Fig. 2,483.—Curve drawing voltmeter records at Kennett, Cal. The upper curve shows voltage regulation with synchronous condenser out of service, and the lower curve, with synchronous condenser in operation.
If the same size of wire were used at both unity and .6 power factor lagging, the energy loss would be about 2.8 times the loss at unity power factor, or about 28 per cent. Low lagging power factor on a system, therefore, will generally mean limited output of prime movers; greatly reduced kilowatt capacity of generator, transformer and line; and increased energy losses. The regulation of the entire system will also be poor.
Cost of Synchronous Condenser vs. Cost of Copper.—Referring to the example given in the preceding paragraph, and calculating the necessary extra investment in copper with the .6 power factor load, and copper at 17 cents per pound, the result is that 29,292 pounds more copper is required than with the power factor of .9 which means a total extra investment in copper alone of $5,000 (29,292 × $.17). A synchronous condenser of sufficient capacity to accomplish the same result would cost about the same amount. It would therefore cost less to install the condenser because at the same time a considerably increased capacity would be obtained from the alternators, transformers, etc.
Fig. 2,484.—Diagram showing the field current taken by a synchronous motor of normal design when operating at normal kva. input at various power factors. It will be noted that a slight departure from unity power factor necessitates a considerable change in field current. As the field curves increase with the square of the current, there is a rapid increase in temperature with leading current. This action of leading or lagging current serves automatically to keep the flux constant in the armature with changes in field excitation. When the motor is running at unity power factor, an increase in field excitation causes a leading current to flow, and at the same time this leading current demagnetizes the field until the density of the armature is restored to its normal value. If the field be decreased a lagging current flows which in turn magnetizes the field bringing the density back to its original value. Therefore, with a constant line voltage, the iron losses in a synchronous motor are approximately constant irrespective of the field excitations with the exception that the internal voltage will vary slightly due to the armature I R drop, the density being a trifle lower at full load than at no load.
Synchronous Condenser Calculations.—In figuring on the installation of a condenser for correcting power factor troubles, a careful survey of the conditions should be made with a view of determining just what these troubles are and to what extent they can be remedied by the presence of a leading current in the system.
