Page 220 - Decision Making Applications in Modern Power Systems

184 Decision Making Applications in Modern Power Systems

connections. Other connections (mostly solar) are connected at the con-
sumer level, that is, to the low voltage side. The consumers are responsi-
ble for these connections [4 5].
2. Such active sources include solar photovoltaics, fuel battery, etc. These
have introduced certain challenges. Unidirectional power flow has been
replaced by bidirectional power flow, which affects the traditional protec-
tion practices, voltage, and frequency control. The intermittent nature of
the green energy sources also introduces harmonics and transients. All
these need to be addressed by the utility through an appropriate device.
3. High power reliability: Due to deregulation, the utilities are striving hard
to increase the power reliability. With the help of suitable monitoring
devices in the distribution system, the reliability of power supply can be
enhanced such as restoring power supply rapidly after a power failure.
4. Change of loads nature: Nowadays, most of the motor-based equipment
as well as other equipment use power electronic devices. This makes the
loads less affected by voltage and frequency and, in turn, injects harmo-
nics. The power quality thus gets affected. Thus a suitable device to mon-
itor and control these harmonics is required.
5. Increasing geographical sprawl: The geographical extent of modern dis-
tribution system is increasing at a rapid pace. Thus the area for measur-
ing, monitoring, and protection of the distribution system is now not
constrained to a small area. Hence, suitable devices to handle this vast
extent are needed.
6. Cost: Due to all the above reasons, it becomes necessary to install a large
number of measuring and protection devices in the distribution system.
Installing such devices for individual protection purpose is uneconomical.
Therefore devices that will make distribution system completely observ-
able by installing them in a few number at an economical cost are needed.

Besides all the above reasons, the µPMUs have to face more challenges
than the PMU in the transmission system due to the following inherent char-
acteristics of the distribution system.

1. Low X/R ratio: The distribution system is inherently resistive. Hence, real
and reactive power flow equations cannot be decoupled, and standard
power flow approximate equation that is used for transmission system as
in Eq. (7.1) becomes invalid, where V a and V b are the voltages of two
points, and X is the inductance between two points. The operating states
thus cannot be derived from these equations. Hence, a separate set of
equations is needed to define the sensitivity of reactive and active power
to θ ab and V [12].

j
j V a j V b j
P ab sinθ ab ð7:1Þ
X