EP0384552A2 - Process for operating a power circuit breaker - Google Patents

Abstract

2.1 A process is described which allows inductive circuits to be interrupted using a vacuum circuit breaker, without any disturbing overvoltages. …<??>2.2 The switching process of the vacuum circuit breaker (2) is influenced by a trip control device (4) to which there is supplied, as a correction parameter, a measured value of the trip delay of the vacuum circuit breaker from the time when the trip signal is produced to the time when the contact pieces separate in a preceding switching off process. The temperature of the drive device (35) of the vacuum circuit breaker, the stoppage time of the circuit breaker and the operating voltage and temperature of a trip magnet can also be used as further correction parameters (44, 45, 46). …<??>2.3 The process described is suitable for use in the case of vacuum power circuit breakers in circuits having inductive loads. …<IMAGE>…

Description

The invention relates to a method for operating a circuit breaker, in particular a vacuum switch, using a tripping control device which, regardless of the time of a command to switch off, causes the opening of the contact pieces at a time which is in a fixed relationship to the zero crossing of the current.

A method of this kind is known, for example, from US-A-3,555,354. The purpose of this method is to limit the duration of the arc discharge between the switching elements of the circuit breaker as much as possible, on the other hand to ensure a sufficient contact opening at the time the current passes through zero. For this purpose, the trigger control device detects the flowing current via transducers and obtains periodic pulses therefrom at the zero crossing of the current and in the maximum or minimum of the current curve. Both pulses are supplied to an AND gate via a timing element, which can additionally be acted upon by a signal which is derived from the absolute magnitude of the current. The trigger signal emanating from the AND gate arrives in the usual way at a trigger magnet which actuates a valve or a latching arrangement to release the switching mechanism or the switch drive.

Vacuum switches, in a similar way to certain types of gas pressure switches, have the property that their switching paths achieve high dielectric strength in an extremely short time after a power interruption. They are therefore particularly prone to so-called multiple re-ignitions in strongly inductive circuits, which are a rapid sequence of extinguishing and ignition processes between the open contacts put. High overvoltages can be associated with this process. In three-phase networks, multiple re-ignitions in the first quenching pole of the circuit breaker can lead to a virtual current cut in the last quenching poles of the circuit breaker, which also creates overvoltages.

To avoid such overvoltages, attempts have already been made to use contact materials in vacuum switches which, because of the relatively high vapor pressure of individual components, maintain a switching arc as close as possible to the zero crossing of the current. However, this advantageous property is offset by a reduced ability to interrupt high switching powers, which results in the difficulty of creating a circuit breaker suitable for interrupting high switching powers, which at the same time avoids the occurrence of overvoltages.

Furthermore, it is known to avoid the overvoltages which occur in particular when switching motor circuits by means of surge limiters or by combinations of resistors, capacitors and inductors with similar properties. In addition to the difficulty of accommodating such elements at a point in a circuit arrangement that is suitable for ensuring their effectiveness, these components must also be individually adapted to the properties of the circuit in question.

With the aim of avoiding the difficulties described above, a switching method is already known in which two of the switching paths of a three-pole circuit breaker are opened at least a third of a cycle of the mains frequency later than the first switching path, plus the minimum arc duration in the first switching path (DE -C-28 54 092). This procedure basically prevents the occurrence of the so-called virtual downstream crack in the last two poles of the circuit breaker. However, due to the fact that the switching process can start at any time, the multiple re-ignitions in the first extinguishing pole cannot be prevented, which are also the cause of overvoltages.

If a circuit breaker is operated using a tripping control unit, it is in principle possible to carry out switching operations without overvoltages even in three-phase networks if the control is carried out in such a way that there is such a distance between the contact pieces in the zero-crossing of all poles of the circuit breaker that the arc is under the influence the recurring voltage cannot reignite. Such a switching method proves to be extremely difficult to carry out because the so-called opening window, i.e. H. the period in which the switching pieces must be opened in a network with a frequency of 50 Hz has a width of only about 2 ms. Conventional circuit breakers are unable to open with such precision. In addition, the mechanical properties of circuit breakers can change over the course of their use to such an extent that they can no longer keep the opening window after a long period of operation and changed environmental conditions, even if they are suitable for this purpose when new.

