Medium-voltage (MV) induction motors are widely used in the industry and are essential to industrial processes. The breakdown of these MV motors not only leads to high repair expenses but also causes extraordinary financial losses due to unexpected downtime. To provide reliable condition monitoring and protection for MV motors, this paper presents a comprehensive survey of the existing condition monitoring and protection methods in the following five areas: thermal protection and temperature estimation, stator insulation monitoring and fault detection, bearing fault detection, broken rotor bar/end-ring detection, and air gap eccentricity detection. For each category, the related features of MV motors are discussed; the effectiveness of the existing methods are discussed in terms of their robustness, accuracy, and implementation complexity. Recommendations for the future research in these areas are also presented.

A Survey of Condition Monitoring and Protection Methods for Medium-Voltage Induction Motors

A method includes positioning a medical device within a body between adjacent spinous processes, moving the medical device from a collapsed configuration to an expanded configuration within the body using an actuator removably coupled to the medical device, and removing the actuator from the body while the medical device remains between the adjacent spinous processes.

Percutaneous spinal implants and methods

Fast acting static synchronous compensator (STATCOM), a representative of FACTS family, is a promising technology being extensively used as the state-of-the-art dynamic shunt compensator for reactive power control in transmission and distribution system. Over the last couple of decades, researchers and engineers have made path-breaking research on this technology and by virtue of which, many STATCOM controllers based on the self-commutating solid-state voltage-source converter (VSC) have been developed and commercially put in operation to control system dynamics under stressed conditions. Because of its many attributes, STATCOM has emerged as a qualitatively superior controller relative to the line commutating static VAR compensator (SVC). This controller is called with different terminologies as STATic COMpensator advanced static VAR compensator, advanced static VAR generator or static VAR generator, STATic CONdenser, synchronous solid-state VAR compensator, VSC-based SVC or self-commutated SVC or static synchronous compensator (SSC or S2C). The development of STATCOM controller employing various solid-state converter topologies, magnetics configurations, control algorithms, switching techniques and so on, has been well reported in literature with its versatile applications in power system. A review on the state-of-the-art STATCOM technology and further research potential are presented classifying more than 300 research publications.

Static synchronous compensators (STATCOM): a review

Three-phase multipulse AC-DC converters (MPC) are developed for improving power quality to reduce harmonics in AC mains and ripples in DC output. This paper deals with the multipulse AC-DC converter configurations, state of art, their performance, power quality aspects, components selection considerations, latest trends, future developments, and potential applications. It is targeted to provide broad perspective on multipulse converter technology to the researchers, engineers, and designers dealing with them. A classified list of more than 250 research publications on the subject is also given for quick reference.

Multipulse AC–DC Converters for Improving Power Quality: A Review

An electric drive apparatus and method for controlling medium-voltage alternating current motors wherein a multi-phase power transformer having multiple secondary windings provides multi-phase power to multiple power cells, each of which have a single-phase output and are controllable by a modulation controller. The primary and secondary windings in the power transformer may be star- or mesh-connected; the secondary windings may be shifted in phase. Because the power cells are connected in series, the maximum output voltage for each cell may be less than the maximum line-to-line voltage. The power cells can have a tri-state output which can be controlled using pulse-width modulation techniques. AC input power is converted to DC output power for each output phase. Output power modulation can be produced by interdigitating a selected number of carrier signals so that harmonic components reflected back to the input are attenuated.

Medium voltage PWM drive and method

Simple practical techniques which sense ac line current afford protection of motor windings for many applications. A more complete protection system is described which continuously monitors average winding resistance and hence temperature by means of an easily applied dc injection technique. No additional motor connections are required.

Motor Thermal Protection by Continuous Monitoring of Winding Resistance

This paper establishes the fundamental laws relating to the speed control of induction motors by simple voltage control and emphasizes the problems that may be caused by excessive input currents which cause stator overheating. Eight different thyristor voltage control circuits have been tested to determine a best control circuit for three-phase motors and test results are given. A practical speed control for a 4-hp motor is described and the way in which a special rotor design can minimize the problem of excessive stator losses is convincingly demonstrated.

Induction Motor Speed Control by Stator Voltage Control

A 18-pulse converter system operates without interphase transformer and neutral point on the DC side by providing three rectifier bridges across the DC terminals, one rectifier bridge being coupled with the AC terminals and the two other rectifier bridges being operated at + and -40 degress phase shift, while the rectifier devices are controlled for 40-degree current conduction.

Optimized, 18-pulse type AC/DC, or DC/AC, converter system

Low voltage GTO inverter modules are combined to form a high-voltage multi-inverter system by connecting standard modules in a string with isolated DC links. Modular construction is arranged for building multiphase systems. Voltage control is effected by controlling selected modules on the DC sides, or by pulse-width modulation of the inverter of a selected module.

High voltage modular inverter and control system thereof

In a multiphase AC/DC converter system a single transformer is used having phase shifted tappings drawn from a polygonal succession of long and short windings wherein some of the windings carry only the difference between the outputted currents derived from the tappings.

Derek A. Paice

Papers

Motor Thermal Protection by Continuous Monitoring of Winding Resistance

Induction Motor Speed Control by Stator Voltage Control

Optimized, 18-pulse type AC/DC, or DC/AC, converter system

High voltage modular inverter and control system thereof

Multi-pulse converter system