Radu Saulescu

Conceptual Design of a Chain Speed Increaser for Small Hydropower Stations

Most small hydropower stations drive trains include a gearbox to increase the speed of the turbine shaft to the generator. An increase in speed is needed because the hydro turbines shafts turn at a much lower speed than is required by most electrical generators. The range in which the input angular speed must be increased is 4–8. The speed increasers for this kind of applications must have an acceptable efficiency, reduced overall dimensions and complexity and, therefore, a reduced technological cost. The paper objective is to enlarge the base of speed increasers for small hydro stations with chain transmissions. The concept of the proposed chain transmission to be used as speed increaser is developed using a conceptual design algorithm. The algorithm is based on the VDI model and consists in the following steps: 1°. Requirements list establishment; 2° Global function establishment; 3°. Global function description by structures of sub-functions; 4°. Solving structures generation by: solving the sub-functions, sub-solutions composition and elimination of inadequate solution; 5°. The best solving structure selection by evaluation. The speed increaser function is detailed as part of a hydropower station. The sub-functions of the speed increaser are further analyzed in order to generate the solving structures. Sixteen distinct structural variants are presented in the paper. But only those structural variants, whose technical characteristics fulfill, quantitatively, the requirements, are considered as solving structures (for the speed increaser function). In order to select the solving structures, the synthesis of the sprockets teeth numbers for all the structural variants is performed and their efficiency is calculated. Then, their evaluation is made taking into account the technical-economic criteria; thus, the optimal solution that fulfils the requirements list (the principle solution) is found. The principle solution is an innovative concept of the chain speed increaser and represents an input data for the embodiment design phase.Copyright

The Synthesis of a Linkage with Linear Actuator for Solar Tracking with Large Angular Stroke

In the bi-axial tracking of the PV modules (aiming to maximize the normal direct solar radiation on panels), one of the two axes, which has a large angular stroke (180° . 360°), is usually driven by a gear speed reducer and the other axis, which has a smaller angular stroke (⩽ 90°), is driven by a linear actuator. Because a linear actuator is more economical than a rotary one, the paper reports on the use of linear actuators for the large angular strokes; this aim is fulfilled by the synthesis of a linkage composed of two simple linkages, serially connected: a triangle linkage with a linear actuator and a four-bar linkage which amplifies the output angle of the first linkage up to about 180°.

Four-Bar Linkages with Linear Actuators Used for Solar Trackers with Large Angular Diurnal Strokes

The paper presents a detailed analysis on four-bar linkages, driven by linear actuators, used in solar tracking systems with large diurnal strokes. Based on the analysis of representative solutions in literature, a dimensional synthesis algorithm is proposed for a four-bar linkage, actuated by a linear actuator, linked with the connecting rod and with the base. The results are supporting the design of efficient, tracked solar energy conversion systems.

Planetary Gear for Counter-Rotating Wind Turbines

A specific problem of the wind turbines refers to the difference between the low rotation speed of the wind turbine rotor and the high rotation speed needed for the electrical generator. Usually, the adaptation between the speed of the turbine rotor and the electrical generator speed is achieved by means of a speed increaser. A recent alternative relates to the use of coaxial counter-rotating wind turbines, which can achieve higher power and improve the conversion efficiency of the wind energy into electrical energy (up to 25%) with a reduced cost of approx. 20-30% compared to similar single rotor turbines. Conceptually, the counter-rotating wind turbine systems can integrate a particular generator wherein the rotor is coupled to a row of blades and the stator with another row of blades, or a commonly generator, coupled to a differential planetary gear, that allows the summation of the blades motions.The paper describes and analyzes kinematic and dynamic aspects of a system consisting of two coaxial counter-rotating turbines and a generator, interconnected by a planetary gear with two inputs (the two turbines) and an output (the generator). The algorithm is based on the property of the differential planetary gear of adding two input motions into one output motion. The kinematic and dynamic parameters of the planetary gear are established in the paper, and a case study is further presented: a small wind turbine equipped with a transmission enabling input speed multiplication.

