GB1579493A

GB1579493A - Axial flow fan for a reversible electric rotating machine

Info

Publication number: GB1579493A
Application number: GB3681977A
Authority: GB
Original assignee: Skoda op; Skoda np
Current assignee: Skoda op; Skoda np
Priority date: 1976-10-01
Filing date: 1977-09-02
Publication date: 1980-11-19
Also published as: CS223352B1; DE2736773A1

Description

(54) AN AXIAL FLOW FAN FOR A REVERSIBLE ELECTRIC ROTATING MACHINE (71) We, SKODA, oborovy podnik, a Czechoslovak body corporate, of Plzen, Czechoslovakia, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to an axial flow fan for a reversible electric rotating machine, the impeller of which is adapted to be fixed on a rotor of this machine, and the movable blades of which are connected to a hub by means of cylindrical pivots having radially orientated axes.

In electric rotating machines having one direction of rotation, advantageously axial flow fans are used, the impellers of which are seated directly on the shaft of the machine.

These axial flow fans move cooling gas (air or hydrogen), which takes away the waste heat from active parts of the machine. Usually, two fans are used, which suck cooling gas from the outer casing of the machine and deliver it into the machine. Relatively good efficiency and an advantageous orientation of gas from the fan to other parts of the machine, are advantages of axial flow fans.

However, in reversible machines, axial flow fans could not hitherto be applied.

Known axial flow fans change the direction of a gas flow if the direction of rotation of the fan blades is changed, which does not comply with the requirements of a ventilation circuit.

Besides that, the aerodynamic efficiency of an axial flow fan with movable blades descreases rapidly, when the direction of rotation is changed.

That is why ventilation of reversible machines (e.g. generator-motors for pumped storage hydro-electric power plants) have up to now required radial flow fans, sometimes in combination with the ventilation effect of a rotor spider. All these designs have some drawbacks with respect to an axial flow fan application, viz. an increase in ventilation losses, or a more complicated design.

The aim of the invention is to obviate some of the mentioned disadvantages.

Accordingly the present invention provides an axial flow fan for a reversible electric rotating machine which comprises an impeller adapted to be fixed to a rotor of the machine and movable blades which are fitted to a hub by means of cylindrical pivots having radially orientated axes, so that they may be pivoted about their respective axes, the end positions of the pivoting movement of the blades being limited by stops, the axis of each blade being so situated with respect to the respective blade, that the direction of the moment affecting the blade during rotation as a result of aerodynamic forces about the axis is determined for any position of the blade only by the direction of rotation and is changed if the direction of rotation is changed whereby the moment due to aerodynamic forces is, at a selected speed of rotation which is lower than the rated one, higher than the sum of the moment of gravity and centrifugal force of the blade and frictional moment of the pivoting of the blade at the respective speed, whereby the resulting direction of gas flow is the same for either direction of rotation.

The developed section of a movable blade at any radial distance from the axis of the fan may have a symmetrical drop shape profile, the axis of which intersects drop shape profile, the axis of which intersects the pivotal axis of the blade.

It is advantageous for th geometry of the blades to be such that the connection lines of a point of a possible contact of the two adjacent moving blades and of the pivotal centre of each of them make an acute angle with one another. This permits simultaneous position change of the blades if the direction of rotation is changed. Another possible arrangement, for a similar purpose, consists of projections formed on the trailing edges of the blades, that are formed in an extension of the blade profile on a part of the radial height of the blades. It is advantageous to apply rollers rotatably mounted on the trailing edges of the blades or on projections of the trailing edges.

With respect to a simultaneous change of all blades, it may also be advantageous for connecting pull rods to be pivotally mounted on the trailing edges of the blades by means of pivots; the connecting pull rods, being mutually interconnected, forming a closed peripheral system.

Stops limiting end positions of the pivoting movement of the blades may be advantageously represented by extensions on the outer surface of the fan hub. Cylindrical pivots having radially orientated axes about which the blades pivot may be formed either on the blades of the fan and rotatably mounted in the fan hub, or they may be fixed to the fan hub and on them there may be movably mounted blades of the fan.

In some cases there may be advantages in such an arrangement of blades when limit positions of the blades are asymmetrical with respect to an axial plane passing through the pivotal axis. Such a fan provides a different flow of cooling air for each direction of rotation. In this way different amounts of waste heat produced at different loadings in the operation of the generator or motor may be compensated.

The outer surface of a fan hub, or a part of an air branch of the fan, may be shaped as a spherical surface, the centre of which is in the point of intersection of the axis of the machine and of the pivotal axis of the blades.

In the above described axial flow fan, the blades, after a definite rotation speed has been reached, which is lower than a nominal one, have a stable position, which corresponds to the respective direction of rotation and after the direction of rotation has been changed, automatically change their position due to the effect of aerodynamic forces. So the axial flow fan provides an identical direction of cooling gas flow for both directions of rotation, at high aerodynamic characteristics and good efficiency.

