kinetic energy storage theory and practice of advanced flywheel systems pdf

Kinetic Energy Storage Theory And Practice Of Advanced Flywheel Systems Pdf

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The book first gives an introduction to the use of flywheels, including prehistory to the Roman civilization, Christian era to the industrial revolution, and middle of the 19th century to

Kinetic Energy Storage. Theory and Practice of Advanced Flywheel Systems

Flywheel energy storage FES works by accelerating a rotor flywheel to a very high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of conservation of energy ; adding energy to the system correspondingly results in an increase in the speed of the flywheel.

Most FES systems use electricity to accelerate and decelerate the flywheel, but devices that directly use mechanical energy are being developed. Advanced FES systems have rotors made of high strength carbon-fiber composites, suspended by magnetic bearings , and spinning at speeds from 20, to over 50, rpm in a vacuum enclosure. A typical system consists of a flywheel supported by rolling-element bearing connected to a motor—generator. The flywheel and sometimes motor—generator may be enclosed in a vacuum chamber to reduce friction and reduce energy loss.

First-generation flywheel energy-storage systems use a large steel flywheel rotating on mechanical bearings. Newer systems use carbon-fiber composite rotors that have a higher tensile strength than steel and can store much more energy for the same mass.

To reduce friction , magnetic bearings are sometimes used instead of mechanical bearings. The expense of refrigeration led to the early dismissal of low-temperature superconductors for use in magnetic bearings.

However, high-temperature superconductor HTSC bearings may be economical and could possibly extend the time energy could be stored economically. High-temperature superconductor bearings have historically had problems providing the lifting forces necessary for the larger designs, but can easily provide a stabilizing force.

Therefore, in hybrid bearings, permanent magnets support the load and high-temperature superconductors are used to stabilize it. The reason superconductors can work well stabilizing the load is because they are perfect diamagnets. If the rotor tries to drift off center, a restoring force due to flux pinning restores it. This is known as the magnetic stiffness of the bearing. Rotational axis vibration can occur due to low stiffness and damping, which are inherent problems of superconducting magnets, preventing the use of completely superconducting magnetic bearings for flywheel applications.

Since flux pinning is an important factor for providing the stabilizing and lifting force, the HTSC can be made much more easily for FES than for other uses. HTSC powders can be formed into arbitrary shapes so long as flux pinning is strong. An ongoing challenge that has to be overcome before superconductors can provide the full lifting force for an FES system is finding a way to suppress the decrease of levitation force and the gradual fall of rotor during operation caused by the flux creep of the superconducting material.

The maximal specific energy of a flywheel rotor is mainly dependent on two factors: the first being the rotor's geometry, and the second being the properties of the material being used.

For single-material, isotropic rotors this relationship can be expressed as [9]. For energy storage, materials with high strength and low density are desirable. For this reason, composite materials are frequently used in advanced flywheels. Several modern flywheel rotors are made from composite materials. For these rotors, the relationship between material properties, geometry and energy density can be expressed by using a weighed-average approach.

One of the primary limits to flywheel design is the tensile strength of the rotor. Generally speaking, the stronger the disc, the faster it may be spun, and the more energy the system can store. When the tensile strength of a composite flywheel's outer binding cover is exceeded, the binding cover will fracture, and the wheel will shatter as the outer wheel compression is lost around the entire circumference, releasing all of its stored energy at once; this is commonly referred to as "flywheel explosion" since wheel fragments can reach kinetic energy comparable to that of a bullet.

Composite materials that are wound and glued in layers tend to disintegrate quickly, first into small-diameter filaments that entangle and slow each other, and then into red-hot powder; a cast metal flywheel throws off large chunks of high-speed shrapnel. For a cast metal flywheel, the failure limit is the binding strength of the grain boundaries of the polycrystalline molded metal.

Aluminum in particular suffers from fatigue and can develop microfractures from repeated low-energy stretching.

Angular forces may cause portions of a metal flywheel to bend outward and begin dragging on the outer containment vessel, or to separate completely and bounce randomly around the interior. The rest of the flywheel is now severely unbalanced, which may lead to rapid bearing failure from vibration, and sudden shock fracturing of large segments of the flywheel.

Traditional flywheel systems require strong containment vessels as a safety precaution, which increases the total mass of the device. The energy release from failure can be dampened with a gelatinous or encapsulated liquid inner housing lining, which will boil and absorb the energy of destruction. Still, many customers of large-scale flywheel energy-storage systems prefer to have them embedded in the ground to halt any material that might escape the containment vessel.

This change in orientation is resisted by the gyroscopic forces exerted by the flywheel's angular momentum, thus exerting a force against the mechanical bearings. This force increases friction. This can be avoided by aligning the flywheel's axis of rotation parallel to that of the earth's axis of rotation. When used in vehicles, flywheels also act as gyroscopes , since their angular momentum is typically of a similar order of magnitude as the forces acting on the moving vehicle.