Proceeding from this, the object of the invention is to design the method for operating a circuit breaker in such a way that changes in properties occurring over the course of the service life of a circuit breaker are automatically taken into account and the opening window can thus be maintained even after a long operating time.

According to the invention, this object is achieved in that the tripping control unit receives a measured value of the tripping delay of the circuit breaker from the time the tripping signal is issued to Time of separation of the contact pieces is supplied as a correction variable in a previous switch-off. The delay in triggering is the result of a whole series of mechanical influencing variables, which are difficult to detect individually. The delay in tripping, however, can be determined in different ways with sufficient accuracy and relatively little effort. This creates the possibility of carrying out the switching free of overvoltages, in particular of motor circuits and choke coils with vacuum switches, with economically justifiable effort.

Within the scope of the invention, a circuit breaker is suitable for carrying out the new method, to which a measuring device is assigned to determine the tripping delay, which is set in motion by the receipt of a tripping signal and stopped when the contact pieces are separated, and in that a storage device is provided which Saves the measured value of the tripping delay at least until the next switch-off process. Although a delay in tripping that is based on a switch-off that has already taken place some time ago may be used as a correction variable for the control of the circuit breaker, it has nevertheless been shown that this procedure is suitable for relatively narrow opening windows to apply when the switch is opened.

Both electrical and electro-mechanical or electronic-mechanical evaluation devices are suitable for measuring the delay in tripping. In particular, when switching with current, the occurrence of an arc voltage between the contact pieces can be used as a criterion for the contact separation.

Instead of the measuring device explained above or in addition to this, the evaluation device for detecting the contact opening can contain a circuit arrangement for measuring the capacitance between the contact pieces. This measurement too The process works without contact and therefore does not require any changes to the contact system itself.

However, it is also possible to determine the point in time of the contact opening to be determined in order to determine the tripping delay directly from the relative movement of the contact pieces. For this purpose, a drive element which is directly connected to a movable contact piece can be provided with a reflector and an optical waveguide can be fixedly arranged opposite it at a short distance and cooperates at its end facing away from the reflector with a light source and a receiving circuit for reflected light.

As already explained at the beginning, a large number of interrelated influencing variables for the mechanical sequence of the switching process are already taken into account by measuring the trigger delay. If, however, it is to be expected, for example, that a circuit breaker is exposed to strongly changing temperatures at its installation site, the size of the delayed delay once determined may prove to be insufficiently accurate for controlling the circuit breaker. In this case, it can be advantageous to supply the trip control unit with the temperature of the drive device of the circuit breaker as a further correction variable. This can be done in a relatively simple manner by means of a temperature sensor fitted in the drive housing. If a series of tests is used to determine what influence the temperature has on the delay in tripping, the expected positive or negative deviation from the standard value can be determined by assigning the respective temperature to a standard value of the tripping delay.

Another criterion for the mechanical sequence of the switching process is the time that has elapsed since the last switching operation. Basically, a regularly used circuit breaker is more likely to hold the value of the delayed tripping once determined for a circuit breaker that is operated only rarely and possibly only at intervals of months or years. This influence can be taken into account by using a suitable correction variable. For this purpose, the time that has elapsed since the last switching operation can be measured, and here, too, tests are to be carried out to determine how the tripping delay changes based on a standard value depending on the downtime.

The switching mechanism of circuit breakers is generally released by an electromagnet, which is fed from an auxiliary network. Since the voltage of this auxiliary network can fluctuate and the response speed of the tripping magnet depends on it, the value of the supply voltage of the tripping magnet also has a direct influence on the tripping delay. According to a development of the invention, this influence can also be taken into account by supplying the supply voltage of the tripping magnet to the tripping control device in order to obtain a further correction variable. The temperature of the winding of the tripping magnet can also be detected, since the resistance and thus the current through the winding depends on the voltage.

All of the above-mentioned measured values or correction values can expediently be fed to a real-time microprocessor, which provides a trigger signal for the circuit breaker by comparison with measured values or standard values taken from a memory. In connection with this, threshold value elements can be provided, which bring about an undelayed triggering when the current falls below a lower limit or when the current exceeds an upper limit.

