Two of the most common causes of electrical-equipment failure involve bad connections and deteriorated insulation. “Surely this is a mistake,” you’re thinking. Inappropriate storage of equipments and materials that is possible to find at the warehouse areas of manufacturers and contractors, but also in Owners installations, are a first step to a quick deterioration of those pieces, a fact that sooner or later will lead to failures that can be disastrous. 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. Also too keep defective pieces inside the warehouse area and not strictly identified as defective and clearly segregated from other pieces is a step forward for failures in equipments and materials. 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. This is a voltage event. 10)  Establish a safety plan for the operation and the maintenance (preventive and corrective) of the plant. Non existence of installation manuals provided by the manufacturer of equipments and even existing they are not generally followed. In transport practice there are no vibrations that consist only of a single frequency. Failures which occur that can be left or maintained in an unrepaired condition, and do not place the system out of service, are not considered failures under this definition. equipment. Improper package, handling and transportation. Mechanical characteristics are not in accordance with the foreseen stress of the material than can lead to premature mechanical fatigue. Hence, short-circuits may appear and a failure in equipments and materials will be observed. The 110 kV bushings of two power transformers 110/22 kV, 25/30 MVA (ONAN/ONAF) (. 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). This sensor is designed to transmit signals in a pre-determined frequency band to the PD-detection, distance between the PD signal source and the sensor, air-insulated and gas-insulated circuit breakers, potential, current, and control power transformers. Typical faults are loose joints leading … 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. 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. When preparing technical specifications, if there are incomplete definition of the characteristics of equipments, an absence of information about the working conditions of equipments and the lack of definition of applicable standards and wiring regulations, a high risk of using unsuitable materials and manufacturing procedures exists. Micro-circuit analysis including computer boards, circuit boards, chips and other specialty equipment; Motor testing of single and three-phase motors to determine and analyze performance and output for proper operation ; Our experts put all the pieces together and provide all the solutions for Electrical Failure Analysis. Contact him directly at Non existence of updated documentation, such as “. Power factor may also decrease this meaning increase of service currents. Hence, the risk of failures of equipments and materials is also high. Load changes/additions, circuit changes and changing voltage conditions without a re-design of installation. MTBF value prediction is an important element in the development of products. • type of cable shield 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. Variations in the voltage and current signals are analyzed in relation to some failure patterns. The first system failed at 100 hours, the second failed at 120 hours and the third failed at 130 hours. When looking at the failure patterns, the first three can be group together as the equipment having a defined life, in which the failure rates increase once the equipment has reached a certain age. Insulation, on the other hand, deteriorates with age. EP. 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. For this reason it is important to know main causes of those failures, their consequences and the procedures and tests to be performed in order to find the reasons why equipment or its materials failed. Do not forget that what is cheap sooner or later will become very expensive. 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. 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. What is the most common method of equipment failure root cause analysis? Most of failures result from overheating of equipments and materials what causes the weakness or loss of mechanical, physical and/or chemical properties of those materials, this leading to premature ageing, situation that is particularly sensitive for insulation materials that will lose their dielectric properties. Forensic inquiry into the failed process or product is the starting point of failure analysis. Follow, © Copyright 2020, All Rights Reserved 2012-2020 by. Vibrations are capable of exciting resonance vibrations or co-vibrations (resonance vibrations are generated if the natural frequency of a body coincides with a frequency of the inducing vibration and this induced vibration has sufficiently large amplitude; the body’s natural frequency depends on its material properties such as mass and modulus of elasticity). 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. Wrong erection procedures and use of inappropriate tools. • bushings If the location of concrete foundations of equipment metallic support in substations and overhead lines towers and poles is done improperly, not using topographic equipment, the consequent misalignment of metallic structures may subject conductors and high voltage equipments terminals to additional mechanical stress, which can cause a reduction of their mechanical strength and may happen the destruction of those materials and equipments failures. Stringently collect all relevant data required for the design of the plant. 