These techniques may include time-of-flight, For cables, PD testing helps pinpoint defects in insulation, splices, and terminations. Contact him directly at Steve.Park@Vertivco.com. Experience shows that this case represents major causes for failures (this fact justifies the large length of this chapter); main reasons for equipments and materials mounting errors and deficiencies of equipments and materials are: Mistakes in wiring and cabling of power and control panels and cabinets are a quiet normal situation that can be correct with control of performed work or during FAT and SAT (see Chapter 9). Accurate interpretation of test data will provide operations with actionable information and, ultimately, lead to more-informed risk-management decisions. The first system failed at 100 hours, the second failed at 120 hours and the third failed at 130 hours. The five PD. SAT (In the absence of other relevant Standards use NETA Standard ATS-2009 (InterNational Electrical Testing Association (USA)) to define the type of tests to be performed on each type of equipment and the acceptance criteria) are performed after installation is complete and prior to energizing, to verify if packing, transportation and erection of equipments did not cause any harmful effects to the equipment and if they meet the specifications and the requests of the installation. Use of spare parts different from those recommended by the manufacturers. If working control, FAT and SAT are not performed, a simple wiring mistake may cause protections and/or circuit breakers tripping command, remote protection or remote trip not to actuate, situation that can lead to the total failure and destruction of the system. Establish an operation manual and a strictly switching program and define clearly the responsibilities. Under this assumption, any one particular system will survive to its calculated MTBF with a probability of 36.8% (i.e., it will fail before with a probability of 63.2%). Typical examples of use of inappropriate erection accessories are steel or iron pipe for the protection of alternating current single core cables and fixing steel or iron clamps to the same type of cables. Procedures & Tests to Detect Failures Causes. Another problem found in manufacturing processes is that iron and steel used in manufacturing do not have the required characteristics and an incorrect surface preparation and coating of metallic pieces, whether is hot-dip galvanization, cold galvanization or finishing painting upon galvanization (It is recommended that steel characteristics for metallic structures and surfaces protective coating and finishing painting shall be in accordance with the following standards: EN 10027; EN 1090-1; EN 10051; EN ISO 14713-2; EN ISO 12944-5; ISO 2063.). This age may be time or usage such as hours, widgets produced etc. As a consequence of those wrong procedures (examples: packages and the equipments are exposed to environment conditions that are not suitable; poor fixing and/or locking of the equipment/package are the most common problems in transportation), packages may be destroyed and mechanical shocks and vibration will be amplified with consequences that may be catastrophic to equipments. Intertek’s failure analysis and investigation services identify root causes of failures to improve future performance and solve problems. The safety of electrical equipment depends to a large extent on sound mechanical design. Failures can be caused by excess temperature, excess current or voltage, ionizing radiation, mechanical shock, stress or impact, and many other causes. Once a PD signal is detected, knowing the exact type of PD will help determine steps for dealing with the issue. Electrical systems, equipments and materials are subjected to failures that can cause the total destruction of equipments and severe power outages. 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. 11)  Keep records of all failures and their causes, as well as the inspections and tests performed in the investigation. Equipments and materials manufacturing errors and deficiencies. These transformers may hence have a permanent overload. It is common to see electrical and control panels and cabinets, designed to work indoors within a controlled environment, stored outdoors and which protection grade IP (defined by IEC Standard 60529) not suitable for storage outdoors; equipments and connections of those panels and cabinets will suffer the action of adverse environment and several types of contaminants. • void discharge Equipments and materials mounting errors and deficiencies. The most common method is to place a high-frequency current transformer (HFCT) sensor around the cable and/or drain shield before it is earthed. New technologies and techniques are improving detection of damaging heat and failure-predicting partial discharge. Tests to be performed for the evaluation of equipments status are not defined. Faulty picking and degreasing of the surface and poor surface cleaning will decrease the adherence of zinc coating, leading to corrosion of the metallic piece. • corona discharge In the United States a 100 MVA power transformer dated from 1945 and a 75 MVA power transformer dated from 1954 were found working still in good conditions, and