• Die Figur 1 zeigt als Blockschaltbild die grundsätzliche Anord­der Komponenten eines Leistungsschalters.
• Die Figur 2 zeigt vereinfacht eine Anordnung zur Messung des Auslöseverzugs, bei der die Änderung der Kapazität von Schalt­stücken bei deren Trennung ausgewertet wird.
• In der Figur 3 ist das Prinzip der Erfassung des Zeitpunktes der Trennung von Schaltstücken mittels der Lichtbogenspannung dargestellt.
• Die Figur 4 zeigt die Anordnung einer opto-elektronischen Meß­einrichtung zur Erfassung der Trennung der Kontaktstücke.
• Die Figur 5 zeigt schematisch einen Antriebskasten eines Vakuum-Leistungsschalters mit einem Auslösesteuergerät, dem wahlweise eine oder mehrere Korrekturgrößen zuführbar sind.
• In der Figur 6 ist ein Blockschaltbild des Programmablaufes bei der Auslösung eines Leistungsschalters unter Verwendung eines Echtzeit-Mikroprozessors dargestellt.

The invention is explained in more detail below with reference to the exemplary embodiments shown in the figures.

• Figure 1 shows a block diagram of the basic arrangement of the components of a circuit breaker.
• FIG. 2 shows in simplified form an arrangement for measuring the tripping delay, in which the change in the capacitance of switching elements is evaluated when they are separated.
• FIG. 3 shows the principle of detecting the point in time at which switching pieces are separated by means of the arc voltage.
• Figure 4 shows the arrangement of an opto-electronic measuring device for detecting the separation of the contact pieces.
• FIG. 5 schematically shows a drive box of a vacuum circuit breaker with a tripping control device, to which one or more correction variables can optionally be supplied.
• FIG. 6 shows a block diagram of the program sequence when a circuit breaker is tripped using a real-time microprocessor.

FIG. 1 shows a three-phase motor 1 which can be switched on and off by means of a three-pole vacuum circuit breaker 2. The symbol for a switching lock denotes a latching device 3, which is responsible for releasing the switching contacts of the circuit breaker 2 for opening. The latching device 3 can only be actuated by a trigger control device 4, which in turn is to be acted upon by a trigger 5 or manually operated command transmitter 6. The trigger control device 4 are supplied with current-dependent signals which are obtained at current transformers 7.

The tripping control device 4 contains a memory unit 10 which is used to store at least one measured value for the tripping delay of the circuit breaker 2 during the previous opening is provided. In addition, the memory unit 10 can be designed in such a way that it can take up both further measured values of the delay in triggering from previous switching operations and additional variables which are essential for the mechanical sequence of the switching operation.

An example of the measurement of the time of opening of the switching elements of the circuit breaker 2 is shown in FIG. 2. A high-frequency measuring voltage from a voltage source 13 is applied to the switching path of the circuit breaker 2 via protective resistors 14 and support insulators 11 and 12, the capacitance of which is shown in dashed lines with the symbol for a capacitor. For example, a voltage with a frequency of 5 MHz is suitable. A high-frequency voltage is taken from terminals 15 for evaluation. In the course of this high-frequency voltage, a characteristic jump occurs due to the change in the capacitance of the measuring circuit as a result of the opening of the circuit breakers of the circuit breaker 2. To understand this process, it should be mentioned that the circuit breakers of a vacuum switch have flat contact surfaces which can be either circular or annular . While there is no capacitance in the closed state of the switching elements, one arises through the formation of a plate capacitor as soon as the switching elements separate from one another. The activation of this capacitance in the measuring circuit is evaluated in an evaluation device 16 provided with a protective device 17 by comparison with the time at which the latching device 3 is released and results in the tripping delay of the circuit breaker 2.

