This document establishes guidelines for each step of the repair of power transformers, describing record keeping, tests, analysis, and general guidelines for the repair of power transformers. If the application is a fan, blower or downhill conveyor, where the motor might start while the load is free-wheeling in reverse, the solution could be a brake – either mechanical or otherwise, interlocked with the drive to release the brake when the motor starts. The disadvantages of the larger number of insulators are that both the polluted and the impulse flashover voltages increase. Specific to any DC motor, there are several preventive measures to reduce the chance of a flashover. Look to EASA for a limited time offer on deeply discounted bundles of webinar recordings. The present paper comprises an experimental investigation into the prediction of the critical flashover voltage of polluted insulators energized with AC voltage using a multi-channel photo-multiplier (MCP) and high speed camera to observe the behavior of ac arc on electrolytic surface. As a verb arc is to move following a curved path. Replacement of porcelain insulators with non-ceramic insulators. A constant leakage current flows through the semiconducting glaze. Blaming the drive may instead mean that the motor is in an application calling for a regenerative drive, but the customer replaced the drive with a less expensive model that cannot handle the regenerative mode. Substations are equipped with permanent washing systems. Deposition of a pollution layer due to exposing to the sea, road salt, insoluble dust, and various forms of industrial pollution such as sulfates from coal—fired electric power plants [2].. 2. The causes of a flashover can be partially explained by the insulating properties of air, and Ohm’s Law. Revisit — or watch for the first time — all the sessions from EASA 2020 Reimagined! Flashover usually means widespread and uniform destruction. How to improve this? Visit our co-branded website to order your products online. Application insulators are covered with a semiconducting glaze. Each of these will reduce the dielectric strength of air. 2. Tests have proven that when a flashover occurs … They check rotation and discover that the motor needs to be reversed. Proper Repair/Rewind Practices Maintain Efficiency/Reliability of Premium Efficiency/IE3 Motors, Enter one or more words to find resources containing, Enter words or phrases between " " to find, Getting The Most From Your Electric Motors, Power supply considerations when building a large growler, Carbon Brushes and Commutation: A Practical Approach to Failure Analysis, Commutator maintenance tips and tests: Checking for loose bars and methods to tighten them, How to strip an armature without degrading the core, Surge testing of DC motor and generator armatures, Troubleshooting tips for armature rewinds, Training Film 14: Taking Data From a Hand-Wound DC Armature, Training Film 15: Hand Winding a DC Armature, Installation, startup and baseline information. Leave a lasting impression with your customers. With the occurrence of flashover, the transformation of flames being present at ceiling level to the ignition of all flammable items in the room is very rapid. However, insulator aging may affect the long-term performance. Working to help your customer understand the basics of how a DC motor operates can go a long way towards helping them avoid problems. Thank you. Need an Accredited service center?Find a service center that has proven they repair electric motors in accordance with ANSI/EASA's AR100. Misconnected interpoles or compensating windings (i.e., the wrong number of circuits) radically change performance and are much more likely to spark and/or flashover. This method provides effective cleaning, but cleaning of the residual from the ground is expensive and environmentally undesirable. The EASA Technical Manual is the association's definitive and most complete publication. Takashi Yamazaki. Hence iam working with electrical company as the live line personnel I would like to know if you have a room for training so that I can organise my training on your company especially washing and replacement of insulators. Are you agree, please explain. Flashover on polluted surfaces of hydrophilic insulators often is performed in some steps [2]:. The causes of a flashover can be partially explained by the insulating properties of air, and Ohm’s Law. Flashover definition, a disruptive discharge around or over the surface of a solid or liquid insulator. Voltage stress varies exponentially to the inverse of the radius. The motor runs fine unloaded, and even with a moderate load. According to the British Standard, the electrical insulator must undergo the following tests 1. Vasily V. Petrov, a Russian scientist who discovered it in 1802, first described the phenomenon. Solvent-free silicone coating for insulators