Doctor of Philosophy
Electrical and Computer Engineering
With the rapid growth of renewable energy resources, energy efficiency initiatives, electric vehicles, energy storage, etc., distribution systems are becoming more complex such that conventional protection, control, and measurement infrastructure – typically concentrated at the main substation, with little to no access to information along the feeder – cannot maintain the reliability of the system without some sort of additional protection, control and measurement functionalities. As an example, a dedicated communication channel for carrying the transfer trip signal from the substation to the Point of Common Coupling (PCC) to prevent islanding operation of alternative resources, has been a requirement for many utilities. In the transformation of the distribution system from a simple radial system to a bidirectional energy flow network, integration of many intelligent devices and applications will also be required. Thus, this situation calls for investment in communication infrastructure, and augmentation of protection, control, and measurement functionalities.
The value of power system communication technologies such as synchrophasor measurement technology – which includes the Phasor Measurement Unit (measuring and providing voltage and current phasors in the real time via communication), communication infrastructure, and Phasor Data Concentrator (PDC) – is being recognized through large-scale deployments around the world. However, these implementations are predominantly limited to some monitoring-type applications and are being realized primarily in transmission systems and bulk power systems (≥100 kV), where performance requirements are much more stringent compared to distribution systems.
So contrary to transmission systems, the current status of synchrophasor measurement technology can be utilized to its full extent in distribution systems, as shown in current research for anti-islanding and open-phase faults in the distribution feeder protection application, where the number of PMUs and performance required is somewhat lower than the bulk of power energy. Thus, the opportunity to invest in the implementation of synchronized measurement technology in distribution system is timely as it can be coordinated with other investments in feeder modernization, distributed generation (DG) integration, and infrastructure enhancements that are underway, including “smart grid” initiatives.
In the first use case of this research, the behavior of the major DG types during islanding is studied through accurate transient modeling of utility type distribution systems using PSCAD-EMTDC and MATLAB. The study proposes augmentation of PMU-based solutions to the current passive islanding protection elements, such as voltage and frequency, and improving the non-detection zone of the passive elements by adapting their settings based on normal loading conditions at closest known instant prior to the fault or islanding occurrence. The solution proposes a system architecture that requires one PMU at each PCC bus and in the main substation. The communication aspect is based on the IEC 6850-90-5 report, where the PMU can subscribe directly to the data stream of the remote PMUs such that the need for PDCs in this application is eliminated, yielding better performance.
In the second use case, an open-phase fault – a major concern for distribution utilities from safety of public and equipment perspective – has been studied. Clearing the open-phase fault without identifying the type of fault could result in an attempt by the recloser to reenergize the downed wire; conversely, an undetected open-phase fault could initiate ferro-resonance, thereby stressing equipment and increasing the risk to public safety, both urban and rural. This work discusses comprehensive analysis of symmetrical components of various types of open-phase faults in the distribution feeder with the presence of distributed generators (DGs) and proposes the use of phasor measurement data located at substation and PCC to identify the open-phase fault. The proposed algorithm relies on the rate of change of the various current and voltage sequence components. In the study conducted, the utility type feeder and substation are modeled in PSCAD-EMTDC, and different types of open-phase fault and shunt faults are studied to verify the dependability and security of proposed algorithm.
Summary for Lay Audience
Electricity is a form of energy, and in simple terms it is defined as the flow of electric charges and charge is a property of matter like mass, volume, etc. We produce electricity, from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power, and other natural sources such as Wind and Solar. The system which produces, transfers, and distributes electricity in the cities and rural area is called an electrical grid. The sections of the grid distribute electricity to the consumers is called a distribution system. Distribution systems, historically, only distributed electricity and did not participate in the production. However, with the global warming effect and desire of the society to use a clean carbon free electricity many renewable sources including solar; wind, hydro power, and geothermal are integrated into the distribution systems. Thus, distribution systems now and in the future will have to integrate more resources which add significant complexity and challenges for utilities and asset managers in terms of protection of electrical assets, safety, and quality of power delivered to the consumers. The focus of this work has been on protection of the distribution systems for two specific incidents open phase or broken conductor and islanding operation. These two undesirable situations can cause serious risks and damages to the distribution system. This research proposes new methodology to deal with these types of problems and encourages utilities and regulators to invest in the grid’s communication technology infrastructure more real time system data to become readily available. This information can then be utilized for diagnostics and detection of failures and thereby, lower the risk of safety to the public to the system’s equipment.
Jalali, Mansour, "Synchrophasor Based Islanding & Open phase fault Protection in Distribution Systems" (2020). Electronic Thesis and Dissertation Repository. 6947.