Mojdeh Abdi-Khorsand

Real-Time Contingency Analysis With Transmission Switching on Real Power System Data

Transmission switching (TS) has shown to be an effective power flow control tool. TS can reduce the system cost, improve system reliability, and enhance the management of intermittent renewable resources. This letter addresses the state-of-the-art problem of TS by developing an AC-based real-time contingency analysis (RTCA) package with TS. The package is tested on real power system data, taken from energy management systems of PJM, TVA, and ERCOT. The results show that post-contingency corrective switching is a ready to be implemented transformational technology that provides substantial reliability gains. The computational time and the performance of the developed RTCA package, reported in this letter, are promising.

The Role of Out-of-Market Corrections in Day-Ahead Scheduling

In order to ensure a reliable and continuous supply of electric energy, operators must manage hundreds to thousands of generators with complex operating requirements, maintain synchronism, and manage thousands of transmission assets. Further complications arise due to stringent reliability standards, resource uncertainty, and limited economical energy storage. With advances in algorithmic performance and hardware, such optimization problems still require an engineered and simplified market structure. Market operators must therefore adjust the proposed market solution in order to obtain a valid solution. An overview of existing industry practices related to such market adjustments, referred to as out-of-market corrections, is presented. This paper also analyzes the market implications and required out-of-market corrections for the day-ahead scheduling process. Multiple out-of-market correction algorithms are created and used to analyze the potential impacts on market solutions and settlements. Finally, such solutions are compared against an extensive form stochastic unit commitment solution.

Real-Time Contingency Analysis With Corrective Transmission Switching

Transmission switching (TS) has gained significant attention recently. However, barriers still remain and must be overcome before the technology can be adopted by the industry. The state-of-the-art challenges include AC feasibility, computational complexity, the ability to handle large-scale real power systems, and dynamic stability. This paper investigates these challenges by developing an AC corrective TS (CTS) based real-time contingency analysis (RTCA) tool that can handle large-scale systems within a reasonable time. The tool quickly proposes multiple high-quality corrective switching actions for contingencies with potential violations. To reduce the computational complexity, three heuristic algorithms are proposed to generate a small set of candidate switching actions. Parallel computing is implemented to further speed up the solution time. Moreover, time-domain simulations are performed to check for dynamic stability of the proposed CTS solutions. The promising results, tested on the Tennessee Valley Authority (TVA) system and actual energy management system snapshots from the PJM Interconnection (PJM) and the Electric Reliability Council of Texas (ERCOT), show that the tool effectively reduces post-contingency violations. It is concluded that CTS is ripe for industry adoption for RTCA application.

Modeling Protection Systems in Time-Domain Simulations: A New Method to Detect Mis-Operating Relays for Unstable Power Swings

Large power system disturbances can cause stable or unstable power swings. Unstable power swings result in generator pole slipping. A generator or group of generators may accelerate or decelerate, leading to voltage depression at the electrical center along with generator tripping. This voltage depression may cause protective relay mis-operation and unintentional separation of the system. In order to avoid unintentional islanding, the potentially mis-operating relays should be blocked from tripping. This paper proposes a novel method to determine the location of the mis-operating relays at the planning phase. Blocking these mis-operating relays, combined with an appropriate islanding scheme, help avoid a system-wide collapse. The proposed method is tested on data from the Western Electricity Coordinating Council. A triple line outage of the California-Oregon Intertie is studied. The electrical center is determined and appropriate out-of-step blocking schemes are identified. The results show that the correct design of out-of-step protective relays improves the dynamic performance of the power system and causes less fluctuations in voltage and frequency throughout the system.

Corrective Transmission Switching for N- 1-1 Contingency Analysis

System operators are required to serve the load in the most cost-effective way while maintaining the integrity of the system and heeding reliability requirements. In the day-ahead market, operators acquire reserves in an attempt to guarantee N-1 reliability; yet, reserve deliverability is not guaranteed. Prior research has shown that the use of transmission switching, or topology control, may help improve reserve deliverability. In this paper, transmission switching is used as a corrective mechanism to help the system achieve N-1-1 reliability, where not only has the system lost a single element, but also it experiences the loss of a second major element after an adjustment period. In an attempt to preserve N-1-1 reliability, for this paper, a day-ahead unit commitment model that acquires supplementary reserves is solved. The day-ahead market solution is then tested for N-1-1 reliability using contingency analysis models with and without transmission switching. The methodology can be employed at the day-ahead time stage to ensure the system has acquired sufficient supplemental reserves. The results demonstrate that not only can corrective transmission switching be beneficial post-contingency without inhibiting the ability to return to N-1 reliability, but it can also help obtain an N-1-1 reliable solution.

Identification of Critical Protection Functions for Transient Stability Studies

Historical information and ex-post analysis of blackouts reaffirm the critical role of protective devices in cascading events, thereby confirming the necessity to represent protective functions in transient stability studies. The representation of protection functions greatly enhances the accuracy of the transient stability study and leads to a better understanding of power system states during emergency conditions. Although modeling all of the protective relays within transient stability studies may result in a better estimation of system behavior, representing, updating, and maintaining the protection system data becomes an insurmountable task. Inappropriate or outdated representation of the relays may result in incorrect assessment of the system behavior. This paper presents a systematic method to determine essential relays to be modeled in transient stability studies. The desired approach should identify protective relays that are critical for various operating conditions and contingencies. The proposed strategy is verified as a viable technique based on results obtained from the WECC 179-bus and the IEEE 145-bus test cases, while considering various operating states and contingencies. The results of the transient stability studies confirm that modeling only the identified critical protective relays is sufficient to capture system behavior and precludes the need to model all of the protective relays.