The effect of stator and rotor grooves on the electrical parameters of the machine (by applying three-phase winding error)

Dissertation of the master's course in the field of electricity (M. Sc)

Strength: power

Abstract:

In this thesis, electrical and mechanical defects in electric machines are examined first, and the factors causing them and the methods of fixing these defects are stated. After that, with the help of the winding function method of the simulation machine and the intended error, i.e. the stator wiring error, it has been applied and the results have been investigated. The main parameter that we have used to detect the fault in this thesis is the three-phase current of the stator in healthy and faulty state, under different loads. Then the effect of stator and rotor slots on the induction machine ref is used in its real form with the inverse air gap function. Then, how to apply the effect of stator and rotor grooves in the winding function method is explained and the method of calculating the internal and mutual inductance matrices of the stator and rotor and the inductance derivative matrices with the presence of stator and rotor grooves in four cases are investigated. Then, the application of stator wiring error with the effect of stator and rotor grooves is investigated and finally the results obtained are compared.

According to the mentioned contents, it is concluded that by timely detection of each of the primary defects in the induction machine, it is possible to prevent the occurrence of secondary accidents that lead to heavy damages. In this regard, it has been tried to analyze, examine and diagnose one of these errors, the stator wiring error of a squirrel cage induction motor, to take an effective step in the implementation of a predictive maintenance system and to prevent heavy damages to industries and national resources by applying condition monitoring systems to such machines.

Introduction:

Electric motors play an important role in They play an effective role in setting up machines and industrial processes. Especially squirrel cage induction motors, which are known as the workhorses of the industry. Therefore, diagnosing the errors of these engines can have many economic benefits. Among other things, it makes the management of industrial factories easier, raises the level of reliability of the system, lowers the cost of maintenance and reduces the cost-to-profit ratio significantly. Bonnett and Soukup have proposed five failure modes for stator failures of three-phase squirrel cage induction motors, which are: ring to ring, coil to coil, phase disconnection, phase to phase and coil to ground [1]. For squirrel cage motors, stator winding failures and bearings are considered as total failures, and also most induction motor stator winding failures result from ring-to-ring insulation breakdown.[2] Some researchers have divided motor failures as follows: failure of balls (bearings) 40-50%, failure of stator insulation 30-40% and failure of rotor rack 5-10% [3] which if ring-to-ring failure is not prevented, it leads to phase-to-ground or phase-to-phase fault, which is more severe phase-to-ground fault. In the articles [4] [5] the theory of winding function and its application in the transient analysis of induction motors under fault are described. This theory has been used in stator ring-to-ring error modeling. In addition to the above methods, the stator error of the induction motor can be studied with the help of space vectors [6].

1- Introduction: [7]

The failures of a squirrel cage motor can be divided into two categories, electrical and mechanical. Each of these failures is caused by several factors and stresses. turn around These stresses are generally in the form of thermal, magnetic, dynamic, mechanical or environmental stresses that cause failure in different parts of the machine such as the axis, bearings, stator windings, rotor core sheets and stator and rotor rack. Most of these failures are caused by not using the right machine in the desired working conditions, lack of coordination between the designer and the user, and improper use of the machine. In this part, an attempt has been made to first examine the types of stresses on the machine, the factors that cause them, and their effects.

Before examining the types of stresses on the induction machine, the following should be considered:

1- By specifying the working conditions of the machine, thermal, mechanical and dynamic stresses can be predicted and the machine suitable for those conditions can be selected. For example, the working cycle of the machine and its type of load, the number of times it is switched off and on and the time interval between them, are factors that will have a direct effect on the occurrence of stresses on the machine.

2- The state of the machine's power supply network in terms of voltage drop in the permanent state and the starting conditions and the amount of network harmonics will also be effective in the occurrence of the type of stress and as a result the occurrence of breakdowns in the machine.

1-2- Investigating the types of stresses applied to the induction machine:

1-2-1- Stresses effective in the failure of the stator: [1.7]

A. Thermal stresses: This type of stress can be considered as the result of the following factors:

? Start-up cycle: the heat increase in induction motors is more during start-up And the stop is created. During starting, a motor draws five to eight times the rated current from the mains to run under full load conditions. Therefore, if the number of starts of a motor increases in a short period of time, the temperature of the winding will increase rapidly, while an induction motor has a limit for heating, and if this limit is not considered, the readiness of the motor to cause an error will increase. The stresses that occur due to the sudden stop of the motor are far more effective than other stresses.

? Thermal overload: due to voltage changes and unbalanced voltages, the winding temperature increases.

According to an empirical rule, for every 1-3% of unbalanced phase voltage, the temperature of the phase winding with its maximum current increases by 25%. .

? Thermal wear: according to the empirical law, with a 10?c increase in the stator winding temperature, its insulation life is halved. Therefore, the usual effect of thermal wear is the vulnerability of the insulation system.

B. Stresses caused by the poor quality of the work environment: The factors that cause these stresses are as follows:

moisture

chemical

scratch (abrasion)[1]

Small foreign particles

C. Mechanical stresses: The factors that cause these stresses are as follows:

? Rotor hits: The collision of the rotor with the stator causes the stator sheets to destroy the coil insulation, and if this contact continues, the result is that the coil in the stator groove will ground very soon, and this is because The excess heat produced is at the contact point.

? Coil displacement: The force applied to the coils is caused by the coil current, which is proportional to the square of the current (F?). This force has its maximum value during start-up and causes coils to vibrate with twice the frequency of the network and their displacement in both radial and tangential directions. rtl;">? Non-uniform distribution of heat: this issue often happens when starting the engine, but the non-uniformity of the rotor material due to the manufacturing process may also cause this issue. Continuous start-ups and skin effect increase the possibility of thermal stresses in the rotor rods.

? Sparking of the rotor: In manufactured rotors, many factors cause sparking in the rotor, some of which do not cause problems for the rotor (non-destructive sparking) and others cause errors (destructive sparking). Non-destructive sparks occur during normal operation[2] of the engine and mostly during start-up.

? Hot spots and excessive losses: Several factors may cause excessive losses and hot spots.