UA69003A - Method for loading a synchronous motor in testing and a device for the realization of the method - Google Patents

Abstract

The proposed method for loading a synchronous motor in testing consists in connecting the motor to a frequency converter, accelerating the motor to the synchronous rotation frequency, providing the synchronization of the motor with the mains, connecting the motor to the mains, setting the amplitude of the variable component of the motor excitation current, varying the frequency of the variable component of the excitation current, determining the frequency corresponding to the maximal motor power, and setting the amplitude of the variable component of the excitation current according to the motor load parameters. In the testing process, the stator voltages and currents as well as the motor excitation current are measured and monitored. The proposed device for the realization of the method contains a controlled power frequency converter, a thyristor exciter with a control circuit, two switches, instantaneous value transducers for the motor stator voltages and currents, an analog-to-digital converter, a digital-to-analog converter, a central control unit, and a computing unit.

Description

Description of the invention

The invention relates to the field of electrical engineering, in particular, to the testing of synchronous motors in the conditions of 2 electrical repair shops.

A method of testing synchronous machines using the method of mutual loading is known (A.S. USSR 1412457 01K31/34 "Stand for loading synchronous machines during testing"). Stator windings of synchronous machines, connected by shafts, are powered by transformers with unsolders, with the help of which the phase shift of the voltages of the stator windings is regulated and the required load current is set. 70 The disadvantages of the described method are: - the need to install two engines with the same parameters, which is difficult to do in the conditions of electrical repair shops, because engines of a wide variety of designs are being repaired; - complexity of mechanical connection between shafts.

The closest technical solution is the method of testing alternating current (asynchronous) motors for heating and vibration (Economic patent of the NDR 257691 (01K31/34, pub. 88.0622 "Methods for testing asynchronous motors for heating and vibration"). The loading method is that the motor is accelerated to the required speed with the help of a frequency converter, the output frequency of the power supply is modulated, the direct and reverse field of the motor is formed, the current of the stator windings is maintained at a given level, the vibration level of the motor under load is measured.

The disadvantages of the given method are: - low load probability due to the fact that when powered by a frequency converter, the current in the stator circuit is non-sinusoidal, as a result of which the distribution of losses in the copper and steel of the motor, which is characteristic of the mains power supply mode, will not be observed in the test mode (increased heating of the engine steel due to the fact that losses in it depend on the harmonic frequency of the current). 29 - when testing synchronous motors with a current load, their tendency to oscillate when the supply voltage changes is revealed; - the known method does not link the voltage modulation frequency with the parameters of the tested engine.

A well-known device for testing synchronous machines using the method of mutual loading (Ass. USSR 1412457 (501k31/34 "Stand for loading synchronous machines during testing"). The stand contains two working loading places for attaching synchronous motors. The tested motors are connected by shafts Ha") with each other. Stator windings of synchronous machines are connected using transformers with solder pads.

By switching the unsoldering transformers, the phase shift of the voltages of the stator windings of synchronous machines is regulated, while the current load of the motor changes. F

The disadvantages of this device are:

Zo - the need to install two engines with the same parameters, which is difficult to implement in the conditions of electrical repair shops, because engines of a wide variety of designs are repaired; - complexity of mechanical connection between shafts; - the complexity of the design due to the need to install complex transformer equipment "the power of which must not be less than the power of the tested engine. With 50 The closest technical solution is a device for testing alternating current (asynchronous) motors for heating and vibration (Economic patent of the GDR 257691 (01K31/34, publ. 88.0622 "Methods of testing

from" asynchronous motors for heating and vibration"). The device consists of a frequency converter with the help of which the motor is accelerated to the required speed. With the help of this same frequency converter, the output frequency of the power supply is modulated, the direct and reverse field of the motor is formed, and the stator current is maintained at a given level winding. b The disadvantages of the given device are as follows: (se) - the converter must be able to return energy to the network, which complicates the design of both the power part and the control system; o - the power of the converter for powering the motor must be equal to the power of the tested motor, o 20 Which increases the price of the installation, complicates the design and maintenance; - increased losses in the frequency converter during tests, in contrast to systems powered from the mains.

