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Volume 47, No 4 July-August 2011 Influence of Motor Operating Parameters on Discharge Bearing Current Activity "While the cause-and-effect chains of inverter-induced bearing currents have been well understood today, not much is known about the damage mechanism inside the bearings. Research has suggested that the bearing degradation is approximately proportional to the frequency of occurrence of the bearing currents. For bearing currents that occur statistically distributed-such as discharge bearing currents-this parameter has not been thoroughly researched yet. In this paper, we present an analysis of the influence of different motor operating parameters on the frequency of occurrence (“discharge activity”) of discharge bearing currents, using a non-intrusive detection method. When analyzed individually, the motor speed, motor shaft temperature, inverter switching frequency, and inverter dc-link voltage influence the discharge activity. However, the overall running time of the motor, the state-steady-state versus instantaneous-and the “operating history” on the time-scale of several days have the strongest effect on the frequency of the discharge bearing current occurrence.." Page 1741

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5766742



Volume 47, No 4 July-August 2011 Overvoltage Mitigation of Inverter-Driven Motors With Long Cables of Different Lengths "This paper presents an intensive discussion on an overvoltage appearing at the motor terminals of an adjustable-speed drive that consists of a voltage-source pulsewidth-modulated inverter, an induction motor, and a three-phase symmetric long cable. It describes a design procedure for a simple passive electromagnetic-interference filter based on parallel connection of an inductor and a resistor, which is intended for mitigating the overvoltage at the motor terminals. The modeling of the cable and the motor is characterized by focusing on the natural frequency or ringing frequency inherent in the cable used, which is inversely proportional to cable length. Impedance mismatch at the inverter and motor terminals causes the overvoltage that may reach double the inverter dc-link voltage. The effectiveness and validity of the simple design procedure of the filter are confirmed on the 400-V 15-kW experimental system with either a 100- or 200-m-long cable, as well as on computer simulation based on the modeling of the cable and the motor." Page 1741

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5766034



Volume 47, No 4 July-August 2011 Design Considerations When Applying Various LV ASD Topologies to Meet Harmonic Compliance "To limit the harmonic distortion produced by adjustable speed drives (ASDs), manufacturers have introduced several methods of both passive and active harmonic mitigation. Users of ASDs however, who are faced with the various options often find it difficult to select the most appropriate one for their particular application. Using computer simulation and laboratory measurements, this paper analyzes the most common passive solutions for low voltage (LV) applications which include ac line reactors or dc link chokes, phase shifting to produce multi-pulse ASDs and inline passive harmonic filters. Various design considerations, particularly related to power system parameters, are addressed." Page 1578

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5771097

 

Volume 47, No 3 May-June 2011 Applying High-Resistance Neutral Grounding in Medium-Voltage Systems "The application of high-resistance neutral grounding (HRNG) to medium-voltage (MV) distribution systems is one of the least understood and often misapplied methods of system neutral grounding. An HRNG grounded system is the only intentionally grounded neutral grounding method suitable for industrial systems that allows normal operation (no voltage dips, no power surges, no shutdowns, and minimal damage) for an indefinite time period after the inception of the most common of all faults, i.e., the single-line-to-ground fault. The complexity of applying an HRNG system is due to lesser understood factors, such as the relationship between system charging current, neutral grounding resistor let-through current, and point-of-fault ground-fault current; point-of-fault arcing voltage magnitudes; escalating arcing fault phenomena; and point-of-fault energy levels, all of which are not easily determined nor easily estimated. This paper addresses the application of HRNG neutral grounding systems on MV industrial ac power distribution systems. The seemingly perfect HRNG grounding system, with ground-fault-current magnitudes often limited to 10 A or less, has a limited window of application on MV systems, such that when misapplied may actually place the electrical system backbone components at risk, as well as trip the system offline due to escalating arcing faults resulting in phase-to-phase faults. HRNG applications in MV generator protection and MV arc flash mitigation are not within the scope of this paper." Page 1220

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5729812



Volume 47, No 3 May-June 2011Transient Overvoltage Protection of Shore-to-Ship Power Supply System "It is known that an unpredictable threat of transient overvoltage exists in a power system. Therefore, transient overvoltage protection analysis, commonly known as insulation coordination, should be performed to design cold-ironing power systems. This paper provides a review of the transient surge environment, transient overvoltage analysis, and the application of metal-oxide surge arresters at specific locations within the shore-to-ship power supply system to enhance transient overvoltage protection to minimize equipment damage." Page 1193

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5728905

 

Volume 47, No 2 Mar-Apr 2011 Transformer Failure Due to Circuit-Breaker-Induced Switching Transients "Switching transients associated with circuit breakers have been observed for many years. Recently, this phenomenon has been attributed to a significant number of transformer failures involving primary circuit-breaker switching. These transformer failures had common contributing factors such as the following: 1) primary vacuum or SF-6 breaker; 2) short cable or bus connection to transformer; and 3) application involving dry-type or cast-coil transformers and some liquid-filled ones. This paper will review these recent transformer failures due to primary circuit-breaker switching transients to show the severity of damage caused by the voltage surge and discuss the common contributing factors. Next, switching transient simulations in the electromagnetic transients program will give case studies which illustrate how breaker characteristics of current chopping and restrike combine with critical circuit characteristics to cause transformer failure. Design and installation considerations will be addressed, particularly the challenges of retrofitting a snubber to an existing facility with limited space. Finally, several techniques and equipment that have proven to successfully mitigate the breaker switching transients will be presented, including surge arresters, surge capacitors, snubbers, and these in combination." Page 707

