1,720,961 research outputs found
Design of an integrated hybrid configuration of a Modular Multilevel Converter (MMC) and an Impulse generator
No full textThe penetration of power electronics into the grid is growing rapidly due to the increasing number of renewable generation systems. These power electronic converters introduce electrical stresses in the form of complex waveforms into the grid caused by their switching operations. The High voltage (HV) equipment is subjected to these stresses. To maintain the reliability of the power system it must be able to withstand these kinds of complex stresses. To test the HV equipment with such stresses and assess its correct functioning, it is important to be able to reproduce such complex waveshapes. A new Modular Multi-level Converter (MMC) based arbitrary waveshape generator with 67 sub-modules in each arm rated for 100 kV is being designed to target the testing of medium voltage (MV) class equipment. Since the MMC has its own limitations in generating superimposed Lightning impulse (LI) waveforms, an integrated hybrid configuration combining the conventional Marx generator circuit and MMC is needed to generate the superimposed LI. This thesis intends to design and demonstrate the feasibility of such an integrated hybrid configuration focusing on two major goals. Firstly, to investigate the capabilities of the Typhoon HIL to implement the control of MMC and compare this with the existing OPAL-RT controller, and secondly, to design an integrated hybrid configuration to produce superimposed waveforms. To achieve the first goal the Typhoon HIL hardware, software, MMC topology, and the various modulation techniques were studied in depth. Phase shifted carrier (PSC) modulation-based open loop control was implemented on the CPU and FPGA of the HIL device. The results were compared with the offline simulations, and it was found that the control implemented on the CPU is suitable for up to 1 kHz, and the FPGA control is recommended for higher frequencies. The performance of Typhoon HIL is better than OPAL-RT regarding generating accurate gate pulses at higher fundamental frequencies. The approach for the second goal used is to study the literature on existing composite test setup to understand the requirements to design the decoupling circuit between impulse generator and MMC. A downsized model of an integrated hybrid configuration was designed and validated by offline simulation. Next, a 300 V hardware prototype was implemented in a step-by-step manner. First, Rapid control prototyping was performed separately on the MMC comprising 2 sub-modules in each arm with the FPGA control developed using the Typhoon device. Thereafter, the impulse circuit was coupled with the MMC to test for both power frequency and DC superimposed impulses. It was observed that the real-time simulation results were identical to the offline simulations and the superimposed impulses could be generated with high accuracy. Finally, the output of the MMC for higher signal bandwidth was tested using the Typhoon FPGA control. It was found that the MMC could generate sinusoidal waveforms up to 3 kHz.Electrical Engineerin
Electric field and Ionic current density modelling for HVDC and Hybrid transmission lines using Finite Element Methods
No full textIncrease in demand for electric power and renewable sources of energy drives the need for more transmission & distribution capacity. When using DC, as RMS and peak voltage are the same, transferring more power can be economical but at the same time erecting new transmission lines is often associated with demanding approval procedures, conflicts of interest and mainly with more cost. Thus a more cost-effective option to cater the demand is to share HVAC and HVDC lines on the same tower (called as hybrid lines). Charges due to corona creates problems like radio interference, audible noise and power losses. Also electric field (below transmission lines) at ground level causes head hair sensation resulting in public annoyance. Thus electric field and ion current density with the effect of space charges at ground level needs thorough investigation.This thesis focuses on calculation of electric field (affected by space charges) and ion current density on ground for HVDC and hybrid transmission lines using COMSOL multiphysics software. In HVDC, several configurations like monopolar, bipolar and double bipolar were examined. Effect of wind and ground conductors on space charges were also studied for monopolar models. A verified HVDC model is presented in this thesis which can be used to study the effect of space charges from DC conductors on electric field and current density. This work has been further extended to build a model for hybrid (HVAC+HVDC) configuration.Electrical Engineerin
Improvement of impulse voltage distribution of transformer windings