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. If circuit breakers are not replaced a failure of the system is expected to happen. Annual or semiannual preventive maintenance and testing is recommended to maximize system reliability and availability of electrical systems. Mechanical vibrations may cause the windings to lose their clamping pressure, eventually leading to collapse of the windings during electric faults. In addition, units that are taken down for routine scheduled maintenance or inventory control are not considered within the definition of failure. Bad connections fail because of heat produced by the current passing through the highly resistive connection, which is a current event. Failure analysis is the process of analysing the component data or the component itself to determine the reason (s) for degraded performance or catastrophic failure of a component either, during component manufacturing and testing, during incoming inspection, or after … Vibrations are capable of exciting, To find out the problems of mechanical shocks above, To verify if internal cracks affected bushings, Common situations observed are the storage in conditions for which the equipments and materials and/or the respective package are not design and prepared –, It is common to see electrical and control panels and cabinets, designed to work indoors within a controlled environment, stored outdoors and which, When stored in reels or in similar packages, if cable ends are not be protected against the ingress of moisture, water, dust and other contaminants, the insulation will be damaged and suffers a, In Figure 9 it is shown a type of protective cable (in this case a, To avoid or minimize the damage of cable reels, when stored outdoors the, Equipments & Materials Mounting Errors & Deficiencies, Non existence or not use of updated and approved documents (“. 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. PD-signal detection is the first step in executing an online predictive-testing program. 7)  Establish a regular preventive maintenance program and procedures, keeping the records of all maintenance and repairs activities. To finish this chapter focus will be addressed to the installation of conductors of overhead lines and insulated cables laying and pulling and the execution of joints and terminations. 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. 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. TÜV SÜD is a global leader in failure analysis. Once a PD signal is detected, knowing the exact type of PD will help determine steps for dealing with the issue. 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. No matter the location, effectively detecting PD signals requires the right sensors. This evidence is the result of PD, not the cause. It requires expertise and resources to be able to interpret information gathered during a survey. This age may be time or usage such as hours, widgets produced etc. If these tests are not performed or improper conducted, for example use of not calibrated test equipments or with the respective certificates not valid, and if they are not witnessed by the Owner representative it will not be possible to ascertain any deviations from Standards and specifications and/or use of defective materials. The name is derived from the cross-sectional shape of a bathtub. Lack of care with equipments already installed (see Figure 10. Updated and approved documents and equipments operation manuals not existent. Today’s technology allows equipment-temperature differences of one degree Celsius to be detected. 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. Today, the reliability of electrical distribution equipment is making owners consider this kind of methodology to minimize system failures. 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. The same applies to the MTTF of a system working within this time period. There’s some debate in the industry regarding how far down the cable a sensor can detect PD. Among the reasons of equipments improper use it must referred: Load changes/additions and circuit changes without equipments characteristics modifications and installation of new equipment and without a detailed study of the new situation may lead to an increase of service currents, causing permanent overloads in cables, busbars and transformers, what means permanent overheating of those equipments, and mismatch of rated currents of switching equipments with new service currents. 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. 8)  If necessary use on-line equipments measurement techniques (Emphasis of on-line measurement techniques is on collecting pertinent data on equipments integrity and not on interpretation of data), namely for transformers. Some examples of this situation are: Improper package, not suitable for the particular type of equipment, its fragility, and special requirements of transportation, may cause damages, which of them may not be visible with the preliminary inspection that must be done when equipments arrive to site – visual check up must be done to verify if damage to the equipment and materials has occurred during transportation – and even in site tests. Chemical analysis (color, pH, composition, etc.). However, it is possible to see that the matrix used for the correction was not suitable for the connector dimension. Powerful & Cheap Circuit LED-716 LED Light Schematic, Electrical Earthing – Methods and Types of Earthing & Grounding, How to Calculate the Suitable Capacitor Size in Farads & kVAR for Power factor Improvement, Star Delta Starter – (Y-Δ) Starter Power, Control and Wiring Diagram. If the problem goes away (at least temporarily), the root cause … However, it is incorrect to extrapolate MTBF to give an estimate of the life time of a component, which will typically be much less than suggested by the original MTBF due to the much higher failure rates in the “end-of-life wear out” part of the “bathtub curve”.

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