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 air flow directed from the air inlet to the air outlet, and at least one heating element arranged in the waste heat area, which heating element can be exposed to the air flow while releasing thermal energy.

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

[0003] From the large pool of disclosures, document DE 2020 12100521 U1 is taken as an example, which describes a load bank of the type described above that is specially adapted to wind turbines.

[0004] For load banks with convective heat dissipation, operational reliability is enhanced by monitoring the airflow to ensure it is sufficiently strong. This can ensure, for example, that the fan speed is always sufficiently high to achieve the desired heat dissipation. Furthermore, airflow monitoring can also detect fan defects or air supply disruptions (for example, due to a dirty air inlet or one covered by a plastic sheet being sucked in).

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

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

[0007] The wind vane paddle is typically coupled to a mechanically operated switch, which is activated by sufficient pressure on a control element and automatically returns to its original position when the pressure is released. If the wind vane paddle is in its original position, it exerts no pressure on the control element; the switch is not activated and remains in its first switching state. However, if the wind vane paddle is in its end position, it exerts sufficient pressure on the control element, which activates the switch and moves it to its second switching state. The end position typically marks a mechanical stop of the wind vane paddle on 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 air flow has a specific flow velocity (or not) and, based on this, the fan speed, for example, can be influenced.

[0009] Against this background, the present invention is based on the object of providing a load bank with convective heat dissipation with improved practical suitability, in particular with regard to safety, durability and reliability.

[0010] This object is achieved by the load bank according to claim 1. The load bank for converting electrical energy into thermal energy comprises 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 air flow directed from the air inlet to the air outlet, at least one heating element arranged in the waste heat area, which can be flowed against by the air flow while releasing thermal energy, and an air flow sensor arranged in the waste heat area and designed as a wind vane sensor, against which the air flow can flow.

[0011] The air flow 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 an initial position by a restoring force, in particular by a spring force or gravity, and, with sufficiently strong air flow, can be continuously moved via an intermediate position into an end position. The distance between the reed switch and the corresponding magnet in the intermediate position differs from the corresponding distance in the initial position in such a way that the reed switch has a first switching state in the initial position and a second switching state in the intermediate position.

[0012] The invention is primarily based on the finding that in load banks with convective heat dissipation, in the prior art, a stationary state of the wind vane paddle is often not achieved despite a constant fan speed, but rather flutters (or vibrates) back and forth between the end position and an intermediate position (or the initial position). This phenomenon is likely to be related in particular to the fact that relatively high flow velocities occur in the waste heat area of ​​the load bank and that many sharp-edged components (e.g. heating elements) are flowed around in an extremely compact installation space, so that highly turbulent flow conditions develop. In the prior art, the (high-frequency) fluttering or vibration of the wind vane paddle also causes the button to switch quickly and frequently back and forth between the two switching states, since the button only has the second switching state when the wind vane paddle is in the end position.This, in turn, leads to significant wear on the mechanical sensor. Furthermore, the fluttering and vibration of the wind vane paddle and the high-frequency switching of the switching states make it difficult to draw reliable and meaningful conclusions about the airflow condition.

[0013] Against this background, the inventors recognized that the synergistic interaction of the inventive features can provide a load bank with improved practical suitability in several respects: The use of the wind vane switch with a reed switch in the waste heat area of ​​the load bank according to the present invention prevents high-frequency switching back and forth between the switching states despite fluttering (or vibrating) of the wind vane paddle. This success is due to the characteristic properties of the reed switch, which are utilized here in the specific application of the inventive load bank.

[0014] A reed switch typically comprises two ferromagnetic reeds encased in a hermetically sealed glass tube. The reeds overlap and are typically spaced apart by a few micrometers to approximately 1 mm. If the reed switch enters the sphere of influence of a sufficiently strong and appropriately oriented magnetic field, the two reeds move toward 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 significantly weaker than the magnetic field required to close the switch.

[0015] Within the scope of the present invention, the magnet and the reed switch are coordinated in such a way that the reed switch already has the second switching state for a wind vane paddle in the intermediate position. Thus, the wind vane paddle does not need to be moved to the end position, as is usual in the prior art, 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 position and the end position without changing the switching state of the reed switch.

[0016] This inventive approach 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 deflectors or by providing flow calming sections by preventing the fluttering (or vibration) of the wind vane paddle.

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

[0018] The wording that the reed switch is located on the housing or wind vane paddle, or the magnet on the wind vane paddle or on the housing, is intended to express that – of the two interacting components, reed switch and magnet – one of the two components is located on the housing and the other on the wind vane paddle. Therefore, if the reed switch is located on the housing, the magnet is located on the wind vane paddle. However, if the reed switch is located on the wind vane paddle, 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] Particularly advantageously, the distance between the wind vane paddle in the 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, 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, while simultaneously ensuring high reliability of airflow condition detection, is only made possible by the inventive interplay of the individual features.

