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.