LOW-VOLTAGE PROTECTION SWITCH

Description

[0001] The invention relates to an electric motor connection section according to claim 1.

[0002] Electrical installations often contain inductive or capacitive loads or devices that typically draw high currents when switched on. For brief periods, these currents are so high that a circuit breaker upstream of the installation trips and shuts it down.

[0003] Firstly, the tripping of the circuit breaker in question is unintentional, as it stops the system from starting up and the network has to be restarted. Secondly, it is not a false trip in the true sense, since the current detected by the circuit breaker is indeed high enough to justify a tripping in accordance with normal operation. However, this condition usually only lasts a very short time, so there is no risk of damage to the wiring.

[0004] In particular, the operation and starting of electric motors therefore requires considerable facilities to ensure both safe operation and uninterrupted start-up.

[0005] Devices are known that are designed and configured to limit the inrush current when starting up certain types of loads. However, these are each intended only for specific types of loads. Star-delta switching, for example, is widely known and used in certain types of three-phase motors. Other such devices are specifically designed for capacitive or inductive loads.

[0006] The disadvantage of these devices is that they are always separate units that must be installed in addition to the devices required by law, thus increasing installation effort. Furthermore, they are restricted to use with specific loads, which means that manufacturers and distributors already have to provide a wide variety of such devices.

[0007] US 2003 / 202296 A1, US 2011 / 062933 A1, and US 6,459,606 B1 each describe a device that switches a semiconductor arrangement on and off to limit inrush current. However, these are power supplies for integrated devices or standalone control units. None of the three documents describes a device that can also perform a protective function.

[0008] US 2007 / 0121257 A1 describes a hybrid circuit breaker with pulsed current limiting.

[0009] The object of the invention is therefore to provide an electric motor connection section of the type mentioned above, with which the aforementioned disadvantages can be avoided, and which supports the starting or switching on of an electric motor without any further device.

[0010] According to the invention, this is achieved by the features of claim 1.

[0011] This allows the inrush current of both capacitive and inductive loads to be safely limited without any additional device. Essentially, any capacitive or inductive load can be switched on and operated using only a single device, without the need for an additional switch, inrush current limiter, or circuit breaker. This eliminates the need for a separate inrush current limiter specifically designed for a particular load type. This reduces the installation effort and complexity of electrical installations, especially when operating high-power loads. It also increases the flexibility of the installation.

[0012] By using a single low-voltage protective switching device, all other equipment typically required for operating an electric motor can be eliminated. Only if motor control is desired would a modern inverter be necessary. Otherwise, the previous arrangement of separate motor protection switches, circuit breakers, fuses, and motor starters is no longer required. This allows multiple devices to be replaced by a single unit, significantly reducing installation effort.

[0013] The dependent claims relate to further advantageous embodiments of the invention.

[0014] Reference is hereby expressly made to the wording of the patent claims, whereby the claims are incorporated into the description at this point by reference and are deemed to be reproduced verbatim.

[0015] The invention is described in more detail with reference to the enclosed drawings, in which only preferred embodiments are shown by way of example. These show: Fig. 1 a first embodiment of a switching device in a schematic representation; Fig. 2 a first preferred embodiment of an electric motor connection section as a schematic representation; Fig. 3 a second embodiment of a switching device in a schematic representation; and Fig. 4 A second preferred embodiment of an electric motor connection section as a schematic representation.

[0016] The Fig. 1 and 3Each figure shows an embodiment of a low-voltage protective switching device 1, in particular a motor protection switch, with at least one external conductor path 2 from an external supply terminal 3 of the low-voltage protective switching device 1 to an external load terminal 4 of the low-voltage protective switching device 1, and a neutral conductor path 5 from a neutral conductor terminal 6 of the low-voltage protective switching device 1 to a neutral conductor load terminal 7 of the low-voltage protective switching device 1, wherein a mechanical bypass switch 8 is arranged in the external conductor path 2, wherein a semiconductor circuit arrangement 11 of the low-voltage protective switching device 1 is connected in parallel to the bypass switch 8, wherein at least in the external conductor path 2 a current measuring arrangement 12 is arranged which is connected to an electronic control unit 13 of the protective switching device 1, wherein the electronic control unit 13 is configured toto control the bypass switch 8 and the semiconductor circuit arrangement 11 in a predefinable manner, wherein the control unit 13 is designed to limit an inrush current of a downstream load 23, to switch the semiconductor circuit arrangement 11 on / off in a predefinable manner when the bypass switch 8 is open.