The invention will now be described by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a section through a generatormotor rotatable in both directions of rotation, Figures 2a and 2b are developed radial views of a blade cascade of an axial flow fan, Figures 3a, 3b and 3c show in detail two adjacent movable blades of a blade cascade, Figure 4a is an axial view of a group of movable blades of another embodiment allowing simultaneous pivoting of all the blades, Figure 4b is a developed radial view of the group of blades shown in Figure 4a, Figure 5 shows a mounting of a movable blade, Figure 6 shows another mounting of a movable blade, and Figure 7 shows a detail of a section through a fan.

In the embodiment shown in Figure 1, two axial flow fans deliver cooling air from the outer casing into the machine, the direction of flow being marked by arrows. The impeller of each of the fans comprises a fan hub 1 and movable blades 2. A stationary part of each fan is an air branch 3. The pivotal axis of the movable blades 2 is marked 4.

The blade cascade of an axial flow fan according to Figures 2a and 2b has movable blades 2 in two limit positions; the full line position corresponds to a left direction of rotation, the dash line position corresponds to a reverse direction of rotation. A developed section of the blade 2 has a drop shape profile, symmetrical to its axis 18 in each radius of the fan. The moving blades 2 of the fan are fitted on the hub 1 of the fan pivotally about cylindrical pivots 5, the axis of each of which is radial. The end positions of the blades 2 for the respective direction of rotation are limited by stops 6, which are formed as radially low projections of the hub 1 of the fan. End positions of the blades 2 in Figure 2a are symmetrical with respect to an axial plane 7 passing through the pivotal axis, but are assymetrical in the case of Figure 2b, i.e. the angles between the axis 18 of a blade profile and tangential plane 17 passing through the pivotal axis 4 are not identical in the case of Figure 2b for end positions of the blades 2 (i )and 3e show two Figures 3a, 3b and 3c show two adjacent blades 2 of a blade cascade in movement where the left moving blade pivots from the initial dash line position by aerodynamic forces, after the direction of rotation has been changed, while the right one keeps in its initial position because of higher friction. At the moment shown in Figures 3a, 3b, and 3c the blades 2 have just touched at the point 8.

The angles aa, ah and ac formed by connection lines of the touch point 8 to the centre of rotation of the two blades 2, are acute ones.

So a condition is achieved in that the blade 2 which starts moving first, exerts a force on an adjacent blade 2, which forces it to pivot as well. In Figure 3b, there is a blade profile extended in a projection 9 on a part of a radial height of a blade; a touch point 8 is situated on the surface of the projection 9.

So, under similar conditions, the angle a is reduced (O'b < (a) with a resultant increase in the force exerted by the pivoted blade 2 on the unpivoted one.

In Figure 3c a roller 16 is fitted on the end of the projection 9 which roller 16 turns a little when leaning against an adjacent movable blade 2 so that pivoting of the blade may take place. Again the angle a is reduced (ac < aa).

Another embodiment allowing simultaneous pivoting of all blades 2, is shown in Figures 4a and 4b. In this embodiment, connecting pull rods 11 are rotatably fitted to the trailing edges 10 of blades 2 by means of pivots 12; the' pull rods 11 form a closed peripheral system. When changing the direction of rotation, the system of connecting pull rods 11 enables a simultaneous pivoting of all movable blades 2 about the axes 4 of rotation into the desired position. A cable connection may be used instead of the connecting pull rods 11.

Figure 5 shows a mounting of a movable blade 2, where a cylindrical pin 13 with a radially orientated pivotal axis 4, carried out as a part of the movable blade 2 of the fan, is pivotally mounted in the hub 1 of the fan. To decrease the moment needed for pivoting of the blade 2 bearing bushes 14 are used.

In the mounting of a movable blade 2 shown in Figure 6, a hub 1 is provided with cylindrical pivots 15 having radially orientated pivotal axes 4 and on which are pivotally mounted the movable blades 2 of the fan.

To decrease the moment needed for pivoting the blade 2, bearing bushes 14 are used.

In Figure 7 the outer surface of the fan hub 1 in the part marked "A" and the inner surface of the fan air branch 3 in the part marked "B" are formed as parts of a spherical surface, the centre of which is in the point of intersection of the fan axis 19 and pivotal axis 4 of the blades 2 having a radius rA, or rB.

An axial flow fan according to the invention may be advantageously applied to generator-motor units of pumped storage hydro electric power plants which rotate in one direction for generator operation and in the other direction for motor operation. But the invention may also be used for reversible electric rotating machines.

WHAT WE CLAIM IS: 1. An axial flow fan for a reversible electric rotating machine which comprises an impeller adapted to be fixed to a rotor of the machine and movable blades which are fitted to a hub by means of cylindrical pivots having radially orientated axes, so that they may be pivoted about their respective axes, the end positions of the pivoting movement of the blades being limited by stops, the axis of each blade being so situated with respect to the respective blade, that the direction of the moment affecting the blade during rotation as a result of aerodynamic forces about the axis is determined for any position of the balde only by the direction of rotation and is changed if the direction of rotation is changed whereby the moment due to aerodynamic forces is, at a selected speed of rotation which is lower than the rated one higher than the sum of the moment of gravity and centrifugal force of the blade and frictional moment of the pivoting of the blade at the respective speed, whereby the resulting direction of gas flow is the same for either direction of rotation.