The method of loading synchronous motors and the device for its implementation are explained by graphic materials: 29 Fig.1. Block diagram of a device for implementing a method of loading a synchronous motor. in. Fig. 2. Block diagram of the thyristor exciter control system.

The task of the invention is to increase the probability of tests on the heating of synchronous motors, to increase the energy indicators of the test process. The goal is achieved by the fact that the synchronous motor is accelerated to synchronous speed with the help of a frequency converter and, after synchronization, is connected to the 60 network, the variable component of the excitation current of constant amplitude and variable frequency is set, the maximum power is determined when the frequency of the variable component of the excitation current changes, the frequency value is fixed at maximum power, set the specified amplitude of the variable component of the excitation current in accordance with the task of the loading mode, measure the voltage on the stator, the stator current and the excitation current determine the power consumed. Thus, the load is carried out by a sinusoidal current, which is close to the mode of operation of the synchronous motor, the losses in the tested motor are reduced, the losses in the converter in the load mode are eliminated, the power is reduced (up to 7-1095 of the power of the tested motor) and the overall parameters of the converter, load of the engine is carried out by changing the parameters of the low-power source - the thyristor exciter of the engine.

The essence of the proposed loading method is as follows. The electromagnetic moment of the synchronous motor is determined by the equation: zipv

M EM O- Z - E M YMZB- 6 ю6«ю--5- od: ha de, и - e.r.s. engine and its supply voltage; 70 2d - synchronous motor speed; ha - synchronous inductive resistance of the motor along the longitudinal axis; b is the load angle.

Equation of electromechanical balance of a synchronous motor: t5 р че

ChYA.-ya Kk, - - - Kk. 8 M, where Mu is the load moment; -- moment of inertia;

KU, - coefficient that takes into account the calming moment of the synchronous motor (depends on the parameters of the damper winding); ka - the coefficient that takes into account the synchronizing torque of the motor, it is proportional to the excitation current of the synchronous motor:

KevKeiv « where Kn is the coefficient at the rated current.

Let's present the excitation current in the following form: iv ev s from where, y - coefficients, the values of which are s10 se where, n | "in)

Then: 2 | "c) at av -

I --e vK u - 2 Kon vovi I.V - M i what F

This is an equation with periodic coefficients that cannot be solved theoretically. The differential equation, c, which describes the behavior of the motor rotor when the parameters change, fully corresponds to the differential equation of an electric circuit, which includes inductance L, capacitance C, active resistance K (M.P. Kostenko, L.M.

Piotrovsky, Electric machines, Part I Gosznergoizdat, M-L, 1958, p. 372). At the same time, the moment of inertia corresponds to the inductance, the Kk coefficient corresponds to the resistance, the Kon coefficient corresponds to the capacitance; load angle «

Corresponds to the current flowing through the electric circuit under the action of external E.S. The value of the coefficient k(y) that ShSH08 s will change is equivalent to the change in capacity over time. At the same time, the equivalent capacity can be represented as follows: h 1 1 i? с - -- В 5 -- Ж 6 6 -й 6 6 | "5:

Ka 0 Kon -nv.5ipX V

Ko-sh 79 -ok U Sk vipk oh o ner (o) k-i (se) des - constant component of equivalent capacity; aw! сСк- the maximum values of K- the capacity that changes with the frequency of K.x,; o 20 fdk - the shift angle between the control signal and the capacitance change curve. "so It is known from the theory of circuits that if one of the parameters changes according to the harmonic law, then at the output we have a signal that has a spectrum containing CC frequencies... Therefore, the solution of the differential equation can be represented as follows:

В) - В AB, вып и- з» ЖАВ. vip2x yin AV - vipKOHM OI

In order for one of the parameters 24 to have the maximum value, it is necessary that Kk -10 of them correspond to the resonant frequency of the electromechanical system, which is determined by the expression:

EE

60 from Ve

NO. where RK. - the number of motor pole pairs; -- moment of inertia of the engine.

