SU1661895A1 - Dc mains short protection - Google Patents

Abstract

The invention relates to electrical engineering and can be used to protect DC power grids from short circuits. The aim of the invention is to increase the sensitivity and reduce the number of false positives. The device contains a current derivative sensor, a starting element, an integrator, three comparators, two prohibition elements, a time element, the inputs of the integrator, the starting body and the second comparator are connected to the output of the current derivative sensor, the inputs of the first and third comparators are connected to the output of the time element between the output of the second comparator and the input of the second prohibition element, the output of the second prohibition element is connected to the prohibition input of the first prohibition element. Due to this, the detuning from the increments of load currents is increased, the possibility of failure in operation in the rc. Mode is removed. 1 hp f-ly, 2 ill.

Description

The invention relates to the field of electrical engineering and can be applied to protect DC networks from short-circuit currents.

The purpose of the invention is to increase the sensitivity and reduce the number of false positives.

FIG. 1 is a schematic of a device for protecting a direct current network; in fig. 2 - timing charts showing the operation of the device.

The device for protecting the DC network contains a sensor 1 of the derivative of current, a trigger 2, an integrator 3, the first 4, the second 5 and the third 6 comparators, the first 7 and the second 8 prohibition elements, a time element 9, the output of the sensor 1 of the derivative of the current is connected to the inputs of the starting body 2, the integrator 3 and the second comparator 5, the output of the integrator 3 is connected to

the input of the first 4 and third 6 Comparators, the output of the second comparator 5 is connected to the input of time element 9, the output of the latter is connected to the input of the second prohibition element, the output of the starting element is connected to the input of the first prohibition element, the output of the second prohibition element is connected to the prohibition input of the first prohibition element, the third comparator input is connected to the integrator output, the third comparator output is connected to the prohibition input of the second prohibition element, the output of the first prohibition element is connected to the integrator control input.

In addition, time relays 10, element 11 can be entered into the device, the time relay input 10 is connected to the integrator control input 3, time 10 relay output is connected to the first input of element 11, the output of the first comparator 4 is O5

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keys to the second input of the logic element AI.

The device works as follows.

In the load mode, which can be characterized by the superposition of two adjacent current increments, the current change is shown by curve 12 to the left (Fig. 2). The derivative of this current is shown by curve 13. It is represented by two exponents superimposed on one another. The trigger level of trigger 2 is shown direct K2. It allows you to determine the change in current at which the integrator should work in the case of c. The output of the trigger is represented by curve 14. The response threshold of the second comparator 5 is shown direct K5. Its output signal is represented by curve 15. Time element 9 is a duration limiter, it produces a short signal 16, each time the second comparator 5 is triggered. Since in this case the input signal of the second prohibition element 8 is zero, i.e. the prohibition from the third comparator 6 is absent, the signal at the output of block 8 (curve 17) repeats the signal at the output of time 9. This signal enters the prohibition input of the first prohibition element 7, its output signal (curve 18) is briefly interrupted. The integrator 3 performs integration only when there is a signal at its control input. In the absence of a signal (zero level) the integrator is reset. Interrupting the signal at the control input of the integrator each time the second comparator is triggered results in a reset of the accumulated value of the previous current increment, which allows for a detuning from the previous load increments. The increments selected by the integrator are represented by curve 19, and curve 20 is the output protection signal. The maximum value of them is less than the trigger threshold of the first comparator; it is represented by 1 kb.

In the mode shown in FIG. 2 on the right, the current increases in one large jump (curve 12), however, at the end of the current rise, the solar field will rise. an increment of load current appears. This can happen because a. H. is considered with a minimum current, i.e., located at a remote point from the feeder to be protected, and the load can be applied near the feeder, with a remote control station. the voltage near the feeder decreases slightly and rolling stock can start. In such a rare case of coincidence, there is a risk of a failure of protection in the presence of a short-circuit. Since repeated operation of the second comparator can lead to the reset of the integrator. To avoid this, the reset signal generated by the time element 9 is blocked when a third signal is triggered.