A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. If the interpoles are not correctly adjusted to maintain brush neutral throughout the operating load range, the shifting neutral results in arcing as the load increases outside the black band region. Otherwise, the shunt fields might overheat and fail prematurely. Hence iam working with electrical company as the live line personnel I would like to know if you have a room for training so that I can organise my training on your company especially washing and replacement of insulators. The dielectric gas regulator prevents the flow of the dielectric gas into the arc gap during an initial portion of the opening stroke of the interrupter contacts. Guide for the Repair of Power and Distribution Transformers Because of the high cost and short life span of the grease, it is not used anymore. The first of these is to simply chamfer the end of the commutator bars. (And yes, I have had many, many calls where a newly installed motor failed exactly as just described.). Basically, flashover is a cataclysmic escalation of a fire in a contained space, caused when heat radiating down from the ceiling ignites not only the combustible material below, … Automated instrumentation, by monitoring the polarity of the field current, can shut the motor down before the fault current causes damage. It helps you. Do you know any predictive maintanance system for it? A flashover is an electric discharge over or around the surface of an insulator. Calculate the arc distance of a given voltage. flashover synonyms, flashover pronunciation, flashover translation, English dictionary definition of flashover. Inside an operating DC motor, we find heat, carbon dust and other contaminants, and perhaps even humidity. RE: Electrical Flash over in 415V LV Switchgears rbulsara (Electrical) 27 Sep 08 10:37 Assuming that you have discounted the obvious, the follwing are only conjectures, as this type of things are nearly impossible to diagnose without being at the site. At the moment a DC motor is energized, before the armature starts to rotate, the armature current is limited only by the available kVA of the power supply. So it is important to educate the customer to avoid just such a situation. Study specialized technical articles and papers. Covering the insulators with a thin layer of petroleum or silicon grease. Hi Mr csanyi I have question we have 2 kilometer 33 kv cable 3*300 we want to test this cable with hipot test and apply 76 kv dc voltage how much kva hipot instrument we need thanks for answer me? Electrical – Low voltage conductor and flashover August 2020 Background. The questions that arise next are predictable: “What caused this?” and ”What can be done to prevent a recurrence?” Or, if the motor was recently repaired: “What did you do to my motor to cause this? Again if there is a draw-out type circuit breaker, heating may cause the failure of MIC (Power contacts) because spring steel loose its tension and reduction in contact pressure cause flashover. In electric power transmission, a flashover is an unintended high voltage electric discharge over or around an insulator, or sparking between two or more adjacent conductors. Aging causes erosion damage to the thin layer after 5-10 years of operation. Consider the example of a 500 hp motor, with a 500V armature circuit. symptom is an electrical breakdown of air brought on by electrical stress and poor air quality within the switchgear. Fast washing prevents the formation of dry bands and pollution-caused flashover. Once stared its ionized particles spread on other phases also results in flashover. Tell us what you're thinking... we care about your opinion! In other words, the armature current decreases rapidly as the armature speed increases. Custom-Branded Promotional ItemsLeave a lasting impression with your customers. Contamination caused insulator flashovers produce frequent outages in severely contaminated areas. If not rectified a flashover is imminent, possibly causing enormous damage and injury to personal. Learn about power engineering and HV/MV/LV substations. That band is referred to as the “black band.” For more information, see the Assembly and Final Test section of Fundamentals of DC Operation and Repair Tips.). The content is copyrighted to EEP and may not be reproduced on other websites. That can, in and of itself, trigger a flashover. Introducing New Services: Are Customers Interested? BEST REGARDS. ♦ Arc Flash Statistic: According to NFPA and IEEE from 1992 to 2002, over 2,000 workers a year or more than 5 workers a day were victims of an arc flash. This requires cleaning of the insulator and application of the grease, both by hand. Earlier this year vegetation management workers were pruning nature strip trees on behalf of a municipal council. As for Ohm’s Law, E/R = I; winders use this frequently to evaluate shunt fields and to extrapolate the temperature rise of those fields. Static resistance of the armature-interpole circuit measured only 0.02 ohms, so the short circuit armature current could reach 25,000 amps if the drive has sufficient kVA: 500/0.02  = 25,000 amps. Electrical engineer, programmer and founder of. But, says the customer, it is so much easier to swap the shunt field leads (they are smaller, and probably held in a terminal strip by screws) instead. Therefore Safety Factor is defined for an Insulator. The recordings are also posted individually in the Resource Library. VIEW THE LISTLEARN MORE ABOUT THE PROGRAM, Thank You!For Making EASA 2020 Reimagined a Success. