RU71822U1 - DEVICE FOR CONTROL OF BRUSH CURRENT BRUSH-CONTACT DEVICE OF SYNCHRONOUS GENERATOR - Google Patents

Abstract

The utility model relates to current-measuring devices for controlling current distribution between brushes of brush-contact devices of synchronous devices during their maintenance and adjustment. The technical result of the device is the possibility of reliable measurement of the average current of each brush, as well as numerically assess the degree of its stability, that is, its difference from constant, as well as the possibility of using the left hand more ergonomically, which is convenient for left-handed people. A device for monitoring brush current, comprising a current measuring head in the form of a composite magnetic circuit with a Hall sensor, an opening mechanism, an analog-to-digital converter, a microcontroller and / or processor, indication means, control keys, characterized in that it contains a controlled clock generator whose function is to generate synchronizing pulses with a frequency equal to the rotational speed of the rotor of the synchronous generator, also contains an adder, summing the recorded signals in the period between synchronize pulses, and the opening mechanism is made in the form of a magnetic circuit and is removed from the control keys to a distance of at least 200 mm, with the possibility of rotation around the longitudinal axis of the device.

Description

Application area

The utility model relates to current-measuring devices for monitoring the current distribution between brushes of brush-contact devices of synchronous devices during their maintenance and adjustment.

State of the art

The brush-contact device of synchronous generators provides direct current from the stationary current-carrying parts of the excitation circuit to the rotating excitation winding of the generator rotor by means of a sliding contact. The fixed part of the apparatus includes a traverse with brush holders and brushes installed on it.

It is assumed that the brushes connected in parallel operate as linear resistive elements, and therefore the current of any brush of the contact device is constant and repeats the shape of the total current of the rotor. For this reason, DC clamps are used to control the brush current.

Oscillography of the current of the brushes operating as part of the brush-contact device of the synchronous generator indicates that the current is unstable, clearly pronounced pulsed character. An example of a waveform of the brush current is shown in FIG.

Such a current cannot be called constant even in the first approximation. The current is a sequence of random pulses of the same polarity of different amplitude and duration. For this reason, measuring the current of brushes using any industrial manufactured DC clamp produces unstable and unreliable results.

The method of measuring current by such devices is the analog-to-digital conversion of the instantaneous value of a signal obtained after amplification of the primary signal of a magnetically sensitive element located in the gap of an open magnetic circuit. The measurement of the average value of a random signal is largely determined by the averaging period and the number of measurements taken during the averaging period.

Strictly speaking, based on the elementary definition of the current value as a quantity

electricity passing through the conductor in 1 second, the measurement of the pulse current should be reduced to the integration of pulses for a period of 1 s. There are two ways to integrate brush current pulses and, accordingly, two main methods for measuring brush current of a brush-contact device: analog and digital.

The analog measurement method consists in integrating the signal with an analog adder, followed by analog-to-digital conversion of the resulting signal. The measurement accuracy in this way depends on the spectral composition of the pulses making up the measured signal and the integrator time constant. In addition, with this measurement method, the ability to determine the degree of stability of the brush current is completely lost.

The second method, digital, is the rapid analog-to-digital conversion of the signal directly received from the primary converter. This method is implemented in most digital DC ticks.

Due to the misconception that the current of a separate brush of a brush-contact device of a synchronous generator is constant, no special methods for measuring it were developed, but the methods implemented in standard measuring instruments for direct current were used.

Digital integration of a signal formed by a sequence of pulses of different durations and amplitudes should be carried out according to the formula:

where n1 is the number of measurements in 1 second, i _k is the current measured digital current value.

Synchronous generators are characterized by a stable rotor speed.

This fact is one of the reasons that random processes in the sliding contact, which are the cause of the formation of an unstable pulse current of each brush, are repeated on each revolution of the generator rotor. The waveform (see Figure 1) of the brush current of the brush-contact device operating at a rotation speed of 3000 rpm (50 Hz) shows a signal repetition period of exactly 20 ms. Since the rotor makes exactly 50 revolutions in 1 second, the digital integration of the signal in 1 second does not significantly increase the accuracy compared to the integration in 1 revolution.

At the same time, the rotational speed of the rotors of synchronous hydrogenerators, depending on the design, can be from 46.9 to 1500 rpm (see Electrical Manual

machines, In two volumes, Under the general editorship of Doctor of Technical Sciences I.P. Kopylova and Ph.D. B.K. Klokova, M. "ENERGOATOMIZDAT" 1988.) i.e. for some designs of hydrogenerators, the rotor makes less than one revolution in 1 second. Thus, in some cases, the integration of the signal in 1 second or a multiple period can give incorrect results.