also in Europe similar cases have been recorded. That’s why online predictive tools such as IR surveys and PD testing are becoming increasingly important. In fact, today’s technology is very effective at detecting PD in the vast majority of medium- and high-voltage electrical-distribution equipment, including: • insulating boards We depends on ad revenue to keep creating quality content for you to learn and enjoy for free. The complex transportation environment always results in a frequency composition (frequency spectrum) with individual frequencies having different amplitudes. Failure of cutting off a portion of cable after pulling to assure an undamaged end. Experience shows that power transformers, cables (including, However, failures of other equipments and materials due to those causes must not be neglected and it must also be paid a particular attention to operation mechanism of medium and high voltage. The MTBF of the system is the average of the three failure times, which is 116.667 hours. 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)) . 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. • floating electrode SAT reports must be compared with FAT reports, in order to verify any deviation from the values measured during FAT. Complete cutting of insulation, which will not avoid damages in the conductors’ strands. A wrong connection will cause the motor to rotate in the opposite direction that it should, what can damage main contacts and operating mechanism and even support insulators. Commonly Infrared Analysis is done each 2 or 3 years, while equipment is energized and under full load, if possible, but special functioning and environment conditions may require to conduct IR annually. Maintenance activities not scheduled in accordance with the type, duty cycle and working conditions of equipments and materials. If the “Down time” (with space) refers to the start of “downtime” (without space) and “up time” (with space) refers to the start of “uptime” (without space), the formula will be: The MTBF is often denoted by the Greek letter θ, or “MTBF = θ”. will circulate in those accessories causing heating (by Joule effect) and cables will be subjected to overheating, which consequences and the influence in equipments failures were already analyzed. In these cases, it’s not the level of a PD signal that should cause concern, but, rather, any changes in it. Your email address will not be published. If PD is found to be coming from an asset during an initial survey—but more information is needed to determine the cause—advanced techniques and technologies may be required to pinpoint the source. All Rights Reserved. Package of equipments and materials must be suitable to the type of equipments and to the means of transportation and, whenever justifiable, must also have specific handling signs, according to ISO (International Organization for Standardization) Standard 780-2005 showing the care that must be taken when handling, as shown in Figure 6. Please consider supporting us by disabling your ad blocker. “Surely this is a mistake,” you’re thinking. PD signals should not be classified by magnitude alone. In summary, in order to establish basic failure analysis capabilities for an in-house or independent lab, the costs, facilities, maintenance, supplies, inspections, and personnel selections must be taken into account. A typical example of use of inappropriate tools is, Figure 11 shows an example of incorrect crimping of, Another typical error of erection activities that may be responsible for equipments failures is the, Typical examples of use of inappropriate erection accessories are, Another erection error that requires a special attention is, If these conditions were not fulfilled the, The main problem for the installation of conductors of overhead lines, apart from. Nike Zoom-Air tennis shoe worn by a boy struck by lightning at a bus shelter. Typical manufacturers’ data for MTBF of oil-immersed transformers are 30 years, although experience shows that transformers may have higher MTBF and a useful life of about 50 years, or even more. Understanding its causes and how to address them based on survey results is more complicated. Electrical surges and failures can seriously damage this kind of valuable, fragile equipment. and metallic structures, such as overhead lines poles, supports of high voltage equipments, transformers tanks and lighting poles, are the most affected equipments and materials by failures resulting from the causes above referred. When exothermic welding is used for earth grid connections (using a proper kit) the work must be performed by specialized personnel and it must be assured that the number of exothermic welding done with each mold will not exceed the indications of the manufacturer. Understanding the causes and how to best address them based on survey results is much more complicated—and may require expert assistance. Let us look at the following example, corresponding to a real situation: The 110 kV bushings of two power transformers 110/22 kV, 25/30 MVA (ONAN/ONAF) (ONAN/ONAF refers to the cooling method of transformers: ONAN: oil natural, air natural; ONAF: oil natural, air forced) were transported to site by sea, separated from the transformers. Identifying