SU845189A1 - Device for measuring the time of burning electric arc on switching apparatus contracts - Google Patents

Description

(54) DEVICE FOR MEASURING THE TIME OF COMBUSTION OF THE ELECTRIC ARC ON THE CONTACTS OF THE COMMUTATION

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The invention relates to a group of devices used to register the duration of an electric arc at the contacts of a switching device. The need to record the duration of the arc arises when testing the device for switching capacity or electrical resistance. When testing electrical equipment for electrical durability, a large number of similar measurements are required — current, voltage, arc duration, etc. The measurement results are processed by statistical methods to determine the average value of the parameter. In this case, devices are needed that allow fast and accurate measurement of the arc duration at the contacts of the switching device.

A device is known in which indirect measurement methods are based on recording as a function of the arc current time and voltage at the contacts of the electrical apparatus 1. The recording is performed using an electromechanical oscilloscope with an electromechanical scan or storage oscilloscopes. In case of using an oscilloscope it is possible to charge

writing of arc current and arc voltage with a scan of 2 or more ms / cm. Accuracy of measurements depends on sweep time and accuracy of waveform interpretation. When testing for electrical durability, where a large number of experiments are required to be carried out across the full scale of nominal currents, for example, at least 3 experiments at each current value, the indirect methods are very laborious. After each experiment, it is necessary to process the oscillograms, then from them, knowing the sweep time, determine the time of the arc arc duration. The burning time is determined by the coincidence of the arc current and the voltage drop across the arc. Then, the following experiment is carried out, etc. Thus, a device is needed that gives the necessary information in direct form after every experience.

Devices are known for recording time intervals between two processes or the time of coincidence of two or more processes 2. In the event of a coincidence

30 in time of the arc current and the voltage drop across the arc, the arc burning time starts counting; if any of the current or voltage parameters disappears, the counting stops. For these measurements, industrial frequency meters can be used, for example, of the type F571, etc. But to start them, you need to have square pulses, in order to form them from the current and arc voltage, special transducers are needed. A device for automatically measuring the arc time at the contacts of a switching apparatus, comprising a first sensor for detecting the start of arc, a second sensor for detecting the end of arc burning, and a measuring circuit, is known. A voltage divider having a galvanic connection to the power circuit is used as the first sensor. and as an end-of-arc sensor, there is a switch on the reed switch 3. When the contacts of the apparatus open, and when an arc arises, the voltage rise is detected by the first sensor issuing output pulse counting time integrator start time. The time counting stops when the switch on the reed switch is operated, which occurs when the current approaches zero. This device has several disadvantages. The arc start sensors — a voltage divider — has a galvanic connection to the power circuit. When testing low-voltage switching devices according to the test conditions, the power circuit is not grounded, i.e., its potential is not determined with respect to the measuring device. This is the cause of the false positive of the counting device. When testing three-phase switching devices, the presence of three sensors, galvanically connected to each phase of the power circuit, practically makes such a device inapplicable due to the large number of false operations. When switching from one current limit to another, such a device requires additional tuning along the voltage channel at the response threshold, which reduces the manufacturability of the measurement. Indeed, when the current changes, the voltage drop on the closed contacts changes, and if the voltage channel is not adjusted, then as the current increases, the device will falsely operate, and if the current decreases, an error (negative) will occur due to the delay of the trigger signal on this channel. The use of a switch on a reed switch as an end-of-arc sensor also introduces a similar error, since the moment of actuation of the reed switch depends on the current steepness in the circuit. In addition, the own response time of the reed switch introduces its own error. True, this error is somewhat compensated by the one way of closing the contacts of the reed switch until the magnetic field disappears, but this compensation is uncertain. In some cases, for example, when extinguishing with a current cut, this compensation will not be at all. When the arc in the apparatus burns for several half-periods, when the current passes through zero values, the switch on the reed switch will do pecks, stop the counting of time, with an increase in the number of half-periods, the error in the count will increase. The aim of the invention is to increase the measurement accuracy and simplify the measurement of the duration of the arc. This is achieved by the fact that in a known gauge containing a first sensor for detecting the start of an arc; the second sensor for determining the end of the arc and measuring circuit through additionally introduced series-connected limiting amplifier and a second module allocation circuit to the second input of said circuit AND whose output is connected to the device for counting time eni When measured in AC circuits, the current sensor is made in the form of an air current transformer. This sensor is used to tune out high-frequency interference induced by unauthorized sources of current flow through the presence of a half arc and current. The presence of signals at both inputs of the circuit AND a countdown is made. At the time of the current flow in the test circuit, the switching is not performed and the lags are not very reliable. An induction sensor is placed in the area of the magnetic field of the arc that induces a voltage in it. This voltage is composed of two components. The first of them are formed by fields of conductors, through which currents of industrial frequency flow, fields of scattering of transformers, motors, generators, etc., pickup signals; the magnetic field of the arc in the sensor area due to different phenomena in the arc when the contacts diverge: fast, chaotic, movements of the arc trunk, formation of branches of fools of their structure, etc. This component has terms from tens of kilohertz ultiple megahertz. Its presence is characteristic of arc burning. The drawing shows a block diagram of the meter duration of the arc. The contacts of the test switch 1 are connected in series with the measuring shunt 2, which is a current sensor. In the zone of alternating magnetic field