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Parator 6, the threshold of which is triggered (forward KB) is lower than the threshold of the first comparator (curve K4). Due to this, the signal arriving at the control input of the integrator is not interrupted; the integration continues until the end of the current change, which is determined by the triggering organ. When the integrator output signal exceeds the threshold of operation of the first comparator, a signal appears at its output (curve 18), which serves as a command for the feeder switch-off unit (not shown). Thus, each increment of the load current is analyzed separately, without being summed up with each other, which ensures a reduction in the number of false positives of protection. Neighborhood load increments and to. H. does not affect the detection of c. h. mode. and warns of failures in work.

A further increase in sensitivity is obtained by adding a time relay device and an AND gate connected so that the time relay input is connected to the integrator control input, the time relay output is connected to the first input of the AND gate, the output of the first comparator is connected to the second input of the logic element I. The time relay with this connection determines the duration of the current rise. Due to this, the increments of the load current and the short-circuit current are different, even if they are close to each other in magnitude. The larger increments of the load current through the feeder can be formed only when the locomotive is close to the feeder, since with a two-way powering of the feeder zone only in this case almost the entire load current falls on the feeder to be protected. And in this case, the inductance of the traction network will be small due to its short length and the current will increase faster than the current of the remote to. Therefore, in the specified load mode, although the first comparator works, but the time relay does not work yet, and there will be no signal at the output of the logic element. The output of this logic element is used as the output of the protection device.

The setting of the comparator of the starting organ 2 is chosen relatively small, so that it is possible to isolate almost all the current increments at K. h. In addition to the comparator, the start block 2 may have a signal loss delay block connected in series with it, which allows to increase the detuning from the harmonics in the output signal of the sensor 1. Then the input of the trigger is the comparator input and the output of the trigger organ is the output of the delay block signal failure. The triggering organ can, for example, include a serially connected comparator and a one-shot, with a one-shot output, and thus will determine the current increment over a fixed time or have a different construction, it is only important that it determine the current increment in terms of the current derivative.

The setpoint of the second comparator is chosen higher than the setpoint of the starting organ comparator so that by the time the second current increment starts, the value of the derivative of the current of the first current increment falls below the setpoint of the second comparator.

The minimum pulse duration of the time element 9 must ensure that the integrator resets to zero, for this is enough fractions of a millisecond, for a time of the order of a few milliseconds, the device additionally receives a detuning from fast increments of load currents, since it does not take into account the initial part of the current increment, and it does the same time from the beginning of the increments is greater for the specified increments of the load currents than for the increments of the currents removed. Therefore, it is advisable to choose the pulse duration from the condition of additional detuning from increments of load currents.

The setting of the third comparator is selected in connection with the threshold value of the second comparator, namely, during the time the derivative of the current reaches the threshold level of the second comparator, the current increment selected by the integrator must exceed the threshold of the third comparator. Since the magnitude of the current increment and the initial derivative of the short circuit current is known in advance, the response threshold is easy to determine.

The application of the proposed device permits the adjustment of inrush currents, thereby increasing the sensitivity of the protection of the direct-current traction network, and increasing the overall reliability of the power supply system.

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In those cases when the imposition of a launch on the mode K. h. not dangerous, the third comparator and the second prohibition element may be missing, and the output of time element 9 is directly connected to the prohibition input of the first prohibition element.

Claims (2)

1. Device for protection against short circuits of a direct-current network containing a sensor of a derivative of a current, a triggering organ, an integrator, the first and second comparators, the first prohibition element, the output of the sensor of the derivative of current being connected to the inputs of the triggering organ, the second comparator and an integrator, the output of the integrator connected to the input of the first comparator; the output of the triggering organ is connected to the input of the first inhibit element, characterized in that, in order to increase the sensitivity and reduce the number of false alarms, a third computer is introduced arator, second prohibition element, first time element, the output of the second comparator is connected to the input of the first time element, the output of the last one is connected to the input of the second prohibition element, the output of the second prohibition element is connected to the prohibition input of the first prohibition element, the third comparator input is connected to the integrator output, the output of the third comparator is connected to the prohibition input of the second prohibition element, the output of the first prohibition element is connected to the control input of the integrator. 2. The device according to claim 1, characterized in that a second time relay and an AND element are entered into it, the second time relay input is connected to the integrator control input, the second time relay output is connected to the first input of the And element, the first comparator output is connected to the second input element I. // one 1 1B P P 17 P P 18 c  HX1 Mode nagruemRezhim. snowball FIG. Z //