Ahmed Sayed-Ahmed

Analysis and Diagnostics of Adjacent and Nonadjacent Broken-Rotor-Bar Faults in Squirrel-Cage Induction Machines

In this paper, faults associated with the rotor of an induction machine are considered. More specifically, effects of adjacent and nonadjacent bar breakages on rotor fault diagnostics in squirrel-cage induction machines are studied. It is shown that some nonadjacent bar breakages may result in the masking of the commonly used fault indices and, hence, may lead to a possible misdiagnosis of the machine. A discussion of the possible scenarios of these breakages as well as some conclusions regarding the types of squirrel-cage induction machines (number of poles, number of squirrel-cage bars, etc.) that may be more prone to these nonadjacent types of failures are presented. This discussion is supported through both simulation and experimental results. It is also shown that secondary fault effects can be used to diagnose such nonadjacent bar breakages.

Fault-Tolerant Operation of Delta-Connected Scalar- and Vector-Controlled AC Motor Drives

Operation and analysis of delta-connected ac motor-drive systems under fault-tolerant open-phase mode of operation is introduced in this paper for both scalar- and vector-controlled motor-drive systems. This technique enables the operation of the three-phase motor upon a failure in one of its phases without the need of a special fault-detection algorithm. It is mainly used to significantly mitigate torque pulsations, which are caused by an open-delta configuration in the stator windings. The performance of the fault-tolerant system was verified using a detailed time stepping finite element simulation as well experimental tests for a 5-hp 460-V induction motor-drive system and the results are presented in this paper This paper also compares the operation of this fault-tolerant mode of operation for the cases of scalar-controlled and closed-loop vector-controlled motor-drive systems.

Fault-Tolerant Technique for Δ-Connected AC-Motor Drives

A fault-tolerant technique for motor-drive systems is introduced in this paper. The technique is merely presented for ac motors with Δ-connected circuits in their stator windings. In this technique, the faulty phase is isolated by solid-state switches after the occurrence of a failure in one of the stator phases. Then, the fault-tolerant technique manages current-flow in the remaining healthy phases. This technique is to significantly mitigate torque pulsations, which are caused by an open-Δ configuration in the stator windings. The performance of the fault-tolerant technique was experimentally verified using a 5-hp 460-V induction motor-drive system and the results are presented in this paper.

A Reconfigurable Motor for Experimental Emulation of Stator Winding Interturn and Broken Bar Faults in Polyphase Induction Machines

The benefits and drawbacks of a 5-hp reconfigurable induction motor, which was designed for experimental emulation of stator winding interturn and broken rotor bar faults, are presented in this paper. It was perceived that this motor had the potential of quick and easy reconfiguration to produce the desired stator and rotor faults in a variety of different fault combinations. Hence, this motor was anticipated to make a useful test bed for evaluation of the efficacy of existing and new motor fault diagnostics techniques and not the study of insulation failure mechanisms. Accordingly, it was anticipated that this reconfigurable motor would eliminate the need to permanently destroy machine components such as stator windings or rotor bars when acquiring data from a faulty machine for fault diagnostic purposes. Experimental results under healthy and various faulty conditions are presented in this paper, including issues associated with rotor bar-end ring contact resistances that showed the drawbacks of this motor in so far as emulation of rotor bar breakages. However, emulation of stator-turn fault scenarios was successfully accomplished.

Analysis of Stator Winding Inter-Turn Short-Circuit Faults in Induction Machines for Identification of the Faulty Phase

The main objective of this paper is to develop and experimentally verify a method of identifying the faulty phase in a three-phase armature of an induction motor with concentric coil construction, when such an armature suffers from an inter-turn within one of its phases. This work leads to a new technique for identifying the faulty phase in concentric wound machines and estimating the associated fault severity without any requirement for additional sensors, wiring constrains, or knowledge of any other details of the machine design. The technique has been verified through several experimental test results

A Reconfigurable Motor for Experimental Emulation of Stator Winding Inter-Turn and Broken Bar Faults in Polyphase Induction Machines

