Electrical characteristics analysis (dielectric strength, resistance, etc.). Updated and approved documents and equipments operation manuals not existent. Figure 11 shows an example of incorrect crimping of C connector, where unsuitable crimping tool and matrix were used and the correction done by the contractor using an adequate crimping tool. According to IEEE (Institute of Electrical and Electronic Engineers (USA) standard 493-1990 the failure rate (failures per Unit-Year) is: Economic life time of an installation may be defined as “the time from installation to a situation where the annual maintenance and equipment caused outage costs exceed the discounted annual cost for new equipment”. Today’s technology allows equipment-temperature differences of one degree Celsius to be detected. Non existence of updated documentation, such as “. That said, it’s not just the equipment that makes a PD survey effective. Poor preparation of the cable, namely conductors’ core (, Use of abrasives and emery clothes with conducting grit or particles (. The real answer as observed in the field is … GUESSING! A similar situation may occur if fiber fusion of optical fiber cables is incorrectly executed or done by not qualified personnel. Damage to the tank and radiators protective coating and finishing, whether they are just hot-dip galvanization or painting, leading to corrosion (see Figure 8). He holds Bachelor’s and Master’s degrees from Purdue Univ. Excessive torque will cause mechanical stress on materials, which can lead to their destruction. Safe clearance between the tank and the active part may be compromised. To verify if internal cracks affected bushings tan δ measurement test (tan δ indicates the dielectric losses of an insulation material, that is to say, its dielectric strength) (see IEC Standard 60137) must be performed during FAT and SAT and the results of both tests must be compared. If new transformers are added and intended to work in parallel with existing transformers, It also must be taken into account the situation of existing and new transformers intending for work in parallel: in these circumstances all transformers must the, When transformers working in parallel do not have the. Personnel, in turn, will know exactly what needs to be replaced before even opening equipment, thus minimizing downtime. Thermographic or infrared (IR) surveys have been effectively used for decades to detect abnormal heating of electrical connections. With regard to PD, keep in mind that signal detection is just the first step in executing an online predictive-testing program. Eurofins E&E compliance and engineering teams perform failure analysis on electrical and electronic consumer products for manufacturers, brand owners and retailers to determine the cause of market-place failures and returns. Use of metal alloys with lower resistance to dezincification. Infringement of manufacturers’ instructions. When the bushings arrived to site and prior to the installation in the transformers tan δ was measured and the results compared with the IEC Standard 60137 acceptance criteria and with FAT results (that were properly conducted and witnessed by the owner representative). As steel and iron are magnetic and conductive materials eddy currents (Eddy currents or Foucault currents are induced currents in conductive materials when subjected to a variable magnetic flux.) The main problem for the installation of conductors of overhead lines, apart from deficient fixation, is the mechanical tension at which the conductors are subject in line poles; if that tension is close to or higher than tensile strength of the conductors’ material(s) a failure can occur. Identifying an asset that is emitting a PD signal may be all the information that operating and/or maintenance personnel need. It is recommended that for non armored cables pulling tension shall not exceed 5 kg/mm2 for copper conductors and 3 kg/mm2 for aluminium conductors. The name is derived from the cross-sectional shape of a bathtub. Although there’s no such thing as good PD in an electrical-distribution system, some equipment may have low levels of it with no signs of damage. An extensive 328-page resource manual includes hundreds of photos of a wide range of failures, with the likely causes listed, and a clear methodology for confirming the probable cause of each failure. The maintenance technician guesses at an answer and tries a fix. Your email address will not be published. Improper chemical composition of the materials. The process can prove challenging for individuals that don’t have experience diagnosing electrical-equipment problems. Several factors contribute for those errors and deficiencies and to expedite equipments without their correction; most common factors for such a situation are: One manufacturing error that unfortunately is much more common that the desirable are defects in welding processes (It is recommended that quality of electric arc welding shall be in accordance with the following standards: EN ISO 3834, EN ISO 15609-1, EN ISO 17635:2010, EN ISO 17636-2:2013 and EN ISO 17640:2010) such as existence of fissures or gaps, porosities, incomplete fusion of welding cord, existence of scoria/detritus, affected areas due to welding over temperature and heterogeneity of the welding cord (This type of error is also common in site works); Figure 4 shows some of these defects. The five PD. Mechanical characteristics are not in accordance with the foreseen stress of the material than can lead to premature mechanical fatigue. The consequence of these defects is weakness of mechanical resistance of the metallic structure that will lead to severe failures. Failure Electrical, LLC performs a wide array of investigations ranging from electric power systems to semiconductor devices. Insufficient torque may lead to bolts and nuts to unfasten; contact resistance may increase, causing excessive heating, a decrease of safety insulation distance between conductors and between conductors and ground can occur and short-circuit may take place and metallic structures may collapse, due to electromechanical stress. If circuit breakers are not replaced a failure of the system is expected to happen. Another problem that medium and high voltage cables face and that may contribute to failures is joints and terminations, which are known as the week points of the cables and if not properly executed, will lead later to failures. Visible evidence of PD can be a deposit of white powder (nitric acid) or green patina (verdigris) of copper. These can be classified in various ways, such as by time or cause. Leveraging multiple sensor technologies in these procedures helps ensure accurate data for improved diagnostics. Failure analysis and investigation can determine the root cause of failure should your product, component or asset fail or not perform as expected. Accurate interpretation of test data will provide operations with actionable information and, ultimately, lead to more-informed risk-management decisions. Corrosion may appear in the metallic structure of panels and cabinets, but also in the connection terminals of equipments and cable terminal blocks, which increase the contact resistance; which will lead to overheating of the equipments, causing the degradation of the dielectric strength of insulation (Dielectric strength: ability of an insulation material to withstand electric stress without breaking down (kV/mm)) . Such inquiry is conducted using scientific analytical methods such as electrical and mechanical measurements, or by analyzing failure data such as product reject reports or examples of previous failures of the same kind. Loss of nitrogen gas pressure due to leaks (. Defective restoration of insulation, using non suitable materials and techniques (, Poor tightness of joints and terminations, allowing the, Poor cutting, preparation, continuity and earthing of metallic screen and armor, if existing (, FAT & SAT Not Conducted or Improper Conducted. 9)  In the absence of other relevant Standards use NETA Standards MTS-2007 and ATS-2009 to define the periodicity of maintenance program and the type of tests to be performed on each type of equipment and the acceptance criteria. Procedures & Tests to Detect Failures Causes. For complex, repairable systems, failures are considered to be those out of design conditions which place the system out of service and into a state for repair. • particle discharge. Main factors for deficiencies in the execution of cable joints are terminations usually are: It shall be noted that the consequences of some the errors referred above only occurs after an indefinite period of time upon energizing. When such situations occur it is mandatory to test all welding using ultrasonic (Ultrasonic inspection uses high frequency sound waves to conduct examinations and make measurements) (NDT =Non-destructive test) method because of data accuracy, i.e., the depth of penetration for flaw/fault detection or measurement is superior to other NDT methods. types are: • surface discharge We depends on ad revenue to keep creating quality content for you to learn and enjoy for free. A measure to avoid failures in important equipments, such as power transformers, overhead lines, generators and medium voltage motors, and materials It must be referred that electrical equipments and systems, namely, – Master Degree in Electrical and Computers Engineering (2017 – Faculdade de Ciências e Tecnologia/Nova University of Lisbon), – Senior Consultant in Substations and Power Systems; Professional Instructor. 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