NL9002415A - Storage system for electrical energy - uses high density flywheel in vacuum incorporating motor-generator set to store and release energy - Google Patents

Abstract

A fast spinning rotor of high density material (1) is contained in a vacuum container (2). The external wall of the container is double skinned and contains fluid, e.g. water. The water mantle is designed to absorb the energy released if the rotor disintegrates. The rotor is suspended on magnetic levitation bearings and contains a brushless motor and generator. Kinetic energy is stored in the flywheel action initially through the motor and discharged via the generator as electrical energy. The unit is very compact and suitable for use with traction or road vehicles.

Description

STORING ELECTRICAL ENERGY WITH A FLYWHEEL.

Modern society can be freed from a number of problems when electric energy can be stored for a long time, efficiently, pollution-free with a high energy density. This is possible with a flywheel. The primary property of a flywheel is to store energy, but in today's practice usually for a short time. A long storage time must be achieved by making the rotational losses of the rotor small, which also the efficiency is increased. In the figures ^, and 5 the principle of respectively a cylindrical and a spherical flywheel has been drawn which this invention is about. The rotor (1) of the flywheel rotates in vacuum3 and on the inner diameter the electric motor (4) and the dynamo (5), each of which works brushless for itself and uses the semiconductor technique for this purpose. The motor serves for charging and the dynamo for discharging the flywheel. the very small rotational losses, the rotor is mounted on magnetic levitation using the permanent magnets (A), (B), (C) and (D). To this, for the stability of the rotor, a small mechanical bearing (8) has been added. For the losses the rot rotates or in vacuum The vacuum vessel (2) is for the most part surrounded by a liquid (7) (water) which is located inside the outer vessel (6). The construction of the whole is dimensioned in such a way that any disintegration of the rotor, this process takes place entirely within the outer vessel. The conversion of the water into steam helps to dissipate the emerging energy. A large energy density means that the flywheel must be small and light and the rotor must rotate very quickly. This requires the use of very strong and light materials. The forces that occur in each volume element of the rotor rotating at a given speed are proportional to the square of the distance (r) from the shaft and to the specific weight (henceforth sg ) of this volume element. The forces are greatest on the outside and decrease 2 inwards with r. The invention ensures that 2 the sg inversely proportional to r.This ensures that every volume element in the rotor is loaded by equal forces, so that no layer separation can occur and it is possible to realize these flywheels.This homogeneity of forces is obtained by winding the rotor on the matrix of the lym and the very strong fiber add a heavy and very fine-grained powder per layer in the Correct amount. The following calculations will underpin the invention. Calculations.

The energy of movement (E) stored in a perfect solid rotating at an angular velocity (u3) about its axis satisfies: E = “- Τω2 (Nm) 1

Here T is the Mass Inertial Moment (M.T.M.) of this body relative to the axis of rotation. of a cylinder is similar to:

Tcyl = imR2 (kgl “2) 2 and of a sphere

Tbol = | mR2 (kgm2) 3

The respective masses M are: ncyl “^ Fly ξ> Qcg) 4” mumps j®3? (Kg) 5

The energy content of these rotating bodies is therefore: • j__ (Nm) 6 ^ 01 = 305 ^ 5 ^ (Hm) 7

Herein is the s.g. of the rotating body. It can be deduced from these comparisons that the cylinder can store a greater amount of energy per kg weight, at the same angular velocity, than the sphere. About 25% more. The cylinder will be calculated on this basis. The interior of the cylinder does not contribute much to the energy content. In addition, this space is needed to accommodate the engine, alternator and low-ring, so we are dealing with a hollow cylinder for which the ratio of the inner radius (ΐΐφ) βη is the outer-

radius (R) meets: D

/> R0 F> ΊΓ 8

The energy content of this cylinder with a hole complies with: Ecy 1 = R4 h νυ2 (1) (Nm) 9 u? = 2Un and this gives in comparison 9:

Ecyl = R4h n2 ^ (1 -ƒ & *) (Nm) 10

Now it applies that 1kwh is equal to 3 »6 10 Nm. It follows from this:

Ecyl_ (1-M) kwh 11 7 3.6 10 ^ '

Tangential (P.) and radial (P) voltages occur in the rapidly rotating rotor of the flywheel, which do vM to the equations 12 and 13.

