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188 Decision Making Applications in Modern Power Systems

exploited in the operation of µPMU to obtain various measurements from
different locations in a distribution system to obtain phasors based on a com-
mon time reference.

7.4 Principal components of a basic microphasor
measurement unit
There are multiple types of µPMU available in the market produced by dif-
ferent companies. Every manufacturer has different configurations. Hence, it
is not possible to show the configurations individually. However, a basic
µPMU incorporating all the common and essential features can be discussed.
Fig. 7.5 shows the principal components of a basic µPMU. All the
µPMUs primarily incorporate a current transformer/potential transformer
(CT/PT) module, a low-pass filter module, analog-to-digital (A/D) converter
module, CPU module, GPS module, communication interface module, and a
power module. The analog inputs comprise the current and voltages of the
measuring circuit obtained from the secondary side of the CT and voltage
transformer, respectively. All the three-phase current and voltage are fed to
the µPMU in the case of a three-phase line. Similarly, for two-phase line,
both the phase current and voltage are used in µPMU. Generally, µPMUs are
not used frequently in single phase line.
In the CT/PT module (Md1), after acquiring the current and voltage sig-
nals, shunts transformers scale down the signals in a range suitable to be fed
to A/D converter. This range is generally between 210 and 110 V. Before
feeding the signal to A/D converter, high-frequency noises are discarded
with the low-pass filter module (Md2). The cutoff frequency of such filters
are typically less than half the sampling frequency in order to maintain the

Analog input AC supply Control center

Switch mode Communication
power supply GPS module
(Md5) module (Md6)
module (Md0)

CT/PT module Low pass filter A/D converter CPU module
(Md1) module (Md2) module (Md3) (Md4)

Data collection module

FIGURE 7.5 Principal components of a basic µPMU. μPMU, Microphasor measurement unit.