EP1677323A1 - Low voltage power switch and method to avoid damage to contacts - Google Patents

Abstract

The method reduces the risk of contacts burning in a lower voltage power switch having at least one controllable semiconductor device (10) and at least one electromechanical switch device (20) connected in parallel to the semiconductor device. The method involves identifying the start and/or end of a switch on/off signal for closing and/opening the switch device. The method also involves generating an oscillating control signal lasting a predetermined period of time, to repeatedly successively switch the semiconductor device on, as soon as the start/end of the switch on/of signal is recognized. Independent claims also cover the low voltage switch and the use of such a switch.

Description

The present invention relates to a method for avoiding contact erosion in low-voltage circuit breakers according to the preamble of claim 1, as well as a corresponding low-voltage circuit breaker according to the preamble of claim 5.

Low-voltage circuit breakers are used inter alia for switching on and off and thus for operating consumers, such as motors. In particular, in three-phase motors must be paid to a "soft start" of the motor, so as to achieve, for example, a jerk-free start of the three-phase motor or to avoid the high start-up currents and torques occurring when directly switched on.

In today known low-voltage switches, this soft start is done by limiting the start-up current in a start-up phase. For this purpose, the motor voltage is reduced by a phase control and raised within a ramp time from an adjustable starting voltage to the rated voltage for operation.

Power parts of today known low-voltage circuit breakers therefore have corresponding semiconductor switching devices in the phases to be switched. The semiconductor switching devices are usually constructed of anti-parallel connected thyristors, which are controlled by a corresponding phase control. In addition, such power parts have electromechanical switching devices connected in parallel with the semiconductor switching devices.

After the soft start the then switched off semiconductor switching devices are bridged by the then switched electromechanical switching devices in nominal operation. Thus, in continuous operation instead of the comparatively high power losses of the semiconductor switching devices only a small power loss of the electromechanical switching devices. Thus, the power unit and thus the low-voltage switching device can be made smaller overall.

When switching on and off, today also commonly referred to as bypass electromechanical switching devices, but arcs arise. These lead to an increased contact erosion and thus to a wear of the contact surfaces of the electromechanical switching devices. Together with the bouncing of the contacts of the electromechanical switching devices occurring during switching on and off, this ultimately leads to a reduction in the service life of low-voltage circuit breakers.

In order to avoid such an unwanted reduction of the life, appropriate measures must be taken. So it is already common today to provide appropriate arc extinguishing equipment for deleting such arcs. In addition or alternatively, simply more contact material could be applied to the switching contacts of the electromechanical switching devices. Both variants are not exactly inexpensive.

The object of the present invention is to specify a less expensive method for avoiding contact erosion in low-voltage circuit breakers and a corresponding low-voltage circuit breaker.

This object is achieved by the method having the features of claim 1, as well as by the low-voltage circuit breaker having the features of claim 5.

Characterized in that according to the invention in a low-voltage circuit breaker with at least one controllable semiconductor switching device and at least one, parallel to the semiconductor switching device, electromechanical switching device, a predetermined period lasting, oscillating control signal for repeated successive switching on the at least one semiconductor switching device is generated as soon as a start and / or end time of an on / off signal for closing and / or opening the at least one electromechanical switching device is detected, a resulting in the electromechanical switching device switching arc can be almost instantaneously deleted by the periodic switching of the semiconductor switching device. In particular, with this oscillating signal, the switching arcs that occur as a result of contact bouncing on the electromechanical switching device, repeatedly and briefly in succession, can also be rapidly erased.

Thus, the lifetime of low-voltage circuit breakers can be increased overall by the device according to the invention and the method according to the invention. Known from the prior art measures, such as an increased application of contact material on the contact surfaces of the electromechanical switching device or additional extinguishing devices can be omitted.

By using the method according to the invention and the device according to the invention in soft starters, they can thus be manufactured inexpensively and with little effort.

