RU2323448C2 - Method for monitoring of insulation of sheets of stator laminated cores in motors and generators and device for its realization - Google Patents

Abstract

FIELD: monitoring of motors and generators.

SUBSTANCE: an annular alternating magnetic flux with a low level of induction is produced in the core under check with the aid of a magnetizing coil. Scanning of the core recess surface is accomplished with the aid of an inductive pickup. The amplitude of the difference between the pickup signal and the references signal equal to the signal of the pickup installed in a defect-free point is measured, the conduction of the insulation is judged according to this measurement. The device has a magnetizing coil, pickup, adjustable power supply unit of the magnetizing coil, reference signal source and a control unit. The control unit has a device for adjustment of the reference signal in amplitude and phase, and a voltage measurement device. The reference signal source is connected to the input of the regulator device. The output of the regulator device is opposite-connected to the pickup output. The obtained difference signal is applied to the input of the voltage measurement device via a filter tuned to passage only of the output voltage frequency of the magnetizing coil supply source. The reference signal source may be built in the control unit.

EFFECT: enhanced accuracy of defect-shooting and determination of sensitivity at raised frequencies, simplified design.

4 cl, 5 dwg

Description

The invention relates to the field of electrical engineering and is intended to control the state of insulation between sheets of electrical steel of the charged cores of the stators of electric machines.

In Russia and abroad, the electromagnetic method of monitoring the state of insulation between sheets of electrical steel of the charged cores of the stators of electric machines is widespread [1]. The method consists in creating an annular alternating magnetic flux with a low level of induction (not more than 0.1 T) in the test core using a magnetizing coil wound around this core, setting the reference signal equal to the signal of the inductive sensor scanner mounted on a defect-free the location of the core bore, after which this sensor scans the surface of the core bore with a constant reference signal. In this case, local insulation defects of the sheets are detected by comparing the sensor signal and the reference signal. Currently, three methods are used to determine the insulation state from the results of scanning: measuring the component of the sensor signal at an angle of 90 degrees with respect to the reference signal (quadrature component) [1], measuring the phase difference between the sensor signal and the reference signal [2], measurement of additional losses in the studied area by the amplitude of the sensor signal and the phase difference between the sensor signal and the reference signal [3]. All these methods are based on the assumption that, in the event of insulation failure, a closed loop (damage loop) is formed in the core body, the active resistance of which is much less than inductive, which, in turn, entails the in-phase synchronization of the emf induced in the damage loop by the ring flow and generated by her current.

This assumption is quite true in those cases when an annular flow of industrial frequency (50-60 Hz) is created in the core during testing. Recently, however, in order to increase the accuracy and reliability of defect detection, as well as to reduce the power of the magnetizing winding power supply, cores are tested at a frequency significantly higher than the industrial frequency (200-5000 Hz) [4]. In this case, neglecting the inductive resistance and, as a result, the current shift in the damage circuit relative to the emf that generated it leads to gross errors.

These positions are illustrated in figure 1, which shows the generally accepted diagram of the test device and the vector diagram (figure 2). Figure 1 marked:

1 - inductive sensor;

2 - magnetizing winding;

3 - reference signal source;

4 - checked core;

5 - adjustable power source of the magnetization winding;

6 - control unit;

7 - ammeter;

8 - the inner case of the tested machine;

9 - the outer casing of the tested machine;

10 - computer.

The tested core 4 is mounted on the ribs in the inner case 8, which, in turn, is located inside the outer case 9. A magnetizing coil 2 is wound on the core, powered by an adjustable AC source 5, and a reference signal source 3, which may have a different device, and in this case represents one control turn. The outputs of the reference signal source 3 and the inductive sensor 1, which is a coil on a ferromagnetic or non-magnetic core, are connected to the control unit 6, and through it to the computer 10.

