Harmonic-adjusted power factor meter

• US 5,298,855 A
• Filed: 10/06/1992
• Issued: 03/29/1994
• Est. Priority Date: 02/25/1992
• Status: Expired due to Fees

• Current Assignee: Basic Measuring Instruments, Inc.
• Original Assignee: Basic Measuring Instruments, Inc.
• Inventors: McEachern, Alexander, Grady, W. Mack
• Primary Examiner(s): Karlsen, Ernest F.
• Application Number:
  US07/957,356
• Time in Patent Office: 539 Days
• Field of Search: 324/142, 324/141, 324/137, 324/138, 324/116, 364/483, 340/646
• US Class Current: 324/142
• CPC Class Codes: G01R 21/006 Measuring power factor

Abstract

An electric power measuring system wherein power factor measurements are adjusted to reflect the adverse economic effects of harmonic currents and voltages. Well-known techniques are used to acquire frequency spectra that represent the voltages and currents present at the measuring point. These spectra are weighted in such a way that non-fundamental currents are increased and non-fundamental voltages are decreased. The weighted spectra are used to calculate a harmonic-adjusted volt-ampere measurement, which is then accumulated to form a harmonic-adjusted volt-ampere-hour measurement. The weighting functions for voltage and current are selected to approximate the economic impact on the AC power generating, transmission, and distribution system of non-fundamental currents and voltages. The resulting harmonic-adjusted volt-ampere-hour measurement is used to calculate a harmonic-adjusted power factor measurement.

Claims

1. An instrument for measuring electric power consumed by a power consumer, comprising:

a. first means for measuring time-domain current samples;

b. second means, coupled to receive the time-domain current samples, for transforming the time-domain current samples to frequency-domain current samples;

c. first storage means, coupled to the second means, for storing current adjustment tables;

d. first adjustment means, coupled to receive the frequency-domain current samples and to the first storage means, for adjusting the frequency-domain current samples and for forming an adjusted current having a predetermined relationship to the frequency-domain current samples;

e. third means for measuring time-domain voltage samples;

f. fourth means, coupled to receive the time-domain voltage samples, for transforming the time-domain voltage samples to frequency-domain voltage samples;

g. second storage means, coupled to the fourth means, for storing voltage adjustment tables;

h. second adjustment means, coupled to receive the frequency-domain voltage samples and to the second storage means, for adjusting the frequency-domain voltage samples for forming an adjusted voltage having a predetermined relationship to the frequency-domain voltage samples; and

i. fifth means for calculating, coupled to receive the adjusted current and the adjusted voltage, for forming an adjusted power factor.