On the Use of 2 DOF Planetary Gears as “Speed Increasers” in Small Hydros and Wind Turbines

A specific issue both for small hydropower plants and wind turbines refers to the discrepancy between the relatively low speed of the water turbine / wind rotor and relatively high speed of the electric generator: the turbine / rotor has higher performances at lower speeds, while the generator performances are increasing with the speed. Usually, this problem can be solved connecting a proper speed increaser between the turbine and generator. This paper aims to model and simulate a new solving variant for this issue. The solution uses 2 turbines and a generator, connected through a planetary gear with 2 inputs (the turbines) and 1 output (generator). The counter-rotating system functioning is based on the property of the 2 DOF planetary gear sets about summing 2 input motions into an output motion. The transmissions running conditions are modeled in the paper, with examples in relevant applications; the numerical simulation results are comparatively analyzed to those of classical solutions and recommendations concerning their use are settled.Copyright

Comparative Analysis of Two Wind Turbines with Planetary Speed Increaser in Steady-State

Planetary transmissions used as speed amplifiers in wind/hydro conversion systems typically rely on the conventional concept of mechanism with one input and one output. This concept is found in the most of the high power wind turbines; however, the need to implement in the built environment smaller wind turbines with speed amplifiers led to new turbine concepts such as counter-rotating rotors and classical generator. The paper presents a comparative analysis of two wind turbines with one rotor and respectively two counter-rotating rotors, which contain identical electrical generators and the same type of mechanical amplifier used as a 1 DOF mechanism and differential one respectively. With the assumption of maintaining the same electrical generator running point for both wind turbines, the steady-state behaviour of the considered turbines is identified and a comparative kinematic and static performance analysis is performed, aiming at highlighting the impact on efficiency and on constructive design and development of the two turbines.

On New High Performance Systems with Linear Actuators for Diurnal Orientation of PV Platforms

The paper presents new mechatronic systems used to perform the diurnal orientation of photovoltaic (PV) platforms, aiming to achieve high angular strokes and also low cost, high precision, constructive simplicity and relative low pressure angles. Starting from the disadvantages of the existing tracking mechanism identified in the literature (patents, scientific articles, market documentation, etc.), new high performance linkages and gear mechanisms driven by linear actuators are proposed in the paper. Hence, four new tracking mechanisms, achieving high angular strokes (over 180o), are described: a) quadrilateral type, b) rhombus type, c) slider-crank type, and d) linkage with gears type. These mechanisms are designed especially for concentrating PV systems, which require high orientation precision on the entire angular stroke.

INFLUENCE OF PROFILE ANGLE ON FORCES DISTRIBUTION ON SILENT CHAIN TRANSMISSIONS

The aim of this paper is to define and to analyze the theoretical contact forces that appear in a sprocket silent chain joint. The contact force between the links and the teeth flanks of the sprocket can be considered as a reaction to the axial force (tensioning force) transmitted throughout the pins. The centrifugal force is considered to be constant and the friction between the elements is not considered. This paper is presenting the steps to obtain the relationships for the forces from the sprocket-link contact depending on the tensioning force component between the links and the centrifugal force. These forces are computed in order to establish their distribution on links.

On the Centrifugal Effect on the Load of Chain and Belt Transmissions

The literature on chain and belt transmissions talks about the effect of centrifugal forces on chains and belts as creating a constant Fc = (m/l) v2 constant component along belt or chain. This component is only depending on the mass per unit of length (m/l) and the velocity of chain or belt. Our experimental data and also theoretical approach on the centrifugal effect on the load of chain and belt transmissions shows that chain/belt supplementary loading but also shaft unloading are different. This effect must consider not only the mass per unit of length and the velocity of chain/belt but also the stiffness of chain/belt and the stiffness of shafts and other bearing components. The conclusions of this paper are changing significantly the recommendations from the literature about the centrifugal effect on the load of chain and belt transmissions.

The Influence of the Bush-Bushes Pocket Geometry on the Bush Contact Angle

The chain drive transmissions are used mainly in the automotive industry as distribution transmissions in cars. In the specific literature, the kinematics and the dynamic analysis problems are accomplished depending on the European and American standards. The contact between the chain’s bush and the chain wheel is influencing the transmissions dynamics and is influenced directly by its geometry. According to these, the paper presents the influence of the chain wheel’s geometry on the contact angle which depends on the point’s position where the normal and transversal forces are acting.