When a voltage of increased frequency f is applied from the power supply unit 5 to the terminals of the magnetizing winding 2, a current I _о flows through it (Fig. 2, the scales are not met for clarity), which generates a ring magnetic flux Ф _о in the core under test 4, part of which Ф _so branches into sensor core 1. The flow Ф _so induces in its winding the emf E _so . If somewhere under the sensor the insulation between the sheets of steel is broken, then at this point a short-circuited circuit is formed, which is penetrated by the flow Ф _о (or its part), which induces the emf Е _к in this circuit. If the frequency f is equal to the industrial frequency (the values related to the industrial frequency are marked by index 1, and those related to the increased frequency are marked by index 2 and thick lines), then the indicated emf generates a current I _k1 in the circuit, which practically coincides in phase with the emf E _k . The current I _k1 , in turn, gives rise to the flux Ф _к1 , part of which Ф _{sк1 is} closed through the sensor 1. The stream Ф _sк1 induces in it the emf E _sк1 , which is in quadrature with the emf E _so . As a result, the vector of the resulting emf of the sensor E _{s1 is} rotated by a certain angle with respect to the vector of the “defect-free” emf E _so and the in-phase emf of the reference signal source E _o . In this case, the control signal 3 serves as the reference signal source. This coil is pierced by the same annular flow Ф _о , therefore its emf E _о coincides in phase with the emf E _so . Thus, the quadrature component of the sensor signal is proportional to the current of the damage circuit and therefore it can serve as a criterion for the state of the core, on which the above methods of core monitoring are based.

When applying voltage to the excitation winding with an increased frequency of 500-5000 Hz, the vector diagram changes significantly. The inductive resistance of the damage circuit becomes comparable with the active one, and when the damage is located even at a shallow depth below the surface of the core, it exceeds it several times. In this case, the loop current I _k2 substantially lags behind the emf that generated it and, together with the fluxes Ф _k2 and Ф _sk2 created by it (analogues of the already mentioned flows Ф _k1 and Ф _sk1 ), it occupies the position shown in Fig. 2 by bold arrows. Accordingly, the component emf of the sensor E _sk2 deviates from the vertical, which is a measure of the fault current I _k2 , and the resulting sensor emf occupies the position indicated by the vector E _s2 . Now its quadrature component cannot serve as a measure of the state of isolation, and using it as such a measure can lead to erroneous conclusions. Their exclusion is the purpose of the present invention.

Closest to the proposed device is the device described in [5] (prototype). Here in the core of the magnetic circuit create an alternating ring magnetic flux of increased frequency. Scanning of the working surface is carried out by an inductive sensor on a non-magnetic core (Chattock potentiometer). Using a phase-sensitive detector, its signal is decomposed into two components: one in-phase with a reference signal, the other in quadrature. Using these components, an output signal is formed, which is used to judge the state of insulation in a given place. In other words, when supplying a magnetizing winding with an increased frequency, the control is based on the assumption of a 90-degree shift between the reference signal and that component of the sensor signal, which is caused by a sheet insulation defect, which, as mentioned above, is no longer true.

The proposed control method is free from this drawback. When it is also used, an alternating ring magnetic flux of increased frequency is created in the core of the magnetic circuit, the magnitude of the reference signal is set equal in amplitude and phase to the magnitude of the sensor signal (no matter what design) installed on a defect-free location in the core bore, i.e. equalize the emf of the sensor E _s0 and the emf of the source of the reference signal E ₀ in magnitude and phase, and then scan the working surface with an inductive sensor with a constant reference signal. In this case, the sensor signal is turned on with the reference signal, and this difference is applied to the millivoltmeter. It is obvious that if during the scanning process at a constant value of E _{0 the} sensor will be at the location of the defect, the difference signal will be exactly the emf E _sk2 , which is a measure of the defect.

To implement this method, a device is proposed, the scheme of which is presented in figure 3. Indicated here:

11 - device for adjusting the reference signal;

12 - voltage regulator;

13 - phase shifter;

14 is a voltage measuring device.

All other installation elements are similar to those shown in figure 1. The control device for the reference signal in this case is made in the form of a voltage regulator 12 and a phase shifter 13 connected in series. The output of the reference signal source 3 is connected to the input of the reference signal control device, and the output of this device is turned on in opposition to the signal of the sensor 1, and this difference signal is applied to the voltage measuring device 14, which in the simplest case can be a digital or analog millivoltmeter. If necessary, this device may have an output for connecting a computer 10, used for visualization, archiving and documenting the results of control.

The control begins with setting the value of the reference signal: when the magnetizing winding 2 is turned on, sensor 1 is installed in the core bore 4 to a defect-free place (place it in several samples, if the sensor accidentally finds itself in a damaged area, this will be revealed during the test), by adjusting the amplitude (with using the voltage regulator 12) and the phase (using the phase shifter 13) of the reference signal, the difference signal is minimized. After that, without changing the settings of the voltage regulator and phase shifter, they scan the working surface of the core. Moreover, the magnitude of the difference signal in this place is a characteristic of the quality of insulation of the sheets.

