Apparatus and method for power disturbance analysis and storage of power quality information

• US 5,899,960 A
• Filed: 08/21/1996
• Issued: 05/04/1999
• Est. Priority Date: 05/19/1994
• Status: Expired due to Term

• Current Assignee: Reliable Power Meters, Inc. (Fortive Corp.)
• Original Assignee: Reliable Power Meters, Inc. (Fortive Corp.)
• Inventors: Moore, Robert E., Nitz, Frederic W., Gipe, Michael A.
• Primary Examiner(s): Stamber, Eric W.
• Application Number:
  US08/701,030
• Time in Patent Office: 986 Days
• Field of Search: 364/483, 364/487, 364/492, 324/102, 324/112, 324/113, 324/121 R, 360/5, 361/97, 361/111, 702/57, 702/58, 702/59, 702/60
• US Class Current: 702/60
• CPC Class Codes: G01R 19/2513 Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging
• CPC Class Codes: G01R 31/42 AC power supplies

Abstract

A power monitoring system with associated signal processing and storage capabilities. Each leg of a three-phase power signal is simultaneously sampled on a plurality of channels to capture the instantaneous content of the power signal without time-skewing between the channels. In a further embodiment, the sampled data is converted into the frequency domain and parameters relating to the power quality of the power signal is derived from frequency-domain data.

Claims

1. A method for monitoring power disturbances in a three-phase power system:

simultaneously sampling at least three voltage measurements and at least three current measurements in a periodic fashion to obtain a plurality of sequences of analog samples, wherein said voltage measurements and current measurements are made on three power signals corresponding to each of three phases of the three-phase power system;

digitizing said plurality of sequences of analog samples to obtain sequences of digital samples;

converting said sequences of digital samples to frequency domain representations;

determining power quality information from said frequency domain representations; and

storing said power quality information.

2. The method of claim 1 further comprising steps of;

deriving root-mean-square (RMS) values for said voltage measurements from said frequency domain representations;

marking, responsive to a first disturbance of a selected one of said power signals, a beginning of a segment;

recording a time of the beginning of the segment and a steady-state value of the RMS voltage for said selected one of said power signals after the beginning of the segment;

recording a first group of samples of said selected one of said power signals surrounding the beginning of the segment;

marking, responsive to a second disturbance of said selected one of said power signals, an end of the segment;

recording a time of the end of the segment; and

recording a second group of samples of said selected one of said power signals surrounding the end of the segment.

3. A power measurement apparatus comprising:

a sampler for periodically and simultaneously sampling a plurality of electrical inputs to produce a plurality of sequences of samples with each one sequence corresponding to one of said plurality of electrical inputs, wherein said plurality of electrical inputs represent measured voltages and currents for a plurality of phases of a power signal;

an analog-to-digital converter coupled to an output of said sampler; and

a processor coupled to said analog-to-digital converter for transforming said sequences into a frequency domain representation.

4. The power measurement apparatus of claim 3 wherein the processor, is a digital signal processor.