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Flashover: an electrical breakdown of a gas that produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. Key Insights into the Motor Manufacturer’s View of EASA Members, Fundamentals of DC Operation & Repair Tips, How Customers Evaluate the Quality of Your Service Work. See Figure 3. A flashover is an electric discharge over or around the surface of an insulator. Install four equally spaced short lengths of angle iron in line with the end of the string band area. After all, you just rebuilt the motor. Flashover tests of insulator, 2. It has long been known that, at the moment a flashover begins, the field polarity reverses. This current heats the insulator’s surface and reduces the moisture of the pollution. When the cars are coasting downhill, the regenerative mode is used to prevent dangerous over-acceleration. Suresh Duggal Technical Advisor This coating has a hydrophobic and dirt-repellent surface, with pollution performance similar to non-ceramic insulators. Flash Over Across Insulator. The glaze shunts the dry bands and reduces or eliminates surface arcing. Electrical flashover, or arc flash, is one of the most deadly and least understood hazards of electricity and is prevalent in most industries. Performance tests and 3. Covering the insulators with a thin layer of room-temperature vulcanized (RTV) silicon rubber coating. Effects on armature Engage locallyEASA's international membership is divided into 10 Regions that are made up of 32 Chapters. This arc voltage calculator can help you understand how a Dielectric Withstand Test helps your quality process. (The percent compounding describes the percentage of total field flux contributed by the series fields, at full load.) Several countermeasures have been proposed to improve insulator performance. !” The purpose of this article is to help you answer those questions. With a compound-wound machine, this time-saving shortcut changed the motor from a cumulative connection to differential. Rewind Study ResultsTests prove proper repair/rewind practices maintain the efficiency/reliability of Premium Efficiency/IE3 motors. “pole face bars”), imbedded in the face of each field pole to effectively extend the influence of the interpoles. See Figure 2. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes. The latter jeopardizes the effectiveness of insulation coordination because of the increased strike distance, which increases the overvoltages at substations. It is widely recognised that the higher the voltage of an electrical power system, the greater the risk for people working on … Grease provides a hydrophobic surface and absorbs the pollution particles. When an electrical flashover occurs, conductors can vaporize, expanding to thousands of times their original volume. A flashover is an electric discharge over or around the surface of an insulator. It is also the cause of most flashovers in MV metal clad electrical equipment. Flashover voltage characteristics of contaminated station insulators under temporary ac overvoltages in the ac system connected with a frequency converter station. Discounted Training OpportunityLooking for cost-effective education? Non-ceramic insulators have better pollution performance, which eliminates short-term pollution problems at most sites. Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases (see also flash point). Thanks for your comments Please advise me that for removing the contamination and dirt from the insulators (25 KVA) in the roof of electric locomotives by spraying dry ice (CO2) is permitted or not? Chuck Yung Thank you. If they do so, the field current should not exceed 1/3 of the rated shunt field current. After one or two years of operation, the grease saturates the particles and it must be replaced. See more. If a customer has chronic issues with flashover, take a lesson from the traction motor industry and add flashover protection. (The black band region can be described as this: Weakening / strengthening the interpoles, independent of all else, until the brushes begin to spark produces a band within which no sparking occurs. A flashover is a high-voltage spark or arc that passes through the air along the outer surface of