Pt = n2 r (3 + V) (R2 + R ^ lR / -o) - (1 + 3V) r2 P & 12 P = f29 n2 (R2 + R2 S ^ O -r2X3 + V) Pa 13 r

V is the Poisson ratio, which may be set at 0.3 and r is the distance from the axis of rotation where this span

O

nings occur. Furthermore, R and RQin ra., ^ In kg / nren, n is the number of revolutions per second. The maximum stress ^ tmax occurs at the circumference of the hole (r = RQ) and the maximum radial stress P ^^^ occurs for r = N [0Q and satisfies: 0 0 p n2 (R-Ror (3 + v) Pa 14- rmax 2 1

Comparison 14- shows that Prlnaxvoc, r R = H0 is Selyk to zero i.e. for a cylinder with a very thin wall thickness (RMR) P is very small, this is exactly what is needed, because the strong fiber from which the flywheel becomes wound is usually very strong in the tangential direction, but much weaker for a radial load. It follows that the flywheel must be built up from thin layers.

Let R = 0.6m.Ro = 0.24-m and h = 2Rm. According to equationl2, the tangential stress in the rotor expires when the curve Pj.in fig.

1.The radial stress Pris as follows from comparison 13 and Fig. 1 shows at the hole (r = R ^ and at the circumference zero and maximum for r = YR.RQ. Suppose the wall thickness of the hollow cylinder is 2.5mm .R is thus 0, 6r-0, 'OO25-.0.5975m. The' tangential voltage on the circumference is therefore P ^ j. ^ <Jpn .2.86024- and-. On the inside of the thin wall similar to: <T (2 2

Pt = 2 T n .2.87581. The tangential voltage on the inside of this thin cylinder is thus only 1.0054-4 times greater than on the outside, i.e. a slight difference.

The maximum radial stress for t ^ [r.Rq is equal to:

Ptmax = ^ 2 and 2 ° O0002065 and thus already 7.10 "times smaller than for even thinner cylinders to match the radial strength of the fiber.

The outer layer of the rotor is most heavily loaded.

In that layer, the tangential voltage must not exceed the maximum permissible value P ^ max. Comparison 12, when R, RQ, and ^ are selected, gives the maximum speed (s) that is maximum permissible by this Pj.max. Layered layers rotate at the same angular velocity but become warped because they have a smaller radius * less load.

2. Since proportional to r and ^, the only way to load the inner layers with Pj.max is to change the specific weight (^>) of the matrix, inversely proportional to r2. layer thickness and (a) 'the number of lowii of the rotor-of & f the outer side has been calculated, then' 'the tangential stress in the a-th layer is:

Pta = (R> Ptmax = (1 -f Ptmax 15

To make P equal to P ^ .max, the s.g. of that layer must therefore be made larger by a factor Z -10 z = 16 than p

A cylindrical flywheel has (b) layers, each with a thickness of £ R meter, (b) satisfies: Λ ύ h = LTr- 17

The energy content of this wyze layered cylindrical flywheel satisfies for h = 2 R: j_ vort, .8 2

Thus, in this equation, n is calculated with equation12 for the outer layer of the rotor, that is for Rq = R (1-ê). For very thin layers, e.g. one fiber thick, due to the enlargement of the s.g. per layer according to comparison 16, achieves that all layers are loaded by equal forces.These homogeneous loads of any volume element of the rotor mean that no splitting of the layers can occur. This makes it possible to make reliable cylindrical or spherical flywheels with existing fibers. The strongest fibers currently available have a maximum strength of 2.8 10 ^ Pascal (F) for 9 a.

