Abstracts:An AC-Excited Generator-Motor (ACEGM) is widely used in the variable speed pumped storage power station due to its flexible and powerful power regulation capability. However, the power regulation range can be restricted by the hotspot temperature in the end region of the ACEGM. In order to study the temperature distribution laws of the stator and rotor end structural components, a three-dimensional electromagnetic- fluid-thermal coupling model in the end region of the ACEGM is established. The flux densities, losses and temperatures in the end core, tooth plate, stator clamping plate and rotor retaining ring are studied under the different operating conditions. Through thermal analysis, the hotspot location in the stator and rotor end regions has been pinpointed. The hotspot temperature variations in the stator and rotor end regions along with the changes of the active and reactive powers are studied. The power regulation range of the ACEGM is determined by the thermal limits of the stator and rotor end components. The study can provide a theoretical foundation for optimizing the stator and rotor end-region structures and enhancing the power regulation capability of ACEGMs.

Abstracts:This paper proposes an enhanced distributed control scheme with power imbalance compensation for an Input-Parallel-Output-Parallel (IPOP) AC-DC converter featuring a power imbalance compensator that incorporates non-instantaneous values. Power-sharing imbalances are a common issue in parallel-connected cell converters due to wiring resistance between the load and individual cells under conventional droop control. The proposed compensator, placed in the outer loop of the voltage and current feedback loops, effectively mitigates these imbalances. By leveraging non-instantaneous values, the control scheme accepts low-bandwidth communication, enabling the use of low-speed wireless modules and reducing the required signal lines, thus enhancing system flexibility. The experimental validation is conducted using a 7.2-kW prototype comprising six cells with integrated wireless communication modules. The results demonstrate that the proposed method reduces output current imbalance by up to 94% compared to conventional approaches.

Abstracts:The integration of AC and DC subgrids equipped with variable penetration DERs makes the protection of Hybrid AC/DC microgrids complex and challenging. Diverse topological and operational uncertainties result in variable short-circuit levels of the system. The adaptive relay settings are quite imperative to ensure effective protection coordination for such a dynamic system. This work proposes an adaptive dual-setting scheme for the optimal protection coordination of hybrid AC/DC microgrids(HMG), utilising a novel hybrid relay characteristic. The optimal relay settings are updated offline for the most prominent system operating conditions. Additionally, a fail-safe contingency plan, based on a non-intrusive load detection and communication coordination approach, is employed for system changes other than pre-considered operating conditions. This eliminates any central controller-based communication overhead and reliability concerns. A new performance evaluation framework is also designed to investigate the feasibility of overcurrent protection for low-voltage DC subgrid faults. The effectiveness of the proposed work is validated on a modified MV CIGRE-based 7-bus HMG system, and an extended 39-bus HMG based on the IEEE 33-bus test system, using a real-time digital simulator and a numeric relay development environment for hardware-in-loop (HIL) simulations. The results demonstrate improved performance compared to previous adaptive protection coordination schemes under various network reconfigurations, load-switching scenarios, variable DG penetration, and other system operating conditions.

Abstracts:The loss of field (LOF) is a common phenomenon that occurs in the excitation system of a synchronous generator (SG), and the LOF relay (ANSI code 40) offers crucial LOF protections for SGs in electrical power plants. Conventional LOF relays employ one or two offset Mho elements and exploit measured impedance in the generator terminal to detect LOF events. Although widely used by industry, these relays have low speed in LOF detection, and inadequate security during power swings. During the last decades, LOF protection schemes in SGs have been improved with a higher detection speed and enhanced security. However, several issues remain to be solved, e.g., effects of the generator modeling and its dynamics on LOF studies, and effects of the flexible alternating current transmission system (FACTS) on LOF protection. To address these issues, this paper reviews SG models for LOF studies, different LOF protection schemes, impacts of FACTS on LOF protections, and the restricted operating period of a SG experiencing LOF to restore its excitation system or a safe planned outage. Future research directions in this area are also recommended.

Abstracts:In a ring-structured microgrid, the predominant bidirectional power flow is influenced by the distinct characteristics of distributed energy sources. The traditional approaches struggle to identify the faulty line precisely, particularly when confronted with high-resistance faults that degrade the system's dependability. Recently, the protection methods based on the parameter approach were introduced in the literature to overcome these difficulties. However, these approaches fail to find the fault location since the estimated resistance does not include the fault loop resistance. The primary aim of this research article is to introduce a robust protection algorithm that employs the polarity of change in resistance ($\Delta R$) is computed at both protection devices (PDs) in a line to distinguish the internal and external faults correctly; it enhances the dependability of the protection system. This method also emphasizes the computation of fault location based on calculated resistance, which is straightforward. In addition, a tripping operation using the central intelligent electronic device (CIED) in instances where communication fails between local intelligent electronic devices (LIEDs) and circuit breaker (CB) failure are also considered. The proposed method was also validated on experimental setup to ascertain the duration of operation for the protective technique.

