SWITCHING EQUIPMENT 543 



different circuits. In this way the circuits of poor power-factor 

 can be discovered and steps taken to improve conditions if con- 

 sidered desirable. Where synchronous condensers are used for 

 power-factor correction, the power-factor indicator connected to 

 the bus or circuit to be corrected, becomes particularly valuable. 



(2) Generators in multiple will operate at maximum output 

 when they are all running at the same power-factor, reducing 

 cross currents to a minimum. The power-factor indicator affords 

 the easiest means of making this adjustment, since it shows the 

 power-factor of each machine at a glance without the necessity 

 of computing this from the readings of other instruments. 



(3) The reading of a power-factor indicator in connection 

 with that of an ammeter and voltmeter makes it possible to readily 

 figure the kilowatt output of a machine without the use of an 

 indicating wattmeter. 



Reactive Volt-ampere Indicators. (1) They measure the idle 

 or reactive portion of the power and are the only instruments 

 which do so directly. 



(2) In connection with the reading of an indicating wattmeter 

 the readings of the reactive volt-ampere indicator give an easy 

 means for figuring the power-factor. 



(3) They are considered in some cases more valuable than 

 power-factor indicators since they given an actual quantitative 

 reading in kilovolt-amperes while the power-factor indicator gives 

 a reading in per cent only. This fact can readily be seen from an 

 inspection of the following simple formula: 



f True watts 



Power-factor 



Apparent watts 



(Where the apparent watts is the vector sum of the true watts 

 and the reactive watts.) The reading of a power-factor indicator 

 gives no actual indication of magnitude of the idle current which 

 cause heating. For instance, at light load a power-factor of 0.7 

 or 0.8 would be no cause for alarm, while at full load or overload 

 it might mean serious heating due to idle currents. This is espe- 

 cially true on synchronous converters, where on account of the 

 rectifying action of such machines, the cross-section of copper is 

 made smaller than in a generator of the same capacity. 



Frequency Indicators. (1) Machines operate most econom- 



