Start-up Sequence Research Articles

Simulation of Startup Sequence of an Offshore Wind Farm With MMC-HVDC Grid Connection

This paper proposes a startup sequence for a modular multilevel converter (MMC) HVDC-connected offshore wind farm (OWF) and demonstrates how it can be simulated using an electromagnetic transient-type tool. The objective is to analyze inrush currents of transformers and cables (HVAC and HVDC). Modeling accuracies and computational performances are examined using three existing modeling methods for the MMCs.

Development and experimental investigation of a 500-W class ultra-micro gas turbine power generator

We experimentally investigate the feasibility of a 500-W class ultra-micro gas turbine power generator. System specifications include a design rotational speed of 400,000 rpm, a compressor ratio of 3:1, and a turbine inlet temperature of 1200 K. In a previous study, we used an integrated test rig to examine the feasibility of start-up and self-sustaining capabilities. Here, we describe our development and testing of a new integrated test rig to measure the performance of electric-power generation during self-sustaining and boosting operations. We controlled a motor-generator using an electric controller in fixed speed mode and guided the rotational speed according to the start-up sequence. We employed a radial-thrust integral metal-mesh bumper air foil bearing with which we obtained the design rotational speed of 400,000 rpm in a standalone motoring test. In the combustor, we used liquefied petroleum gas as the main fuel and kerosene as the ignition fuel and partially as the main fuel during the boost operation. The integrated test rig achieved electric power generation of 30 W at 200,000 rpm, 50% of the design rotational speed.

Development of a Sequential Restoration Strategy Based on the Enhanced Dijkstra Algorithm for Korean Power Systems

When a blackout occurs, it is important to reduce the time for power system restoration to minimize damage. For fast restoration, it is important to reduce taking time for the selection of generators, transmission lines and transformers. In addition, it is essential that a determination of a generator start-up sequence (GSS) be made to restore the power system. In this paper, we propose the optimal selection of black start units through the generator start-up sequence (GSS) to minimize the restoration time using generator characteristic data and the enhanced Dijkstra algorithm. For each restoration step, the sequence selected for the next start unit is recalculated to reflect the system conditions. The proposed method is verified by the empirical Korean power systems.

Preliminary investigation of flow dynamics during the start-up of a bulb turbine model

Nowadays, the electricity network undergoes more perturbations due to the market demand. Additionally, an increase of the production from alternative resources such as wind or solar also induces important variations on the grid. Hydraulic power plants are used to respond quickly to these variations to stabilize the network. Hydraulic turbines have to face more frequent start-up and stop sequences that might shorten significantly their life time. In this context, an experimental analysis of start-up sequences has been conducted on the bulb turbine model of the BulbT project at the Hydraulic Machines Laboratory (LAMH) of Laval University. Maintaining a constant head, guide vanes are opened from 0 ° to 30 °. Three guide vanes opening speed have been chosen from 5 °/s to 20 °/s. Several repetitions were done for each guide vanes opening speed. During these sequences, synchronous time resolved measurements have been performed. Pressure signals were recorded at the runner inlet and outlet and along the draft tube. Also, 25 pressure measurements and strain measurements were obtained on the runner blades. Time resolved particle image velocimetry were used to evaluate flowrate during start-up for some repetitions. Torque fluctuations at shaft were also monitored. This paper presents the experimental set-up and start-up conditions chosen to simulate a prototype start-up. Transient flowrate methodology is explained and validation measurements are detailed. The preliminary results of global performances and runner pressure measurements are presented.

Realization of single-phase single-stage grid-connected PV system

This paper presents a single phase single stage grid-tied PV system. Grid angle detection is introduced to allow operation at any arbitrary power factor but unity power factor is chosen to utilize the full inverter capacity. The system ensures MPPT using the incremental conductance method and it can track the changes in insolation level without oscillations. A PI voltage controller and a dead-beat current controller are used to ensure high quality injected current to the grid. The paper investigates the system structure and performance through numerical simulation using Matlab/Simulink. An experimental setup controlled by the MicrolabBox DSP prototyping platform is utilized to realize the system and study its performance. The precautions for smooth and safe system operation including the startup sequence are fully considered in the implementation.

Coordinated Control of Gas and Steam Turbines for Efficient Fast Start-Up of Combined Cycle Power Plants

In the fast start-up for combined cycle power plants (CCPP), the thermal stresses of the steam turbine rotor are generally controlled by the steam temperatures or flow rates by using gas turbines (GTs), steam turbines, and desuperheaters to avoid exceeding the thermal stress limits. However, this thermal stress sensitivity to steam temperatures and flow rates depends on the start-up sequence due to the relatively large time constants of the heat transfer response in the plant components. In this paper, a coordinated control method of gas turbines and steam turbine is proposed for thermal stress control, which takes into account the large time constants of the heat transfer response. The start-up processes are simulated in order to assess the effect of the coordinated control method. The simulation results of the plant start-ups after several different cool-down times show that the thermal stresses are stably controlled without exceeding the limits. In addition, the steam turbine start-up times are reduced by 22–28% compared with those of the cases where only steam turbine control is applied.