Abstracts:Synchronous compensators play a fundamental role in the voltage regulation of systems based on the generation or consumption of reactive power. To increase their underexcited operating range, it can operate in the salience region using negative excitation, also known as the reluctance region of the capability curve. According to the study presented in [1], these conditions introduce the machine to an operating point close to the practical stability limit (PSL), where systemic disturbances can affect the compensator angular stability. Firstly in [1], a power system is modeled to evaluate the increase in the operating range of the compensator. In a second moment, a study to define the tap of the step-up transformer is carried out through power flow analyses between the synchronous machine and the system, determining the operational range of the synchronous compensator. In a third moment, a transient angular stability analysis is conducted through the application of short-circuit contingencies and generation withdrawal to verify the angular stability in operation with negative excitation. Finally, the parameterization and testing of the loss of excitation (LOE) protection coordinated with the Underexcitation Limiter (UEL) of the Automatic Voltage Regulator (AVR) is evaluated in this context. The results indicate that it is possible to increase the underexcited operating range of synchronous compensators using negative excitation, at operating points close to the PSL region. Regarding ANSI 40 protection, the proposed adjustments allow a UEL control action coordinated with the protection actuation.

Abstracts:A method is proposed for locating fault on two-terminal transmission lines using traveling-waves from two-ended unsynchronized current measurements. It considers the line length to be divided into four zones and computes per unit fault locations assuming the fault to be present in each of these zones separately. It then estimates the faulted zone, and the corresponding fault location estimate is displayed as the final output. These computations involve measuring three travelling wave arrivals at each terminal. The method is free of wave speed (or line parameter) input and is inherently immune to data synchronization issues. It is tested on a 200 km transmission line simulated in PSCAD/EMTDC. The performance is also compared with a classical two–terminal method. The method is further validated with a variety of test scenarios. It is applied to series compensated transmission line with the compensator placed at one end, both ends and at any intermediate location on the line. Testing is extended to lines connected to inverter-based renewables and long export cables connecting offshore wind to the main grid. The method works satisfactorily for varied fault cases in the above-mentioned scenarios. It is robust to errors in wave speed and data synchronization errors. To demonstrate performance with practical measurements, the method is tested using a field case of a 400 kV series compensated line in the Indian Power Grid.

Abstracts:The safety, reliability, and resilience of industrial equipment, including drives, Power Electronic Systems (PES), and Distributed Control Systems (DCS), are contingent upon their level of protection. Essential requirements for this sensitive equipment include managing Electro-Magnetic Interference (EMI) and ensuring power quality. Inadequate potential equalization can result in failures or malfunctions of controller cards and internal boards within power electronic devices and distributed control systems. This research offers valuable perspectives obtained from tackling a major challenge within the industry. The research led to the development of a safe, cost-effective, and robust earthing system (SERES) that employs frequency-dependent dynamic soil properties (FDDSP), while also taking into account constraints such as spacing factor (SF) and zone of influence (ZoI). The proposed extension work examines the case study across various seasons and conditions at the test site, emphasizing the performance of the proposed design under dynamic circumstances and evaluating the system’s efficacy through a new SERES model based on impedance parameters.

Abstracts:With promoting the application of renewable energy, distributed photovoltaic (PV) generation has become an important form of electrical source. More and more distributed PVs are connected into the power distribution system via traditional converters. With the continuous increase of PV penetration, the power grid is facing many challenges due to the inherent randomness and fluctuations of PV sources. Micro Energy Control Unit (MECU) is proposed as an alternative approach for the safe, economical, and efficient utilization of PV sources. Based on a multi-port structure, MECU connects photovoltaics, energy storage, the grid, and demand side loads. MECU can offer advantages of energy self-balancing, transient stability support, flexible demand-side integration, and power quality improvement. Two prototypes of MECU are developed for different application scenarios. Light-MECU is designed for small-capacity PV systems with strict space limits; The Modular Stackable Common-bus MECU (MSC-MECU) is used in high-power distributed PV grid-connected scenarios, such as rooftop PV systems. Experimental results show that MECU achieves energy self-balancing and transient stability support. MECU can be an effective solution for ensuring the reliable operation of power systems in the case of high PV penetration.

Abstracts:The ultra-high voltage direct current (UHVDC) transmission project plays a crucial role in global energy interconnection. As a key insulating component in transmission lines, silicone rubber insulators are prone to the deposition of pollution on their surfaces during long-term operation, which can lead to flashover and even cause large-scale power outages in grid. To achieve a high-precision assessment of pollution level on insulators, a non-contact detection method is proposed in this paper based on hyperspectral imaging (HSI) technology and back propagation neural network (BPNN). First, a hyperspectral imager is used to extract spectral data from the surface of the transmission line insulators. Then, four different dimensionality reduction methods are compared, and the Gaussian process late variable model (GPLVM), which provides the best spectral feature extraction performance, is applied to reduce the data dimensionality. Next, the BPNN, which is capable of characterizing complex nonlinear mapping relationships, is selected as the classification model. By incorporating an improved multi-verse optimization (IMVO), the optimal weights and biases for the model are obtained, enhancing the performance of global optimization and local exploration. The results show that the GPLVM-IMVO-BPNN classification model proposed in this study achieves an overall accuracy (OA) of 96.67%, which is a 7.92% improvement compared to the full band model. Additionally, this model successfully enables the visualization of pollution distribution on insulator surfaces in the field. The proposed method provides a basis for the non-destructive evaluation of transmission line insulators and offers solid support for the safe and stable operation of grid.