Further advantageous embodiments and preferred developments of the invention can be found in the dependent claims.

FIG 1

schematisch die Schalteinrichtungen eines Leistungsteils eines dreipoligen Niederspannungsleistungsschalters zum Betreiben eines Motors,

FIG 2

Blockschaltbild der erfindungsgemäßen Vorrichtung,

FIG 3

Diagramme mit dem zeitlichen Verlauf der einzelnen Signale.

The invention and advantageous embodiments thereof are described in more detail below with reference to the following figures. Show it:

FIG. 1

2 schematically shows the switching devices of a power section of a three-pole low-voltage circuit breaker for operating a motor;

FIG. 2

Block diagram of the device according to the invention,

FIG. 3

Diagrams showing the time course of the individual signals.

1 schematically shows a typical structure of a power part of a low-voltage circuit breaker, as provided, for example, in a soft starter for operating a three-phase motor. About the switching devices 10 and 20, the motor M is connected to the three phases L1, L2 and L3 of the power supply switchable.

The semiconductor switching devices 10 consist of two anti-parallel connected thyristors. These are controlled via a, not shown here control device so that a soft start of the three-phase motor M is achieved via a phase control. If this gentle start is completed, that is, the three-phase motor has reached its nominal speed for operation, the electromechanical switching device 20 connected in parallel with the controllable semiconductor switching devices 10 are closed and the semiconductor switching devices 10 are opened. The fact that the current flow L in the individual phases L1, L2 and L3 then passes to the electromechanical switching device 20 ensures that the power loss in nominal operation of the soft starter is reduced.

As mentioned above arise at this switching, but also when later switching off the electromechanical switching devices 20 at these arcs, which leads to a reduction lead the life of the low-voltage circuit breaker.

In order to avoid such Kontaktabbrands is now detected in a first step in the inventive method, whether a start and / or an end time of an on / off signal for closing and / or opening of the electromechanical switching devices 20 is present. If this is the case, an oscillating control signal S2 is generated in a second step for a predetermined period of time. The control signal is designed so that the semiconductor switching devices 10 are turned on several times consecutively within this period. By this ignition and thus driving through the semiconductor switching devices, the current flow is deflected by the arcs on the semiconductor switching devices so that the arcs are deleted. By the repeated successive ignition is also avoided that the resulting as a result of the bouncing successive, again and again emerging arcs are always deleted.

The timing of the individual signals is shown by way of example in FIG. Preferably, the oscillating control signal S2 is generated after the start (te) and / or end time (ta) of the on / off signal S1 and before the first closing and / or opening of the at least one electromechanical switching device 20. In particular, as indicated in FIG. 3, it may be generated simultaneously with the control signal S1, that is to say at the switch-on time point t.sub.1 and the switch-off time point ta.

Due to the inertia of the electromechanical switching devices, the actual current flow L is delayed by these electromechanical switching devices. This means that typically only about 20 ms after the on or off command the electromechanical switching devices open or close for the first time. In addition, it is due to the bounce still come to other unwanted on / off operations, before adjusting a continuous value of the current flow L. Each of the transitions can then create an arc, which must be avoided. To absorb these delay times, the signal S2 is generated for about 60 ms.

Preferably, it is provided that the control signal S2 oscillates after generation with a period T of 100μs to 500μs and at least approximately rectangular pulses having a pulse width tp of 10μs to 50μs for turning on the semiconductor switching device 10 has. In the example shown in FIG. 3, the period T = 200 μs and the pulse duration t P = 20 μs. The choice of these values T and tp depends essentially on the load capacity of the power supply. In addition, care must be taken that the components for controlling the Zündübertragers are not overloaded and thus the power loss is too high.