For this reason, when measuring the brush current of the brush-contact apparatus of any synchronous generator digitally, the integration period should be set as equal to or a multiple of the total revolution of the generator rotor.

The prior art device for monitoring the current distribution of the brush-contact apparatus of an electric machine [Patent RU 2157033], consisting of a current head in the form of a composite magnetic circuit with a Hall sensor, a disconnecting mechanism, a microcontroller based on a processor, alphanumeric indicator, characterized in that the magnetic circuit is made in in the form of a ring with an external diameter of not more than 30 mm, with an internal diameter of at least 15 mm, sawn along radii -60, -90, 150 °, the sector between radii -90 and 150 ° is a contactor, A -60 ° Hall sensor is located, the magnetic circuit is located at a distance of at least 200 mm from the drive button of the disconnecting mechanism, a non-volatile memory chip is introduced into the device, and the alphanumeric indicator is made two-line.

This device is selected as the closest equivalent.

The device is a digital current clamp meter DC.

The device consists of a current-measuring head in the form of a composite magnetic circuit with a Hall sensor, a disconnecting mechanism, a microcontroller based on a processor, an alphanumeric indicator. Distinctive features of the device are the geometric dimensions of the magnetic circuit to be opened, the distance of the magnetic circuit to be opened from the drive button of the opening mechanism (at least 200 mm), as well as the presence of a non-volatile memory chip and a two-line alphanumeric display in the device circuit.

The location of the magnetic circuit at a distance of at least 200 mm from the operator’s hand provides the ability to control hard-to-reach brushes. The volume of non-volatile memory 8K provides a record of the current distribution of brush-contact devices of 15 large electrical machines with a maximum number of brushes at each pole - 256. The disadvantages of the device include the fact that the device measures instant

the value of direct current, which can significantly differ from the average value, which reduces the accuracy of estimating the current load of a particular brush, the device does not allow to evaluate the stability of the brush current, the device is focused exclusively on “right-handed” people (left-handed people are not comfortable working with it).

The technical result of the device is the possibility of reliable measurement of the average current of each brush, as well as numerically assess the degree of its stability, that is, its difference from constant, as well as the possibility of using the left hand more ergonomically, which is convenient for left-handed people.

Brief Description of the Drawings

Figure 1 shows an example of a waveform of the brush current (Brush current is 30 A) - measurement by conventional methods.

Figure 2 shows a diagram of the device, where 1 is a conductor with current, 2 is the fixed part of the measuring magnetic circuit, 3 is the closure, the movable part of the measuring magnetic circuit, 4 is a magnetically sensitive Hall sensor, 5 is the drive rod of the opening mechanism, 6 is a longitudinal rod, 7 - collet clamp, 8 - case, 9 - button for the drive of the disconnecting mechanism, 10 - indicator, 11 - measuring head in a 180 ° position.

Figure 3 shows the electrical block diagram of the device, where 1 is a conductor with current, 2, 3 is a measuring composite magnetic circuit, 4 is a Hall sensor, 12 is a battery, 13 is an indicator, 14 is a keyboard, 15 is a current regulator of a Hall sensor , 16 - An analog-to-digital converter, 17 - a processor, 18 - a serial input / output port, 19 - non-volatile memory, 20 - a voltage reference source, 21 - voltage converters, 22 - a power source, 23 - an adder, 24 - a clock crystal oscillator pulses.

Device essence

The reliability and accuracy of digital measurements based on the integration of the input signal, largely depends on the sampling frequency of digital measurements. The higher the sampling rate, the more reliable the signal is measured, the more accurate the measurement. When measuring the brush current of the brush-contact device of the synchronous generator, it is necessary to provide

reliable consecutive overlapping of the circumference of the contact ring by the sliding surface of the brush in one full revolution of the rotor.

If the diameter of the slip ring is D _K , the circumference is πD _K. If the brush size in the direction of rotation is a, then the complete overlap of the circle occurs when consecutive measurement. If the number of measurements is less than the specified number, then there is the possibility of missing a short pulse of large amplitude, which reduces the accuracy of integrating the complete signal in one revolution. To ensure reliable measurements, it is necessary to provide double overlap, which means that during the passage of the brush’s sliding surface, a distance equal to its length in the sliding direction, two measurements are necessary.

Based on the foregoing, the minimum sampling frequency F _D when measuring the brush current of the brush-contact apparatus of a synchronous generator by a digital method should be

where

f _P is the rotational speed of the rotor of the synchronous generator,

D _K - diameter of the slip ring,

a - brush size in the direction of rotation (tangentially) of the contact ring.

