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

6.5.2 Disturbance monitors
Disturbance monitors are power monitoring instruments that are speciÞcally designed to detect and record
data on power system variations. Typically, power-line disturbance monitors are portable instruments that
contain a wide and varied number of features. These features may include a number of monitoring channels,
data storage and display formats, and other features that enhance the instrumentÕs capabilities.

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IEEE
Std 1159-1995
IEEE RECOMMENDED PRACTICE FOR
32
Disturbance monitor designs can be viewed in terms of the range of frequencies to be measured, how the
data is collected, and how the data is displayed. Once these design parameters are understood, the user can
then select a design that will best meet the intended application.
As an example, some power monitoring applications require rather slow measurement of voltages and/or
currents. An inexpensive instrument that measures voltages a few times a second may meet the needs of this
application. On the other hand, some applications require very high speed measurements of voltage. This
may be the case when high-frequency transients in the power system may be the source of a potential prob-
lem. This measurement would require a more sophisticated power monitoring instrument. These sophisti-
cated instruments can detect and collect data on numerous power system variations that may include voltage
swells and sags, transients, frequency errors, electrical noise, distortion, and notching among others.
A power monitor that looks at a broad range of frequencies may use multiple measurement techniques. For
example, a digital sampling technique may be used to measure rms voltages and distortion, but an analog cir-
cuit may be used to capture transients.
Factors that determine the proper measurement technique not only include accuracy, dynamic range, and fre-
quency response, but how the data is to be processed and presented. As an example, if a fast fourier trans-
form (FFT) is to be applied to capture an event, then the instrument shall employ a digital sampling
technique.
Power-line disturbance monitors can be divided into four basic types. The monitors may be classiÞed as
event indicators, text monitors, solid-state recording volt/ammeters, and graphical display monitors.