No full textWith the aid of the analytical formulas of the disc pair model inter-shielded by different type of shield wires, the total series capacitance of the disc pair could be calculated. After introducing a number of inter-shield pairs to the disc pair model, the influence on the mutual inductance between discs has been thoroughly discussed. Last but no least, after comparing the figures for the voltage response distribution among different configurations and different type of inter-shield pairs, the case which could contribute to the best voltage response performance is selected
Development of Resonance-Based Test System to Measure Lifetime Curves of Dielectric Materials
No full textWith the increasing growth and penetration of power electronic devices in the power system, it is essential to understand the behaviour of insulation materials and systems under the varied signals that are produced with power electronic systems. These signals could be square pulses, sinusoidal or even superimposed. The high-frequency sinusoidal excitation in the range of 50-100kHz is the focus, of this project. The project aims to design a resonance-based test system to measure the lifetime curves of dielectric materials such as oil-impregnated paper and epoxy under high frequencies. The major components of this project are the H-Bridge Circuitry found on the low voltage side and the resonant transformer which is tuned with the test sample to be in resonance. The design techniques and critical factors for the design of gate driver circuits have been provided. Moreover, through simulations in COMSOL Multiphysics and MATLAB along with practical measurements using vector network analyzers the behaviour of the transformer equivalent circuit parameters with changes in geometry is discussed. Through this understanding, the critical parameters to design a test system to obtain the highest gain while in resonance have been highlighted. The final test setup is designed and is used to perform lifetime tests on oil-paper and epoxy samples, both materials exhibited different behaviour during the tests. Due to the high gain of the system, it is very sensitive to changes in the capacitance of the test object and hence a constant voltage is not applied to the oil-paper sample. Therefore the breakdown times cannot be considered for the lifetime curve. Recommendations are provided to improve the test setup. Epoxy showcased a different behaviour, it is observed that the linear voltage gain of the resonance system is lost once partial discharges are initiated, and the voltage across the test sample becomes constant even upon a further increase in the input voltage. Based on these observations recommendations are provided to improve the test setup along with further topics that need to be studied.Electrical Engineering | Electrical Power Engineerin
Pulsed Ageing of Oil-Paper: Test Modulators and Ageing Trends
No full textThe ambitious transition towards a renewable future is being made possible by power electronic systems that facilitate effective control and efficient conversion of energy. One such system is the solid-state transformer (SST) which aims to replace conventional transformers by offering larger energy densities and flexible power flow. However, these benefits come at the cost of severe mixed-frequency stresses experienced by the medium frequency transformer (MFT) of the SST. These stresses are characterised by fast-rising pulsed waveforms of several tens of kilovolts repeating at frequencies of up to a hundred kilohertz. In contrast to pure sinusoids, the behaviour of dielectrics undermixed-frequency stresses is to a large extent unknown. This research gap forms the core motivation behind this thesis project. To analyse these exciting yet extreme phenomenon, the first objective was to build a pulse modulator for testing cellulosic dielectrics under voltages up to 10 kV with rise-times ≈ 2 μs at frequencies between 10 to 50kHz. The topology consists of a rectified DC supply feeding a SiC H-bridge pulse generator connected to a 4:200 pulse transformer and other variable test elements. The work began with selecting the switch and gate driver, simulations in LTspice and TINA-TI, and the fabrication of the PCB pulse generator prototype using Altium Designer. Next, a novel third-order PQR equation was derived for a PT with capacitive load involving the parasitic leakage flux Ls and distributed capacitance Cd. The influence of bobbin geometry on parasitics was studied with 20 different 3D printed iterations designed in Fusion 360. A failure mode analysis was conducted to identify weak points in a transformer, and the solutions detailed in this report. The final objective was to apply the produced waveforms of Tr ≈ 1.8 µs across single-layer OIP samples at 10 kHz and 50 kHz. The sample strength was determined through ramp tests with 1 kV/s slope. The lifetime curves were obtained by performing ageing tests at 10 field strengths each for 21-41 samples, and fitting the median failure time into an inverse power-law model. The results show a clear reduction in lifetime at higher frequencies hinting at the unsuitability of OIP in its current form as an insulation for MFTs. A transition point was observed indicating a shift in the ageing mechanism at lower fields. The report ends with a discussion on future scopes of research. Electrical Engineerin
