Ieee std 1159-1995, ieee recommended Practice for Monitoring Electric Power Quality

7.5.4 Power study monitoring
This type of monitoring is of key importance in understanding how the overall power quality picture is
changing as a result of major changes in the environment. Power studies are conducted for long periods of
time, usually a few years, at multiple locations. Examples of landmark studies include those conducted
throughout the US at computer sites in 1969Ð1972 (phase 2) reported by Allen and Segall [B19] and those
conducted at US telecommunications sites in 1977Ð1979 and reported by Goldstein and Speranza [B23]. 
Currently there are two more extensive power quality studies. One is focused on electric utility distribution
systems throughout the US in 1991Ð1993 as reported by H. Mehta and J. C. Smith [B27]. The other study
covers end use sites in 1990Ð1995 throughout continental USA and bordering Canadian provinces reported
by R. E. Jerewicz [B24] and by D. S. Dorr [B21]. These studies have ability to compare data with past and
future studies.
Finally, the Canadian Electrical AssociationÕs National Power Quality Survey [B4] was initiated in response
to rising power quality concerns from both the utilities and customers. This concern was largely based on the
growth seen in the number of electronic loads sensitive to power quality disturbances (computers, digital
clocks, programmable logic controllers) and producers of these same disturbances (variable speed drives and
consumer electronics power supplies). The two-year, 600-site survey is the Þrst quantitative look at the sys-
tem problem. The site selection was made to provide for an even distribution, while sampling the three major
customer typesÑcommercial, industrial, and residential against different feeder conÞgurations. 
8. Interpreting power monitoring results
8.1 Introduction
Troubleshooting and solving power-related problems involves a number of issues. Many problems are
solved by carefully examining the load, others by verifying correct wiring and grounding practices, and still
others may require the use of power monitoring equipment. No one practice will handle every problem. A
doctor can interpret an electrocardiogram, but would never make a recommendation without also examining
the patientÕs health record, lifestyle, and diet. Similarly, one should not diagnose a power problem simply by
looking at only one piece of information.
All of the efforts to obtain information are meaningless unless the investigator has enough knowledge and
skill to produce a solution from the available data. Interpreting a power monitorÕs output is perhaps the most
critical part of the process of power monitoring. Given the limits and variety of practical Þeld tools, the tre-
mendous range of distribution system and load characteristics, and the limited research done to date, inter-
pretation still remains very dependent on the experience and skill of the user. This subclause discusses many
of the issues which directly impact graph interpretation skills. For further information on analyzing and
interpreting data, please refer to [B3] and [B5].

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IEEE
Std 1159-1995
IEEE RECOMMENDED PRACTICE FOR
48