This property may be detrimental to the vehicle's handling characteristics while turning or driving on rough ground; driving onto the side of a sloped embankment may cause wheels to partially lift off the ground as the flywheel opposes sideways tilting forces. On the other hand, this property could be utilized to keep the car balanced so as to keep it from rolling over during sharp turns. When a flywheel is used entirely for its effects on the attitude of a vehicle, rather than for energy storage, it is called a reaction wheel or a control moment gyroscope.

The resistance of angular tilting can be almost completely removed by mounting the flywheel within an appropriately applied set of gimbals , allowing the flywheel to retain its original orientation without affecting the vehicle see Properties of a gyroscope.

This doesn't avoid the complication of gimbal lock , and so a compromise between the number of gimbals and the angular freedom is needed. The center axle of the flywheel acts as a single gimbal, and if aligned vertically, allows for the degrees of yaw in a horizontal plane.

However, for instance driving up-hill requires a second pitch gimbal, and driving on the side of a sloped embankment requires a third roll gimbal. Although the flywheel itself may be of a flat ring shape, a free-movement gimbal mounting inside a vehicle requires a spherical volume for the flywheel to freely rotate within.

Left to its own, a spinning flywheel in a vehicle would slowly precess following the Earth's rotation, and precess further yet in vehicles that travel long distances over the Earth's curved spherical surface. A full-motion gimbal has additional problems of how to communicate power into and out of the flywheel, since the flywheel could potentially flip completely over once a day, precessing as the Earth rotates.

Full free rotation would require slip rings around each gimbal axis for power conductors, further adding to the design complexity.

To reduce space usage, the gimbal system may be of a limited-movement design, using shock absorbers to cushion sudden rapid motions within a certain number of degrees of out-of-plane angular rotation, and then gradually forcing the flywheel to adopt the vehicle's current orientation. An alternative solution to the problem is to have two joined flywheels spinning synchronously in opposite directions.

They would have a total angular momentum of zero and no gyroscopic effect. A problem with this solution is that when the difference between the momentum of each flywheel is anything other than zero the housing of the two flywheels would exhibit torque.

Both wheels must be maintained at the same speed to keep the angular velocity at zero. Strictly speaking, the two flywheels would exert a huge torqueing moment at the central point, trying to bend the axle.

However, if the axle were sufficiently strong, no gyroscopic forces would have a net effect on the sealed container, so no torque would be noticed. To further balance the forces and spread out strain, a single large flywheel can be balanced by two half-size flywheels on each side, or the flywheels can be reduced in size to be a series of alternating layers spinning in opposite directions. However this increases housing and bearing complexity. In the s, flywheel-powered buses, known as gyrobuses , were used in Yverdon Switzerland and Ghent Belgium and there is ongoing research to make flywheel systems that are smaller, lighter, cheaper and have a greater capacity.

It is hoped that flywheel systems can replace conventional chemical batteries for mobile applications, such as for electric vehicles. Proposed flywheel systems would eliminate many of the disadvantages of existing battery power systems, such as low capacity, long charge times, heavy weight and short usable lifetimes.

Flywheels may have been used in the experimental Chrysler Patriot , though that has been disputed. Flywheels have also been proposed for use in continuously variable transmissions. Punch Powertrain is currently working on such a device. During the s, Rosen Motors developed a gas turbine powered series hybrid automotive powertrain using a 55, rpm flywheel to provide bursts of acceleration which the small gas turbine engine could not provide. The flywheel also stored energy through regenerative braking.

The flywheel was composed of a titanium hub with a carbon fiber cylinder and was gimbal -mounted to minimize adverse gyroscopic effects on vehicle handling. The prototype vehicle was successfully road tested in but was never mass-produced. In , Volvo announced a flywheel system fitted to the rear axle of its S60 sedan. Braking action spins the flywheel at up to 60, rpm and stops the front-mounted engine.

Flywheel energy is applied via a special transmission to partially or completely power the vehicle. The centimetre 7. The company did not announce specific plans to include the technology in its product line. In July GKN acquired Williams Hybrid Power WHP division and intends to supply carbon fiber Gyrodrive electric flywheel systems to urban bus operators over the next two years [24] As the former developer name implies, these were originally designed for Formula one motor racing applications.

Flywheel systems have been used experimentally in small electric locomotives for shunting or switching , e. Larger electric locomotives, e. British Rail Class 70 , have sometimes been fitted with flywheel boosters to carry them over gaps in the third rail.

The Parry People Mover is a railcar which is powered by a flywheel. It was trialled on Sundays for 12 months on the Stourbridge Town Branch Line in the West Midlands , England during and and was intended to be introduced as a full service by the train operator London Midland in December once two units had been ordered. In January , both units are in operation. FES can be used at the lineside of electrified railways to help regulate the line voltage thus improving the acceleration of unmodified electric trains and the amount of energy recovered back to the line during regenerative braking , thus lowering energy bills.

Flywheel power storage systems in production as of [update] have storage capacities comparable to batteries and faster discharge rates.

