Page 218 - Decision Making Applications in Modern Power Systems

182 Decision Making Applications in Modern Power Systems

active with bidirectional power flow. This introduced several challenges,
including unintentional islanding, voltage volt-ampere reactive (VAR) con-
trol, and adaptive protection [6,7], in the distribution system, which needed to
be continuously observed. Multiple DG connection in a feeder introduced
uncertainty, vulnerability, variability, and complexity. Hence, a more refined
measurement for smooth operation of distribution grid was needed.
Motivated from the accomplishment of the PMUs in making the transmis-
sion grid completely observable, the concept of microphasor measurement
unit (µPMU) was materialized to provide new, efficient, and reliable strate-
gies for the proper management of the distribution system [8].A µPMU is a
device that provides synchronized voltage, current, and phase angles with
ultraprecision [9]. The first software and hardware of the µPMU were devel-
oped in a collaborative project among Power Sensors Limited, the University
of California, and Lawrence Berkeley National Lab (LBNL) in 2013. The
project was entirely sponsored by the US Department of Energy ARPA-E
with the aim of developing a tool for enhanced observability, understandabil-
ity, and manageability of the distribution grid [10,11]. Such µPMUs were
installed in several electrical utilities distribution system termed as µPMU
network (µPnet) to make it more suitable for practical applications. Fig. 7.1
shows such a network. The µPMUs are installed at various locations of a dis-
tribution feeder such as substation and feeder end [10].Each µPMU transfers
data to a µPnet where it is equated against other µPMU data to reach a deci-
sion. Berkeley Tree Database (BTrDB) was created to store a huge amount
of data [10]. Fig. 7.2 demonstrates the abilities of the µPMU that is approxi-
mately shown in a logarithmic scale. Since then, several other projects have
started digging the potential applications of the µPMU.

7.2 Need of microphasor measurement unit in modern
distribution system
Earlier, there was little monitoring of distribution system as compared to
transmission system. The distribution system possessed a passive nature, that
is, power flow was unidirectional (from high-voltage to low-voltage grid).
Hence, monitoring of distribution system was not paid much attention.
However, in modern distribution system, with its active nature, that is, bidi-
rectional power flow, it becomes necessary for the utility to monitor the dis-
tribution system due to the following reasons [12,13]:
1. Integration of DGs in distribution system: Due to the advancement of
technology in green energy, a large number of DGs are now being con-
nected to the distribution system. There are several topologies to connect
the DGs to the distribution systems. Some connections (mostly hydro and
wind) are directly connected at bus level, that is, to the medium voltage
side [14,15]. The distribution companies are responsible for these