Min Lwin

Designing and Integrating Wind Power Laboratory Experiments in Power and Energy Systems Courses

The goal of this paper is to describe the approach in designing and constructing wind power laboratory experiments for undergraduate- and graduate-level courses in power and energy systems. These are separated into basic hands-on laboratory and advanced simulation-based experiments. The basic experiments are integrated into an undergraduate course that includes topics such as the steady-state operation of induction machines, fixed-speed, and variable-speed wind turbines. Advanced experiments are integrated into a stand-alone course dedicated to wind energy and power systems. Topics include the modeling of aerodynamic, mechanical, and electrical components for each type of wind turbine along with their steady-state and dynamic operations. The experiments were originally designed at the University of Texas at Austin. Their transferability to a different laboratory platform at the University of Texas Pan American is also discussed.

Steady-State Analysis and Performance of Low Frequency AC Transmission Lines

The steady-state performance of low frequency AC (LFAC) systems for bulk power transmission is proposed and investigated in this paper. It is demonstrated that the LFAC is superior to the conventional 60 Hz AC system in terms of power transfer capability and voltage stability. An existing power system can increase its power transfer capability by up to more than eleven times if it operates at 5 Hz. In low operating frequency conditions, the transmission overhead line reactance is significantly lowered and thus results in less voltage drop along the line. If the system operating frequency is in the range of 1 to 10 Hz, the voltage profile along a transmission line is comparable to the surge impedance loading at the no-load condition or approaches that of the HVDC system at the full-load condition. More importantly, the V-P and Q-V characteristic curves show that the dependency of voltage on the real and reactive power flow is greatly reduced. In other words, the sensitivity of voltage on reactive power variations is diminished and results in a more stable voltage and a higher stability margin for the LFAC system compared to the conventional 60 Hz system.

Model-based relaying supervision for mitigation of cascading outages

Several major outages have been traced to the failure of remote backup protection elements in distance relays. Experience has shown that coordination of remote backup zones in stepped-distance protection can be vulnerable during stressed conditions. Furthermore, relay settings are typically biased for high dependability, resulting in lower security especially when several unexpected events coincide. An incorrect response by a relay during such a condition can trigger or propagate the disturbance. Therefore, a new framework for Model-Based Relaying is introduced to supervise and secure the operation of remote backup protection elements, such as Zone 3. The framework utilizes the fact that while a single relay can observe a 3-phase fault or stressed system condition with similar apparent impedances, other system parameters will be significantly different. Therefore, the framework proposes to include the capability in relays to quickly run circuit model simulations at the relay level. The proposed method aims to work in parallel with and supervise the conventional distance relays zone 3 for discrimination between 3-phase faults and stressed conditions using the output of local circuit model simulations. Several case studies are evaluated to demonstrate that dependability is not degraded for true fault conditions and security is enhanced for stressed system conditions.

Time-domain modeling and validation of overcurrent/reclosing relay operation

The goal of this work is to develop and validate a time-domain simulation model which can emulate the reclosing capabilities of an overcurrent and reclosing relay. The model is capable of performing multiple reclosing shots and can be programmed to operate on standard TCC curves by specifying the desired equations. The duration of the reclose intervals can also be specified. The performance of the model is compared to the performance of the reclosing relay by simulating the same fault scenarios on each and comparing the resulting fault current waveforms. Specifically, the operating times of the time-overcurrent trip function and duration of the reclose intervals are compared. The operating times are also compared with the theoretical values from the TCC curve equations. The accuracy of the reclosing relay model is compared to the actual relay for similar fault scenarios. The results show that both the model and the reclosing relay operate close to the expected theoretical values.

Optimal placement of edge-of-grid low-voltage SVCs in real-world distribution circuits

This paper proposes a method to determine optimal locations to deploy edge-of-grid low-voltage static var compensator (SVC) devices in large real-world distribution circuits. The SVC device operation, characteristics, and modeling are also discussed. The optimization problem formulation developed in this work has the objective of mitigating undervoltage violations in the circuit using the minimum number of SVCs while improving the traditional voltage regulation device operations and circuit losses. Undervoltage area criterion is used to identify effective candidate locations and the binary particle swarm optimization (BPSO) algorithm with quasi-static time series (QSTS) simulations are used to determine the optimal SVC locations. The results show that the proposed method is effective in identifying the optimal SVC locations in large distribution circuits.

Analysis of distance protection in low frequency AC transmission systems

This paper extends the analysis of low frequency AC (LFAC) transmission systems and investigates short-circuit fault characteristics and distance protection considerations. Due to operation at a low frequency, transmission line reactance is reduced and thus the power system transfer capability is increased significantly. The transmission line impedance reduction, however, creates a drawback in LFAC systems when faults occur. The analysis shows that fault currents are expected to be much higher than in a 60 Hz system. In addition, LFAC has a longer current wavelength and requires the protection system perform quickly to clear faults. This paper first examines distance protection in LFAC systems and determines that LFAC systems have a larger separation between distance protection zone characteristic impedance and load impedance in comparison to 60 Hz systems. Next, several typical fault types in a power systems are analyzed at different frequencies. A fault clearing time case is also calculated and compared between different systems. The analysis shows that the critical clearing time (in seconds) is less for LFAC systems in comparison to conventional 60 Hz systems.

Supervision of power swing blocking using model-based distributed intelligence relaying framework

The power swing phenomenon is characterized by oscillations in power flow between two areas of a power system due to an abrupt imbalance in mechanical and electrical power. Unintentional operation of distance relays during power swings can propagate a disturbance and result in a cascading outage. It is therefore critical that relays operate securely under such conditions. Modern distance relays can provide a function for power swing blocking (PSB). However, the PSB settings can be difficult to calculate without extensive stability studies and may fail to block if the slip frequency is too fast. In this work, we investigate the application of a model-based relaying framework applied to power swing blocking. The framework is named Model-Based Distributed Intelligence (MBDI) because it integrates, at the relay level, real-time knowledge of the network structure and system state in the form of simulation circuit models. We investigate the efficacy of a relay equipped with MBDI to supervise PSB operation during power swing and fault scenarios.