다단연소사이클 엔진 파워팩 시동해석

본 연구에서는 다단연소사이클 액체로켓엔진 파워팩에 대해 시동과정에서의 동특성 변화를 예측하였다. 시동특성과 관련된 주요 인자 중 밸브 개방시점에 대해 분산값을 정의하고 몬테카를로 방법을 적용하여 이들이 시동특성에 미치는 영향을 살펴보았다. 해석 결과, 연소기 연료 밸브 개방시간 및 시동터빈 종료시간이 시동특성과 관련된 주요 변수임을 확인하였다. 연소기 연료 밸브 개방시점과 시동터빈 종료시점을 분리하여 해석한 결과, 연소기 연료 밸브 개방시점이 시동특성과 매우 밀접한 관련이 있음을 확인하였고 안정적 시동을 위해서는 시동터빈 작동이후 약 1초 이전에 밸브가 개방되어야함을 알 수 있었다. 이를 통해 안정적 시동을 위한 시동 시퀀스 설정이 가능함을 확인하였다. It was examined that start-up characteristics of a staged combustion cycle engine powerpack. Among various parameters, valve opening time was considered as a main factor affecting the start-up characteristics. Using monte-carlo method, characteristics variation was analyzed when the valve opening time deviates from the nominal value. As a result, the main fuel valve opening time and the start turbine ending time were significant associated with the startup characteristics. When separating main fuel valve opening time and start turbine stop time, main fuel valve opening time was an important factor. For stable operation, the main fuel valve opening time must be set one second before after driving the start turbine. Likewise, it was confirmed that the startup analysis can suggest an appropriate startup sequence for a stable startup.

Wavelength bistability based on optical injection in a novel tunable dual mode laser.

A novel tunable dual mode laser is proposed based on a double-layer Bragg grating structure, named double-layer grating distributed Bragg reflector (DLG-DBR) laser. With controlling the gain saturation condition, different oscillating states can be observed. The nonlinear dynamics characteristics including bifurcation of the laser under optical injection with two different start-up sequences are analyzed with numerical simulations. Furthermore, we investigate the lasing wavelength bistability of the laser combined with its tuning characteristics theoretically. Optical memory operation based on the external optical injection locking bistability of the dual mode device is proposed. The memory operation can be achieved in the whole wavelength window with a 10 nm tuning range. A mode suppression ratio (MSR) of more than 45 dB is achieved between the two bistable states.

Optimisation model for power system restoration with support from electric vehicles employing battery swapping

The energy stored in the batteries of electric vehicles (EVs) could be employed for starting generators when a blackout or a local outage occurs. Considering the feature of the battery swapping mode, an available capacity model of the batteries in a centralised charging station is first developed. Then, the authors analyse the start-up characteristics of a generator powered by batteries and propose a bi-level optimisation-based network reconfiguration model to determine the restoration paths with an objective of maximising the overall generation capability. In the upper-level optimisation model, the generator start-up sequence is optimised, whereas the restoration paths are optimised in the lower-level one. Moreover, they consider the uncertainties associated with the available capacity of the batteries. The bi-level optimisation model for the network reconfiguration is developed in the chance-constrained programming framework and solved by the well-established particle swarm optimisation algorithm. Finally, case studies are employed to demonstrate the effectiveness of the presented model. Simulation results show that a centralised EV charging station could act as a power source to effectively restore a power system without black-start (BS) generators or with insufficient cranking power from BS generators, and the presented model could be used to guide actual system restorations.

Effect of the Modification of the Start-Up Sequence on the Thermal Stresses for a Microgas Turbine

Microgas turbines (MGT) are an alternative for small-scale energy production; however, their small size becomes a drawback since it enhances the heat transfer among their components. Moreover, heat transfer drives to temperature gradients which become higher during transient cycles like start-up. The influence of different start-up curves on temperature and thermal stresses of a microgas turbine was investigated. Stationary and rotational blades of the turbine were numerically simulated using CFD and FEM commercial codes. Conjugated heat transfer cases were solved for obtaining heat transfer from fluid toward the blades. Changes of temperature gradients within the blades during the start-ups were calculated under transient state with boundary conditions according to each curve to assess accurate thermal stresses calculations. Results showed that the modification of the start-up curves had an impact on the thermal stresses levels and on the time when highest stresses appeared on each component. Furthermore, zones highly stressed were located near the constraints of blades where thermal strains are restricted. It was also found that the curve that had a warming period at the beginning of the start-up allowed reducing the peaks of stresses making it more feasible and safer for the turbine start-up operation.