When measuring the brush current of a brush-contact device of a synchronous generator, it is necessary to know the degree of stability of the electrical sliding contact, i.e. numerically evaluate how much the brush current differs from the constant, average brush current. To do this, it is advisable to use the statistical parameter "average deviation", which is a measure of the spread of the data set. This parameter is calculated by the formula:

where

n is the number of measurements

- average value of the data array

The operation of the claimed device is based on the fact that determine the time of the averaging period, a multiple of one revolution of the shaft of the rotor of the generator, and the minimum sampling frequency is determined from the formula:

where

f _P is the rotational speed of the rotor of the synchronous generator,

D _K is the diameter of the slip ring,

a is the size of the brush in the direction of rotation (tangentially) of the contact ring;

then summation of all values is carried out, the resulting amount is divided by the total number of measurements, then the difference between the obtained average value and each measurement is found, the absolute values of the difference between the average value and each value are summed, and the resulting amount is divided by the number of measurements. As a result of this method of measuring current in the device, the value of the brush current and the average deviation characterizing the stability of the current in the sliding contact of a particular brush are obtained.

The claimed technical result is achieved due to the fact that in the device for monitoring the brush current containing a current head in the form of a composite magnetic circuit with a Hall sensor, a disconnecting mechanism, an analog-to-digital converter, a microcontroller and / or processor, an indication means, control keys, the difference is that it contains a controlled clock, the function of which is the formation of synchronizing pulses with a frequency equal to the rotational speed of the rotor of the synchronous generator, also contains an adder that sums the signals recorded in the period between pulses sihroniziruyuschimi and disconnection mechanism designed as a yoke and submitted from the control keys by a distance not less than 200 mm, rotatably around the longitudinal axis of the device.

The magnetic circuit is placed on a longitudinal rod, the function of which is the ability to rotate the magnetic circuit breakable around the longitudinal axis, while the drive drive of the disconnecting mechanism passes along the axis of the rod. This allows you to more ergonomically rotate the magnetic circuit breaker, as well as use your left hand, which is convenient for lefties.

The magnetic core is made of ferromagnetic material.

The device operates as follows. Around the conductor with current (1) (see Figure 2), the value of which is to be determined, an annular magnetic field is created. The magnetic field is concentrated in the magnetic circuit (2, 3), made of a ferromagnetic material, which has a great value of magnetic permeability.

The magnetosensitive element (4) based on the Hall sensor generates an electrical signal, which is fed to an analog-to-digital converter (16) (see Figure 3). The power supply of the entire electrical circuit is carried out from the battery (12) (battery or battery). To reduce the mutual influence of the individual elements of the digital circuit, their power is supplied through a stabilizer (15), which is a galvanically isolated high-frequency DC-DC converter (DC-DC converter). For accurate digital measurement of the signal level, a highly stable reference voltage source (20) is used, which allows numerically assessing the degree of current stability. The measured signals are digitally transmitted to the adder (23) and processor (17), in which the calculated quantities are calculated. The operation of the entire digital circuit is synchronized by a crystal oscillator (24). The controlled clock generator (24) generates pulses with a frequency equal to the rotational speed of the rotor shaft of the synchronous generator. Clock pulses limit the operating time of the adder (23) and determine the number of signals used to calculate the average current and average deviation. The result of the calculation is reflected in the indicator (13). To transfer information to external devices, a serial input-output port (18) is used.

The ability to reliably measure the average current of each brush is ensured by establishing a sampling frequency that guarantees guaranteed measurement of the instantaneous value of the brush current at any contact point of the sliding path, and integrating the signal over time exactly equal to or a multiple of the rotation period of the rotor of the synchronous generator.

Claims (2)

1. Device for monitoring brush current, comprising a current measuring head in the form of a composite magnetic circuit with a Hall sensor, an opening mechanism, an analog-to-digital converter, a microcontroller and / or processor, indication means, control keys, characterized in that it contains a controlled clock generator, the function of which is the formation of synchronizing pulses with a frequency equal to the rotational speed of the rotor of the synchronous generator, also contains an adder that sums the recorded signals in the period between ruyuschimi pulses and disconnection mechanism designed as a yoke and submitted from the control keys by a distance not less than 200 mm rotatable about the longitudinal axis of the device. 2. The device for controlling the brush current according to claim 1, characterized in that the magnetic circuit is placed on a longitudinal rod, the function of which is to rotate the magnetic circuit breakable around the longitudinal axis, while the drive rod of the opening mechanism passes along the axis of the rod.