Page 97 - Decision Making Applications in Modern Power Systems

64 Decision Making Applications in Modern Power Systems

GPS
PMU I satellite
ON

PMU II
Communication
ON
network
PDC
PMU III
ON
FIGURE 3.1 A typical WASMS. WASMS, Wide area synchrophasor measurement system.

of the equipment and hostile weather conditions. These faults, if not detected
in the real time, may lead to cascading failures resulting in a blackout [1].
These blackouts have catastrophic consequences, which may result a huge
loss of resources. For example, a blackout in 2003 caused an economic loss
of 10 billion US dollars as per the report of the Electricity Consumers
Resource Council [2]. Subsequent investigation of the blackout revealed that
the catastrophe could have been prevented if there was an early warning sys-
tem [3]. Similar other blackouts across the globe forced the power system
engineers to devise an effective solution for detection and control of the
power system abnormalities. The consequence of these efforts is the wide
area synchrophasor measurement system (WASMS) [4]. The WASMS con-
sists of several measurement devices that are termed phasor measurement
units (PMUs) that collect the real-time information concerning the health of
the power grid in the form of time-stamped voltage and current phasors.
These measurements are known as synchrophasors and are communicated
to the central control center or the phasor data concentrator (PDC) for the
detection of power system anomalies.
In the past few decades the PMUs have carved their niche as important
sensors for estimating the state of the power system [5] and are being widely
installed at the electrical nodes, separated by large geographical distances.
The communication of the synchrophasor data from these geographically
separated PMUs to the PDC is the responsibility of the synchrophasor com-
munication system (SPCS) [6]. Thus the PMUs, the PDCs, and the SPCS
together constitute the WASMS and are illustrated in Fig. 3.1.

3.1.1 Phasor measurement unit
The PMU is defined by the Institute of Electrical and Electronic Engineers
as “a device that produces synchronized phasor, frequency, and rate of
change of frequency (ROCOF) estimates from voltage and/or current signals