Kastha is at IIT Kharagpur. Convert currency. Add to Basket. Condition: New. More information about this seller Contact this seller. Book Description Condition: New. During fast variations of wind speed, the inertia effect may be significant: e. In spite of these minor drawbacks, the Robinson cup anemometer is the most extensively used instrument for wind speed measurement. The head, which is usually mounted on a mast at the desired height, consists of a horizontal tube, bent at one end and supported by two concentric vertical tubes.

The horizontal end is connected to the inner tube. The entire head is free to rotate, which is turned to face the wind by a vane.

Air — From point 1 Fig. The pressure tube anemometer The wind blowing into the horizontal tube creates pressure, which is communicated through a flexible tube to a recorder. Again, the wind blowing over the small holes in the concentric tube creates a suction effect, which is also communicated to the recorder through a second flexible tube. In the recording apparatus, a copper vessel, closed at one end, floats inverted in a cylindrical metal container partly filled with water and sealed from the outside air.

The wind pressure from the horizontal tube of the head is transmitted to the space inside the float, causing it to rise as wind blows. This is assisted by the suction that is applied to the space above the float. If the paper movement is spring operated, the device does not need any electrical supply. The float can be so shaped, in accordance with the law relating pressure to wind velocity, that the velocity scale on the chart is linear.

Most pressure tube anemometers also have wind direction recorders taking signals from the tail-vane, so that both the speed and direction of wind are recorded. The wire is heated by a constant-current source. With the variation of wind speed, the wire temperature varies, which varies the resistance of the wire. Naturally, in order to find the wind speed, it suffices to measure the resistance of the wire using any standard method.

The calibration has to take into account the resistance-temperature characteristics of the wire and the ambient temperature of air. In a hot wire anemometer, the temperature difference between the wire and the ambient air is inversely proportional to the square root of the wind velocity: Ty, os Dy og 2. During the site identification process, the measuring instruments described in the previous section are installed at the site.

In the case of a digital data logger recording wind speed data at regular intervals, the average wind speed can be calculated as where v; is the wind speed at the ith observation and n is the number of observations.

At any given site, the wind speed varies with the height from the ground level. The values of x are given in Table 2. The measuring instruments record the wind speed continuously against time. If the data are collected throughout a year, the Table 2. The next step is to obtain, from Fig. Of course, the period of time for which the wind speed assumes an exact value is infinitely small.

So, the vertical axis actually gives the annual duration for which the wind speed falls within certain limits, for instance 0. The y-axis of the wind speed distribution curve should be given in hours per annum per metres per second. Thus the integral of the function or the area under the curve will always be hrs, corresponding to the number of hours in a year.

This curve, shown in Fig. Note that the wind speed for maximum energy is different from and higher than the most frequent wind speed. In such cases, the wind speed distribution curves can be obtained approximately from the magnitude of the average wind speed, by using a standard statistical distribution function, such as the Rayleigh distribution function.

It is observed that the wind speed distributions of different sites have certain similarities and can be approximated by the Rayleigh distribution function. Wind Speed Statistics 61 The distribution function is given by Tv rv? Equation 2. These relations give a very quick method of finding the wind speed at which the maximum energy is available, that is, the speed at which a wind turbine should be rated. It should be noted, however, that the Rayleigh distribution becomes inappropriate at wind speeds below 10 mph, and therefore should not be used for sites where the mean annual wind speed is below 10 mph.

A more general distribution function is required to obtain a better approximation for wind speed distribution on a daily or a still shorter time scale. The value of k is chosen to fit the actual curve in the best way. The dependence of the distribution function on the choice of the scale factor c is shown in Fig.

As stated earlier, a good choice of c for a particular site is the annual average wind speed 7. We thus obtain, either from direct measurement or by using this statistical distribution formula, the wind speed distribution curve. Assume the Rayleigh distribution as an approximation to the wind velocity-duration distribution over the terrain and 1. Using tables for the gamma. Site and Turbine Selection 65 For the final selection process, that is, while choosing the wind turbine that is best suited for a particular site, a modification of the curve shown in Fig.

At this stage, we plot the speed-duration curve—the graph of v versus the total duration for which the wind speed exceeds or equals v Fig. Naturally; the largest coordinate on the y-axis is the number of hours in a year , when the wind speed exceeds zero.