an electric arc arising from the opening of the contacts of switch 1, an induction sensor 3 is installed. When installing the sensor, care must be taken that it is not shielded from the floor of the arc by electrically conductive parts of the switch and other structures. The induction sensor 3 is connected to the filter 4, which is necessary for detuning, the output of the filter is connected to the input of the first amplifier-limiter 5, the output of which is connected to the first input of the circuit AND through the module allocation circuit 6. The current channel sensor is made in the form of a shunt 2 when measuring on a direct current, or in the form of a current transformer when measuring on an alternating current. The sensor is connected to the limiting amplifier 7, the output of which is connected to the second input of the circuit I via the second allocation circuit 8 of the module I. The output of the circuit I is connected to the time counting device 9.

The device works as follows.

The signal from sensor 3, which contains a wide frequency spectrum, is filtered through filter 4, which cuts low-frequency components from the signal, induced by industrial frequency currents, is amplified and limited by amplifier-limiter 5. The signal from the output of amplifier-limiter is bipolar, limited by steep edges, arrives at the input of the module allocation circuit 6, where a rectangular unipolar pulse is formed from it with a steep front and a slope equal in the duration of the arc time. This pulse arrives at the first input of the circuit I. A signal from a current sensor, proportional to the current in the circuit, is fed to the input of the second limiting amplifier, where it is amplified and limited, and a two-polar limited signal is fed to the second selection circuit of the module, where it is formed from A square rectangular pulse with a steep front and a drop equal to the duration of the current flowing through the circuit. This pulse is applied to the second input of circuit I. If two rectangular pulses coincide in the first and second channels of the meter, at the output of the circuit I, a rectangular signal appears, the duration of which is equal to the duration of the arc at the contacts of the apparatus. The duration of this pulse is recorded by the device 9 of the counting time.

Claims (3)

1. A device for measuring the arc time at the contacts of a switching apparatus, comprising a first sensor for detecting the start of arc, a second sensor for determining the end of arc burning, and a measuring circuit, characterized in that, in order to improve the accuracy and simplify the measurement technology, the first sensor made in the form of an induction coil, the output of which is connected to an additionally introduced series-connected filter, the first amplifier-limiter, the first allocation circuit of the module, and the second Occupancy is configured and connected to a current introduced additionally and successively switched to the second amplifier-limiter circuit and a second extracting unit, wherein the isolation circuit outputs are connected to inputs modulation scheme I. 2. The device according to claim 1, characterized in that, in order to increase safety when measured in alternating current circuits, the current sensor is made in the form of an air current transformer. Sources of information taken into account in the examination 1. Magnetoelectric oscilloscope type H 115. 2. Industrial frequency meter type F571. 3. USSR author's certificate number 654970, cl. H 01 H 9/50, 1977.