They are mainly used to provide load leveling for large battery systems, such as an uninterruptible power supply for data centers as they save a considerable amount of space compared to battery systems.

Flywheel maintenance in general runs about one-half the cost of traditional battery UPS systems. The only maintenance is a basic annual preventive maintenance routine and replacing the bearings every five to ten years, which takes about four hours.

A long-standing niche market for flywheel power systems are facilities where circuit breakers and similar devices are tested: even a small household circuit breaker may be rated to interrupt a current of 10 or more amperes, and larger units may have interrupting ratings of or 1 amperes.

The enormous transient loads produced by deliberately forcing such devices to demonstrate their ability to interrupt simulated short circuits would have unacceptable effects on the local grid if these tests were done directly from building power. Typically such a laboratory will have several large motor—generator sets, which can be spun up to speed over several minutes; then the motor is disconnected before a circuit breaker is tested. Tokamak fusion experiments need very high currents for brief intervals mainly to power large electromagnets for a few seconds.

Also the non-tokamak: Nimrod synchrotron at the Rutherford Appleton Laboratory had two 30 ton flywheels. The Gerald R. Ford -class aircraft carrier will use flywheels to accumulate energy from the ship's power supply, for rapid release into the electromagnetic aircraft launch system.

The shipboard power system cannot on its own supply the high power transients necessary to launch aircraft. It used a carbon fiber rim with a titanium hub designed to spin at 60, rpm, mounted on magnetic bearings. Weight was limited to pounds. Storage was W-hr 1.

Review of Magnetic Flywheel Energy Storage Systems

Michael A. Conteh a. Emmanuel C. Lamina and laminate mechanical properties of materials suitable for flywheel high-speed energy storage were investigated. Low density, low modulus and high strength composite material properties were implemented for the constant stress portion of the flywheel while higher density, higher modulus and strength were implemented for the constant thickness portion of the flywheel. Design and stress analysis were used to determine the maximum energy densities and shape factors for the flywheel.


Kinetic Energy Storage - 1st Edition - ISBN: , DRM-free (Mobi, PDF, EPub) Kinetic Energy Storage: Theory and Practice of Advanced Flywheel Systems focuses on the use of flywheel systems in storing.


Kinetic Energy Storage: Theory and Practice of Advanced Flywheel Systems by G. Genta

Flywheel energy storage FES works by accelerating a rotor flywheel to a very high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of conservation of energy ; adding energy to the system correspondingly results in an increase in the speed of the flywheel. Most FES systems use electricity to accelerate and decelerate the flywheel, but devices that directly use mechanical energy are being developed.

The result of the analysis can be used to set the support position of the rotor system, limit the ratio of transverse moment of inertia and the polar moment of inertia, and direct the flywheel prototype future design. The presented simplified rotordynamic model can also be applied to rotating machines. Later in the s, flywheel energy storage was proposed as a primary objective for electric vehicles and stationary power backup [ 1 ]. With the improvements in materials, magnetic bearing technology, and power electronics, flywheel energy storage technology has large developments. Compared with traditional battery energy storage system, flywheel energy storage system has many advantages such as higher energy storage density, higher specific power and power density, lower risk of overcharge or overdischarge, wide range of operation temperature, very long life cycle, and environmental friendliness [ 2 ].

The Theory and Synthesis of High Effect Flywheel with Variable Equivalent Mass Moment of Inertia

International Journal of Rotating Machinery

To reduce the angular velocity fluctuation of the input shaft to a machine, we deduced that a machine under the combined action of the inertia and the load may keep running smoothly if the equivalent kinetic energy EKE of the machine is constant during its operation. Furthermore, we introduced a novel type of flywheels with variable equivalent mass moment of inertia VEMMoI and without fixed connection with the input shaft to the machine. The kinetic energy fluctuation of the flywheel is used to dynamically decrease the EKE fluctuation of the original machine, thereby realizing smooth machine operation. Three types of flywheels with VEMMoI driven by a two-link dyad, a pair of noncircular gears and a planet cam respectively were designed as examples. The velocity fluctuation of the machine is significantly reduced.

The book first gives an introduction to the use of flywheels, including prehistory to the Roman civilization, ChristianMoreKinetic Energy Storage: Theory and Practice of Advanced Flywheel Systems focuses on the use of flywheel systems in storing energy. The book first gives an introduction to the use of flywheels, including prehistory to the Roman civilization, Christian era to the industrial revolution, and middle of the 19th century to The text then examines the application of flywheel energy storage systems. Basic parameters and definitions, advantages and disadvantages, economic considerations, road vehicle applications, and applications for fixed machines are considered. The book also evaluates the flywheel, including materials, radial bar and filament flywheel, composite material disc flywheel, rotor stress analysis, and flywheel testing. The text also discusses housing and vacuum systems and flywheel suspension and transmission systems. Aerodynamic drag on wheels, burst containment, types of bearings, rotor dynamics, dampers, and types of transmissions are described.

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