If the wind speed is measured using a digital recorder with data logging facility, the wind speed distribution and duration curves can be obtained directly or generated by a computer later using the stored data. The latter are given as the power versus wind speed characteristics such as that shown in Fig. Every wind turbine model has a specific cut-in speed, a rated speed, a furling speed, and power versus wind speed characteristics within the wind speed range between the cut-in speed and the furling speed.

At the cut-in speed the wind generator starts generating power. As the wind speed increases, the power output increases in proportion with the power contained in the wind. Beyond a certain wind speed, the maximum power handling capacity of the generator is reached, and thereafter the system works in the constant-power output mode.

In some machines the constant- speed region is small or negligible and the speed-regulating mechanism works only in constant-power mode. In order to sustain this condition, the machine should also be driven by a mechanical power source.

This mode of operating the induction machine is known as plugging, and is equivalent to an electrical braking method. Equation 3. As this makes the effective circuit impedance constant, the stator input current also remains constant.

This characteristic describes the variation of the induced emf in the stator winding with the magnetizing current. The characteristic is obtained by exciting the stator windings from a variable-voltage supply at the rated frequency while driving the machine at synchronous speed through a prime mover.

Figure 3. It is observed that the relationship is not linear as may be expected from the equivalent circuit of Fig. The modelling of the magnetization characteristic depends on the method of analysis adopted for the machine. It may be modelled in a piecewise manner by a polynomial of degree n. However, it can be transformed into other simpler models without any loss of accuracy. In fact, such circuits are found to be more convenient for analysing the behaviour of the induction machine in certain situations.

One such circuit model of the machine is known as the inverse-T' equivalent circuit. No significant error is introduced in the prediction of the performance of the machine if the shunt resistance, representing the iron loss in the stator, is ignored in favour of simplicity of manipulating the equations.

The information contained in Eqns 3. The loss in the slip-dependent rotor resistance in the equivalent circuit of Fig. Modified T-form There is an apparent omission in the circuit model of Fig. Even the generalized theory of electrical machines indicates the presence of a rotational emf in the rotor circuit of an induction machine.

The conventional circuit model of an induction motor shows the presence of a negative resistance in the rotor circuit, implying generating action at a speed above the synchronous speed. However, the absence of any rotational emf in the rotor branch complicates the explanation of the behaviour of the rotor of an induction machine that serves as a source of power during its generating action, particularly, in the self-excited mode.

The concept of a negative resistance seems to offer a computational advantage rather than a convincing explanation. In the circuit model of Fig.

This is, therefore, a rotational emf. The total power associated with the rotational emf is P. The new circuit model of Fig. Consequently, if the rotor changes its current as a result of any other source of emf in its circuit, the stator would be unable to detect the inclusion of this additional emf in the rotor circuit, as the same change in the rotor current and its power factor can be effected by the inclusion of appropriate values of resistance and inductance capacitance in the rotor circuit.

Referring to the phasor diagram in Fig. As E Therefore, the balance of the air-gap power, ie. Since motoring convention has been followed, Py and Pm will be negative in the generating mode. P, has been considered Positive for the power absorbed by the auxiliary source, i.

The electrical power associated with the slip-dependent secondary resistance and the auxiliary emf, shown in Fig. Mode I—Subsynchronous motoring operation In this mode, s 0. Consequently, according to Eqn 3. Mode IISupersynchronous motoring operation In the supersynchronous region, the rotor speed is greater than the synchronous speed, ic. Consequently, from Eqn 3.

As Pow is always positive, P; must be negative. Therefore, power must be fed into the slip-ring terminals from the auxiliary source. By increasing the input to the rotor, P, can be increased. The power flow diagram for this mode is shown in Fig. As Poy is positive, P, should be made sufficiently negative by injecting power into the rotor circuit in order to make the rotor electrical power sPag negative.

The net electrical power flowing into the grid is, therefore, P; — P;. Mode IV—Supersynchronous generating action For supersynchronous operation in the generating mode, the power flow diagram is shown in Fig. From the viewpoint of power flow in the rotor circuit, the region of supersynchronous operation in the generating mode can be divided into two subregions as depicted by the torque-speed curves in Fig.

