Load bank

Abstract

The present invention relates to a load bank (1) for converting electrical energy into thermal energy, comprising a waste heat chamber (10), a fan (14) arranged in the waste heat chamber (10) which is capable of generating an airflow, at least one heating element (13) arranged in the waste heat chamber (10) which can be exposed to the airflow while emitting thermal energy, and an airflow sensor (16) arranged in the waste heat chamber (10) and exposed to the airflow, configured as a wind vane sensor. The airflow sensor comprises a housing (18), a wind vane paddle (20) movably mounted on the housing (18), a reed switch arranged on the housing (18) which can be actuated by a magnetic field, and a corresponding magnet arranged on the wind vane paddle (20) which generates the magnetic field.The wind vane paddle (20) can be brought into a starting position by a restoring force and, with a sufficiently strong airflow, can be brought via an intermediate position to a final position, wherein the distance between the reed switch and the corresponding magnet in the intermediate position differs from the corresponding distance in the starting position such that the reed switch has a first switching state in the starting position and a second switching state in the intermediate position.

Description

[0001] The present invention relates to a load bank for converting electrical energy into thermal energy comprising a waste heat area with an air inlet and an air outlet, a fan arranged in the waste heat area which is suitable for forming an airflow directed from the air inlet to the air outlet and at least one heating element arranged in the waste heat area which can be exposed to the airflow while emitting thermal energy.

[0002] These load banks are also known as high-power resistors and typically use heating elements in which electrical energy is converted into heat (thermal energy). This heat is then dissipated by forced convection via a fan to prevent the heating elements from overheating. Load banks with convective heat dissipation have been known for many years and are used in a wide variety of applications, such as braking resistors or load banks for generator testing.

[0003] From the large body of disclosures, document DE 2020 12100521 U1 is selected as an example, which describes a load bank of the type described above, specifically adapted for wind turbines. Document DE 20 2022 103996 U1 discloses another example of a load bank.

[0004] For load banks with convective heat dissipation, monitoring the airflow to ensure it is sufficiently strong enhances operational reliability. This ensures, for example, that the fan speed is always high enough to achieve the desired heat removal. Furthermore, airflow monitoring can detect fan defects or air supply disruptions (such as a dirty air intake or one obstructed by a piece of plastic film).

[0005] For this purpose, airflow sensors designed as wind vane switches are typically used, which are arranged in the waste heat area so that the airflow can reach them.

[0006] Wind vane switches consist of a housing and a wind vane paddle that is movably (in particular, rotatably) mounted on the housing. The wind vane paddle is positioned so that it can be subjected to the airflow being monitored. If the airflow exceeds a specific flow velocity, the wind vane paddle is moved from an initial position by the airflow against a restoring force (continuously) through an intermediate position to a final position.

[0007] The wind vane paddle is typically coupled to a mechanically operated push button, which is activated by sufficient pressure on a control element and automatically returns to its starting position when the pressure is released. When the wind vane paddle is in its starting position, it exerts no pressure on the control element, the push button is not activated, and it is in its first switching state. Conversely, when the wind vane paddle is in its end position, it exerts sufficient pressure on the control element, thereby activating the push button and setting it to its second switching state. The end position typically marks a mechanical stop of the wind vane paddle against the housing of the associated wind vane switch.

[0008] In this way, conclusions can be drawn from the switching states of the button as to whether the airflow has a specific flow velocity (or not) and, based on this, for example the fan speed can be influenced.

[0009] Against this background, the present invention aims to provide a load bank with convective heat dissipation with improved practicality, particularly with regard to safety, durability and reliability.

[0010] This problem is solved by the load bank according to claim 1. The load bank for converting electrical energy into thermal energy comprises, for this purpose, a heat recovery area with an air inlet and an air outlet, a fan arranged in the heat recovery area which is suitable for forming an airflow directed from the air inlet to the air outlet, at least one heating element arranged in the heat recovery area which can be approached by the airflow while emitting thermal energy, and an airflow sensor arranged in the heat recovery area and approached by the airflow and designed as a wind vane sensor.

