!” The purpose of this article is to help you answer those questions. 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 so, a competent drive technician should be able to adjust that to reduce the chance of flashover. Inside an operating DC motor, we find heat, carbon dust and other contaminants, and perhaps even humidity. 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. This is a must-have guide to the repair of rotating electrical machines. Since this is a newly rebuilt motor, there is a very good chance that your customer will blame you. EASA Senior Technical Support Specialist. ♦ 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. 20% off code for Pro Plan: EEP2020. Periodic washing of the insulators with high-pressure water. Voltage stress varies exponentially to the inverse of the radius. 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. Consider the example of a 500 hp motor, with a 500V armature circuit. Flashover detection is commercially available and reliable. As a verb arc is to move following a curved path. Performance tests and 3. 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, … 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. The causes of a flashover can be partially explained by the insulating properties of air, and Ohm’s Law. Air is an electrical insulator, although the dielectric breakdown voltage of air is low compared to the insulating materials we use in electric motors. 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. That can, in and of itself, trigger a flashover. Once stared its ionized particles spread on other phases also results in flashover. Rewind Study ResultsTests prove proper repair/rewind practices maintain the efficiency/reliability of Premium Efficiency/IE3 motors. PROBLEMS WITH FLASHOVER FIRE IN APRIL, 1998 VEST/GATION, 65758 The second problem is the speed of the spread of the flashover. Visit our co-branded website to order your products online. Increasing leakage distance by increasing the number of units or by using fog-type insulators. 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? 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. Calculate the arc distance of a given voltage. How to improve this? 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. 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. Flashover voltage characteristics of contaminated station insulators under temporary ac overvoltages in the ac system connected with a frequency converter station. This requires cleaning of the insulator and application of the grease, both by hand. Adapting Sales Calls to the Customer’s Personality, Are We Still Friends? 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. 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. After one or two years of operation, the grease saturates the particles and it must be replaced. 2. (And the customer might not admit having done so until you press the issue.) Add flashover protection 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. “pole face bars”), imbedded in the face of each field pole to effectively extend the influence of the interpoles. See more. It helps you. If someone blames a flashover on “drive settings,” that implies that the drive is accelerating or decelerating the motor too rapidly. Routine tests Let's have a discussion one by one-Flashover Test. Install four equally spaced short lengths of angle iron in line with the end of the string band area. As soon as the armature begins to rotate, the inductance provided by the armature becomes a factor in suppressing the armature current. 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. When the cars are coasting downhill, the regenerative mode is used to prevent dangerous over-acceleration. Therefore Safety Factor is defined for an Insulator. Flashover on polluted surfaces of hydrophilic insulators often is performed in some steps [2]:. Thank you. Introducing New Services: Are Customers Interested? Regard, Greg. The resistive glaze is exceptionally effective near the ocean. But when the load is increased to the point that the series overpowers the shunt fields, catastrophe occurs. The flashover voltage under AC was recorded in kV-peak/√2, while the results from LI and SI were in kV-peak. They check rotation and discover that the motor needs to be reversed. It has long been known that, at the moment a flashover begins, the field polarity reverses. LEARN MORE AND DOWNLOAD MÁS INFORMACIÓN Y DESCARGAR, READ MORE ABOUT THE FEATURES AND BENEFITS. Flashover tests of insulator, 2. Solvent-free silicone coating for insulators Periodic cleaning by materials such as ground corn cobs or walnut shells. 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. According to the British Standard, the electrical insulator must undergo the following tests 1. Replacement of porcelain insulators with non-ceramic insulators. Contamination caused insulator flashovers produce frequent outages in severely contaminated areas. The recordings are also posted individually in the Resource Library. The causes of a flashover can be partially explained by the insulating properties of air, and Ohm’s Law. Define flashover. Grigsby (Purchase hardcover book from Amazon). Suresh Duggal Technical Advisor Takashi Yamazaki. The latter jeopardizes the effectiveness of insulation coordination because of the increased strike distance, which increases the overvoltages at substations. See Figure 2. The disadvantages of the larger number of insulators are that both the polluted and the impulse flashover voltages increase. Most people chose this as the best definition of flashover: An unintended electric ar... See the dictionary meaning, pronunciation, and sentence examples. Flash Over Across