Austin H. Bonnett

Cause and analysis of stator and rotor failures in three-phase squirrel-cage induction motors

The authors attempt to identify the various causes of stator and rotor failures in three-phase squirrel cage induction motors. A specific methodology is proposed to facilitate an accurate analysis of these failures. It is noted that, due to the destructive nature of most failures, it is not easy, and is sometimes impossible, to determine the primary cause of failure. By a process of elimination, one can usually be assured of properly identifying the most likely cause of the failure. It is pointed out that the key point in going through this process of elimination is to use the basic steps of analyzing the failure class and pattern, noting the general motor appearance, identifying the operating condition at the time of failure, and gaining knowledge of the past history of the motor and application.<<ETX>>

Analysis of the impact of pulse-width modulated inverter voltage waveforms on AC induction motors

The purpose of this paper is not to reveal any new technology or major break through pertaining to the impact of pulse width modulated (PWM) adjustable speed drives operating on AC motors. Nor is it to discuss the merits of the various designs of the drives. The applications are also well defined. The area where much confusion still exists deals with the voltage waveform impact on the motor performance. Hence, this is the central theme of the paper. The author has assumed that the traditional fundamental sinewave voltage is (except for starting or outside influences) a steady state condition, with a maximum and an RMS value. The effects of the maximum voltage, rate of rise, switching frequencies, resonance and harmonics are all considered.<<ETX>>

Rotor Failures in Squirrel Cage Induction Motors

During the past two decades, tremendous improvement has been made in the design and manufacture of stator windings. This has been accomplished primarily through the development of improved insulation materials and treatment processes. As a result, the expected life from a thermal, dielectrical, mechanical, and environmental standpoint has been significantly increased. The rotor design and manufacturing remains basically unchanged. A survey of warranty data and service facilities suggests that rotor failures now account for a larger percentage of the total induction motor failures. The majority of these failures are caused by various stresses which act on the rotor assembly. These various stresses and how they affect the life of the motor and contribute to premature failure are discussed.

Root cause AC motor failure analysis with a focus on shaft failures

The squirrel-cage induction motor remains the workhorse of the petrochemical industry because of its versatility and ruggedness. However, it has its limitations, which, if exceeded, will cause premature failure of the stator, rotor, bearings or shaft. This paper is the final abridgement and update of six previous papers for the Petroleum and Chemical Industry Committee of the IEEE Industry Applications Society presented over the last 24 years and includes the final piece dealing with shaft failures A methodology is provided that will lead operations personnel to the most likely root causes of failure. Check-off sheets are provided to assist in the orderly collection of data to assist in the analysis. As the petrochemical industry evolves from reactive to time based, to preventive, to trending, to diagnostics, and to a predictive maintenance attitude, more and more attention to root cause analysis will be required. This paper will help provide a platform for the establishment of such an evolution. The product scope includes low- and medium-voltage squirrel-cage induction motors in the 1-3000 hp range with anti friction bearings. However, much of this material is applicable to other types and sizes.

A comparison between insulation systems available for PWM inverter fed motors

This paper establishes the need for two levels of motor insulation systems depending upon the available voltage waveform. An analysis of the various winding stresses is presented. The different requirements for the two insulation systems is discussed (MG1-Parts 30 and 31 for General Purpose and Definite Purpose Inverter Fed Motors), and test results show the need for higher dielectric insulations when the voltage levels of Part 30 are exceeded. The differences between existing, rebuilt and new motors is also explored.

Analysis of Winding Failures in Three-Phase Squirrel Cage Induction Motors

Every motor user is faced with the fact that someday his motor will fail. Due to the destructive nature of most failures, it is not easy to determine the cause. The purpose of this paper is to introduce a procedure for analyzing these failures and determining the cause so that further steps can be taken to eliminate them.

Understanding Efficiency in Squirrel-Cage Induction Motors

The various design considerations affecting motor efficiency application are presented. Various application suggestions are offered for efficiency instruments. Recommendations are made for testing and comparing efficiencies along with economic considerations.

Repair or replace

In the past, the decision whether to repair or replace an electric motor has been one of economics. Replacement of an older electric motor with a more efficient model often makes sense for a motor operating continuously. However, in most cases, the decision is more complex. The purpose of this article is to explore both the choices and present some of the many options available. An application checklist, types and levels of repair for the motor are provided in this article.

Operating temperature considerations and performance characteristics for IEEE 841 motors

This paper reviews the operating temperature considerations and performance characteristics for totally enclosed fan cooled motors (TEFC) as covered in the IEEE 841-2000 motor standard. NEMA MG-1-1998 motor standards are also included since they are embodied in the IEEE standard. Although the scope of product covered is for AC squirrel cage induction motors through 500 HP, the material presented has application with many other sizes and types of motor. The paper reviews this standard as it applies to the motor operating temperature and various performance characteristics. The impact of temperature on the stator winding, rotor cage, bearings, lubrications, as well as the effects on motor efficiency and other applicable life factors are considered.

Understanding the changing requirements and opportunities for improvement of operating efficiency of AC motors

The need for higher levels of motor efficiency is increasing significantly. Numerous opportunities are available to reach these levels, many of which are being influenced by changes in government regulations, rebate programs and industry standards. The opportunities available to achieve higher performance levels, the activities that are driving these higher levels and the impact of adjustable frequency drives are discussed. Future required performance levels and the method of demonstrating compliances are summarized. The relationship and tradeoffs between efficiency and power factor are addressed.<<ETX>>