Obviously, the measuring system will be the more sensitive to the detection of defects in the insulation of the core sheets, the more accurately the minimum of the difference signal will be set when setting the value of the reference signal. Theoretically, it should be equal to zero, but in practice it differs from zero due to the presence of higher harmonics and ambient noise in the signals. Therefore, it is advisable to use the differential signal from the sensor 1 and the reference signal source 3 to the voltage measuring device 14 through a filter 15 configured to pass only the frequency of the output voltage of the magnetizing coil power supply 5 (Fig. 4).

In known devices for monitoring the insulation of sheets of laminated cores of stators of electric machines by creating an alternating magnetic flux in the cores with an induction of no more than 0.1 T, the reference signal 3 is either a special coil [1] or a sensor that is completely similar to a scanner sensor [2 ], or a special coil wound during the test around the yoke of the test core [4, 5]. However, regardless of the design, in all cases this source is an additional device installed on the core under test 4 and external to the control unit 6, which increases the composition of the entire control device and increases the complexity of testing. A method based on the use of a difference signal allows you to embed the reference signal source in the control unit 6. A diagram of a device with such an integrated reference signal source is shown in Fig. 5.

Here 16 is the built-in reference source.

The built-in reference signal source is a low-power transformer, the primary winding of which is connected to the output of the regulated power supply of the magnetization coil 5 in parallel with the magnetization winding 2, and the secondary winding is connected to the input of the reference signal regulation device 11, the signal from which, as in previous cases (Fig. .3, 4), turned on in the opposite direction with the signal of sensor 1. Obviously, in this case, too, before supporting the scanning of the surface of the tested core 4, the support should be installed a signal consisting in the alignment of the amplitude and phase (with the device 11) and the reference signal sensor mounted on a defect-free site. If necessary, the transformer 16 can be replaced by other devices (for example, an optocoupler pair), however, in all cases, for safety reasons, it is advisable to exclude the galvanic connection of the power source of the magnetizing winding with all measuring circuits of the control unit.

Information sources

1. Sutton J. EICID: an easier way to test stator cores. Electrical Review, 207, 1, July, 1980.

2. Patent for invention RU 2082274, 08/09/1994.

3. Butov A.V., Pikulsky V.A., Polyakov F.A., Shandybin M.I. The electromagnetic method for detecting faults in sheets of active steel of a stator of a turbogenerator. "Electric stations", 1998, No. 11.

4. Patent for the invention RU 2195681, 04.06.2001.

5. Patent for invention GB 2382878, 12/04/2001.

Claims (4)

1. A method for controlling the insulation of sheets of laminated cores of stators of electric machines, in which an alternating magnetic flux with induction of not more than 0.1 T is created in the core under test, the reference signal is set equal to the signal of the sensor installed on the defect-free location of the core undergoing boring, after which this sensor scanning the surface of the bore, during which the sensor signal and the reference signal are compared, characterized in that when the sensor scans the surface of the core bore The difference amplitude between the sensor signal and the reference signal is measured, and the value of the insulation of the core sheets is judged by the magnitude of this amplitude. 2. A device for monitoring the insulation of sheets of laminated cores of stators of electric machines by creating an alternating magnetic flux in the cores with an induction of not more than 0.1 T, containing a magnetizing coil, a sensor, an adjustable magnetizing coil power supply, a reference signal source and a control unit, characterized in that the control unit contains a device for adjusting the reference signal in amplitude and phase and a voltage measuring device, moreover, to the input of the control device for the reference signal under for prison source reference signal, the output signal of said reference adjustment device included with the counter output of the sensor, and the resulting difference signal is fed to the input of the voltage measuring device. 3. The device according to claim 2, characterized in that the control unit comprises a filter configured to pass only the frequency of the output voltage of the magnetizing coil power supply, the difference signal being fed to the input of the voltage measuring device through this filter. 4. The device according to claim 2 or 3, characterized in that the source of the reference signal is made in the form of a transformer, the primary winding of which is connected to the output of the power supply unit of the magnetizing winding, the secondary winding is connected to the input of the control device of the reference signal, and the specified transformer is built into the control unit .

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