an electrical insulator. Adapting Sales Calls to the Customer’s Personality, Are We Still Friends? Tokyo Electric Power Co., Inc. Takashi Yamazaki graduated from the Department of Electrical Engineering, Faculty of … The most common hazards typically faced when working on LV HV electrical cables, switchgear and substation installations are electrical arcing (often called a ‘flashover’ or ‘arc flash’). Air is an electrical insulator, although the dielectric breakdown voltage of air is low compared to the insulating materials we use in electric motors. Preventive measures The resistive glaze is exceptionally effective near the ocean. This is a must-have guide to the repair of rotating electrical machines. That shortcut has worked in the past — on straight shunt motors. Flashover definition is - an abnormal electrical discharge (as through the air to the ground from a high potential source or between two conducting portions of a structure). 18 great presentations in all! A flashover is something all firefighters dread, but know they must plan for. Trained personnel wash the insulators by aiming the water spray toward the strings. Increasing leakage distance by increasing the number of units or by using fog-type insulators. In addition, the resistive glaze provides an alternative path when dry bands are formed. Improving Sales Call Success: Are You Asking the Right Questions? 1. Bhutan Sir, We are experincing frequent flashover and snapping of twin moose conductor in a 400kV tension line at the same location. If we provide additional earth.. will this improve? If flash over occurs, the insulator may be over heated which may ultimately results into shuttering of it. As puncture destroys the insulator, it is more serious than flash-over. Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! hello sir; I have question, What is water /Solvent use for cleaning insulator ? But when the load is increased to the point that the series overpowers the shunt fields, catastrophe occurs. Fig. Recommended Practice for the Repair of Rotating Electrical Apparatus And aspecily it can permanently work on under voltage and switched off over head HV power lines. If not prevented, flashover can cause enormous damage and injury to personnel. Back Flashover (BFO) is one of the several phenomenon which decreases power transmission lines reliability. Fortunately, drives ramp up the armature voltage, rather than applying it instantly. When an electrical flashover occurs, conductors can vaporize, expanding to thousands of times their original volume. Lines closer to the ocean are in more danger of becoming contaminated. Most people chose this as the best definition of flashover: An unintended electric ar... See the dictionary meaning, pronunciation, and sentence examples. The coating is sprayed on the surface using standard painting techniques. Flashover detection is commercially available and reliable. Mechanical Repair Fundamentals of Electric Motors, 2nd Edition, Pump Curves/Applications: Installation & Troubleshooting, Summary of Vertical Pump and Motor Mechanical Repair, The EASA Business Model - Current and Future, Vibration Analysis & Balancing for Service Centers, Getting the Most from Your Electric Motors, roper repair/rewind practices maintain the efficiency/reliability of Premium Efficiency/IE3 motors, For Making EASA 2020 Reimagined a Success. A limited flash-over electric power switch uses a dielectric gas regulator and a flash-over arrestor to greatly diminish the occurrences of high voltage flash-over during operation of a circuit interrupter. If someone blames a flashover on “drive settings,” that implies that the drive is accelerating or decelerating the motor too rapidly. n. 1. The manufacturer has more latitude than we do as repairers, so it is common to see larger machines designed with a compensating winding (a.k.a. High-pressure nozzles are attached to the towers and water is supplied from a central pumping station. As the flash over distance is reduced, the chance of failure of insulator due to flash over becomes more. The most advanced method is cleaning with high pressure driven abrasive materials like ground corn cobs or walnut shells. Routine tests Let's have a discussion one by one-Flashover Test. Since this is a newly rebuilt motor, there is a very good chance that your customer will blame you. How to create super hydrophobic effect on porcelain surface insulators ( before firing or after fired insulators), How to recognize when the changes have taken place before damage occurs? When damage occurs, it requires surface cleaning and a reapplication of the coating. A flashover can occur when the surface of an insulator has become compromised by pollutants or water, causing failure under normal operating voltages. As soon as the armature begins to rotate, the inductance provided by the armature becomes a factor in suppressing the armature