[0011] The airflow sensor comprises a housing, a wind vane paddle movably mounted on the housing, a reed switch arranged on the housing (or on the wind vane paddle) and actuated by a magnetic field, and a corresponding magnet arranged on the wind vane paddle (or on the housing) that generates the magnetic field. The wind vane paddle can be brought into a starting position by a restoring force, in particular by a spring force or gravity, and, with a sufficiently strong airflow, can be continuously moved through an intermediate position to a final position. The distance between the reed switch and the corresponding magnet in the intermediate position differs from the corresponding distance in the starting position such that the reed switch has a first switching state in the starting position and a second switching state in the intermediate position.

[0012] The invention is based primarily on the finding that, in prior art load banks with convective heat dissipation, a steady state of the wind vane paddle often does not occur despite a constant fan speed, but rather flutters (or vibrates) back and forth between the end position and an intermediate position (or the starting position). This phenomenon is likely related to the fact that relatively high flow velocities occur in the heat dissipation area of ​​the load bank, and that many sharp-edged components (e.g., heating elements) are subjected to flow in an extremely compact installation space, resulting in highly turbulent flow conditions. In the prior art, the (high-frequency) fluttering or vibration of the wind vane paddle causes the switch to rapidly and frequently toggle between the two switching states, since the switch only exhibits the second switching state when the wind vane paddle is in the end position.This in turn leads to high wear and tear on the mechanically operated switch. Furthermore, the fluttering or vibration of the wind vane paddle and the high-frequency switching back and forth between states make it difficult to draw reliable and meaningful conclusions about the state of the airflow.

[0013] Against this background, the inventors recognized that the synergistic interplay of the features according to the invention could provide a load bank with improved practical suitability in several respects: By using the wind vane switch with reed switch in the heat dissipation area of ​​the load bank according to the present invention, it is possible to prevent high-frequency switching back and forth between switching states, even if the wind vane paddle flutters (or vibrates). This is achieved due to the characteristic properties of the reed switch, which are fully realized in the specific application of the load bank according to the invention.

[0014] A reed switch typically comprises two ferromagnetic reeds hermetically sealed and fused into a glass tube. The reeds overlap and are typically separated by a few micrometers to approximately 1 mm. When the reed switch enters the influence of a sufficiently strong and appropriately oriented magnetic field, the two reeds move towards each other against their spring action, and the switch closes (this applies to normally open reed switches). The magnetic field required to open the switch is typically much weaker than the magnetic field required to close it.

[0015] In the present invention, the magnet and the reed switch are coordinated such that the reed switch already has the second switching state when the wind vane paddle is in the intermediate position; thus, unlike in the prior art, the wind vane paddle does not need to be moved to the end position for the switch to assume (have the second switching state). This allows the wind vane paddle to flutter (or vibrate) back and forth between the intermediate and end positions without changing the switching state of the reed switch.

[0016] This approach according to the invention represents a fundamental departure from the prior art, since there, attempts are often made to reduce the high-frequency switching back and forth of the switching states by using flow guide plates or by providing flow calming sections, thereby preventing the fluttering (or vibration) of the wind vane paddle.

[0017] In this way, the invention provides a load bank in which switch wear is reduced, thus increasing durability and reliability. Furthermore, the high-frequency switching back and forth of switching states can be prevented, thereby increasing the reliability of airflow monitoring.

[0018] The wording that the reed switch is located on the housing or wind vane paddle, or that the magnet is located on the wind vane paddle or the housing, is intended to express that—of the two interacting components, the reed switch and the magnet—one component is located on the housing and the other on the wind vane paddle. Therefore, if the reed switch is located on the housing, then the magnet is located on the wind vane paddle. Conversely, if the reed switch is located on the wind vane paddle, then the magnet is located on the housing.

[0019] According to a preferred embodiment of the invention, a particularly compact load bank can be realized if the fan is designed as an axial fan and has a rotor with a rotor diameter and a rotor axis.

[0020] In a particularly advantageous manner, the distance between the wind vane paddle in its initial position and the rotor in the direction of the rotor axis is less than the rotor diameter, in particular less than half the rotor diameter, and in particular less than a quarter of the rotor diameter. This allows for a particularly compact load bank. The positioning of the wind vane sensor close to the fan, combined with high reliability in the airflow condition detection, is made possible by the interaction of the individual features according to the invention.

