RU2303272C1 - Method for indication of sparking of direct current machines - Google Patents

Abstract

FIELD: electric machines, namely direct current collector machines, possible use for evaluating sparking on collector of direct current machines.

SUBSTANCE: suggested method for evaluating sparking of direct current machines includes measuring current of commutated section, which is used to determine presence of sparking, while value and shape of current passing between separate parts of cut brush, mounted in brush holder clip, are recorded, after current signal is transformed by means of current transformer to the value comfortable for measurement.

EFFECT: simplified indication of sparking on collector of direct current electric machine with cut brushes, without preparation of electric machine structure.

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Description

The invention relates to electric machines, namely to DC collector machines, and can be used to evaluate sparking on a collector of DC machines.

A known method of indicating the sparking of DC collector machines [Karasev MF On the issue of setting up switching DC machines. Tomsk: Proceedings of TEMIIT, v.14, 1948]. The essence of the method is to oscillograph the voltage in the contact by connecting an electronic oscilloscope between the runaway and runaway edges of the brush. On the oscilloscope screen, voltage peaks corresponding to one collector revolution are distributed in a line and allow one to judge the distribution of sparking throughout the collector.

The disadvantage of this method is the difficulty of its implementation through the use of additional brushes.

A known method of indicating sparking [E. Arnold. DC Machines, t.1, M .: Gostekhizdat, 1931. - 498 p.]. To determine the current curve in the short-circuited section, one of the sections of the armature winding of the tested machine is cut and a small resistance is included in it, the ends of the resistance are connected to the oscilloscope loop via contact rings and brushes. With this connection, you can record with the help of an oscilloscope a potential difference curve between the contact rings or a current curve flowing in the section.

The disadvantage of this method is the complexity of its implementation and the need for preparation of the machine.

A known method of indicating the sparking of a DC machine [K.I. Schenfer. Dynamos and DC motors. - M .: - L .: Gosenergoizdat, 1934. - 384 p.], Selected as a prototype, namely, that they cut the winding of the armature of the tested machine in one place, connect the ends of the armature winding to two contact rings electrically connected to the fixed section, laid in the channels of the uncoiled armature, in the same channel there is a measuring wire connected to the oscilloscope, then when the DC machine is operating, the EMF curve induced in this wire by changing the current in the section is visible on the oscilloscope screen. The disadvantage of this method is the difficulty of measuring the current of the switched section and the need to prepare an electric machine.

The objective of the invention is to simplify the indication of sparking on the collector of an electric DC machine with split brushes without dissecting the design of the electric machine.

The problem is solved due to the fact that the method of indicating the sparking of DC machines, as well as in the prototype, consists in measuring the current of the switched section, which is used to judge the presence of sparking. According to the invention, the magnitude and shape of the current flowing between the individual parts of the split brush installed in the holder of the brush holder is recorded, after converting the current signal with a current transformer to a value convenient for measurement.

To achieve this, a split brush is used, which is a brush cut along so that the lead ends are each on its own half of the brush. When the individual parts of the brush are isolated from each other, then currents flowing through them differ in the amount of current i _k . A change in the magnitude of this current during switching leads to a change in current densities under the edges of the brush. The excess of this current of some acceptable value, according to the energy theory of switching [A.E. Alekseev. Traction electric machines and converters. - L .: Energy, 1967. - P.225.], And leads to the appearance of sparking, therefore, the registration of this current can serve as an estimate of the magnitude of the sparking. It is known [A.B. Ioffe. Traction electric cars. - L .: Energy, 1965. - 232 S.] that the intensity of sparking of the brushes is determined by the power released under a unit length of the brush per unit time

where L _ú - brush length (mm);

t _k - collector division;

ϑ _k - collector peripheral speed (rad / s);

L _c - section inductance (H);

i _k is the transverse current of the split brush (A);

ΔР - power (W).

Figure 1 shows a schematic diagram of the inclusion and operation of the spark sensor.

Figure 2 - waveform of the transverse current of a split brush (dark switching).

Figure 3 - waveform of the transverse current of a split brush (degree of sparking 3 points).

Figure 4 is a characteristic of the dependence of the signal at the output of the current transformer Uu and spark arches.

The circuit implementing the invention (Fig. 1) consists of a direct current motor, a collector 1 and contact brushes 2, a split brush 3, which is made on the basis of a standard motor brush, previously cut into two identical parts along, to which a current transformer 4 is connected, the outputs of which are connected to the oscilloscope 5, a voltmeter 6 is connected in parallel with the oscilloscope.

When the engine is running on the collector 1, currents flow, which are removed using a contact brush 2 and a cut contact brush 3, from which a signal is fed to measuring equipment 5 and 6 through a current transformer.

A series of experiments was carried out with oscillography of the current value of one of the split brushes. The oscillograms corresponding to the dark switching (Fig. 2) were obtained (the degree of sparking is less than 1 point, the signal at the output of the current transformer Uu = 99 mV), and various degrees of arcing at the collector (Fig. 3) (the degree of sparking is 3 points, the signal is at the transformer output current Uu = 900 mV).

Analysis of these waveforms allows you to judge the degree of sparking on the reservoir without visual observation of the spark. The spark rate was determined by the magnitude of the signal from the output of the current transformer 4 recorded by voltmeter 6. To analyze the relationship between the spark rate and the signal at the output of the current transformer 4, the characteristic shown in Fig. 4 is constructed. There is a direct relationship between the change in voltage at the output of the current transformer and the magnitude of the sparking.

Claims (1)

A method for evaluating the sparking of DC machines, which consists in measuring the current of the switched section, by which it is judged that there is sparking, characterized in that the magnitude and shape of the current flowing between the individual parts of the split brush installed in the holder of the brush holder are recorded, previously converting the current signal using a transformer current to a value convenient for measurement.

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