Another example of the measurement of the tripping delay of the circuit breaker 2 is shown schematically in FIG. In this case, by means of suitable isolators 20 and 21, which can be, for example, optoelectronic devices, the voltage across the switching path of the circuit breaker 2 is supplied to a measuring device 22 leads. This therefore receives the voltage signal "0" when the switching elements of the circuit breaker 2 are closed and a voltage signal corresponding to the arc voltage when the switching elements of the circuit breaker 2 are opened when current is flowing. The delay in tripping of the circuit breaker 2 is obtained by comparing the times at which this arcing voltage occurs and the time at which the switch lock 3 is released. The dashed line connection between the switch lock 3 and the measuring device 22 indicates the comparison of the times mentioned.

While the devices explained with reference to FIGS. 2 and 3 measure the triggering delay by electrical means, optoelectronic detection can also be considered. This has the advantage that no effort is required for the electrical isolation between the high voltage at the circuit breaker and the measuring device. This measuring method is explained with reference to FIG. This figure shows, partly in section, a vacuum circuit breaker of a known type (cf. DE-B-27 17 958), the switching tubes 25 of which can be actuated by an insulating drive rod 26 each. These drive rods engage via an angle lever 27 on a linearly displaceable support bolt 30 of the movable contact piece 31. If, for example, this support pin is provided with a reflective marking and a sensor is placed opposite it, a movement of the support pin and thus of the switching element 31 can be determined. For this purpose, FIG. 4 indicates that the light is supplied and the reflection is returned through an optical waveguide 32, which is connected to an evaluation unit 33 consisting of transmitter and receiver. The evaluation unit 33 again determines the delay in tripping by comparing the point in time of a movement of the support bolt 30 with the point in time at which the latching in the drive box of the circuit breaker 2 is released. The evaluation unit 33 can be integrated in the tripping control unit 4 (FIG. 1).

FIG. 5 shows a vacuum circuit breaker 2, similar to FIG. 4, partially in section, which has a tripping control device 4 and sensors for influencing variables which can influence the tripping delay. The trip control unit 4 is housed in the drive box 35 of the circuit breaker 2. In the switched-on position, the switching tube 25 is held by a ratchet lever 36 which engages at one end of a two-armed lever 40 seated on a switching shaft 37. As has already been explained with reference to FIG. 4, the movable contact piece 31 is actuated by a drive rod 26 and an angle lever. In the switch-on position shown, the control shaft 37 is locked against rotation in the sense of switching off by means of the two-armed lever 40 and the ratchet lever 36.

The pawl lever 36 can be moved by a switch-off magnet 41 into the switch-off position shown in broken lines, in which the switching shaft 37 is released for switching off. Switch-off springs 37 are then rotated counterclockwise by means of switch-off springs (not shown) and the drive rod 26 is carried along. As indicated by an arrow 42, the switch-off magnet 41 can be actuated by the trigger control device 4. This happens when the trigger 5 or a command entered manually (arrow 42) has requested that a switch-off operation be carried out and the trigger control device 4 has determined the appropriate time for this. For this purpose, the trigger control device 4 first determines the times of the following current zero crossings on the basis of the measured values transmitted by the current transformers 7. The triggering command is then passed on to the trigger magnet 41, taking into account the value of the trigger delay stored in the trigger control device 4 during the previous switch-off, as well as other variables provided by sensors. This includes a temperature sensor 44 for the current temperature in the drive box of the circuit breaker 2 and a further temperature sensor 24 for the temperature of the winding of the Tripping magnet 41. The voltage available to supply the tripping magnet 41 is also detected by a further sensor. A timer 47 as a component of the trigger control unit 4 provides the time that has elapsed since the last switch-off operation for correcting the delay in triggering.

Depending on the results obtained for a particular circuit breaker, all of the sensors mentioned or only a part of them can be used. If, for example, a circuit breaker is only exposed to slight changes in temperature, the influence of temperature on the state of the switching mechanism can be neglected and the sensor 44 is accordingly unnecessary.

When switching off now, the trigger delay is determined again by means of a sensor 50 and is entered into the trigger control unit for comparison with the value of the trigger delay located in the memory 10 of the trigger control unit 4. Either the previous stored value can be replaced by the new measured value or the new measured value can also be saved in order to determine the change in the tripping delay in the course of several circuits and to calculate the tripping delay to be expected with the greatest possible probability by extrapolation of the stored measured values.

