Measurement of maximum demand

“Maximum demand” has become an increasingly important item in rates for the sale of electric service since the appearance of Doctor John Hopkinson´s notable paper, “Cost of Electricity Supply,” in the year 1892 — nearly 50 years ago. The writer estimates that the demand-measuring equipment which is now being used by the public utilities of the United States has a value of the order of $100,000,000. This is an index of its present importance. The object of the present paper is to describe in detail the thermal-storage method of measuring the maximum demand of a user of electric service. A comparison is made between this method, which at each instant of time indicates the logarithmic average load over some nominal time interval, and the commonly used “block-interval” method, which indicates the arithmetic average load over the same time interval. Also, the effect of using a modified design of thermal-demand meters is discussed. The writer has contributed a number of previous papers dealing with this same general subject, reference to which will be found at end of paper.