An Investigation of Transient Thermal Analysis of 1st Stage Gas Turbine Blade Manufactured by Directional Solidification and Mechanically Alloyed Nickel-Based Superalloys

The turbine rotor blades of a gas turbine engine are designed for operation at elevated temperatures, particularly first stage gas turbine blades. During operation, the turbine blades are subjected to high temperatures and large centrifugal forces. In addition to these, the temperature variations occur at start-up and shutdown cycles of the engine. Due to sudden changes in temperature, transient thermal effects are sighted and time-dependent temperature gradients appear. The estimates of the thermal variations sighted on the turbine blade at various operational speeds of the gas turbine rotor are important in determining the fatigue life. The thermal condition during the startup sequence initiated is considered as a major factor in determining the rotor maintenance interval and individual rotor component life. This work has primarily focused on transient thermal stresses arising in the rotor blade by using Finite Element Analysis. Nowadays, the thermal stresses of the gas turbine parts are determined by user defined software’s that is based on numerical methods which are being used significantly. A typical turbine rotor blade has been modeled by using CATIA V5R21. Turbine blades are made of Nickel-based superalloys have been selected for transient thermal analysis by using ANSYS 15.0. Comparative analysis has also been carried out to determine the suitability and strength of turbine blade material under the same operating conditions. Two blade materials such as IN 792 DS and IN 754 MA have been selected for comparative analysis and these blades were manufactured by Directional solidification and mechanical alloying methods respectively. The physical and mechanical properties are updated to the model and appropriate boundary conditions are applied. Thermal stresses are evaluated for both materials and the results have been compared with IN 738 LC. Static analysis has also been carryout out to examine the structural performance of the alloys. It has been observed that maximum stress and strain are sighted near the root of the turbine blade. The temperature gradients sighted on the turbine blade during acceleration and decelerations are below the melting temperature of the blade materials. It has been noticed that the transient thermal stresses are higher than the steady state thermal stresses. It has been observed that IN 792 DS has better physical and thermo mechanical properties that can withstand higher turbine inlet temperatures and could be suitable material for the manufacturing of turbine blade at Marine and Related Environments.

Evaluation of Restoration Sequence of DG in Black-Start

With the rapid expansion of the grid, how to solve the security and stability of power system has become a hot problem. As a power system after a serious accident the necessary security measures, black-start programs are expected to play an extremely important role in reducing the loss of equipment and user outage and decreasing the outage time. The present paper proposes a series of advantages about distributed generator (DG) and raises evaluation indexes of DG in black-start. The fuzzy hierarchical model is built based on the general steps of fuzzy decision theory. According to the concept of triangular fuzzy number, considering the indexes of which the weight value is judged by means of trapezoidal fuzzy number complementary judgment matrix. Finally, by actually case anglicizing, the paper demonstrates the scientific nature, effective and easy to operate of the method. And a new decision-making method for the optimal DG start-up sequences based on fuzzy AHP is proposed.

Turn-on optimization for Class D series-parallel LCC-type constant current high power LED driver design based on traditional fluorescent control IC

This research investigated a method to optimize the start-up performance of a dimmable light-emitting diode (LED) driver based on half-bridge Class D series-parallel LCC topology. This LED driver is designed for outdoor or high bay applications with 347-480 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sub> input voltage. The total maximum output power is 100 W with a wide tunable output current range (from 50 to 800 mA). The wide load range makes it difficult to achieve a start-up time of less than 1 s under each load condition as well as limit the output overshoot level to below 150% by implementing only one set of KI values in the feedback loop. Moreover, in this design, a fluorescent control IC is used due to the cost efficiency of repurposing existing fluorescent ballast manufacturing systems. The start-up sequence of the fluorescent control IC introduces an additional challenge to the start-up design. In order to comply with Energy Star, which requires the output current to reach 75% of its nominal value and also limit the overshoot level, a self-adjusted-duty-cycle control algorithm is designed. This duty-cycle signal generated by measuring the load condition through a secondary side microcontroller is used to determine the switching frequency of the LCC tank. With this method, the start-up performance is greatly improved and meets all requirements.

An interpretative structural modeling based network reconfiguration strategy for power systems

The network reconfiguration is an important stage of restoring a power system after a complete blackout or a local outage. Reasonable planning of the network reconfiguration procedure is essential for rapidly restoring the power system concerned. An approach for evaluating the importance of a line is first proposed based on the line contraction concept. Then, the interpretative structural modeling (ISM) is employed to analyze the relationship among the factors having impacts on the network reconfiguration. The security and speediness of restoring generating units are considered with priority, and a method is next proposed to select the generating unit to be restored by maximizing the restoration benefit with both the generation capacity of the restored generating unit and the importance of the line in the restoration path considered. Both the start-up sequence of generating units and the related restoration paths are optimized together in the proposed method, and in this way the shortcomings of separately solving these two issues in the existing methods are avoided. Finally, the New England 10-unit 39-bus power system and the Guangdong power system in South China are employed to demonstrate the basic features of the proposed method.

