1 Introduction
2 Main notions and brief review of the work
3 Conclusions
1.1 Urgency of subject
The indicated causes are responsible for the increase of the motor vibration and they accelerate the wear of bearings. In some cases it is quite possible that the rotor will touch the inside surface of the stator. Such damages lead to the prolonged restoration repairs of IMs.
It is known, as a result of eccentricity changes the efficiency of an IM can be reduced by 2.8 %, the breakdown and locked rotor torques are reduced within the limits 20 % and 8 % correspondingly, the slip can increase by 10%. The noticeable effect on the above mentioned operating variables becomes apparent as the eccentricity increases more than by 30-35 percent.
The damages under such conditions require long-lasting IM reconstruction repair.
Expenses in this case are similar to the new machine cost.
1.2 Production purposes and problems
Specified methods did not find a broad application in industry. Thereby, the problem of creation of more efficient method of the air gap eccentricity checking is still actual. The development of diagnosing method, excluding above mentioned disadvantages is the aim of this work
1.3 Scientific novelty and practical value
2.1 Why given strategies have been used where
2.2 Particularities of strategy of study
Determination of air gap on axis of each slot of rotor can be determined using the expression:
Specified phenomena are stipulated by unevenness of sharing an attached voltage between spools of phases and breaking a symmetry of phase stator currents that causes growing of high harmonicas in the magnetic flux of air gap and increasing the inductances of machine.
Normal transient process during short-time disconnection of the IM from the supply used as a test influence can give essential advantage versus known methods.
Efficiency evaluation of express-method under investigation requires determination of a diagnostic parameter of machine, choice of possible diagnostic signal and evaluation of its sensitivity to air gap eccentricity change.
2.3 Results of studies
As the test influence the normal transient process during a hort-time disconnection of the IM from the supply was taken.
The test was carried out on the commonly used 1.5kW motor with 380V rated voltage.
The aims of this test were:
As the result the qualitative dependencies of stator and magnetic flux voltage were obtained. The physic model of air gap eccentricity was developed, but it requires experimental evidence.
3 Conclusion
1.1 Urgency of problem
1.2 Purposes and problems
1.3 Scientific novelty and practical value
2.1 Why qiven stateges have been used
2.2 Particularities of study strategy
2.3 Results of studies
The problems concerned with energy losses decreasing and raising reliability of induction motors (IMs) are of primary importance. Both of these problems manifest themselves as the air gap eccentricity. The mentioned phenomenon is a consequence of the gradual wear of bearings, deformation of the end shields, etc.
To the most well known methods of indirect control it is possible to refer a method of synchronous inductive resistance value control [1], as well as short-circuit inductive resistance value and zero sequence control method, explored in DPI. The disadvantages of these methods are:
Scientific novelty is the creation of new solutions and improvements of strategies of the air gap eccentricity control of IM.
Practical value is that these new solutions enable to define the developments of damaging on early stage and forecast further check or conclusion in the motor repair. This efficiency is immeasurable in industrial conditions.
2 Main notions and brief review of the work
Increasing of asynchronous machine reliability is one of actual tasks of industrial energy. The questions of ensuring possible value of unevenness of the air gap eccentricity play major role. The air gap eccentricity is defined as a measure of breaking symmetry of air gap on the basis of direct measurements in face parts of stator on the known formula:
,
– average and maximum value of air gap, accordingly. [2]
Because of minute value of the air gap this factor turns out to be highly sensitive to deformation of the bed locks, bearings panels and gradual wear of bearings of the machine under exploitation. [3] As it is known, when there is the air gap eccentricity in asynchronous machine the starting moment falls, unilateral magnetic attraction and vibration of rotor grow and efficiency falls because of increasing the steel losses.
Figure 1 – Space coordinate of IM air gap eccentrycity
During investigation the test program was created and the experiment was carried out.
Figure 2 – Dependencies of stator and magnetic flux voltage
stator voltage – blue curve,
magnetic flux voltage – red curve.
Thereby, this strategy gives theoretical base for the air gap eccentricity device development for industrial motors. This device will allow to give an evaluation of air gap eccentricity during a short period of measurements and data processing and take measures of its elimination.
4 Literature