KR100878726B1 - Electronic trip device comprising a capacitor for supply of a trip coil - Google Patents

Abstract

The trip device includes a system drive power supply circuit having a trip coil capacitor. When operating the trip device, at the time t ₁ -t ₂ , the capacitor charges and, if necessary, the voltage V ₁ is adjusted according to a first reference voltage (19 volts) sufficient to activate the trip coil. After the preset period T, at the time t ₂ -t ₃ , the voltage adjustment at the capacitor terminal is performed according to the second reference voltage (10 volts) smaller than the first reference voltage. At the time t ₃ when the measured current reaches a preset threshold which constitutes an indication of the presence of the fault to be tripped, the reference voltage returns to the first value during the same preset period. Thus, in general, since the capacitor is charged at a voltage lower than necessary for the tripping, the size of the capacitor can be reduced.

Trip coil, tripping device

Description

ELECTRICAL TRIP DEVICE COMPRISING A CAPACITOR FOR SUPPLY OF A TRIP COIL

Other advantages and features will be described in detail through specific embodiments of the invention, which are created by way of non-limiting example and are shown in the accompanying drawings.

1 is a schematic view showing an electronic trip device according to the prior art.

2 is a view showing a power circuit of a trip device according to the prior art;

3 shows a specific embodiment of a trip device according to the invention.

FIG. 4 is a diagram showing the amount of change in voltage over time at the supply capacitor terminal and the amount of change in power signal of the trip device electronic circuit over time according to FIG.

FIG. 5 shows a specific embodiment of a flowchart of the operation of the trip device power supply circuit according to FIG. 3; FIG.

Explanation of symbols on the main parts of the drawings

1, 6 current sensor 2 electronic processing circuit

3, 9: electronic switch 4: trip coil

5 power supply 7 rectifier circuit

8: conductor 10: diode

11: adjusting circuit D: tripping signal

The invention comprises a power supply capacitor and means for adjusting the voltage at the capacitor terminal according to a preset reference voltage and connected to an electronic processing circuit designed to perform a protective function and comparing the measured current with one or more tripping thresholds. An electronic trip device comprising a current measuring means connected to a power supply circuit.

In general, in the conventional trip device, the trip coil is fed by the supply capacitor of the power supply circuit. In a system driven trip device, the supply capacitor is charged by a current sensor connected to the conductor of the power system to be protected. In general, the power supply circuit is a switching power supply type capable of adjusting the voltage at the supply capacitor terminal.

In general, in a conventional trip device, a first supply voltage of about 18 volts is required at a supply capacitor terminal in order to achieve reliable tripping by the trip coil. For example, from the voltage at the tripping capacitor terminal, a low second supply voltage of about 10 volts sufficient to supply the electronic circuit of the tripping device is diverged.

Since the lifetime of a capacitor is determined by the difference between the maximum voltage (nominal voltage) allowed by the capacitor and the actual operating voltage, the reliability of the tripping capacitor involves the use of a capacitor of sufficient size.

It is an object of the present invention to provide a tripping device which can maintain or increase the reliability of the tripping capacitor and at the same time reduce its size and cost.

According to the invention, the object is that the electronic processing circuit comprises means for comparing the measured current with a preset threshold which is less than the tripping threshold, and the preset when the trip device is operated or the measured current is above the preset threshold. The fact that the trip device comprises means for setting the reference voltage of the adjusting means to the first preset value during the period and to a second preset value smaller than the first preset value after the preset period.

According to the development of the present invention, the second reference voltage value is lower than the voltage required to activate the trip coil of the trip device.

1 shows an electronic trip device according to the prior art. In the drawings, only the elements necessary for understanding the present invention are shown. A current sensor 1 connected to the conductor of the power system to be protected supplies a signal representing the current flowing in the conductor to the electronic processing circuit 2. The electronic processing circuit 2 is preferably designed based on a microprocessor to perform a protective function, comparing the measured current with one or more tripping thresholds and tripping in case of a fault such as an overload or a short circuit. Supply the ping signal D. For example, the tripping signal D is applied to the control electrode of the electronic switch 3 composed of a thyristor. The closing of the electronic switch 3 by the tripping signal D causes excitation of the trip coil 4 connected in series with the electronic switch to the terminal of the first supply voltage V ₁ .

The power supply circuit 5 supplies the first supply voltage V ₁ . In the system driven trip device, the power supply circuit 5 is supplied by a current sensor connected to the conductor of the power system to be protected. The current sensor connected to the power supply circuit may be a current sensor 1 or, as shown in FIG. 1, a current sensor 6 different from the current sensor 1. In the latter case, the current sensor 1 is preferably an air sensor composed of, for example, a Rogowski coil, while the current sensor 6 is preferably an iron core sensor.

