Jeffery L. Kohler

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>>

On-line condition monitoring of induction motors

Condition monitoring of induction motors is a process that may be used to great advantage in mining and other industrial applications. The early detection of motor winding deterioration prior to a complete failure provides an opportunity for maintenance to be performed on a scheduled routine without the loss of production time. Presented in this paper is a theoretical and experimental analysis of a voltage mismatch technique that may be used in operating situations to monitor the health of induction motor windings. It extends previous work in this area by demonstrating the robust nature of the monitoring process not only under conditions of power supply unbalance but also in situations where motor construction imperfections exist and mechanical loads are unpredictable. A suggested procedure for application of this condition monitoring process in industrial situations is also included.

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.

Technological innovations in deep coal mine power systems

Various innovations and changes have occurred to underground coal mine power systems during the past ten years. Some of these are the use of higher utilization and distribution voltages and associated switchgear, the use of programmable logic controllers for control, monitoring and diagnostic applications, improved protective relaying with built-in test circuitry, power-factor correction near loads for improved voltage regulation and modifications to power system component arrangements. Many of the innovations were necessitated by significant increases in power requirements of face equipment, particularly longwall equipment, while others are the result of improved technology. In either case, improved power system operating characteristics, as well as enhanced levels of safety, have resulted. This paper describes many of the major innovations that have evolved during recent years.

Location Strategy for Methane, Air Velocity, and Carbon Monoxide Fixed-Point Mine-Monitoring Transducers

The placement of mine-monitoring system sensors, or transducers, requires considerable planning and forethought so that the potential benefits of mine monitoring can be realized. The intended use of the monitored data will often dictate specific locations for sensors, although in many cases technical constraints, imposed by sensor or measured characteristics, will affect the choice of locations. Some of the factors and considerations that should be examined prior to sensor installation are presented. Some proposed decision-making procedures to help the system designer select appropriate locations are given. The conclusion is a description of forthcoming in-mine experimental programs that will be used to learn more about sensor location procedures and to further evaluate the recommendations given here.

An improved model for analyzing industrial power systems

A new program for performing the computer analysis of industrial power systems is presented. This program can be used for load flow, fault, and machine starting analyses, and to compute, interactively, desired levels of reactive power compensation. A brief review of the application of such programs is given. This program is described, and an example of its application to mine power systems is presented. >

Power factor and power factor control alternatives for mines

The benefits of controlling power factor are briefly reviewed. Power-factor compensators suitable for mine power systems are discussed along with a novel implementation of an adaptive power factor controller. An economic analysis technique for determining the amount and type of compensation is given. A procedure for sizing compensators in mine power systems is recommended.<<ETX>>

An analysis of air volume-flowrate determinations for mines

Abstract The proper control and distribution of ventilation air is a key aspect in the productivity of an underground mining operation, and is crucial to the health and safety of mine workers. Accurate measurement of air velocity is an essential component in achieving effective ventilation planning and control. However, the measurement methodology and application is problematic, especially in the use of correction factors. This paper examines the accuracy of these factors as they are affected by measurement location, instrument, and flow characteristics. Definitive recommendations are presented to improve the accuracy of flowrate determinations.

New insight into the detection of high-impedance arcing faults on DC trolley systems

High-impedance arcing faults are difficult to detect with conventional switchgear, and the presence of these faults in coal mine power systems represents a significant fire hazard. Research was performed to identify plausible techniques that would discriminate between the high-impedance arcing faults and legitimate load currents on the DC trolley system. This paper briefly summarizes that effort, and focuses on the frequency characteristics of the arc current. After the arc was modelled as a stochastic process, good agreement was obtained between experimental observations and mathematical predictions.