[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 shortest 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 when the airflow is oriented vertically upwards). Alternatively, in special installation situations, it may be advantageous to position the airflow sensor upstream of the fan (especially when 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 contact or as a normally close contact.

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

[0026] A further 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 paddle of the airflow sensor. Thus, by arranging the magnet, which is designed as a permanent magnet, on the wind vane paddle, the movable part of the airflow sensor (i.e., the wind vane paddle) does not need to be connected to electrical wires, enabling a simple and reliable design.

[0027] Particularly advantageously, the air flow sensor further comprises a storage device which is immovably connected to the housing and on which the wind vane paddle rests in its initial position.

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

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

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

[0031] An embodiment of the invention is explained in more detail below with reference to the drawing. Fig. 1 a load bank according to the invention in a sectional view, Fig. 2 an enlarged section of Figure 1 , Fig. 3the wind vane sensor according to the Figure 1 and 2 in a perspective oblique view in the starting 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 of all, referring 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 executed.

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

[0034] An opening on the underside of the housing body 3, provided with a first grille 6, serves as the air inlet 7, and an opening on the top of the housing body 3, provided with a second grille 8, serves as the air outlet 9. A waste heat area 10 extends between the air inlet 7 and the air outlet 9. Two cover and baffle 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 are each screwed to two housing body 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 (supported on a support cross member 5) is designed to form an air flow directed from the air inlet 7 to the air outlet 9, which flows against the heating elements 13 and releases thermal energy. The fan 14 is designed as an axial fan with a rotor 15, a rotor diameter D, and a rotor axis R. An air flow sensor designed as a wind vane sensor 16, which can be exposed to the air flow, is arranged between the fan 14 and the heating modules 12 in the waste heat area 10 and is screwed to the housing 3 by means of a sensor holder 17.

[0036] As particularly 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 which is 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 comprises 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. Also arranged on the housing 18 is a reed switch 22, designed as a normally open contact and actuated by a magnetic field, which 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 tongues arranged in the reed switch 22 are pressed against each other against their spring force, thereby actuating the reed switch 22 and assuming the second switching state, in which current can flow through the reed switch.

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

[0039] A corresponding (permanent) magnet 24 generating 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 clarify the different positions of the wind vane paddle 20, Figures 4A to 4C a horizontal line H is drawn.

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

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

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

[0044] Starting from the starting position according to Figure 4A the wind vane paddle 20 is moved by the air flow around the axis of rotation 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 approximately 30°, relative to the starting position.

[0045] The wind vane paddle 20 can be rotated beyond the intermediate position around the axis of rotation of the hinge 19 into the final position according to Figure 4Cin which the magnet 24 rests against the reed switch 22. The magnet 24 and the reed switch 22 thus form a mechanical stop, which 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 rotated by the angle w_E - w_Z, i.e. approximately 5°, relative to the intermediate position (according to Figure 4B ) was 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] If the wind vane paddle 20 is in the position shown 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 the latter is in the first switching state; therefore, there is no sufficiently strong magnetic field acting on the reed switch 22. If the wind vane paddle 20 is now rotated around the axis of rotation of the hinge 19 into the intermediate position according to Figure 4Brotated, 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. The magnetic field of the permanent magnet 24 acting on the reed switch 22 is sufficiently strong in the intermediate position (of the wind vane paddle 20) that the reed switch 22 is actuated and the second switching state is assumed. The wind vane paddle 20 can now be moved between the intermediate position and the end position (according to 0 Figure 4C ) can be moved back and forth as desired (flutter or vibrate) without the switching state changing.

Claims

1. A load bank (1) for converting electrical energy into thermal energy, comprising - a waste heat area (10) with an air inlet (7) and an air outlet (9), - a fan (14) arranged in the waste heat area (10) and suitable for forming an air flow directed from the air inlet (7) to the air outlet (9), - at least one heating element (13) arranged in the waste heat area (10) against which the air flow can flow, releasing thermal energy, and - an air flow sensor arranged in the waste heat area (10) and against which the air flow can flow, designed as a wind vane sensor (16), wherein - the air flow sensor comprises a housing (18), a wind vane paddle (20) movably mounted on the housing (18), a reed switch (22) arranged on the housing (18) or on the wind vane paddle (20) and actuated by a magnetic field, and a reed switch (22) arranged on the wind vane paddle (20) or on the housing (18) arranged corresponding magnets (24) generating the magnetic field,- the wind vane paddle (20) can be brought into a starting position by a restoring force, in particular by a spring force or gravity, and can be brought continuously via an intermediate position into a final position if the air flow is sufficiently strong, 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 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 downstream or 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 downstream or 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 contact or as a normally closed contact.

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 storage device (24) immovably connected to the housing (18) on which the wind vane paddle (20) rests in its initial position.

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

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

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