[0017] This allows the inrush current of both capacitive and inductive loads 23 to be safely limited without any additional device. Essentially, any capacitive or inductive load 23 can be switched on and operated using only a single device, without the need for an additional switch, inrush current limiter, pre-charging circuit, or circuit breaker. This eliminates the need for a separate inrush current limiter specifically designed for a particular load type. This reduces the installation effort and complexity of electrical installations, especially for operating high-power loads 23. It also increases the flexibility of installations.

[0018] The low-voltage protective switching device 1 in question, as well as the protective switching device according to WO 2015 / 028634 A1, are low-voltage protective switching devices. Low voltage is generally defined as the range up to 1000 V AC or 1500 V DC.

[0019] Fig. 1 und 2 Figure 1 shows a protective switching device. This device has at least one live conductor 2 and one neutral conductor 5, with versions for three-phase current, comprising three live conductors 2, also being provided. The live conductor 2 runs through the protective switching device 1 from a live conductor supply terminal 3 to a live conductor load terminal 4. The neutral conductor 5 runs through the protective switching device 1 from a neutral conductor terminal 6 to a neutral conductor load terminal 7. The respective terminals 3, 4, 6, and 7 are preferably designed as screw terminals or plug-in terminals and are arranged in the protective switching device 1 and are accessible from the outside.

[0020] The protective switching device 1 preferably has an insulating housing.

[0021] In the phase conductor 2, a mechanical bypass switch 8 with single or multiple contact interruption is arranged. In the low-voltage protective switching device 1, preferably and as shown, a first mechanical disconnect switch 9 is further arranged in series with the bypass switch 8 in the phase conductor 2. In the neutral conductor 5, a second mechanical disconnect switch 10 is arranged. A semiconductor circuit arrangement 11 is connected in parallel with the bypass switch 8. The disconnect switches 9, 10 can also be arranged at another location in the low-voltage protective switching device 1, provided that galvanic isolation of the connected load 23 from the network 16 is achieved.

[0022] Furthermore, a surge arrester 19 is connected in parallel to the bypass switch 8.

[0023] The protective switching device 1 further comprises a current measuring arrangement 12, which is arranged in the outer conductor section 2, and which preferably includes a shunt resistor or a current transformer.

[0024] The current measuring arrangement 12 is connected to an electronic control unit 13 of the protective switching device 1, which preferably comprises a microcontroller or microprocessor. The electronic control unit 13 is configured to control the bypass switch 8 and the first semiconductor circuit arrangement 11, as well as the first mechanical disconnect switch 9 and the second mechanical disconnect switch 10, and thus to actuate or switch them in a predefinable manner. For this purpose, the electronic control unit 13 is preferably connected circuit-wise to the first semiconductor circuit arrangement 11, as well as to, in particular electromagnetic, actuating elements of the mechanical switches, i.e., the bypass switch 8, the first mechanical disconnect switch 9, and the second mechanical disconnect switch 10. The corresponding connections originating from the electronic control unit 13 are not shown in Fig. 1 depicted.

[0025] The first semiconductor circuit arrangement 11 preferably comprises a rectifier circuit 20, which is preferably designed as a full bridge, and, in the embodiment according to Fig. 1 Two power semiconductors 21, which are in this case designed as IGBTs, serve as the actual switching or control elements. A larger power semiconductor 21 can also be provided.

[0026] Alternatively, the use of so-called back-to-back IGBT 90 semiconductor switching elements can also be considered. Fig. 3 Figure 1 shows a correspondingly designed low-voltage protective switching device 1. Each of the back IGBTs 90 is assigned an antiparallel diode 91. Except for the design of the semiconductor circuit arrangement 11, the two embodiments of the low-voltage protective switching device 1 are essentially identical.

[0027] IGBTs, as actual switching elements, have the advantage that they can switch high power levels and can be switched off more easily compared to a thyristor.

[0028] It is particularly preferred that the semiconductor switching arrangement 3 is configured as a bidirectional four-quadrant converter or four-quadrant switching regulator. This enables operation independent of the type of load. As a result, the transient response of both capacitive and inductive loads 6 can be controlled.