an asset that is emitting a PD signal may be all the information that operating and/or maintenance personnel need. According to the National Fire Protection Association in 2011 an estimated 47,000 home structure fires and 16,400 non-home structural fires were attributed to an electrical malfunction or failure. Design will not be correctly carried out, calculations will be inaccurate and equipments will not be properly chosen and specified. If these conditions will be disregarded during design stage, sooner or later equipments and their materials will fail. Steve Park is the manager of Technical Services for Vertiv’s (Columbus, OH, Vertivco.com) Electrical Reliability Services business. That said, it’s not just the equipment that makes a PD survey effective. • particle discharge. An example of incorrect surface coating situation represented in Figure 5. It is an important discipline in many branches of manufacturing where it is a vital tool used in the development of new products and for the improvement of existing products. It should be noted that the failures caused by internal cracks in bushings usually only occurs after an indefinite period of time upon energizing. Deteriorated insulation can be detected by a partial discharge (PD) survey, which detects signals emitted from the partial discharges occurring in deteriorated or stressed insulation. Root Cause Analysis: Electrical Fires & Explosions. and an MBA from Indiana Wesleyan Univ. Non existence of updated documentation, such as “. There’s some debate in the industry regarding how far down the cable a sensor can detect PD. A typical example of use of inappropriate tools is crimping operation of cable jointing connectors and terminals and C connectors (for copper bare cable of earthing grid), when a duly calibrated mechanical, pneumatic or hydraulic crimping tool suitable for the terminal to be crimped is not used and the the matrix employed is not compatible with the cross section of the cable and/or the dimensions of the connector. Personnel, in turn, will know exactly what needs to be replaced before even opening equipment, thus minimizing downtime. 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. 3)  Establish restrictive rules and procedures inside the company for materials and equipments storage and impose them to manufacturers (for a specific contract) and contractors. 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 same impedance voltage drop and the same vector group that is to say that transformers have the same internal resistance and that there no phase shift between the voltages. Also pulling in rough soil, with stones, detritus and other abrasive elements (plants, tree roots, etc.) Lack or poor supervision and control of performed work. A similar situation may occur if fiber fusion of optical fiber cables is incorrectly executed or done by not qualified personnel. IR analysis should also be conducted after any maintenance or testing to see if connections that were broken were remade properly. Measures to Avoid Equipments & Materials Failures. It describes a particular form of the hazard function which comprises three parts: The first part is a decreasing failure rate, known as early failures. This sensor is designed to transmit signals in a pre-determined frequency band to the PD-detection Use of equipments with environment conditions, function and duty cycles different from those initially foreseen. But, with so many sites operating around the clock, maintenance schedules can stretch beyond the comfort level of plant managers. 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. Infringement of manufacturers’ instructions. Errors and deficiencies during erection and incorrect mounting of equipments and materials occur much more frequently than it was supposed to happen and are an important cause of equipments and materials failures. 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. Microscopic examination (optical or scanning electronic microscopy). Technical improvements in new equipment may as well reduce the economic life time of the existing equipment if the overall outage time is reduced and production losses decreased. Use qualified and trained personnel and suitable tools and test equipment. MTBF is the predicted elapsed time between inherent failures of a system during operation, and can be calculated as the arithmetic mean (average) time between failures of a system, and is typically part of a model that assumes the failed system is immediately repaired (Mean Time to Repair, or MTTR), as a part of a renewal process. Even in qualified and certified manufacturers with installations that meet all the requirements manufacturing errors and deficiencies may happen. Having this level of detail makes it easier to acquire the correct spare parts prior to a scheduled outage. EP. An initial PD investigation will establish a baseline that can be compared with future testing results. Although all type of installations are subject to fails and every time that a failure occurs an investigation must be conducted, a special care must be taken with power plants, Design Errors & Deficient Equipments & Materials Specification. Chemical analysis (color, pH, composition, etc.). Design errors may be a