Inertia Decrease and Frequency Performance: Assessment Study to Analyse the Impact of System Inertia Reduction on the Frequency Performance of the Dutch Power System Caused by the High Penetration of Renewables
No full textThe shifting of the European countries, including the Netherlands, towards an electricity production dominated by renewable energy sources to be (nearly 70%) by mid-century will have a significant impact on the frequency performance of electric networks. This would cause the level of grid inertia to be considerably reduced. From this perspective, I have been working with DNVGL for a period of 9 months on developing a dynamic power system model that provides the possibility of assessing the frequency performance of the Dutch electric network as part of the Synchronous Grid of Continental Europe. The main aim of this model is to consider the anticipated decrease in system inertia caused by the high penetration of renewables in a future situation.Electrical Engineering | Sustainable Energy Technolog
VHF Magnetic and Electric Sensors for Partial Discharge Measurements in GIS
No full textThe energy transition towards decarbonization and modernization of the electric network requires the development of new technologies. Offshore windfarms, essential to this transition, rely on Gas-Insulated Systems (GIS) due to their compactness and extended lifespan. Despite the reliability of GIS, the high maintenance costs and severe consequences of power outages leave no room for failure risks. The primary source of failures in GIS is attributed to defects in electric insulation, producing Partial Discharges (PDs) that serve as a tool for defect detection.The current approach for standardized PD measurements proves impractical for implementation in GIS under operation. Consequently, unconventional methods have been employed with Ultra-High Frequency (UHF) sensors standing out. Despite the notable signal-to-noise ratio of the UHF system, it is still susceptible to interference and does not yield calibrated measurements suitable for comparison with other methods and for assessing insulation degradation. In response to these challenges, this study introduces a Very-High Frequency (VHF) system capable of providing calibrated and reliable measurements....High Voltage Technology Grou
Cable Capacity Enhancement by Utilizing Trapezoidal Voltage Waveform
No full textTo avoid installation of expensive new underground cable connections in locations where peak load exceeds existing cable capacity, it is advantageous to transfer more power through a cable than its nominal power capacity, without endangering its reliability. Dynamic current rating of cables is a typical approach that is used to exceed the nominal cable capacity for a short time period. In this paper a new method for cable capacity enhancement based on dynamic voltage rating is introduced. The method can be applied if multilevel converters are installed at both ends of cable as will become more commonplace in the future when an inverter rich power system is realized. In this study the influence of trapezoidal voltage waveform on the electric field distribution inside cable insulation is investigated. The results shows that by using trapezoidal waveform it is possible to achieve a more homogeneous field distribution inside the cable insulation. This enables better utilization of the insulation system which translates into higher continuous power transfer capacity.High Voltage Technology Grou
Space Charge Pulsed Electro Acoustic Method, Calibration for Flat Samples and Crosstalk Reduction for HVDC Cable Measurements
No full textThe Pulsed Electro Acoustic Method (PEA) is a widely used method for the measurement of space charges in High Voltage (HV) dielectrics. This thesis aims to contribute to the optimization of the PEA method by being able to make measurements from different test setups comparable and enhance the reliability of the results interpretation. This work is divided in two main parts with different scopes. In the first part, the work is focused utilizing flat samples, in which the effects of the different electrode materials at the dielectric interface and the use of reference samples for measurement characterization is analyzed. In the second part of this work, the focus is on measurements at HVDC cables for which the effects of different pulsed voltage injection configurations are tested, with a special focus in reduction of the crosstalk between the applied pulse and the acoustic sensor. The obtained results contribute to optimize the application of the PEA method for measurements of the space charge phenomena in HVDC components.DC systems, Energy conversion & Storag
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