[0029] In the Fig. 1 In addition to the actual protective switching device 1, the electrical environment is also indicated. The supply network is represented by the AC / DC mains voltage source 16, the network internal resistance 17, and the network inductance 18. Furthermore, an electrical load 23, in particular an electric motor 80, and an electrical fault 22 in the form of a short circuit are shown.

[0030] In a switching device according to Fig. 1 It is provided that a shutdown process is carried out by the bypass switch 8 and the first semiconductor circuit arrangement 11, and the first and second disconnect switches 9, 10 serve only to ensure galvanic isolation of the load circuit after shutdown.

[0031] The low-voltage protective switching device 1 is designed, in addition to its protective function, to switch a load 6, in particular a capacitive or inductive load, on or off during operation. In particular, the protective switching device 1 is intended to be used in the form of, or instead of, a motor protection switch for the operational operation of an electric motor 80.

[0032] It is therefore provided that the control unit 13 is configured to switch the semiconductor switching arrangement 11 on and off in a predefinable pulsed manner when the bypass switch 8 is open, in order to limit the inrush current of a downstream load 23. The previously described disconnection functions of the low-voltage protective switching device 1, especially in the event of a short circuit, remain unaffected by this. It is therefore preferably provided to disconnect or interrupt an overcurrent or a short circuit directly, i.e., without prior current limitation using the inrush current limiting methods described herein.

[0033] Different clocking methods can be used. In particular, the control unit 13 is designed to switch the semiconductor switching arrangement 11 on and off according to pulse width modulation. This has proven to be particularly practical.

[0034] Preferably, the control unit 13 is connected to the current measuring arrangement 12, and the control unit 13 is configured to adjust the on / off switching times depending on a measured load current. This forms a control loop that enables more precise limitation of the inrush current.

[0035] It is further preferably provided that a first voltage measurement arrangement 95 is arranged in the area of ​​the grid-side connections 3, 6 and a second voltage measurement arrangement 96 is arranged in the area of ​​the load-side connections 4, 7, each of which is connected to the control unit 13. The zero crossing of the applied voltage can be detected by measuring the voltage at the grid-side connections 3, 6. The voltage at the load-side connections 4, 7 allows the voltage at the load to be measured and taken into account during pulse width modulation.

[0036] The control unit 13 is of course designed or configured for the predetermined control or switching of the semiconductor switching arrangement 11.

[0037] The Fig. 2 and 4 As a further object of the present invention, two embodiments of an electric motor connection section are shown, wherein a mains connection is connected to the Fig. 2 and 4 Each reference numeral 16, 17, 18 indicates that a low-voltage protective switching device 1 is connected to it. An electric motor 80 is connected to the low-voltage protective switching device 1.

[0038] By using a low-voltage protective switching device 1, all other equipment otherwise required can be dispensed with when operating an electric motor. As in Fig. 2 As shown, the entire chain from the mains connection to the electric motor consists of only one low-voltage protective switching device 1. According to the prior art, four devices are typically required between the mains and the electric motor 80: a separate motor protection switch, a circuit breaker, a fuse assembly, and a motor starter. All of these can be omitted in the electrical installation of an electric motor 80 shown here.

[0039] Only if control of the electric motor is desired would a currently used inverter 78 or a frequency converter 70 be required. Otherwise, the previous arrangement can be dispensed with. This allows several devices to be replaced by just one, thus significantly reducing installation effort.

[0040] Fig. 4 Figure 1 shows an arrangement in which, in terms of circuitry, only a frequency converter 70 is arranged between the low-voltage protection device 1 and the electric motor 80. An input filter 75 is assigned to the frequency converter 70. The frequency converter 70 itself consists of a rectifier 76, a downstream capacitor arrangement 77 (also called a capacitor bank), and a downstream inverter 78 (which can also be referred to as a DC-AC inverter). The capacitor arrangement 77 is part of the load as it appears to the low-voltage protection device 1. The pre-charging of the capacitor arrangement 77 can also be achieved by the pre-programmable on / off switching of the semiconductor switching arrangement 11, so that no further circuitry measures are required to charge it.The same applies to the input filter 75, which may contain energy storage devices, such as capacitors, and which can also be pre-charged by the low-voltage protective switching device 1 in question, without this resulting in an increased inrush current.