The coincidence of the frequencies of the natural oscillations and the influence caused by the change in the excitation current leads to the fact that the maximum values of the power circulating between the motor and the network reach such values that the current load of the stator circuit can be comparable to the rated current of the stator

(equal, greater or less than the nominal). At the same time, the load angle changes in the range of 2-20", and power is consumed from the network, comparable to the nominal one, and approximately the same power value is returned. During the period of harmonic influence, power is consumed from the network, which is equal to the electrical and mechanical losses in the engine, which is loaded. It can be seen from what has been said that the conditions are reached in which the motor is loaded with a current load and develops a torque. These two quantities can be selected according to the task of the load mode.

If the frequency of 75 does not correspond to the frequency of schu, then under load, low-quality indicators are possible, because 7/0 components of ybu will be revealed, and those of them that correspond to the polyharmonic curve of the developing torque motor:

MO) - Ma - AM.-vipH-Y . YaAM.. I ate. Amu BIKOH OI

At the same time, the maximum moment is possible at K 7210. In order to form a variable component of the excitation current according to the frequency of natural oscillations, which is usually unknown at the stage of searching for the optimal load mode, during a slow change in the frequency of the excitation current, fixing the instantaneous values of the currents and voltages of the windings of the stator phases, the instantaneous values are calculated with the help of a computer of full power circulating between the engine and the power network. At the same time, the value of the frequency of the variable component of the excitation current, at which the amplitude of the full power is maximum, is determined by the computer software. This corresponds to the maximum electromagnetic moment developed by the engine, i.e. equal to - Ah. The time of the signal change is chosen in such a way as to exclude the influence of the constant time of the excitation winding in the given range of the control effect. This mode corresponds to the mode of optimal load and is observed, as a rule, at frequencies of 0.5-2 Hz of the influence signal. It can be determined experimentally during preparatory work or during tests automatically. "

In the process of loading, the excitation current is maintained at a given level. Its change can occur as the excitation winding heats up. In the process of loading, the frequency at which the most favorable modes are possible is not adjusted. This is explained by the practical independence of the frequency of self-oscillations from resistance changes during the heating of the machine. co

During the loading process, the following mode parameters are fixed:

Id, Iv, Is - instantaneous values of the motor currents on the 3 phases of the stator; at

Od, Ov, Os - instantaneous values of the motor power supply voltage in 3 phases; (av)

Iv - instantaneous values of the excitation current of the synchronous motor.

Based on the received data for the load period, the following parameters are calculated: Ф power consumed from the network; (se) effective value of stator currents; equivalent value of excitation current; the temperature of the stator windings (controlled by changing the active resistance of the stator windings). "

Calculation of the values of the specified parameters during the load period is carried out using a computer programmatically. - c The block diagram of the device implementing the method is presented in Fig. 1. The synchronous motor (SD) 1 is connected to the network through the frequency converter (IF) C using switch 4, or directly to the network using "» using switch 5. In the phase of the stator circuit of the SD, voltage sensor units 7 and 8 are connected. Between the two phases voltage sensor 6 is connected to the power supply network (in front of the switch 5). LED excitation is carried out using a thyristor exciter (73) 2. A current sensor 9 is connected to the excitation winding circuit. (o) Information from the outputs of the current sensors (8, 9) and voltage , 7) enters the corresponding inputs of the analog-to-digital converter (ADC) 12. From the ADC 12, information in digital form is sent to the central controller (CC) 14, which is connected via a serial interface to the computer 15. With the help of a digital-to-analog converter (ав) (DAC) 10 CC 14 issues a task signal to IF 3. With the help of the switching equipment controller 50 (KKU) 11 CC 14 controls switches 4 and 5. The thyristor exciter control system (SKTZ) 13 combines in an analog-to-digital converter (ADC), a digital pulse-phase control system (PSFC) and a task signal generator (PS) (see Fig. 2).