In addition, the power supply circuit 5 is lower than the first supply voltage and supplies a sufficient second supply voltage V ₂ to the power supply of the electronic circuit of the trip device.

In the related art, the power supply circuit 5 is a switching power supply type capable of adjusting the voltage at the terminals of the supply capacitor. In the specific embodiment shown in FIG. 2, the current sensor 1 or 6 preferably comprises two output terminals, one of which is grounded and the other of which is of a full-wave rectifier type connected to the conductor 8. It is connected to the rectifier circuit 7. An electronic switch 9 which performs the function of a chopper is connected in parallel to the output terminal of the rectifier circuit. The first output terminal of the power supply circuit 5 for supplying the first supply voltage V ₁ is connected in such a way that the output voltage of the rectifier circuit 7 is on when the output voltage of V ₁ or more is off and vice versa. It is connected to the conductor 8 via 10). The capacitor C is connected in parallel with the voltage divider between the first output terminal of the power supply circuit 5 and the ground. The voltage divider is a resistor divider consisting of a first resistor R ₁ and a second resistor R ₂ connected in series. The central point of the resistor divider is connected to the input of the adjusting circuit 11 which controls the electronic switch 9. The third resistor (R ₃ ) is connected in series with the capacitor (C) in series with the zener diode (Zd), and the common point of the third resistor (R ₃ ) and the zener diode (Zd) is the second supply voltage (V). A second output of the power supply circuit 5 that supplies ₂ ) is configured.

The voltage V ₃ at the center of the resistor divider represents the voltage V ₁ at the capacitor terminals. As long as the voltage V ₃ is lower than the preset reference voltage, the adjusting circuit 11 keeps the electronic switch 9 open (off in the case of a transistor). Therefore, the capacitor C is charged via the rectifier circuit 7 and the diode 10 from a current transformer. As soon as the voltage V ₃ reaches the reference voltage, the adjusting circuit 11 closes the electronic switch 9 (turns on in the case of a transistor), and short-circuits the output of the rectifying circuit. After that, the diode 10 is turned off and prevents the charging of the capacitor C from continuing. Thus, the first supply voltage V ₁ is adjusted to a preset reference voltage value. After that, the second supply voltage V ₂ is obtained at the terminal of the zener diode Zd.

In a conventional tripping device, a reference voltage is selected to ensure reliable tripping of the trip coil in the event of a failure. For example, if the voltage required for the tripping of the reliable trip coil 4 is about 18 volts, the reference voltage is fixed at 19 volts.

The trip device according to the invention shown in FIG. 3 differs from the trip device described above in that the adjusting circuit 11 has another input connected to another output of the electronic processing circuit 2 of the trip device. The electronic processing circuit 2 changes the reference voltage of the adjusting circuit 11 during the preset period during which the trip device is operated or the measured current I becomes equal to or more than the preset threshold value Is lower than the tripping threshold value. This results in a first preset value, and a second preset value that is lower than the first preset value after the preset period.

Next, the operation of the trip device according to the present invention will be described in more detail with reference to Figs. 4A, 4B and 5.

Initiating, ie when the trip device is activated, the voltage V ₁ at the terminal of capacitor C becomes zero. When the electronic switch 9 is opened, the capacitor starts to charge. The voltage V ₁ increases. At the time t1, as shown in Fig. 4A, the voltage reaches a sufficient value, for example, 8 volts, and is supplied to the electronic circuit of the trip device, more specifically the electronic processing circuit 2. The power supply signal A (FIG. 4A), which has been zero so far, has a value of 1 thereafter, and initializes the starting step F1 (FIG. 5) of the electronic processing circuit microprocessor. Thereafter, this circuit sets the? T value to zero in step F2 and the reference voltage Vref value to the first value in step F3. In the specific embodiment shown, the first reference voltage value is 19 volts. Under the control of the electronic processing circuit 2, during the preset period T, for example, 10 milliseconds to 100 milliseconds, the adjustment circuit 11 uses the first reference voltage value.