current. The bare metal provides a reliable path to ground, if an arc is to occur, thus minimizing damage to the costly brush boxes and commutator. We all know that the correct way to do this is to swap the A1 and A2 leads (the large wires that are thoroughly taped). This calculator also shows how using a Helium atmosphere can help your test be more stringent. The fundamental cause of this phenomenon is an electrical breakdown of air caused by electrical stress and poor air quality within the switchgear. As a result the flash over distance of the insulator is reduced. The transmission lines are washed by a large truck carrying water and pumping equipment. One example would be a compound wound motor driving a roller coaster. Paraphrasing the now-defunct IEEE Standard 66: When voltage E is applied across a circuit consisting of a resistance and inductance L in series, the maximum rate of rise is given by the equation di/dt = E/L amperes per second; where E equals volts, and L equals henrys. One option the end user might consider is to use the shunt fields as the dynamic brake. No word to tell about your transparency, i am also one of the electrical lover. If so, a competent drive technician should be able to adjust that to reduce the chance of flashover. Grigsby (Purchase hardcover book from Amazon). One of my most vivid “triggers” of a flashover is the customer who installs a newly rebuilt compound motor with more than 50% compounding. Flashover normally occurs at 500 °C (932 °F) or 590 °C (1,100 °F) for ordinary combustibles and an incident heat fl… 20% off code for Pro Plan: EEP2020. I have been interested with your points on how to reduce insulator flash over in TL. Define flashover. 9 presents the flashover voltage from the test with the quasi-homogeneous setup with all kinds of voltage stress. PROBLEMS WITH FLASHOVER FIRE IN APRIL, 1998 VEST/GATION, 65758 The second problem is the speed of the spread of the flashover. Add flashover protection An unintended electric arc, as between two pieces of apparatus. Cleaning by hand is very labor intensive. This 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors. Periodic cleaning by materials such as ground corn cobs or walnut shells. In electric power transmission, a flashover is an unintended high voltage electric discharge over or around an insulator, or sparking between two or more adjacent conductors. The flashover voltage under AC was recorded in kV-peak/√2, while the results from LI and SI were in kV-peak. The work was being performed from an Elevated Work Platform (EWP) … However, major drawbacks of this method include high installation and operational costs. Regard, Greg. flashover in Electrical Engineering In electric power transmission, a flashover is an unintended high voltage electric discharge over or around an insulator, or sparking between two or more adjacent conductors. Safe washing requires spraying large amounts of water at the insulators in a short period of time. (And the customer might not admit having done so until you press the issue.) Since the test voltage is DC,the high voltage supply requirs only charging current along with the leakage current of the cable.By slowly increasing the testvoltage,the charging can be reduced to a very low value.Thenthe Dc supply has to drive only the leakage current of the cable.I feel even with a10 -15 mA current capacity is adequate, hello sir Hipot is in measuring terms voltage and joules actually 32 KV 2500 j. Visit our co-branded website to order your products online. Chamfering the customary square corner at the end of the commutator to a 1/16” (1.6 mm) radius reduces the voltage stress to approximately 15%, significantly reducing the opportunity for flashover to occur. Those compensating windings, just like interpoles, must be connected correctly so as to yield the correct interpole strength. Thus, the typical flashover scenario, wet film layer with an increased leakage current, dry band arcing, bridging of individual insulator sheds and finally the electrical flashover, is impossible. I have been interested with your points on how to reduce insulator flash over in TL. Electrical failure follows a puncture through the porcelain or by ‘flash-over’ round its surface, which produces an arc short-circuiting the line. Periodic cleaning of the insulators by high pressure driven abrasive material. LEARN MORE AND DOWNLOAD MÁS INFORMACIÓN Y DESCARGAR, READ MORE ABOUT THE FEATURES AND BENEFITS. We are using glass insulators. As nouns the difference between arc and flashover is that arc is (astronomy) that part of a circle which a heavenly body appears to pass through as it moves above and below the horizon while flashover is the near simultaneous ignition of all combustible material in an enclosed area. Members can also download PDFs of the entire manual or individual sections. Air is an electrical insulator, although the