The release magnet 41 can be both a shunt release and an undervoltage release. Since undervoltage releases operate on the principle of the holding magnet, a higher response speed can generally be achieved than with a shunt release. However, it depends on the given interaction between the release magnet and the switching mechanism whether one or the other type of magnet is more suitable.

FIG. 6 shows a block diagram of the program sequence as it is carried out using a real-time microprocessor. The functional sequence is immediately apparent from the inscription on the blocks. However, it should be mentioned that, on the basis of the signals transmitted by the current transformers, a threshold value element Iu is first used to determine whether a very small current is present or whether it is below a certain low limit. The functional sequence for this case is labeled "A" in the block diagram. In the event that the measured current lies above a certain limit value (threshold element Io), which can be assigned to a short circuit, the triggering takes place without delay in accordance with the functional sequence designated by B. For the currents lying between these limit values, the time at which the tripping command is passed on to the tripping magnet is calculated in the manner already described.

As already mentioned in the introduction, the so-called opening window for surge-free shutdowns in three-phase networks is very narrow. However, if the option is used not to have the poles of a circuit breaker opened simultaneously, as is usually the case for mechanical reasons, but instead staggered or offset, the opening window can be widened to approximately 8.5 msec. Accordingly, the requirements for the accuracy of the mechanical control and the electronic detection of changes in the release delay are alleviated. The method of offset switching is known per se (DE-C-28 54 092).

Claims (11)

1. A method of operating a circuit breaker, in particular a vacuum switch (2), using a trigger control unit (4) which, regardless of the time of a command to switch off, causes the opening of the switching elements (31) at a time related to the zero crossing of the current , characterized in that a measured value of the tripping delay of the circuit breaker is supplied to the tripping control device (4) as a correction variable from the time of the release of the tripping signal until the time of the disconnection of the contact pieces in a previous disconnection. 2. Circuit breaker for the method according to claim 1, characterized in that the circuit breaker (2) for determining the tripping delay is assigned an evaluation device (16; 22; 33) which can be set in motion by the receipt of a tripping signal and when the contact pieces are separated (31) can be stopped and that a storage device (10) is provided for storing the measured value of the tripping delay at least until the next switch-off process. 3. Circuit breaker according to claim 2, characterized in that the evaluation device (22) contains a circuit arrangement for detecting the occurrence of an arc voltage between the contact pieces (31). 4. Circuit breaker according to claim 2, characterized in that the evaluation device (16) for detecting the contact opening contains a circuit arrangement for measuring the capacitance between the contact pieces (31). 5. Circuit breaker according to claim 2, characterized in that a device (33) for detecting a relative movement of the contact pieces is provided for determining the time of separation of the contact pieces (31). 6. Circuit breaker according to claim 5, characterized in that a drive member (30) connected directly to a movable contact piece (31) is provided with a reflector and an optical waveguide (32) is fixedly mounted opposite it at a short distance, which is remote from the reflector End cooperates with a light source and a receiving circuit for reflected light (33). 7. The method according to any one of the preceding claims, characterized in that the trigger control device (4) as a further correction variable, the temperature (sensor 44) of the drive device of the circuit breaker (2) is supplied. 8. The method according to any one of the preceding claims, characterized in that the trigger control unit (4) as a further correction quantity, the time elapsed since the last switching operation (timer 47) is supplied. 9. The method according to any one of the preceding claims, characterized in that the trigger control device (4), the supply voltage (voltage sensor 45) of a trigger magnet (41) of the circuit breaker (2) is supplied to obtain a further correction variable. 10. The method according to any one of the preceding claims, characterized in that the trigger control device (4), the temperature of the winding of a trigger magnet (41) for obtaining a further correction variable is supplied (temperature sensor 46). 11. Tripping control device for the method according to one of the preceding claims, characterized in that a real-time microprocessor (P) is acted upon by input signals corresponding to one or more correction variables and provides a delayed trigger signal for the circuit breaker by comparison with measured values or standard values taken from a memory that threshold elements (Iu; Io) detect an undershoot of a lower limit of the current and an overshoot of an upper limit of the current and cause an instantaneous tripping.

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