RU2009455C1 - Method for determining inertia moment of solid body - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: method involves steps of attaching a reference solid body to the rotor of the electrical motor under test, interposing the stator of the electrical motor in a self-excited oscillator circuit, measuring a period of self-sustaining oscillations, calculating the inertia moment of the rotor. The stator is excited by a controlled direct current. EFFECT: more accurate measurement results. 1 dwg

Description

 The invention relates to measuring technique and is intended to determine the moments of inertia of solids, including rotors of synchronous electric machines.

 The purpose of the invention is to improve the accuracy and simplify the technical implementation of the method of measuring the moments of inertia of solids.

 The drawing shows a functional diagram of the installation for measuring the moments of inertia of solids, explaining the essence of the method. The installation comprises an adjustable direct current source 1, ammeter 2, the tested synchronous motor 3 with a phase system on the stator 4 and permanent magnets on the rotor 5 and a shaft 6, on which is mounted a reference body 7, a phase-shifting filter 8, a power amplifier 9 and a frequency meter 10. Method can be implemented in relation to synchronous motors with permanent magnets, electromagnetic excitation and any other active rotor.

 In the installation, one of the stator windings 4 of the synchronous motor 3 is connected through an ammeter 2 to an adjustable direct current source 1, the other two windings are interconnected via a phase-shifting filter 8 and an amplifier 9 connected in series, a reference body 7 is fixed to the shaft 6 of the motor 3, to the output of the amplifier 9 connected frequency counter 10.

When one of the stator windings of a synchronous motor 3 is connected to a direct current source 1 as a result of the interaction of the magnetic flux generated by this winding and the flux created by the permanent magnets of the rotor 5, the rotor 5 is oriented to the position corresponding to the minimum energy of the electromechanical system (zero). The DC winding in this case plays the role of an adjustable electric spring with a stiffness C proportional to the current I in the DC winding, i.e., C = K _p I, where K _p is the proportionality coefficient.

, (1)
где J - момент инерции колеблющейся части;
К - коэффициент передачи цепи вал-двигатель.To create undamped oscillations of the rotor relative to the zero position, the oscillating magnetic field mode is used, which is ensured by connecting two stator windings according to the oscillator circuit, that is, through a series-connected phase-shifting filter 8 and amplifier 9. When the frequency response of the phase-shifting filter 8 is appropriately selected rotor 5 go into self-oscillating mode with a period
T = 2

, (1)
where J is the moment of inertia of the oscillating part;
K is the gear ratio of the shaft-motor circuit.

 Equation (1) indicates that if the oscillation period T and the transmission coefficient K of the shaft-motor circuit are determined, then the moment of inertia I of the oscillating part can be easily calculated. The main difficulty is the determination of the transmission coefficient K of the shaft-motor circuit, which depends on the period of oscillation. However, it is known that this coefficient as applied to synchronous motors is directly proportional to electromagnetic stiffness and, consequently, to the value of direct current I in the stator winding 4 of motor 3, i.e.

K = γ C = γ K _p I, (2)
where γ is the proportionality coefficient.

 This makes it possible to measure the moment of inertia of the rotor of a synchronous motor according to two experiments, consisting in reproducing undamped oscillations of the rotor of the motor with and without a reference body 7 mounted on it, but at the same frequency.

или, с учетом формулы (2):
T = 2

. (3)
Во втором эксперименте ротор синхронного двигателя 3 жестко соединяют с эталонным телом 7 с известным моментом инерции J_э и возбуждают незатухающие колебания ротора. Так как момент инерции колеблющейся части (J_о+J_э) во втором эксперименте больше, чем в первом, то период колебаний увеличивается. Регулированием тока в обмотке постоянного тока статора синхронного двигателя 3 устанавливают период колебаний ротора с закрепленным эталонным телом равным Т и измеряют величину тока I, соответствующую этому режиму. Соотношение между периодом колебаний Т и током I в обмотке постоянного тока статора при этом имеет вид
T = 2

(4)
Приравняв правые части уравнений (3) и (4) и выполнив математические преобразования, получим формулу
J_o= J

, (5)
по которой по измеренным значениям токов I_o и I в обмотке постоянного тока статора синхронного двигателя 3 и значению момента инерции J_э эталонного тела 7 вычисляют момент инерции J_о ротора 5.In the first experiment, the rotor 5 of the engine remains free. One of the stator windings 4 is connected to a direct current source 1, the other two windings are connected to each other through a phase-shifting filter 8 and an amplifier 9 connected in series. An ammeter 2 is connected in series with the DC winding, and a frequency meter 10 is connected to the output of the amplifier 9. As a result of this inclusion windings of the rotor 5 performs undamped oscillations. According to the readings of ammeter 2, the current I _о in the DC winding of the stator of the motor is determined, and according to the readings of the frequency meter 10, the period T (frequency f = 1 / T) of the oscillations is determined. The period T of oscillations associated with the moment of inertia J _{about the} rotor of the synchronous motor by the ratio
T = 2

or, taking into account the formula (2):
T = 2

. (3)
In the second experiment, the rotor of the synchronous motor 3 is rigidly connected to the reference body 7 with a known moment of inertia J _e and excite undamped oscillations of the rotor. Since the moment of inertia of the oscillating part (J _o + J _e ) in the second experiment is greater than in the first, the period of oscillations increases. By adjusting the current in the DC winding of the stator of the synchronous motor 3, the oscillation period of the rotor with the fixed reference body is set to T and the current value I corresponding to this mode is measured. The relationship between the oscillation period T and the current I in the DC stator winding in this case has the form
T = 2

(4)
Equating the right sides of equations (3) and (4) and performing mathematical transformations, we obtain the formula
J _o = J

, (5)
according to which the measured values of currents I _o and I in the DC winding of the stator of the synchronous motor 3 and the value of the moment of inertia J _{e of the} reference body 7 calculate the moment of inertia J _{about the} rotor 5.

 Thus, since the measurements are made at the same frequency, i.e., at one point of the frequency response of the shaft-motor transmission coefficient, and its value is not determined and is not explicitly included in the computational formula (5), therefore, the measurement accuracy of the moment is increased inertia of the rotor of a synchronous motor. Direct current measurement with modern electrical measuring instruments is simple and high precision.

 The moment of inertia of the rotor of a synchronous motor is determined without disassembling it, directly in the assembled machine, relative to the real axis of rotation, formed as a result of the installation of the rotor and taking into account the influence of bearings, which also improves measurement accuracy.

 Using the proposed method in acceptance and research tests of synchronous motors and other products will improve the efficiency of the tests.

 (56) Copyright certificate of the USSR N 1755080, cl. G 01 M 1/10, 1989.

Claims (1)

METHOD FOR MEASURING THE INERTIA MOMENT OF A SOLID BODY, consisting in the fact that two solids, one of which is the rotor of the electric motor, and the other is rigidly connected to its shaft, are introduced into self-oscillation mode by turning on the stator winding of the electric motor in the oscillator circuit, measure the oscillation period of these bodies and its value is determined by the moment of inertia of one of them, characterized in that a reference element is used as a solid, a synchronous motor is used as an electric motor, the stator winding of which is additionally excited they choke with direct current, at the value of which the oscillation period remains unchanged both for the rotor with the indicated element, and without it and in relation
J _o = J

,
where J ₀ is the moment of inertia of the rotor;
J _e - moment of inertia of the reference element;
I ₀ - direct current without a reference element;
I - direct current with a reference element,
determine the moment of inertia of the rotor of the synchronous motor.

Images