Использование методов сетевого планирования для оптимизации последовательнсоти запуска в обработку деталей кухонной мебели

Использование методов сетевого планирования для оптимизации последовательнсоти запуска в обработку деталей кухонной мебели

The New Black Start: System Restoration with Help from Voltage-Sourced Converters

The very first commercial high-voltage dc (HVdc) transmission system, commissioned in 1954, had black-start capability. This system links the island of Gotland in the Baltic Sea with the Swedish mainland. Gotland had very few generating units, and the HVdc system was required to start up and deliver power without any generation operating on Gotland. Because the HVdc stations used line-commutated converters (LCCs), synchronous condensers were necessary to start up the dc system with a dead receiving network. This complicated the start-up sequence for system restoration.

Near-field/far-field study of the end-effects regime produced by large area ratio nozzles

Vibro-acoustic loads emanating from large area ratio rocket nozzles during start-up can be catastrophic to the launch system and payload. This study quantifies a particular feature referred to as the “end-effects regime”, which is considered the largest source of vibro-acoustic loading during start-up [Nave and Coffey, AIAA Paper 1973-1284]. In this experiment, data acquired during the start-up sequence of several full-scale rocket engines are compared to the laboratory-scale measurements of a thrust-optimized parabolic-contour nozzle conducted in a fully anechoic chamber. The laboratory studies encompass both static and dynamic wall pressures measured inside the nozzle, as well as far-field acoustic surveys. The event produced during the “end-effects regime” was successfully reproduced in the sub-scale model, and was characterized in terms of its mean, variance, and skewness, as well as the spectral properties of the signal obtained by way of time-frequency analyses. The intensity and characteristic frequency of the event of interest are discussed through a comparison of the nominal values for the full-scale and sub-scale system and whether they obey with standard scaling laws.

Development of a low-level RF control system for PET cyclotron CYCIAE-14

The project of a 14MeV PET cyclotron aiming at medical diagnosis and treatment was proposed and started at CIAE in 2010. The low-level RF system is designed to stabilize acceleration voltage and control the resonance of the cavity. Based on the experience of the existing CRM Cyclotron in CIAE, a new start-up sequence is developed and tested. The frequency sweeping is used to activate the RF system. Before the tuner is put into use, a new state called “DDS tuning” is applied to trace the resonance frequency to the designed value. This new option state helps to cover the tuning range, if a large frequency variation occurs because of a thermal cavity deformation. The logic control unit detects the spark, reflection, Pulse/CW state and the frequency of the RF source to perform all kinds of protection and state operations. The test bench and on-line test are carried out to verify the initial design.

Scheduling of multiple chemical plant start-ups to minimize regional air quality impacts

Chemical plant concentrated regions may suffer localized and transient air pollution events that violate national ambient air quality standards (NAAQS). Flaring emissions, especially intensive start-up flaring emissions from chemical plants, have potentially significant impacts on local air quality. Thus, when multiple plants in an industrial zone plan to start-up within a same time period, their start-up plans should be evaluated and optimally controlled so as to avoid unexpected air-quality violations in any air-quality concern regions (AQCRs). In this paper, a general systematic methodology for multi-plant start-up emission evaluation and control has been developed. The methodology starts with collecting regional meteorological information such as wind speed and temperature; geographical information of all of the involved chemical plants and AQCRs; as well as plant operation data such as the start-up time window, start-up duration, and estimated emission profile. Next, a regional air-quality evaluation based on Gaussian dispersion model will be conducted. If any air quality violation is predicted to an AQCR, a multi-objective scheduling problem will be generated and solved to optimize the start-up sequence and start-up beginning time for all chemical plants. The scheduling model minimizes the overall air quality impacts to all of the AQCRs as well as minimize the total start-up time mismatch of all plants, subject to the principles of atmospheric pollutant dispersion. This study may provide valuable quantitative decision supports for multiple stake holders, including government environmental agency, regional chemical plants, and local communities.

Implementation of Control System for Hydrokinetic Energy Converter

At Uppsala University, a research group is investigating a system for converting the power in freely flowing water using a vertical-axis turbine directly connected to a permanent magnet generator. An experimental setup comprising a turbine, a generator, and a control system has been constructed and will be deployed in the Dalälven river in the town of Söderfors in Sweden. The design, construction, simulations, and laboratory tests of the control system are presented in this paper. The control system includes a startup sequence for the turbine and load control. These functions have performed satisfactorily in laboratory tests. Simulations of the system show that the power output is not maximized at the same tip-speed ratio as that which maximizes the turbine power capture.