Page 228 - Decision Making Applications in Modern Power Systems

192 Decision Making Applications in Modern Power Systems

2. Fault identification and fault location: For high-impedance faults in dis-
tribution system, the fault current magnitude is much smaller in magni-
tude and close to the magnitude of load current. Therefore the protective
arrangements are unable to function properly in high-impedance faults.
Moreover, the quality of the data available in the distribution system is
insufficient to support any appropriate fault detection algorithm. Besides
identifying the fault, knowing the location of the fault is also necessary.
Common method of detection of faults involves manually examining the
faulty line section that consumes a lot of manpower as well as time. It
becomes a costly process for underground cables.
With the aid of µPMU, faults can be identified accurately. From the
phasors recorded by various µPMUs in the circuit, the impedance
between various points can be determined through different algorithms.
For example, the impedance between a µPMU and fault point can be
computed with the third harmonic current and voltage phasors as per
Eq. (7.5), where f and j denote the fault location and µPMU location,
respectively [23].
V j 2 V f
Z jf 5 ð7:5Þ
I j
So the detection methodology does not depend only on the magnitude
of current, and hence no chance of confusion. Faults can be identified
almost instantaneously when the impedance of a particular line section
becomes extremely high. Since impedance is calculated, the fault location
can be automatically identified by taking into account the impedance
between the faulted point and µPMU on its either side [24]. There are
some other complex algorithms that use µPMU measurements to detect
faults and its location in distribution system [25]. In general the algorithm
followed for fault detection is shown in Fig. 7.8 for n number of µPMU
considered.
Thus µPMU can drastically reduce the time for fault decisions and
also reduce manual labor and cost for the determination of fault location.
Moreover, as the fault information is communicated to nearby substations
of the faulted area, the substations become aware and prepared for post-
fault effects on the distribution system. This increases the reliability of
power in the distribution system. Thus the µPMU can accurately decide
fault situations and increase the situational awareness during fault
conditions.
3. Reconfiguration: Distribution network reconfiguration is a practice of
modifying the topology of the distribution feeders by changing the
closed/open status of tie and sectionalizing switches [26]. Fig. 7.9 shows
some simple reconfiguration possibilities in a typical distribution system.
The solid line shows the normal configuration of the distribution system,
while the dotted line shows reconfigured network with the help of tie