Frederick C. Trutt

Alternatives for assessing the electrical integrity of induction motors

The authors present alternative appropriate for detecting incipient failures in three-phase induction motors of the sizes commonly found in the process industries, with an emphasis on techniques resulting from a recently completed project. The techniques discussed are divided into three categories: periodic tests, sequence tests, and the decision-function method. The use of the effective negative-sequence impedance test is recommended for in-plant predictive maintenance applications. This test is sensitive to a wide range of degradation mechanisms that will ultimately result in motor failure, and its use can allow for timely repair of the motor before costly downtime or a catastrophic failure is incurred. The technique can be applied while the motor is in operation. It is recommended that this predictor be monitored continuously, rather than being applied on a periodic basis, because an appropriate interval between tests cannot yet be defined. The use of the decision-function method will allow a more detailed analysis of motor performance and condition. However, the price for achieving this increased information is high and may not be warranted in many situations.<<ETX>>

Condition monitoring of stator windings in induction motors. I. Experimental investigation of the effective negative-sequence impedance detector

The former US Bureau of Mines funded a research project aimed at developing the enabling technology for incipient failure prediction in electric power system components as a means of reducing the injuries and fatalities that sometimes occur when equipment malfunctions. Over the ensuing years, interest in this has waxed and waned, but interest has been growing for both civilian and military applications. This paper addresses the level of turn-to-turn insulation deterioration that can be resolved using an online monitoring technique based upon an effective negative-sequence impedance detector. The detection of turn-to-turn defects is especially important because they are believed to represent the beginning stage of most motor winding failures.

Condition monitoring of stator windings in induction motors. II. Experimental investigation of voltage mismatch detectors

For pt.I see ibid., vol.38, no.5, p.1447-53 (2002). Condition-based maintenance (CBM) of industrial equipment is generally recognized as being the most cost-effective means for improving equipment availability. However, a prerequisite to successful implementation of CBM is a reliable detector of failing components. One such detector, termed the effective negative-sequence impedance, had previously been identified as an indicator of an induction motor stator winding degradation. However, a limitation of this detector is that it may not change in a predictable manner for extremely low levels of deterioration. Presented in this paper is an experimental investigation of a technique for online detection of induction motor stator winding degradation that addresses this difficulty. It begins with a brief description of the detectors, followed by a detailed description of the experimental setup, the experiments conducted, and results.

The Newton-Raphson Load Flow Applied to AC/DC Systems with Commutation Impedance

Existing conditions in industrial ac-dc power systems may result in significant commutation resistances. If the resistance to reactance ratio of the commutation impedance is high, significant errors can result in load-flow studies which neglect the resistive portion. A method is presented for inclusion of a resistance-inductance fed bridge rectifier in a Newton-Raphson (N-R) load flow program. Polar form of the power flow equations is assumed. An example problem is provided for comparison.

Condition-based maintenance of electrical machines

Twenty-five years ago, the former US Bureau of Mines funded a research project aimed at developing the enabling technology for incipient failure prediction in electric power system components as a means of reducing the injuries and fatalities that sometimes occur when equipment malfunctions. Over the ensuing years, interest in this has waxed and waned, but interest has been growing for both civilian and military applications. This paper addresses the level of turn-to-turn insulation deterioration that can be resolved using an on-line monitoring technique. The detection of turn-to-turn defects is especially important because they are believed to represent the beginning stage of most motor winding failures.

Complete Analysis of the Operating Modes of the Resistance--Inductance-Fed Bridge Rectifier

Equations describing the ac-dc terminal relationships of the resistance-inductance-fed three-phase full-wave bridge converter from no load to short circuit are provided. Modal boundaries are plotted in the µ-α plane showing the limits within which these equations are valid. Results show the resistance to have a significant effect on the terminal characteristics. Modal boundaries are shown to be nonlinear functions of the commutation resistance-direct current product.

Dynamic Simulation of Coal Mine Electrical Power Systems

A flexible method for modeling mine electrical power systems is presented. Utilizing this simulation procedure, detailed analyses of bus voltages, transmission line power flows, and machine behavior are possible under conditions of steady-state or dynamic operation. Mining machine operation changes, as well as motor starting sequences, may be simulated. The model operates interactively, and the power system is configured as a user responds to program generated questions and requests. The theory behind the programming, as well as explanations of the models, are provided. An example is also given to demonstrate simulation capabilities.

Coordination-Free Ground-Fault Detection for Mine Distribution Systems

A ground-fault relaying scheme is presented that is intended to eliminate the need for time-delay relays for ground-fault detection on mine electrical distribution systems. The concept is based on pilot-relaying logic, and existing ground-check and grounding conductors are used to convey ground-fault information between adjacent relay units. The new scheme should not add any additional work during the installation of mine power systems and should minimize the expertise needed for power-system operation. To illustrate this concept, the design and development of the new relaying system is presented. The performance of a prototype relay during laboratory simulations is also given. Although the work is projected at underground coal mining, the relay appears feasible for any extensive radial distribution system.

Microprocessor-Aided Instruction in Power-System Protection

Supplementary use of microprocessors in electrical engineering education can provide an effective learning environment for introductory as well as advanced studies. In addition, sufficient exposure to microcomputers as a design and analysis tool is consistent with the ever expanding industria applications of these devices. Presented is an approach to the creation of such a situation through interactive application of a low-cost microcomputer system. The procedure given applies to the instruction of power system analysis and overcurrent relaying techniques, but it is evident that these analytical and graphic approaches could also be applied in other areas of electrical engineering.

An APL Laboratory for Power System Engineering Education

Supplementary use of the digital computer in power-system engineering education can provide an effective learning environment for introductory as well as advanced studies. In addition, sufficient exposure to the computer as a design tool is consistent with the expanding application of these devices in power-system planning. Presented is an approach to the creation of such a learning situation through application of an APL interactive programming system. Present instructional modules are oriented towards load-flow, fault, and transient-stability analyses, but may also be applied to other system problems which can be formulated in a bus frame of reference. Students utilizing this system in a computation session are required to define or set-up a problem, analyze results and to decide upon and evaluate any proposed system modifications. A portion of the material presented was developed with the support of the U.S. Department of Interiors Bureau of Mines under USBM Grant G0155003.