| Summary: | Power distribution systems have underwent a lot of significant changes in the last two
decades. Wide-scale integration of Distributed Energy Resources (DERs) have made the
distribution grid more resilient to abnormal conditions and severe weather induced outages.
These DERs enhance the reliability of the system to bounce back from an abnormal situation
rather quickly. However, the conventional notion of a radial system with unidirectional
power flow does not hold true due to the addition of these DERs. Bidirectional power flow
has challenged the conventional protection schemes in place. The most notable effects on
the protection schemes can be seen in the field of islanding or Loss of Mains(LOM) detection
and general fault identification and isolation. Adaptive protection schemes are needed to
properly resolve these issues. Although, previous works in this field have dealt with this
situation, a more comprehensive approach needs to be taken considering multiple topologies
for developing adaptive protection schemes. The most common protective devices widely
deployed in the distribution system such as overcurrent relays, reverse power relays at Point
of Common Coupling(PCC), fuses, reclosers and feeder breakers need to studied in implementing
these schemes.
The work presented in this dissertation deals with simulation based and analytical approaches
to tackle the issues of islanding and adaptive protection schemes. First we propose a multiprinciple
passive islanding detection technique which relies on local PCC measurements, thus
reducing the need of additional infrastructure and still ensuring limited Non Detection Zone
(NDZ). The next step to islanding detection would be to sustain a islanded distribution
system in order to reduce the restoration time and still supply power to critical loads. Such
an approach to maintain generator load balance upon islanding detection is studied next by
appropriate shedding of non-critical and low priority critical loads based upon voltage sensitivity
analysis. Thereafter, adaptive protection schemes considering limited communication
dependency is studied with properly assigning relay settings in directional overcurrent relays
(DOCRs), which are one of the most widely deployed protective devices in distribution
systems by catering to multiple topologies and contingencies. A simulation based technique
is discussed first and then an analytical approach to solve the conventional optimal relay
coordination problem using Mixed Integer Linear Programming (MILP) with the usage of
multiple setting groups is studied. All these approaches make the distribution more robust
and resilient to system faults and ensure proper fault identification and isolation, ensuring
overall safety of system. === Doctor of Philosophy === With widespread integration of inverter-based distributed energy resources (DERs) in the
distribution grid, the conventional protection and control schemes no longer hold valid.
The necessity of an adaptive protection scheme increases as the DER penetration in the
system increases. Apart from this, changes in system topology and variability in DER
generation, also change the fault current availability in the system in real-time. Hence, the
protection schemes should be able to adapt to these variations and modify their settings for
proper selectivity and sensitivity towards faults in the system, especially in systems with high
penetration of DERs. These protection schemes need to be modified in order to properly
identify and isolate faults in the network as well as correctly identify Loss of Mains (LOM)
or islanding phenomenon. Special attention is needed to plan the next course of action after
the islanding occurrence. Additionally, the protective devices in distribution system should
be utilized to their maximum capability to create an adaptive and smart protection system.
This document elaborately explains the research work pertaining to these areas.
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