According to the invention, the low-voltage power switches have the means 30 and 40 indicated in FIG. 2 for carrying out the steps according to the invention. The control is usually carried out via a microprocessor 30. This controls the switching devices of the power section of the low-voltage circuit breaker in the order necessary for the safe operation of the engine. In this case, the switching devices 10 and 20 are controlled so that the engine starts smoothly. According to the invention, an oscillator 40 is now controlled with the on / off signal S1 emanating from the microprocessor or microcontroller for closing and / or opening the electromechanical switching devices. This oscillator then generates at the detected start and / or end times a, a predetermined period lasting, oscillating control signal S2. This control signal is forwarded to an ignition transformer 50 in order to control it with the signal S2 via corresponding control inputs of the semiconductor switching devices.

In the foregoing, only one possible embodiment of the present invention has been described in detail. However, the exemplary embodiments, which likewise fulfill the basic idea of the present invention, namely to prevent possibly occurring arcs as effectively and cost-effectively as possible in order to avoid contact erosion, are also to be covered by the invention. For example, as shown in FIG. 3, the oscillating control signal S2 does not have to be a periodically recurring signal with the period T. Likewise, it is not essential that the pulse shape is exactly rectangular. Rather, it is sufficient if the control signal S2 is sawtooth to rectangular. Likewise, the control signal S2 can be generated directly in a microprocessor or microcontroller 30.

Claims (10)

Method for avoiding contact erosion in low-voltage circuit breakers having at least one controllable semiconductor switching device (10) and at least one electromechanical switching device (20) connected in parallel with the semiconductor switching device (10), comprising the steps: Detecting a start (te) and / or end time (ta) of an on / off signal (S1) for closing and / or opening the at least one electromechanical switching device (20), and Generating a, for a predetermined period of time (Δte, Δta) lasting, oscillating control signal (S2) for repeatedly successively switching on the at least one semiconductor switching device (10) as soon as the start (te) and / or end time (ta) of the input / Off signal (S1) is detected. A method according to claim 1, characterized ge - indicates that the oscillating control signal (S2) after the start (TE) and / or end time (ta) of the on / off signal (S1) and before the first closing and / or opening of at least an electromechanical switching device (20) is generated. The method of claim 1 or 2, characterized indicates overall that the oscillating control signal (S2) periodically oscillates repetitively. A method according to claim 3, characterized characterized labeled in that the oscillating control signal (S2) oscillates with a period duration (T) of 100 .mu.m to 500 .mu.m at least approximately rectangular pulses with a pulse width (tp) of 10 .mu.m to 50 .mu.m for turning the at least one semiconductor switching device ( 10). Low-voltage circuit breaker having at least one controllable semiconductor switching device (10) and at least one, to the semiconductor switching device (10) connected in parallel, electromechanical switching device (20), with first means (30) for detecting a start (te) and / or end time (ta) of an on - / off signal (S1) for closing and / or opening the at least one electromechanical switching device (20), and with further means (40) for generating a, a predetermined period of time (.DELTA.te, .DELTA.ta) persisting, oscillating control signal (S2) for repeated successive following switching of the at least one semiconductor switching device (10) as soon as the start (te) and / or end time (ta) of the on / off signal (S1) is detected by the first means (30). Low-voltage circuit breaker according to claim 5, characterized in that the further means (40) the oscillating control signal (S2) after the start (te) and / or end time (ta) of the on / off signal (S1) and before the first closing and / or opening the at least one electromechanical switching device (20). Low-voltage circuit breaker according to claim 5 or 6, characterized in that the oscillating control signal (S2) is a periodically repeating oscillating control signal. Low-voltage circuit breaker according to one of Claims 5 to 7, characterized in that the oscillating control signal (S2) has a period (T) of 100 μm to 500 μm and at least approximately rectangular pulses with a pulse width (tp) of 10 μm to 50 μm for switching on the semiconductor switching device (10). having. Use of the low-voltage circuit breaker according to claim 5 to 8 as an electronic soft starter for operating a three-phase motor. Use of the method according to claims 1 to 4 in a soft starter for operating a three-phase motor.

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