Aramid Twaron and from 3.4 10 P for Carbon fiber Tenax. For a maximum permissible tangential voltage P. =

a u UlCLA

1.25 10r P, using the equations 12 and 18, the most important quantities of a homogeneously loaded radial rotor have been calculated. Table 1 shows the results of this calculation as a function of R (for, / 3 = 0.5) and as a function of / j (for R = 0.5m). Figures 2 and 3 show the same ". Figure 7 shows the calculated energy content of very large homogeneous rotors. The magnification Z of the sg ^ is subject to technical possibilities. The metal powders suitable for the sgin magnification have a sg of around 8000 kg per m. Zmax can therefore not be made larger than 5. Table 1 shows that a flywheel that must be able to store 1OOkwh must have a rotor with a radius of 0.5 m and a Z = 4 and at a maximum speed of 300 revolutions per second, that is 18000 rpm. must rotate. The height h of the rotor is 1m. This rotor weighs 1480 kg, of which 800 kg is fiber and 680 kg is lym plus filler, which is thus a fyn-grained metal powder. In figure 4 the principle design of the cylindrical flywheel is drawn and figure 5 shows this of a spherical flywheel. rotor must. have sufficient space in the vacuum vessel (2) to allow the volume increase due to the fiber's elongation. The liquid (7) surrounding the vacuum vessel has several functions. The amount of water present must be able to disintegrate by the rotor to dissipate the 100 kwh stored therein. To convert 1 kg of cold water into steam requires approx. 600 kcal. 1kwh = 864kcal.and so the required amount of water is 100x864 / 600 = 144 liters. The other function of the water is the cooling of the electronic parts that are accessible to the water. By the disintegration of the rotor, a lot of energy is also absorbed by the pulverization of the rotor and the rupture of the vacuum vessel, after which the water can dissipate the remaining energy. Also, a slightly spherical flywheel (eg for Ptmax = 10.109Pa) for a gimbal. shock absorbing suspension, for mobile use, can be made floating in the water. In figure 6 the influence of the P ^ max ° P is given the energy density of the flywheel. From this it appears that the sizing is closely related to the progress in the field of the very strong fibers. In this respect, the flywheel technology will not be distinguished from the progress shown by the history of any technology.

The production of the flywheel will have to make use of the most modern techniques in the field of automation and robotisation. The flywheel offers too many possibilities for society to mention here. Some important advantages should not be left unmentioned.

The flywheel operates silently at room temperature.

The flywheel is free from pollutions.

A 1000kwh flywheel makes the electric car compatible with today's car, which means that the fossil-fuel-consuming car can be replaced by the electric car.

The flywheel can bring photoelectric electricity production to a full bloom.

LITERATURE.

POST R.F./POST S.F.'fLIWHEEl "Scie.ntific American Dec. 1973

II II

ROLSTON J.A. Reinforced plastic for rotating structures S.P.E. Journal April 1963 pp. 387/391 TIMOSHENKO S. 'Strength of materials Van Nostrand 1956 tl LENGER A.. Electric energy storage using a

II

flywheel Polytechnic tydschrift Pt 32 nr6

II II

LENGER A. Energy in society Ag on Elsevier 1974-

Claims (1)

CONCLUSIONS. In principle, a flywheel serves to store energy. In general, the storage time is short in the package type. The bearing on magnetic levitation and the rotation in vacuum make it possible to greatly increase the storage time. The availability of light and very strong fibers. opens up the possibility to store a lot of electrical energy in a flywheel, but so far this has not happened with a cylindrical or spherical flywheel. The main reason for this is the inhomogeneous load on the volume elements of the rotor. The flywheels of figure U and 5 », characterized by the homogeneous loading of each volume element of the rotor, enable the construction of reliable cylindrical and spherical flywheels. The construction, characterized by that of each layer of the very strong fiber of which the rotor is wound, the specific weight by adding a very fine-grained heavy powder to the matrix of this fiber and the. lym, is increased in such a way that in the rotating rotor every fiber layer of the rotor is loaded by the same forces, the necessary homogeneity of forces in the rotor is obtained. The use of modern technologies makes it possible to house the motor for charging and the alternator for discharging the flywheel internally in the flywheel. This creates the compact whole that is represented by the figures | and 5 is indicated by the feature to act as the power source of an electric vehicle, which is compatible with the explosion-powered vehicle and permits the gradual introduction of the electric vehicle. Construction of Figures Λ and 5 is characterized by a high energy density and has potential application possibilities to describe here. Together, these possibilities are just as important to contemporary society as the electrical energy itself is to society.