SU976391A1 - Device for measuring asynchronous electric motor rotor current - Google Patents

Description

The invention relates to electrical measuring equipment and is intended for use in automatic control systems for off-phase electric motors.

A technical solution is known for determining the rotor current of an induction motor, which involves measuring with a voltmeter and an idler voltage ammeter and short-circuit current, constructing an operating diagram of the electric motor. l under load and the graphic finding of the desired parameter ij. The disadvantage of the known technical solution is associated with the considerable laboriousness of its practical implementation and the lack of the possibility of automatically retrieving the necessary information.

Closest to the invention is a device for measuring the rotor current of an asynchronous electric motor, comprising an integrator, the input of which is connected to the measuring winding located in the stator of the electric motor, and the output to the input of the first large-scale amplifier - the course of the first large-scale amplifier.

the subtractive input through the second large-scale amplifier - with the output of a shunt connected in series with the phase working winding of the electric motor, and the output - with the input of the recording unit J.

The gain of the first large-scale amplifier of the specified device is characterized by the value

10 of the resistance of the magnetizing circuit of an asynchronous electric motor, which substantially depends on the magnitude of the magnetizing current or magnetic flux in the air gap. The use of the known device in the modes with a large range of changes in the degree of saturation of the magnetic system of an electric motor (brake start, reverse modes

20, etc.) leads to a significant error in the measurement results, reaching 100% or more.

 The aim of the invention is to improve the accuracy of measuring the rotor current of an asynchronous electric motor by eliminating errors caused by the dependence of the resistance of the magnetized circuit in a circuit on the magnetic flux in the air gap. The objective is achieved by the input of which is connected to the measuring winding of the electric motor located in the stator, and the output to the input of the first large-scale amplifier, an algebraic summation unit, in The reading input of which is connected via the second scale amplifier to the output of the shunt connected in series with the phase working winding of the electric motor, and the output to the input of the recording unit between the output of the first scale amplifier and the summing input of the algebraic summing unit is entered a nonlinear correction unit. Figure 1 shows the functional diagram of the proposed device for measuring the rotor of an asynchronous electric motor; in Figure 2, the pass characteristic uses a nonlinear corrective block as a function of the magnetizing current D for the magnetic flux φ assigned to its nominal values. The device consists of an additional measuring winding 1 (figure 1 in the stator of an asynchronous electric motor body, whose axis coincides, with the axis of the phase working winding 2, integrator 3, first 4 and second 5 scale amplifiers, nonlinear corrective block b, block 7 algebra - from the summation of a shunt 8 connected in series with the working winding 2 and the registering unit 9. The device operates as follows: From the output of the measuring winding 1, a signal proportional to the EMF of the electric motor is fed to the input of the integrator 3. The integrator 3 is a FO1 and a signal is proportional to the magnetic flux of the electric motor. This signal is fed to the input of a scale amplifier 4, the transmission coefficient of which (gain factor) is determined according to the expression K-JdilL-Mia., where c 4, 44U) kjjj is the constructive constant of the verification winding 1; j is the nominal frequency of the voltage supplying electric motor} Sch the number of turns of the measuring winding 1; X is the resistance of the magnetizing circuit corresponding to the nominal mode of operation of the motor. As a result, the output of the scale amplifier 4 produces a signal proportional to the magnetizing current of the electric motor, and the value of the magnetizing current will be the closer to the real, the closer to the nominal is the value of the magnetic flux, because xjj (,), and with, m is the increase in XQ (XQ-Xpn). To improve the measurement accuracy at any magnetic flux values, the signal from the output of the scale amplifier 4 is fed to the input of the nonlinear correction unit b, the output of which produces a voltage proportional to the magnetizing current taking into account the change in the resistance of the magnetizing circuit X0 or the nonlinear dependence 3 (Φ} (FIG 2),. The signal is proportional to the current ;;) ,,, from the output of the correction block b, is supplied to the summing input of the algebraic summing unit 7. Simultaneously to the subtracting input of the latter the output of the scale amplifier 5 receives a signal proportional to the current of the motor stator. This signal is generated by scaling the voltage taken from shunt 8 connected to the phase of the working winding 2 of the stator of the electric motor. The gain (gain) of scale amplifier 5 is determined in accordance with R.J - shunt resistance 8. In block 7 of algebraic summation, signals proportional to the stator current and magnetizing current are calculated in accordance with the - - Ч algebraically summed. Output unit 7 A signal is generated that is proportional to the rotor current of the electric motor, which is then fed to the input of the recording unit 9. The non-linear adjustment unit b is performed on the basis of the operational amplifier in combination with diodes and reference sources by fitting the curve of the false line 2 . Practical use of the proposed device provides

a significant increase in the accuracy of measuring the rotor current of an asynchronous electric motor, especially in operating modes associated with a significant saturation of its magnetic system.

Claims (2)

Invention Formula A device for measuring the rotor current of an asynchronous motor containing an integrator, whose input is connected to the measuring winding located in the stator of the electric motor, and the output to the input of the first large-scale amplifier; sequentially with the phase working winding of the electric motor, and the output with the input of the recording unit, characterized in that, in order to improve the measurement accuracy by elimination of errors due to the dependence of the resistance of the magnetizing circuit on the magnetic flux in the air gap between the output of the first large-scale amplifier and the summation of the input of the algebraic sum block, a non-linear correction block was introduced. Sources of information taken into account in the examination 1- Petrovsky L.M. and others. Testing of electrical machines. tI.-L. , Gosenergoizdat, i960, pp.176-179. 2. USSR author's certificate number 822048. class. G01R 19/00, 1978. eight -1,2 -t6 Y Fiz1 / Fn W 1.2 four about -0.8 -t.6