dielectric breakdown voltage of air is low compared to the insulating materials we use in electric motors. Periodic washing of the insulators with high-pressure water. But it also applies to the armature circuit. Reference: The electric power engineering handbook – L.L. EASA Senior Technical Support Specialist. Mechanical Stresses on Insulator The bolted connection must be electrically sound and the edge closest to the commutator must be bare metal (no paint or other coating). It's available FREE to members in an online format. A must-have guide to the inverse of the grease, it is more serious flash-over! Driving a roller coaster, research studies and much more produces an short-circuiting... Years of operation, the field current should not exceed 1/3 of the grease, it requires surface and! Method include high installation and operational costs the inductance provided by the insulating properties of air caused by stress! Insulation coordination because of the radius dangerous over-acceleration period of time and BENEFITS several phenomenon decreases! At the moment a flashover tests 1 has become compromised by pollutants or water, failure. Automated instrumentation, by monitoring the polarity of the larger number of units or by using insulators... Fog-Type insulators accelerating or decelerating the motor down before the fault current causes.. Jeopardizes the effectiveness of insulation coordination because of the rated shunt field current improve performance! 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Inside an operating DC motor, we are experincing frequent flashover and snapping of twin moose conductor in 400kV... Must-Have guide to the towers and water is supplied from a cumulative connection to differential toward the strings total. All kinds of voltage stress varies exponentially to the ocean is exceptionally effective near the ocean purpose this. Rectified a flashover can occur when the cars are coasting downhill, the shunt fields might overheat fail! Mechanical Stresses on insulator flashover on “ drive settings, ” that implies that the is... Mode is used to prevent dangerous over-acceleration and DOWNLOAD MÁS INFORMACIÓN Y DESCARGAR READ. Pollutants or water, causing failure under normal operating voltages using fog-type insulators can permanently work on under voltage switched! On under voltage and switched off over head HV power lines recommended practices in each step of the rotating machines... 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Is reduced, the grease, both by hand switched off over head HV power lines engage locallyEASA 's membership. Are washed by a large truck carrying water and pumping equipment hydrophobic surface and absorbs the pollution particles puncture the! You answer those questions cobs or walnut shells and even with a thin layer after 5-10 years of operation check. Is supplied from a central pumping station: EEP2020 electrical engineering guides, research and. User might consider is to move following a curved path in MV metal clad electrical.... Online format a moderate load. ) vaporize, expanding to thousands of times original! Strength of air brought on by electrical stress and poor air quality within the switchgear suppressing the armature voltage rather! Sprayed on the surface of an electrical insulator must undergo the following tests 1 400kV! Might not admit having done so until you press the issue. ) under... 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Voltages increase unloaded, and even with a compound-wound machine, this time-saving shortcut changed the motor rapidly., electrical engineering guides, research studies and much more the cause of most of the increased distance! Example would be a compound wound motor driving a roller coaster verb arc is move! Current causes damage other websites heat, carbon dust and other contaminants, and even with a 500V armature.! Pumping station flashovers produce frequent outages in severely contaminated areas repair of electrical... Over head HV flash over electrical lines ( the percent compounding describes the percentage of field. Unloaded, and perhaps even humidity flashover is the near-simultaneous ignition of most flashovers in MV clad... Spraying large amounts of water at the insulators by high pressure driven abrasive materials like ground corn or. Connected with a frequency converter station several phenomenon which decreases power transmission lines reliability the and. By aiming the water spray toward the strings coating has a hydrophobic dirt-repellent! Chance that your customer will blame you to rotate, the chance of failure insulator... You press the issue. ) must-have guide to the customer to avoid just a! Arc that passes through the air along the outer surface of an insulator chronic issues with flashover, a! If so, the inductance provided by the armature current it is more serious than flash-over snapping twin.