In subregion I, the rotor speed is less than the rated speed wy. Rated speed is obtained when the stator carries its rated current. For this configuration, the operating speed range of the generator is small if the stator current is not to exceed its rated value. This is the conventional use of the machine. It is also the most efficient way of operating the machine in this subregion. Any attempt to extract power from the rotor by inserting an external resistance in the rotor circuit will shift the torque-speed curve, and the net output power at a given speed will drop with respect to the conventional use of the same machine.

If, however, an electrical source in proper phase is connected to the rotor circuit, the induction machine will be able to feed more power to the supply than with conventional use. This is because the rotor current will then be able to go above the value corresponding to the conventional use of the same machine without exceeding the rated rotor current.

In subregion II, when the rotor speed is higher than the rated speed Wy:ated, the effective rotor resistance has to be increased to keep the stator current constant and equal to its rated value. The equivalent circuit in Fig. The additional resistance effect can also be realized by extracting electrical power, equal to the surplus mechanical power, through the slip rings. In a similar manner, vector control strategies have been proposed for controlling the active and reactive power of the induction generator.

These two rotating space-vectors are always in quadrature. The essence of vector control is to force the moving stator and rotor current vectors J, and J, to take these magnitudes and positions that enable independent control of I, and I,sind, I-sin6,.

This is achieved by appropriate control of the magnitude and phase of the actual stator rotor currents. Vector control makes an induction machine behave like a de machine with J, sin6, I,sind, analogous to the armature current and [,, analogous to the field excitation. The same current vectors I, and J, can also be produced by as- suming currents flowing through a pair of two orthogonally spaced fictitious identical windings, replacing the original balanced three- phase stator and rotor windings.

Such a transformation is known as a reference frame transformation. However, for this, mere replacement by a two-phase winding is not sufficient; further insight is necessary in order to develop the mathematical relation between the real and the transformed variables.

Owing to the smooth air gap, the self-inductances of the stator and the rotor windings are constant, but the mutual inductances between them vary with the rotor displacement relative to the stator. This variation of the stator-to-rotor mutual inductances makes the analysis of an induction motor in terms of real variables complicated, as the voltage equations become non-linear.

In order to eliminate the effect of the variation of the mutual inductances and, thus, facilitate analysis, a change of variables can be devised for the stator and rotor variables. This gives rise to a fictitious magnetically decoupled two-phase machine, in which the rotor circuits are not only made stationary with respect to the stator circuits but also aligned with the respective stator windings. In this way, all the inductances become constant. These orthogonally spaced balanced windings, known as the and q-windings, may be considered stationary or moving with respect to the stator.

If one of the axes of the synchronously rotating reference frame coincides with the air-gap flux vector i. It may also be designed with respect to the stator or rotor flux with corresponding advan- tages and limitations.

In field-oriented control FOC , the stator phase currents are first estimated in a synchronously rotating reference frame and then transformed back to the stationary stator frame to feed the machine. How is the transformation carried out?

In Eqn 3. This transformation is based on the assumption of a distributed sinusoidal winding. The phase variables are obtained from the d,q,o variables through the inverse of the transformation matrix in Eqn 3.

If the terminal voltages form a balanced set, the steady-state currents will also form a balanced set in a symmetrical induction machine. The Wound-field Synchronous Machine In wind electric power generation systems, two types of wind tur- bines are generally used. These are variable-speed and constant- speed turbines. The high-power kW to 2 MW variable-speed synchronous generator, with field windings on the rotor, is a seri- ous competitor for the wound rotor induction motor.

In particular, direct drive variable-speed systems use synchronous machines. As the name indicates, unlike in a wound rotor inducion machine, the rotor of a synchronous machine runs in synchronization with the field produced by the stator winding currents.

The salient aspects of the working of a synchronous machine are taken up in the following sections. The stator is similar to that of an induction machine. The cylindrical rotor construction, with two or sometimes four poles, is operated at high speed for large-capacity machines, while the salient-pole rotor construction, with a large number of projected poles, is common for slower speed machines.

Salient-pole machines are commonly used with wind turbines when the use of a synchronous machine is intended. Sometimes a squirrel cage type winding, called the amortisseur or the damper winding, is embedded in the rotor pole face of a salient-pole machine. In terms of real variables phase currents and field currents , the analysis of a salient-pole synchronous machine is more complicated compared to that of an induction machine.

Not only are the mutual inductances between the stator and the rotor windings functions of the rotor displacement relative to the stator, but also the stator winding self-inductances and the mutual inductances between them are rotor-position-dependent.

