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Irving, TX, United States

Beisert P.,Shermco Industries
EC and M: Electrical Construction and Maintenance | Year: 2010

A proper performance testing of ground-fault protective equipment when first installed onsite is defined in the National Electrical Code (NEC), Art. 230.95 (C). The code says that the neutral conductor in a load circuit must pass through a zero-sequence sensor in the same direction as the phase conductors and the equipment bonding or grounding conductor must not be passed through ground-fault sensor. It is necessary to test the insulation resistance, which include temporarily removing the neutral disconnect link, due to the problems created by grounded neutrals downstream of the sensing device. Primary injection testing consisting of injecting primary current into the equipment phase and neutral conductors to duplicate the flow of ground-fault current under various conditions will prove that the Current transformer (CT) are mounted and wired correctly. Source

Alewine K.,Shermco Industries | Chen W.,TECO Westinghouse Motor Company
2011 Electrical Insulation Conference, EIC 2011 | Year: 2011

A quantitative review of the failure modes of over 1200 wind turbine generators repaired or replaced since 2005 has uncovered that fewer that half of the failures were electrical in nature and most of those were due to mechanical failures of the insulation support structure. In this paper, we will discuss briefly the overall failures and, in more depth, the nature of the electrical failures. Many of the failures appear to be of a serial nature due to inadequate original design of the machine and/or the insulation system. Some possible suggestions will be offered regarding repairs after catastrophic failure to help insure that the same type of failure will be less likely to repeat during the projected life of the turbine. These generators are exposed, at least in some part, to the typical voltage irregularities and mechanical stresses of any machine that operates 100 meters in the atmosphere in a wide variety of weathers. However, they are also sometimes affected by poor power quality from the IGBT based convertors used in most turbines. These failures could result from voltage stresses created by the convertor in the turbine or from neighboring turbines or, as has been suggested, even from neighboring wind parks. Defining actual root causes is therefore very difficult, but the immediate causes within the generator will be reviewed. Statistical information from other industries will also be used as a comparison to the relatively short experience of wind energy equipment. Where proper maintenance and mechanical analytical predictive techniques can drive major improvements in the mechanical life of the generators, the electrical failures are more difficult to identify before failure. © 2011 IEEE. Source

Alewine K.,Shermco Industries | Wilson C.,Siemens AG
2013 IEEE Electrical Insulation Conference, EIC 2013 | Year: 2013

Magnetic wedges (containing a high percentage of ferrite material) have been used successfully to improve the operating performance and optimize the physical size of motors and generators by reducing heating and improving efficiency. They contribute to the overall performance by smoothing the electrical flux characteristics and are utilized primarily in stator applications. In large generators utilizing fully cured coil systems, these wedges are readily inspected and replaced as needed during times where maintenance or reconditioning requires that the rotor be removed. Specialized equipment and techniques have been developed and this process is well implemented in the electrical generation industry. When global vacuum pressure impregnation systems are utilized, replacing loose wedges is very difficult. Reviewed in this paper will be several wind turbine generator applications where this is a common failure mode, some possible weaknesses in the design of the coil/slot configurations and some possible solutions to avoid a repeat failure after repair. Also, some identified but not confirmed causal forces will be discussed. © 2013 IEEE. Source

Moore M.,Shermco Industries
EC and M: Electrical Construction and Maintenance | Year: 2011

Some of the important considerations while assessing service-aged, medium-voltage (MV) power cables, are discussed. Life expectancy should be considered as the MV power cables operating in commercial, electric utility, and industrial locations can be exposed to a variety of environmental and operational stressors. For cables that fail early, their failure can be attributed to one of various failure modes such as particle discharge, treeing, and poor workmanship. A facility maintenance planner must justify the need to test the lifeline of the electrical power system, the MV power cable. The primary goal of any preventive maintenance plan for MV power cables is to test and analyze the overall insulation of the cable as well as to determine the serviceability of the accessories through data trending to prevent catastrophic failures. When an electrical outage is cost prohibitive or lacks internal support, a time-based predictive maintenance approach should be considered. Source

Moore M.,Shermco Industries
IEEE Conference Record of Annual Pulp and Paper Industry Technical Conference | Year: 2012

Developing an "Electrical" Multi-Employer Worksite Protection Program You are the host of many electrical contractors, and their electrical/non-electrical subcontractors who work at your sites on a daily basis. During your large planned outages it is necessary to bring in additional electrical/non-electrical contractors to perform maintenance & repairs on your sites electrical equipment. You are subject to OSHA's Multi-Employer Worksite Policy CPL 02-00-124 and have a completely different set of responsibilities and risks to mitigate. You need to start asking questions and obtaining data from each contractor to protect your company and yourself. You must know what your site hazards are, as well as how your contractor plans to mitigate those hazards. This paper will provide an overview of OSHA's Multi-Employer Worksite Policy CPL 02-00-124. In addition details will be provided on how to prevent regulatory multi-employer worksite issues with contractors that routinely work at your site, as well as those contractors who periodically work on site. © 2012 IEEE. Source

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