Thereafter, in step F4, the microprocessor checks whether the period T has elapsed (Δt = 1 s?). In this case, if the output of step F4 is YES, then in step F5, the microprocess changes the reference voltage Vref value to a second value lower than the first value. In the specific embodiment shown, the second reference voltage value is 10 volts. Under the control of the electronic processing circuit 2, the adjustment circuit 11 uses this second reference voltage value from the time t ₂ (t ₂ = t ₁ + T). After that, the capacitor C is discharged until the voltage at the capacitor terminal has a second reference value. This value is chosen to be sufficient to provide a reliable power source for the trip circuit's electronics, i.e., in the specific embodiment shown, it should be greater than 8 volts while being lower than the voltage required to ensure reliable operation of the trip coil. If the period T has not elapsed (the output of step F4 is not), before returning to step F4, the microprocessor proceeds to step F6 which increments the value of Δt (Δt = Δt + 1).

After step F5, when the reference voltage falls to the second lower value, by means of the measured current I (I ≥ Is?), The microprocess makes a possible operation of the preset threshold Is lower than the tripping threshold. Monitor (step F7). If the measured current is lower than this threshold (no output of step F7), the reference voltage does not change, and by returning to step F7, the microprocessor continues to monitor current generation.

If the current measured at time t ₃ reaches or exceeds the threshold Is (the output of step F7 is yes), the microprocessor returns to step F2. Thereafter, the reference voltage Vref returns to the first higher value, and the capacitor C recharges until it reaches this value. Overshooting of the threshold Is by the current indicates that the current exceeds the standard value, and indicates the likelihood of imminent detection of a failure for which tripping will be required. As an example, if In is the rated current of the trip device, the threshold Is may be 2 (In). If the electronic processing circuit 2 does not detect a fault during the period T subsequent to the time t ₃ , after this period, the reference voltage returns to the second value. On the other hand, if a failure is detected during this period, then, at the time t _{4 in} FIG. 4 (b), the tripping signal D is transmitted. After that, the trip coil 4 now correctly supplied by the just-charged capacitor C performs a current interruption in the power system to be protected. After that, the power supply circuit 5 is no longer supplied by the current sensor, and the capacitor is discharged. At time t ₅ , the voltage at the capacitor terminal is precisely insufficient to supply the electronics of the tripping device (A = 0). In the conventional method, during the period t4 to t5 following the tripping, the microprocessor takes measures to store some data.

In the embodiment of Fig. 5, specific values (19 volts and 10 volts) of the reference voltage are fixed during steps F3 and F5, after which the values are transmitted to the adjusting circuit 11. In another embodiment, two values that can be taken as the reference voltage Vref are preset in the adjustment circuit, and the microprocessor only transmits a binary signal representing the value to use to the adjustment circuit.

Therefore, the present invention can reduce the size and cost of the supply capacitor C of the trip coil 4 while ensuring reliable operation of the trip coil in the case of a failure. Since trips are relatively rare, for example, during a short period of 1 second, where the fault is prone to failure, i.e. during the tripping of the trip device, and only during the period when the measured current reaches the preset threshold Is, It is fully charged.

For example, a 22 μF capacitor with a maximum voltage of 35 volts can be replaced with a 22 μF capacitor with a maximum voltage of 25 volts. Since the difference between the maximum voltage and the operating voltage of the capacitor is reduced from 35 volts minus 19 volts, or 16 volts to 25 volts minus 10 volts, or 15 volts, the lifetime of the capacitor and Reliability is significantly maintained. In contrast, at constant capacitor size, a large increase in the lifetime and reliability of the capacitor can be achieved.

As described above, according to the electronic trip device of the present invention, the size and cost of the supply capacitor C of the trip coil 4 can be reduced, and a reliable trip coil operation can be ensured in case of failure.

Claims (5)

Designed to perform a protective function and connected to an electronic processing circuit (2) comparing the measured current with one or more tripping thresholds, the voltage at the capacitor terminals according to the power capacitor (C) and the preset reference voltage (Vref). An electronic trip device comprising current measuring means (1, 6) connected to a power supply circuit (5) comprising means (11) for adjusting the The electronic processing circuit 2 comprises means for comparing the measured current I with a preset threshold Is, which is lower than the tripping threshold, The reference voltage Vref of the adjusting means 11 is set to the first preset value during the preset period T when the trip device is operated or the measured current I is equal to or greater than the preset threshold Is. And means for setting to a second preset value that is less than the first preset value after the period of time. The method of claim 1, And the second reference voltage (Vref) is lower than the voltage required to activate the trip coil (4) of the trip device. The method according to claim 1 or 2, And said adjustment circuit (11) has an input connected to the output of said electronic processing circuit (2). The method according to claim 1 or 2, The preset period is an electronic trip device, characterized in that between 10 milliseconds and 100 milliseconds. The method according to claim 1 or 2, The power circuit (5) is a switching power supply.

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