[0041] The explanations regarding the Fig. 2 and 4 Regarding the electric motor connection section and its respective description, the description should refer specifically to a complete list. It is therefore particularly preferred that the respective electric motor connection sections actually contain no further components, with fuses being the only possible exception. In any case, no further switches are provided.

[0042] A preferred embodiment of a method for commissioning an inductive or capacitive load 23 is described below, which load 23 is connected to a low-voltage protective switching device 1.

[0043] In a first step, a switch-on control element is activated on the switched-off protective switching device 1, or a switch-on signal is received at an interface of the protective switching device 1 (not shown).

[0044] Subsequently, with the mechanical bypass switch 8 of the low-voltage protective switching device 1 open, the semiconductor switching arrangement 11, which bridges the open mechanical bypass switch 8, is pulsed by the control unit 13 of the low-voltage protective switching device 1 during each half-cycle of the supplying alternating current to limit the inrush current of the load 23.

[0045] Preferably, the semiconductor switching arrangement 11 is switched on / off by the control unit 13 according to a pulse width modulation.

[0046] Once a substantially stable current flow or a substantially stable power consumption has occurred via the low-voltage protective switching device 1, in other words, once the power consumption of the load 23 has settled, the semiconductor switching arrangement 11 is bypassed by closing the mechanical bypass switch 8.

[0047] It is further preferred that a current measuring arrangement 12 measures a load current through the low-voltage protective switching device 1 and transmits a current measurement result to the control unit 13.

Claims

1. An electric motor connecting line, wherein a low-voltage circuit breaker device (1), in particular a motor protection switch, is connected to a network terminal, wherein an electric motor (80) is connected to the low-voltage circuit breaker device (1), wherein the low-voltage circuit breaker device (1) comprises at least one external conductor path (2) from an external conductor supply terminal (3) of the low-voltage circuit breaker device (1) to an external conductor load terminal (4) of the low-voltage circuit breaker device (1), and a neutral conductor path (5) from a neutral conductor terminal (6) of the low-voltage circuit breaker device (1) to a neutral conductor load terminal (7) of the low-voltage circuit breaker device (1), wherein a mechanical bypass switch (8) is disposed in the external conductor path (2), wherein a semiconductor circuit arrangement (11) of the low-voltage circuit breaker device (1) is coupled in parallel to the bypass switch (8), wherein at least one current measuring arrangement (12) is disposed in the external conductor path (2), which current measuring arrangement is connected to an electronic control unit (13) of the circuit breaker device (1), wherein the electronic control unit (13) is configured to control the bypass switch (8) and the semiconductor circuit arrangement (11) in a predeterminable manner, wherein the control unit (13) is configured to switch on / off the semiconductor circuit arrangement (11) in a predetermined manner when the bypass switch (8) is open to limit an inrush current of the downstream electric motor (80).

2. The electric motor connecting line according to claim 1, characterized in that the control unit (13) is configured to switch on / off the semiconductor circuit arrangement (11) in a predeterminable manner, particularly due to pulse-width modulation.

3. The electric motor connecting line according to claim 1 or 2, characterized in that the semiconductor circuit arrangement (11) comprises at least one IGBT (21), particularly two back-to-back IGBTs (90), or at least one MOSFET as a semiconductor switching element.

4. The electric motor connecting line according to any one of claims 1 to 3, characterized in that the control unit (13) is coupled to the current measuring arrangement (12), and that the control unit (13) is configured to adjust the on / off switching times depending on a measured load current.

5. The electric motor connecting line according to any one of claims 1 to 4, characterized in that the control unit (13) is configured to control the bypass switch (8) and the semiconductor circuit arrangement (11) for switching off the low-voltage circuit breaker device (1) in the event of predetermined electrical conditions, particularly an overcurrent or short-circuit current.

6. The electric motor connecting line according to any one of claims 1 to 5, characterized in that the semiconductor circuit arrangement (11) is configured as a bidirectional four-quadrant chopper.

7. The electric motor connecting line according to any one of claims 1 to 6, characterized in that the low-voltage circuit breaker device (1) comprises mechanical breaker contacts (9, 10) for predetermined galvanic disconnection of the external conductor path (2) and the neutral conductor path (5).

8. The electric motor connecting line according to any one of claims 1 to 7, characterized in that in particular only an inverter or a frequency converter (70) is disposed in terms of circuitry between the low-voltage circuit breaker device (1) and the electric motor (80).