[0021] The distance between the wind vane paddle in the starting position and the rotor in the direction of the rotor axis is defined as the smallest distance between the wind vane paddle in the starting position and the rotor in the direction of the rotor axis.

[0022] Particularly reliable detection of the airflow condition can be achieved if the airflow sensor is positioned downstream of the fan (especially if the airflow is oriented vertically upwards). Alternatively, in certain installation situations, it may be advantageous to position the airflow sensor upstream of the fan (especially if the airflow is oriented horizontally).

[0023] According to a further embodiment, the at least one heating element is advantageously arranged downstream of the fan. Alternatively, in certain installation situations, it may be advantageous if the at least one heating element is arranged upstream of the fan.

[0024] According to two advantageous embodiments of the invention, the REED switch is designed either as a normally open switch or as a normally closed switch.

[0025] A particularly simple, reliable and energy-efficient load bank can be realized if the magnet is designed as a permanent magnet.

[0026] Another advantageous embodiment of the load bank according to the invention provides that the reed switch is arranged on the housing of the airflow sensor and the corresponding magnet is arranged on the wind vane of the airflow sensor. In this way, by arranging the magnet, which is designed as a permanent magnet, on the wind vane, the movable part of the airflow sensor (i.e., the wind vane) does not need to be connected to electrical wiring, which enables a simple and reliable design.

[0027] Particularly advantageously, the airflow sensor also has a support device that is immovably connected to the housing, on which the wind vane paddle rests in its starting position.

[0028] A particularly robust and simple airflow sensor can be implemented if the wind vane paddle is rotatably mounted on the housing (especially by means of a hinge).

[0029] In a particularly advantageous manner, the wind vane paddle is rotated at least 15°, and especially at least 20°, 25°, or 30°, relative to its initial position in the intermediate position. If, according to a further advantageous embodiment, the wind vane paddle is then rotated 35° relative to its initial position in the final position, it can flutter back and forth within an angular range of 20° (or 15°, 10°, or 5°) between the intermediate and final positions without the reed switch leaving its second switching state.

[0030] According to a further particularly preferred embodiment of the load bank, the wind vane paddle is rotated at least 5°, and in particular at least 10°, 20° or 30°, relative to the intermediate position in the end position. The wind vane paddle can therefore flutter (vibrate) back and forth in the range between the intermediate position and the end position without changing the switching state of the reed switch.

[0031] An embodiment of the invention will now be explained in more detail with reference to the drawing. The drawing shows Fig. 1 shows a load bench according to the invention in a sectional view, Fig. 2 shows an enlarged section of Figure 1 , Fig. 3 the wind vane sensor according to the Figure 1 and 2 in a perspective oblique view in the initial position, Fig. 4A to 4C, the wind vane sensor according to Figure 3 in a side view with the wind vane paddle in the starting position ( Fig. 4A ), the intermediate position ( Fig. 4B) and the final position ( Fig. 4C ).

[0032] First, with reference to the Figure 1 and 2 The general structure of the load bank will be explained before specific details are given with reference to the Figures 3 to 4C be carried out.

[0033] The Figure 1 and 2 Each figure shows a load bench 1 or a section thereof in a sectional view. The load bench 1 has a housing body 3 resting on feet 2, which has several lateral housing body segments 4. Support crossbeams 5 extend between the lateral housing body segments 4.

[0034] An opening on the underside of the housing body 3, equipped with a first grille 6, serves as an air inlet 7, and an opening on the top side of the housing body 3, equipped with a second grille 8, serves as an air outlet 9. A heat dissipation area 10 extends between the air inlet 7 and the air outlet 9. Two cover and guide plates 11 are located above the air outlet 9.

[0035] In the waste heat area 10, two heating modules 12 are arranged one above the other and screwed to each of two housing segments 4. The heating modules 12 each comprise a plurality of heating elements 13 designed as heating plates, by means of which electrical energy can be converted into thermal energy. A fan 14, arranged upstream of the heating modules 12 in the waste heat area 10 (and supported on a crossbeam 5), is configured to create an airflow directed from the air inlet 7 to the air outlet 9, which flows onto the heating elements 13, thereby releasing thermal energy. The fan 14 is designed as an axial fan with a rotor 15, a rotor diameter D, and a rotor axis R. Between the fan 14 and the heating modules 12, an airflow sensor designed as a wind vane sensor 16 is arranged in the waste heat area 10 and is screwed to the housing 3 by means of a sensor holder 17.

