboard is the place to which the electric power 

 from the generators is supplied and metered and thence 

 distributed to the outside system through a group of feeders. 

 On it are located all the switches, meters, and protective 

 devices of the plant and from it the operation of the whole 

 plant, both inside and outside the power house is controlled. 



Panels. A modern switchboard is divided into a number 

 of panels; each panel serves for the control either of one 

 generator or of a feeder or group of feeders. They are 

 styled the generator panels and feeder panels; in addition 

 there may be panels for exciters, recording meters, etc. 



Construction of a Switchboard. The material of which 

 the board is made must be a good insulator and of pleasing 

 appearance; slate is sometimes used in cheap boards but 

 generally a high grade of marble is employed. The marble 

 is a better insulator than slate (which is likely to have 