2. An axial flow fan according to Claim 1, wherein the developed section of a blade at any radial distance from the axis of the fan has a symmetrical drop shape profile the axis of which intersects the pivotal axis of the blade.

3. An axial flow fan according to Claim 1, wherein the lines connecting the point of a possible contact of two adjacent blades and of the centre of pivoting of each of the blades make an acute angle.

4. An axial flow fan according to Claim 1, wherein on the trailing edges of the blades on a part of the radial height of the blades, are formed as an extension of the blade profile, projections for a point of contact of two adjacent blades.

5. An axial flow fan according to Claim 1 and Claim 4, wherein rollers are mounted on the trailing edges of the blades or on the projections of the trailing edges.

6. An axial flow fan according to Claim 1, wherein connecting pull rods are pivotally mounted on the trailing edges of the blades, the connecting pull rods are mutually interconnected and form a closed peripheral system.

7. An axial flow fan according to Claim 1, wherein the stops, limiting the end positions of the pivoting movement of the blades, are in the form of protrusions on the outer surface of the fan hub.

8. An axial flow fan according to Claim 1, wherein cylindrical pivots having a radially orientated pivotal axis are formed on the blades of the fan and are pivotably mounted on the hub of the fan.

9. An axial flow fan according to Claim 1, wherein the fan hub is provided with cylindrical pivots having a pivotal axis radially orientated, on which the blades of the fan are pivotally seated.

10. An axial flow fan according to Claim 1, wherein the end positions of the blades are symmetrical with respect to an axial plane passing through the pivotal axis.

11. An axial flow fan according to Claim 1, wherein the outer surface of the fan hub is part-spherical, the centre of the sphere being at the point of intersection of the axis of the machine and of the pivotal axis of the blades.

12. An axial flow fan according to Claim 1, wherein the fan has an air branch the inner surface of which is formed, in the part which is opposite the blades, as a part of a sphere, the centre of which is at the point of intersection of the axis of the machine and of the pivotal axis of the blades.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. little when leaning against an adjacent movable blade 2 so that pivoting of the blade may take place. Again the angle a is reduced (ac < aa). Another embodiment allowing simultaneous pivoting of all blades 2, is shown in Figures 4a and 4b. In this embodiment, connecting pull rods 11 are rotatably fitted to the trailing edges 10 of blades 2 by means of pivots 12; the' pull rods 11 form a closed peripheral system. When changing the direction of rotation, the system of connecting pull rods 11 enables a simultaneous pivoting of all movable blades 2 about the axes 4 of rotation into the desired position. A cable connection may be used instead of the connecting pull rods 11. Figure 5 shows a mounting of a movable blade 2, where a cylindrical pin 13 with a radially orientated pivotal axis 4, carried out as a part of the movable blade 2 of the fan, is pivotally mounted in the hub 1 of the fan. To decrease the moment needed for pivoting of the blade 2 bearing bushes 14 are used. In the mounting of a movable blade 2 shown in Figure 6, a hub 1 is provided with cylindrical pivots 15 having radially orientated pivotal axes 4 and on which are pivotally mounted the movable blades 2 of the fan. To decrease the moment needed for pivoting the blade 2, bearing bushes 14 are used. In Figure 7 the outer surface of the fan hub 1 in the part marked "A" and the inner surface of the fan air branch 3 in the part marked "B" are formed as parts of a spherical surface, the centre of which is in the point of intersection of the fan axis 19 and pivotal axis 4 of the blades 2 having a radius rA, or rB. An axial flow fan according to the invention may be advantageously applied to generator-motor units of pumped storage hydro electric power plants which rotate in one direction for generator operation and in the other direction for motor operation. But the invention may also be used for reversible electric rotating machines. WHAT WE CLAIM IS:

1. An axial flow fan for a reversible electric rotating machine which comprises an impeller adapted to be fixed to a rotor of the machine and movable blades which are fitted to a hub by means of cylindrical pivots having radially orientated axes, so that they may be pivoted about their respective axes, the end positions of the pivoting movement of the blades being limited by stops, the axis of each blade being so situated with respect to the respective blade, that the direction of the moment affecting the blade during rotation as a result of aerodynamic forces about the axis is determined for any position of the balde only by the direction of rotation and is changed if the direction of rotation is changed whereby the moment due to aerodynamic forces is, at a selected speed of rotation which is lower than the rated one higher than the sum of the moment of gravity and centrifugal force of the blade and frictional moment of the pivoting of the blade at the respective speed, whereby the resulting direction of gas flow is the same for either direction of rotation.

13. An axial flow fan for a rotatable electric rotating machine, substantially as herein described with reference to and as shown in the accompanying drawings.