[0036] As especially in the Figures 3 to 4C As can be seen, the wind vane sensor 16 has a housing 18 and a wind vane paddle 20 rotatably mounted on the housing 18 by means of a hinge 19. The distance A between the wind vane paddle 20 (in the Figure 1 and 2 (shown starting position) and the rotor 15 in the direction of the rotor axis R is less than a quarter of the rotor diameter D.

[0037] The housing 18 includes an electrical connection 21 by means of which the wind vane sensor 16 is connected to a control unit (not shown) of the load bank 1. A reed switch 22, designed as a normally open contact and actuated by a magnetic field, is also arranged on the housing 18. This reed switch can assume a first and a second switching state. In the first switching state, no current can flow through the reed switch 22. However, if a sufficiently strong and appropriately oriented magnetic field acts on the reed switch 22, two switching reeds arranged in the reed switch 22 are pressed together against their spring force, thereby actuating the reed switch 22 and establishing the second switching state, in which current can flow through the reed switch.

[0038] On the underside, the housing 18 has a protruding, (relative to the housing 18) immovable storage device 23 (cf. Figures 4A to 4C ). On the in the Figures 4A to 4COn the visible side of the housing 18 are screws 18S which allow the wind vane sensor 16 to be attached to the sensor bracket 17.

[0039] A corresponding (permanent) magnet 24, which generates the magnetic field, is arranged on the wind vane paddle 20 and is firmly connected to the wind vane paddle 20.

[0040] The Figures 4A to 4C show the wind vane sensor 16 according to Figure 3 each with different positions of the wind vane paddle 20. To illustrate the different positions of the wind vane paddle 20, the following is shown in the Figures 4A to 4C A horizontal line H has been drawn.

[0041] According to the Figure 4AThe wind vane paddle 20 is in its starting position and rests on the support device 23. In the starting position, the distance between the reed switch 22 and the magnet 24 is a_A, and the horizontal H forms a (negative) angle of w_A with the wind vane paddle 20, which is approximately -5°.

[0042] Figure 4B Figure 1 shows the wind vane sensor 16 with the wind vane paddle 20 in the intermediate position. In this intermediate position, the wind vane paddle 20 is neither resting on the support device 23, nor is the magnet 24 in contact with the reed switch 22. The distance between the reed switch 22 and the magnet 24 is a_Z in the intermediate position, and the horizontal H forms a (positive) angle of w_Z with the wind vane paddle 20, which is approximately 25°.

[0043] Figure 4CFigure 1 shows the wind vane sensor 16 with the wind vane paddle 20 in its end position. The magnet 24 is in contact with the reed switch 22. The distance between the reed switch 22 and the magnet 24 is a_E in the end position, and the horizontal H forms a (positive) angle of w_E with the wind vane paddle 20, which is approximately 30°.

[0044] Starting from the initial position according to Figure 4A With a sufficiently strong airflow, the wind vane paddle 20 is moved around the pivot axis of the hinge 19 into the intermediate position according to Figure 4B rotated. In the intermediate position, the wind vane paddle 20 is rotated by the angle w_A + w_Z, i.e. by about 30°, relative to the starting position.

[0045] The wind vane paddle 20 can be moved beyond the intermediate position around the pivot axis of the hinge 19 into the final position according to Figure 4CThe wind vane paddle 20 is rotated until the magnet 24 is in contact with the reed switch 22. The magnet 24 and the reed switch 22 thus form a mechanical stop that defines the end position of the wind vane paddle 20. In the end position, the wind vane paddle 20 is rotated by the angle w_A + w_E, i.e., approximately 35°, relative to the initial position. In the end position (according to Figure 4C ) the wind vane paddle 20 is turned by the angle w_E - w_Z, i.e. by approximately 5°, compared to the intermediate position (according to Figure 4B ) turned.

[0046] Gravity acts as a restoring force that can bring the wind vane paddle 20 from the end position or the intermediate position back to the starting position.