consequence of incorrect, insufficient and/or incomplete data regarding the characteristics, the duty cycle and the expected functioning of the installation, provided by the Owner. Factors such as heat, moisture, and contamination, however, can lead to premature failure. TÜV SÜD is a global leader in failure analysis. The destruction of cable reels is a typical example (see Figure 7), but damages in the insulators (cracks) of high voltage equipment (circuit breakers. Failure analysis and investigation can determine the root cause of failure should your product, component or asset fail or not perform as expected. The third part is an increasing failure rate, known as wear-out failures. Distribution Equipment Failure Analysis (DEFACS) Fast, accurate analysis of Distribution equipment failures, identification of the root cause, confidential results, and effective recommendations to prevent dangerous and costly reoccurrence. Modifications of plant and equipments operating conditions without refreshment of personnel. For cables, PD testing helps pinpoint defects in insulation, splices, and terminations. When cable reels are in very damaged, or even destroyed, the outer sheath of the cable risks also to suffer damages, which can extend to the insulation, allowing the ingress of moisture, water, dust and other contaminants, with the consequences that were described above. What is the most common method of equipment failure root cause analysis? Poor knowledge of systems and equipments and poor training of personnel. Due to active part movement, the insulation between the turns can be abraded, causing a short circuit and damage to the windings later during operation. Poor preparation of the cable, namely conductors’ core (, Use of abrasives and emery clothes with conducting grit or particles (. MTBF value prediction is an important element in the development of products. That said, it’s not just the equipment that makes a PD survey effective. Note: This paper is registered at IGAC (Portugal) under the number 4239/2016 and protected by copyright, About the Author: Manuel Bolotinha-Licentiate Degree in Electrical Engineering – Energy and Power Systems (1974 – Instituto Superior Técnico/University of Lisbon) – 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, Your email address will not be published. Today’s technology allows equipment-temperature differences of one degree Celsius to be detected. His 35+ years of experience with power systems includes 14 years with the U.S. Air Force, during which he served as a high-voltage lineman, electrical-power-distribution engineer, and instructor. The bathtub curve is widely used in reliability engineering. Design errors and deficient equipments and materials specification. 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. Leveraging multiple sensor technologies in these procedures helps ensure accurate data for improved diagnostics. No matter the location, effectively detecting PD signals requires the right sensors. • type of cable insulation Some discharges, such as a floating electrode, can produce a large magnitude of PD signal but, because of its location, may pose little or no threat to equipment failure. 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. The second part is a constant failure rate, known as random failures. Electronic components have a wide range of failure modes. Simply wiping away the powder or cleaning the patina is not a solution. To find out the problems of mechanical shocks above 3g, SFRA test (Sweep Frequency Response Analysis (SFRA) consists of measuring the impedance of transformer windings over a wide range of frequencies and comparing the results of these measurements to a reference set) (Sweep Frequency Response Analysis – see IEC (International Electrotechnical Comission) Standard 60076) must be performed during FAT and SAT and the results of both tests must be compared. Also incorrect handling may cause several harmful effects on equipments and materials, presenting similar problems to those referred for improper package and a preliminary inspection is also required. If PD is found to be coming from an asset during an initial survey, but more information is needed to determine the cause, advanced techniques and technologies may be required to pinpoint the location of the source. Under these circumstances remote switching operations, necessary to assure the stability of the network or to isolate a faulty section, will not occur, causing the equipments to fail. An Electrical Arc Furnace was facing Electrical Failure from power system harmonic resonance. It is recommended to use impact (or shock) recorders during transformers transportation to evaluate the magnitude of mechanical shocks. The asset can then be taken offline for an inspection to identify the cause of the PD and determine how to deal with it. An inappropriate definition of protection system, not taking into account the characteristics of the installation and the nature of possible faults, and an incorrect coordination and selectivity protection study are a permanent source of electrical systems and equipments failures. types are: • surface discharge The path to success starts with an understanding of what specifically causes these trouble spots—and how