Synchronous motor (SD) 1 is connected to the network through the frequency converter (IF) C using switch 4 and accelerated to the required speed, synchronized with the network, connected directly to the network using switch 5. Synchronization is carried out in the following way: signals from voltage sensors 6 and 7 z" through the ADC 12 are sent to the central control unit 14, which, based on the analysis of the frequencies and phase shifts of the signals, forms a task for the IF 3 through the DAC 10. After acceleration and the fulfillment of the synchronization conditions, the central control unit 14, with the help of the control unit 11, turns off the switch 4 and turns on the switch 5 .

The assignment of the load mode is carried out using SKTZ 13 (see Fig. 2). At the same time, data on the required signal of the excitation current task in the form of coefficients of the amplitudes of the constant and variable component, as well as the frequency of the variable component, are received from Central Committee 14 on 60 SKTtZ. The task signal generator (FS) in real time generates a digital code corresponding to the required task signal received by the CSIFC, which controls the thyristors of TK 2. In the CSIFC, a Pi-regulator of the excitation current is software implemented, which receives a digital code corresponding to the signal difference task and the signal of the real excitation current coming from the 65 current sensor 9 through the ADC.

Converter 3 is an autonomous inverter converter with an output frequency of 0-50 Hz. The output voltage of the frequency converter supply should be approximately equal to the supply voltage of the synchronous motor. At the same time, the power of the starting converter is small - up to 7-1095 of the power of the tested motor (the power must be equal to the losses in the tested synchronous motor), because the load is carried out when the motor is powered from the mains. In addition, losses are reduced, because a significant part of them is excluded (losses in the converter).

In the exam mode, the synchronous motor is loaded for the required time. as i x 7 Z 15 - VA--

And! ! and -IBZ-7 10th

AND

! Her - 6. pi 5 5 shi i -- mi-- A | She is 11

And p-yat Mol -- - she 2 And I- t - Sh shchi

G.71 | - | in with 1-3 "

Y 2-4 1 12 What is the 5th

And sl otv | Ge) zo "7 shi what "c) i 5- - 5 I | "c) - -- - as i po (o) you i-- n 13 (Se)

C on z pzntnya-ya |2-T -- write

Fig. 1 ! " - with ;" , ADC -

Ф Fo С s ba tsIFk oi («c) («c) syu»

Fig. 2

Claims (1)

The formula of the invention 1. The method of loading synchronous motors during tests, which consists in the fact that the synchronous motor is connected to the frequency converter, accelerated to the calculated speed, the motor torque is changed by periodically affecting the control circuits, which differs in that the synchronous motor is connected 60 to the frequency converter, accelerate to synchronous speed, synchronize with the network, connect to the network, set the variable component of the excitation current of constant amplitude and variable frequency, determine the maximum power when the frequency changes, fix the frequency of the variable component of the excitation current, set the specified amplitude of the variable component of the excitation current in accordance with the task of the loading mode , measure stator voltages and currents, excitation current. bo 2. Synchronous motor load device, consisting of a frequency converter, a load mode parameter control unit, which is distinguished by the fact that it is equipped with the first and second switches, sensors of instantaneous values of voltage, stator current and excitation winding, a control system for a thyristor exciter with a signal shaper task, analog-to-digital converter, switching equipment controller, digital-to-analog converter, central controller, computer, the power of the frequency converter is equal to 7-1095 of the power of the tested engine. Official bulletin "Industrial Property". Book 1 "Inventions, useful models, topographies of integrated microcircuits", 2004, M 8, 15.08.2004. State Department of Intellectual Property of the Ministry of Education and Science of Ukraine. " (ze) "c) "c) (o) (Se) - with . and? (o) se) («c) («c) syu» 60 b5