Fig. 2,489.—Diagram for synchronous condenser calculation for cases where it is desired to drive some energy load with the condenser and still bring the total power factor to .9.
The standard 300 kva. condenser would evidently raise the power factor slightly above .9 power factor leading.
By reference to the chart, fig. 2,490, the size of the required condenser can be obtained direct without the use of the above calculation. The method of using this curve is as follows: Assume a load of say 3,000 kw. at .7 power factor and that it be desired to raise the power factor to .9. Run up the vertical line at 3,000 kw. to the .7 power factor line, and from there along the horizontal line to the margin and find a wattless component at this power factor of 3,000 kva., approximately. Again run up the 3,000 kw. vertical line to the .9 power factor line and from there along the horizontal line to the margin and find a wattless component of 1,500 kva. The rating of the condenser will then be 3,000 kva. - 1,500 kva. = 1,500 kva. This table of course can be used for hundreds of kilowatts as well.
Fig. 2,490.—Curve showing the relation of energy load to apparent load and wattless components at different power factors.
For determining the rating of a synchronous motor to drive an energy load this curve is not so valuable, although it can be used in determining the wattless component direct in all cases where the energy component and power factor are known. Knowing this energy component and power factor or wattless component, the energy load can obviously be found by referring to the curved lines on the diagrams, the curve that crosses the junction of the vertical energy line and the power factor or wattless component line giving the total apparent kva.
CHAPTER LXII
INDICATING DEVICES
Alternating current ammeters or voltmeters indicate the virtual values of the current or pressure respectively, that is to say, they indicate, the square root of the mean square of a variable quantity.