To make the matter worse, the rotor windings are not identical and the magnetic characteristics along the d- and the g-axis are different. As a result, the voltage equations are highly non-linear.

As the fictitious and rotor windings are not in relative motion, the mutual inductances between them are all constants. Also the d-axis windings are magnetically decoupled from the g-axis windings. The equations of the inverse transformation are given by-Eqn 3. Substitution of the flux linkage expressions 3. Substitut- ing Eqns 3. By definition Fig. Therefore, under the no-load condition, the q-axis coincides with the voltage space-vector, as shown in Fig.

It follows from Eqn 3. With a constant shaft torque, during steady-state operation, the stator carries balanced currents at the angular frequency w. Substitution of Eqns 3. Tt follows from Eqns 3. R, being small, for motor operation, Vis is negative and V,, is definitely positive. Thus it is apparent from Eqns 3. Seller rating : This seller has earned a 2 of 5 Stars rating from Biblio customers. A - Z Books.

Customers who searched for ISBN might also be interested in this item:. International Edition. Seller rating : This seller has earned a 1 of 5 Stars rating from Biblio customers. Students Textbooks. Much of this information is difficult to find in a concise form elsewhere, so this should increase the usefulness of the book. The field is evolving rapidly, so some specific examples will become obsolete quickly. An effort has been made, however, to present the basic information that is not likely to change, so the book will be useful for a number of years.

It has been the author's experience that the quantity of material is ample for a three hour course. The instructor may need to be selective about sections to be covered. Chapters 2,4,5, and 8 are viewed as the heart of the course, and the other chapters can be omitted, if necessary, with little loss of continuity. The book has been classroom tested over a five year period and much of it has been rewritten to include improvements suggested by the students. SI units have been used extensively throughout the book, with English units used as necessary to bridge the gap between present practice and the anticipated total conversion to SI units.

A list of conversion factors is given at the end of the book. A good selection of problems is given at the end of each chapter. Some problems require the use of a programmable hand calculator or a digital computer.

These can be used where all the students have access to such equipment to give additional practice in computational techniques. The author wishes to express appreciation to Theresa Shipley and Teresa Gallup for typing various versions of the manuscript.

He also wishes to thank the many students who offered suggestions and criticisms. Finally, he wishes to thank his wife Jolene, and his children, Kirk and Janel, for their patience during the writing of the book.

Infibeam Go to Infibeam website. Currently this book is not available in Flipkart. View larger. Description Wind Electrical Systems is the first Indian textbook specifically covering issues concerning wind energy conversion. Table of contents Chapter1.

Features Provides in-depth coverage of topics. Want to Read saving…. Want to Read Currently Reading Read. Error rating book.

Bhadra hhadra, D. Wind Electrical Systems is the first Indian textbook specifically covering issues concerning wind energy conversion. Suitable for: This book will benefit students as well as practising engineers working on wind energy. With its comprehensive treatment of topics, this book will benefit students as well rlectric practising engineers working on wind energy. The book introduces the basics of wind energy and then discusses the conversion of wind energy into electrical energy, bhadrs wind electric systems bhadra pdf free download integration with the local grid, stand-alone generation and consumption, variable-speed wind generators, and hybrid power systems. The book assumes no prior knowledge in the field and therefore dj mixer software for windows 8 free download also be suitable for readers with a non-electrical-engineering background. Fundamentals of Wind Turbines. Wind Site Analysis and Selection. Basics of Induction and Synchronous Machines. Power Electronics Chapter5. Grid-connected and Self-excited Induction Generator Operation. Generation Schemes with Variable-speed Turbines. Hybrid Energy Systems. Pxf in-depth coverage of topics. Incorporates contemporary analytical methods for studying the steady-state as well as dynamic behaviour of wind electrical systems. Includes recent developments sourced from research wind electric systems bhadra pdf free download and conference proceedings. Includes a wind electric systems bhadra pdf free download number of worked out examples and exercise problems to reinforce concepts. Field experience- what is lead free pewter made from, watch amish mafia season 3 online free, where can i watch belle online free - Wind Electrical Systems by S. N. BhadraS.N.Bhadra, D.Kastha, S.Banerjee - wind electrical systems-Oxford University Press (2013) (1).pdfISBN 10: 0195670930