[0047] Is the wind vane paddle 20 located in the Figures 1 to 4AIn the initial position shown, the distance a_A between the reed switch 22 and the magnet 24 is relatively large, and the influence of the magnetic field of the (permanent) magnet 24 on the reed switch 22 is so small that it is in the first switching state; thus, no sufficiently strong magnetic field acts on the reed switch 22. If the wind vane paddle 20 is now moved by a corresponding airflow against the force of gravity acting as a restoring force around the axis of rotation of the hinge 19 into the intermediate position according to Figure 4BAs the permanent magnet 24 is rotated, the distance a_Z between the permanent magnet 24 and the reed switch 22 decreases. This results in an increase in the strength of the magnetic field of the permanent magnet 24 acting on the reed switch 22. In the intermediate position (of the wind vane paddle 20), the magnetic field of the permanent magnet 24 acting on the reed switch 22 is sufficiently strong to activate the reed switch 22 and enter the second switching state. The wind vane paddle 20 can now move between the intermediate position and the end position (according to 0 Figure 4C ) can be moved back and forth arbitrarily (fluttering or vibrating) without changing the switching state.

Claims

1. Load bank (1) for converting electrical energy into thermal energy, comprising - a waste heat region (10) with an air inlet (7) and an air outlet (9), - a fan (14) which is arranged in the waste heat region (10) and is suitable for forming an air flow directed from the air inlet (7) to the air outlet (9), - at least one heating element (13) which is arranged in the waste heat region (10) and which can be flowed upon by the air flow while releasing thermal energy, characterized by - an air flow sensor which is arranged in the waste heat region (10) and which can be flowed upon by the air flow and which is in the form of a wind vane sensor (16), wherein - the air flow sensor comprises a housing (18), a wind vane paddle (20) which is mounted movably on the housing (18), a REED switch (22) which is arranged on the housing (18) or on the wind vane paddle (20) and is actuatable by a magnetic field, and a corresponding magnet (24) which is arranged on the wind vane paddle (20) or on the housing (18) and which generates the magnetic field, - the wind vane paddle (20) is placeable into a starting position by a restoring force, in particular by a spring force or the force of gravity, and is placeable continuously into an end position via an intermediate position, when the air flow is sufficiently strong flowing upon the wind vane paddle (20), and - the distance (a_Z) between the REED switch and the corresponding magnet in the intermediate position differs from the corresponding distance in the starting position (a_A) in such a way that the REED switch (22) has a first switching state in the starting position and has a second switching state in the intermediate position.

2. Load bank (1) according to claim 1, wherein the fan (14) is designed as an axial fan and has a rotor (15) with a rotor diameter (D) and a rotor axis (R).

3. Load bank (1) according to claim 2, wherein the distance (A) between the wind vane paddle (20) in the starting position and the rotor (15) in the direction of the rotor axis (R) is less than the rotor diameter (D), in particular less than half the rotor diameter (D), in particular less than a quarter of the rotor diameter (D).

4. Load bank (1) according to one of the preceding claims, wherein the air flow sensor is arranged air-downstream or air-upstream of the fan (15).

5. Load bank (1) according to one of the preceding claims, wherein the at least one heating element (13) is arranged air-downstream or air-upstream of the fan (15).

6. Load bank (1) according to one of the preceding claims, wherein the reed switch (22) is designed as a normally open switch or as a normally close switch.

7. Load bank (1) according to one of the preceding claims, wherein the magnet (24) is designed as a permanent magnet.

8. Load bank (1) according to one of the preceding claims, wherein the REED switch (22) is arranged on the housing (18) of the air flow sensor and the corresponding magnet (24) is arranged on the wind vane paddle (20) of the air flow sensor.

9. Load bank (1) according to one of the preceding claims, wherein the air flow sensor has a support device (24) which is immovably connected to the housing (18) and on which the wind vane paddle (20) rests in its starting position.

10. Load bank (1) according to one of the preceding claims, wherein the wind vane paddle (20) is mounted rotatably on the housing (18).

11. Load bank (1) according to claim 10, wherein the wind vane paddle (20) in the intermediate position is rotated at least by 15°, in particular at least by 20°, 25° or 30°, with respect to the starting position.

12. Load bank (1) according to claim 10 or 11, wherein the wind vane paddle (20) in the end position is rotated at least 5°, in particular at least 10°, 20° or 30°, with respect to the intermediate position.

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