to detect them. Bad connections can be the result of poor contact pressure (inadequate torquing of bolts, insufficient pressure in compression lugs, poor mechanism pressure), deficient contact surface, or dirt and corrosion. Load changes/additions, circuit changes and changing voltage conditions without a re-design of installation. site tests and laboratorial tests (Laboratory shall be independent and certified) shall be performed by a multidisciplinary team of experts. • dry-type and liquid-filled transformers MTBF describes the expected time between two failures for a repairable system, while MTTF denotes the expected time to failure for a non-repairable system. Once again, if these tests are not performed or improper conducted and if they are not witnessed by the Owner representative a risk of equipment failure exists. The resulting reports can be used: Common errors in hot-dip galvanization are faulty picking and degreasing of the surface, poor surface cleaning and insufficient thickness of zinc coating (According to applicable standards the thickness of zinc coating depends on environment aggressiveness and of the type and dimensions of metallic profiles used in manufacturing process). and not using proper special equipments (see insulated cables erection errors) may damage the conductors by broking or wounding some of the wires. • insulators of all types Use of low quality or not suitable materials. The 110 kV bushings of two power transformers 110/22 kV, 25/30 MVA (ONAN/ONAF) (. The first step in a root cause failure analysis is data collection. ), due to the use of unsuitable calculation tools or a wrong evaluation of the data available may cause a permanent overload of those equipments, which leads to overheating and dielectric breakdown, or the destruction of equipments if they cannot withstand short-circuit thermal and electromechanical stress. Leonard C. Quick & Associates, Inc. can help business owners, investigators and claims specialists understand the root causes of electrical equipment failure or damage — and we can provide detailed reports analyzing equipment failure and the appraisal of relevant systems. Mechanical properties and dimensions analysis. In Figure 9 it is shown a type of protective cable (in this case a heat shrinkable cap) and a cable not protected against the penetration of moisture, water, dust and other contaminants. Then he or she can encapsulate it back into its package and hand over the chip back to you, so you can continue with your debug activities. We will also work with you to determine your goals for the failure analysis examination, determine how the part should operate, and consult with additional subject matter experts, if needed. These techniques can uncover areas of overheating and insulation deterioration—two of the leading causes of equipment failure—sooner than later. It requires expertise and resources to be able to interpret information gathered during a survey. Use of steel with low resistance to corrosion (. These techniques may include time-of-flight 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). 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. This is in contrast to the Mean Time to Failure (MTTF), which measures average time to failures with the modeling assumption that the failed system is not repaired (infinite repair time). Non existence of installation manuals provided by the manufacturer of equipments and even existing they are not generally followed. Some typical tests to detect failures causes are: Taking into account what was explained in the previous chapters it is possible to conclude that the Owner must take all the precautions to avoid equipments and materials failures due to the causes described above, implementing a set of actions and procedures, apart from above referred cared actions: 1)  Designate a team of experienced technicians for: 2)  Establish clear rules inside the company for package, handling and transportation of equipments and materials and impose them to manufactures, carriers and contractors. Failure analysis process TI’s FA process discovers electrical and physical evidence to clearly identify the cause of failure through straightforward but sophisticated analytical measurement systems, bench top equipment, and a range of other techniques. Typical faults are loose joints leading … It is important to be aware that FAT and the applicable Standards must be clearly defined during design/ ordering stage(s) and that their reports must always accompany the equipment when it is expedited. The real answer as observed in the field is … GUESSING! As analyzed above, improper package may cause damages in equipments during transportation, but an incorrect transportation procedure, mainly in sea transportation, namely with troubled sea, and in road transportation, if the road is very rough (although it is known that transportation under these conditions will cause vibrations and small shocks in packages and equipments), may cause severe damages to the equipments. All relevant results of inspection and tests must be recorded, discussed and analyzed and a report must be produced; this report may include recommendations if it is considered pertinent. 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