The advantages and demerits of a 5-hp reconfigurable induction motor, which was designed for experimental emulation of stator winding inter-turn and broken rotor bar faults, are presented in this paper. It was perceived that this motor has the potential of quick and easy reconfiguration to produce the desired stator and rotor faults in a variety of different fault combinations. Accordingly, this would eliminate the need to permanently destroy machine components such as stator windings or rotor bars when acquiring data from a faulty machine for fault diagnostic purposes. Experimental results under healthy and various faulty conditions will be presented in this paper, including issues associated with rotor bar-end ring contact resistances, to demonstrate the benefits and drawbacks of this motor for acquiring large amounts of fault signature data.

Industrial regenerative motor-drive systems

Regenerative motor-drive systems are nowadays widely applied in numerous industrial applications. This paper is centered on comparing the application of the two well-known and widely used types of regenerative front end converters. Namely, Fundamental Front End (FFE) rectifier, and Active Front End (AFE). The paper also introduces a new control topology for the temporary operation of the FFE converter. This topology enables to temporary boost the DC bus voltage and consequently provides an enhanced ride through operation for the FFE. As well be shown, this control topology can be considered as a “quasi-AFE” as it utilizes four switching states of conventional AFE without employing current controllers and with reduced switching losses. Theory, analysis, simulation, and experimental results are presented to prove and support the technical discussion subject of this paper.

Design and analysis of an integrated differential-common mode filter for on site motor bearing problems

In this paper an integrated differential-common mode filter is introduced for solving on site motor bearing problems that are induced by Pulse Width Modulated (PWM) inverters. This topology significantly reduces or eliminates common mode voltage impressed on the motor bearing race that causes fluting as a result of PWM switching action. Prior filtering techniques required either a special inverter design with dc midpoint accessible or a special motor design using a Wye connected machine with available neutral point to solve the bearing fluting problem. The new filter does not require any modification in inverter power structure or motor if applied in motor-drive systems. It also eliminates the need for an isolation transformer that is also used to mitigate the fluting problem. This topology can be included in the power structure design stage or utilized as an optional add-on module for troublesome field applications. Although the introduced filter topology is applicable to any application that involves a PWM inverter, discussion and analysis in this paper is restricted to motor-drive applications. Theoretical background, description of the bearing problem and filter design, and a complete set of supportive experimental results is included.

Diagnosis of Inter-Turn Short Circuit for a Polyphase Induction Motor in Closed-Loop Vector-Controlled Drives

The main objective of this paper is to develop and experimentally verify a new technique to detect an inter-turn short circuit in one phase of a stator winding of an induction motor energized from a vector-controlled drive. This is in order to overcome the fault masking difficulties associated with the concept of depending on the actual magnetic field pendulous oscillation between the conventional voltage and current space vectors with respect to a reference that is unaltered by the compensation action of the drive. This technique is based on the flux pendulous oscillation phenomenon. This flux pendulous oscillation is also described in this paper, this in addition to the magnetic field pendulous oscillation previously addressed in prior publications. The new approach has been verified through experimental results which are represented here.

A new instantaneous point on wave voltage sag detection algorithm & validation

In industrial applications, power quality has been an issue drawing increasing concerns due to its severe consequences on system performance and downtime cost. Voltage sags are classified as one of the most common power quality issues. In order to guarantee system operation under several line sag scenarios, international standards such as SEMI F47, IEC-61000-4-34, and IEC-61000-4-11 have been established as guidelines for electrical/electronics manufacturers. In this paper, an innovative point on wave sag detection is introduced. Although the main focus of this work is centered on applications related to regenerative motor-drive systems, this approach can be utilized in a myriad of other applications such as grid-tie inverters, uninterrupted power supplies and advanced relay protection. In addition, the introduced technique is very effective at detecting repeated line sag conditions. The introduced detection method has been experimentally validated using a 20 HP regenerative motor-drive system setup under various line sag scenarios.