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5674081



Volume 47, No 1 Jan-Feb 2011 Induction Motor Starting in Practical Industrial Applications Starting methods are compared for across-the-line and VFD Starting. Starting frequencies of 7, 8, 9, and10 Hz are compared for various cable lengths between 500 and 4000 meters. ".An electrical submersible pump system with various lengths of downhole cables is used as a motor-starting case study." Page 271

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5621895



Volume 46, No 6 Nov-Dec 2010 The Effect of Nonsinusoidal Current Waveforms on Electromechanical and Solid-State Overcurrent Relay Operation "...This paper has investigated how both an electromechanical and a solid-state protection relay are affected by the nonsinusoidal resulting current within the electrical system. The work was carried out using a commonly used GEC CDG11 electromechanical overcurrent relay and a Multilin 369 Plus digital Motor Management Relay. ..The test results showed that harmonic currents are not filtered out by either of the two relays and that both of the relays tested will operate faster than they are otherwise seen to do due to nonsinusoidal currents. The work further demonstrated that neither of the relays responded to the simple equivalent rms summation of the harmonic current in the circuit.." Page 2127

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5557796



Volume 46, No 6 Nov-Dec 2010 The Three-Phase Ground-Fault Circuit-Interrupter System—A Novel Approach to Prevent Electrocution "...Application of GFCIs at voltages higher than 120 V has not progressed because the higher voltages-to-ground result in higher capacitive charging current of branch and feeder circuits, which in turn leads to “nuisance trips.”...It then describes the three-phase GFCI System (GFCIS-3Ph) that overcomes nuisance tripping by a novel approach to sensing and tripping logic. The system is most applicable for lighting branch circuits due to the historical risk of these circuits, but the GFCIS-3Ph is also appropriate to be considered as an option for all three-phase branch or feeder circuits. Application of the GFCIS-3Ph technology has the potential to almost eliminate electrocution for persons who make direct contact between an energized phase conductor and ground on three-phase systems rated below 1000 V phase-to-phase. " Page 2276

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5560794


Volume 46, No 5 Sep-Oct 2010 A New Flicker Contribution Tracing Method Based on Individual Reactive Current Components of Multiple EAFs (Electric Arc Furnaces) at PCC  "The proposed method decouples the flicker contribution of the interconnected electricity system from the individual contributions of the loads connected to the measured PCC, using the individual current variations of the loads, and the estimated short-circuit system impedance. It has been shown that individual flicker contributions of the loads are mainly caused by the variation of their reactive current components." Page 1746 

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5324849

 

Volume 46, No 5 Sep-Oct 2010 Real-Time Power Quality Measurements From a Conventional AC Dragline "A typical mining facility uses excavation machines like shovels, draglines, etc., for removing overburden and ores during the mining process. These machines are characterized by cyclic loads consisting of high peak power demands as well as regeneration phases. The peak power demand is often as high as 1.6 times the average demand. This kind of a load leads to voltage fluctuations, harmonics, power factor issues, etc., at the main substation. This paper shows that superior results are now achievable with Siemens AC mining drive control system for draglines. By utilizing staggered pulsewidth modulation pulsing and operating the drive with leading power factor, the voltage fluctuation and line-side harmonics are regulated. The data presented in this paper are from an actual operational ac dragline that is now under production." Page 1755

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5523991

 

Volume 46, No 5 Sep-Oct 2010 Transient-Voltage Aspects of Grounding "When the surge suppression device cannot be directly connected at the terminals of the equipment to be protected, the impedance of the connecting means must be examined. High ground resistance and lead inductance greatly diminish the effectiveness of surge suppression. This paper describes a circuit approach to lightning protection starting with a discussion of infinite ground, ground resistance, and lead inductance." Page 1796

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5523987

 

Volume 46, No 5 Sep-Oct 2010 Design and Application of a Low-Ratio High-Accuracy Split-Core Core-Balance Current Transformer " This paper describes the design and application of a split-core current transformer (CT) of large dimensions, specifically designed for mounting in a 13.8-kV switchgear cubical on the phase bus bars. Although split-core CTs of high current ratio are available, the authors believe that the core-balance CT described in this paper is unique, as no similar CT was readily available in the U.S./European market. Thus, there is no equivalent installation in the industry of the specifications described in this paper. The CT discussed in this paper was specifically designed to meet the requirements of dimensions and accuracy for sensitive ground fault and directional ground fault relaying. Page 1856

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5523988

 

Volume 46, No 5 Sep-Oct 2010 Common-Mode Voltage Reduction PWM Algorithm for AC Drives "The impact of common-mode voltage (CMV) generated by pulsewidth modulation (PWM) ac drives on motor bearings is well known. Several algorithms for CMV reduction have been proposed in the literature. While a few algorithms assume ideal switching and fall apart when nonidealities like inverter dead time are considered, some others are effective only in a limited operating range of the drive. In this paper, a previously proposed algorithm is modified for practical implementation to include compensation for dead-time and reflected-wave motor overvoltage stress while still producing output voltage waveforms with reduced common-mode content. Page 1959

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5508411

 

Volume 46, No 5 Sep-Oct 2010 Prediction of Mechanical Shaft Failures Due to Pulsating Torques of Variable-Frequency Drives "This paper shows that the variable frequency drive incorporated in a rotating shaft is one of the main root causes of mechanical-shaft failures. Simple analytical relationships show that the frequencies of the motor air-gap torque have a more significant impact on the mechanical-shaft failure than their magnitudes." Page 1979

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5508410

 

 




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