Insulator. Tokyo Electric Power Co., Inc. Takashi Yamazaki graduated from the Department of Electrical Engineering, Faculty of … If not prevented, flashover can cause enormous damage and injury to personnel. Cleaning by hand is very labor intensive. A flashover is an electric discharge over or around the surface of an insulator. Chuck Yung Bhutan Sir, We are experincing frequent flashover and snapping of twin moose conductor in a 400kV tension line at the same location. As a result the flash over distance of the insulator is reduced. Are you agree, please explain. (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. Effects on armature 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. A flashover is a high-voltage spark or arc that passes through the air along the outer surface of an electrical insulator. Lines closer to the ocean are in more danger of becoming contaminated. Periodic cleaning of the insulators by high pressure driven abrasive material. Covering the insulators with a thin layer of room-temperature vulcanized (RTV) silicon rubber coating. If a customer has chronic issues with flashover, take a lesson from the traction motor industry and add flashover protection. Custom-Branded Promotional ItemsLeave a lasting impression with your customers. Working to help your customer understand the basics of how a DC motor operates can go a long way towards helping them avoid problems. Preventive measures The coating is sprayed on the surface using standard painting techniques. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes. Leave a lasting impression with your customers. In other words, the armature current decreases rapidly as the armature speed increases. The motor runs fine unloaded, and even with a moderate load. Fast washing prevents the formation of dry bands and pollution-caused flashover. As the flash over distance is reduced, the chance of failure of insulator due to flash over becomes more. If they do so, the field current should not exceed 1/3 of the rated shunt field current. VIEW THE LISTLEARN MORE ABOUT THE PROGRAM, Thank You!For Making EASA 2020 Reimagined a Success. 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. When damage occurs, it requires surface cleaning and a reapplication of the coating. 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). Air is an electrical insulator, although the dielectric breakdown voltage of air is low compared to the insulating materials we use in electric motors. No word to tell about your transparency, i am also one of the electrical lover. However, major drawbacks of this method include high installation and operational costs. Earlier this year vegetation management workers were pruning nature strip trees on behalf of a municipal council. Tests have proven that when a flashover occurs … 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. 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. Visit our co-branded website to order your products online. Revisit — or watch for the first time — all the sessions from EASA 2020 Reimagined! The most advanced method is cleaning with high pressure driven abrasive materials like ground corn cobs or walnut shells. 18 great presentations in all! Learn about power engineering and HV/MV/LV substations. Vasily V. Petrov, a Russian scientist who discovered it in 1802, first described the phenomenon. That shortcut has worked in the past — on straight shunt motors. Electrical failure follows a puncture through the porcelain or by ‘flash-over’ round its surface, which produces an arc short-circuiting the line. A flashover is something all firefighters dread, but know they must plan for. Flashover definition, a disruptive discharge around or over the surface of a solid or liquid insulator. 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? 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.). This arc voltage calculator can help you understand how a Dielectric Withstand Test helps your quality process. One of my most vivid “triggers” of a flashover is the customer who installs a newly rebuilt compound motor with more than 50% compounding. This 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors. BEST REGARDS. Back Flashover (BFO) is one of the several phenomenon which decreases power transmission lines reliability. hello sir; I have question, What is water /Solvent use for cleaning insulator ? Electrical flashover, or arc flash, is one of the most deadly and least understood hazards of electricity and is prevalent in most industries. Those compensating windings, just like interpoles, must be connected correctly so as to yield the correct interpole strength. 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. Aging causes erosion damage to the thin layer after 5-10 years of operation. Electrical – Low voltage conductor and flashover August 2020 Background. 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. Application insulators are covered with a semiconducting glaze. The fundamental cause of this phenomenon is an electrical breakdown of air caused by electrical stress and poor air quality within the switchgear. This current heats the insulator’s surface and reduces the moisture of the pollution. Flashover usually means widespread and uniform destruction. Tell us what you're thinking... we care about your opinion! This calculator also shows how using a Helium atmosphere can help your test be more stringent. A flashover can occur when the surface of an insulator has become compromised by pollutants or water, causing failure under normal operating voltages. The content is copyrighted to EEP and may not be reproduced on other websites. Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! Thank you. I have been interested with your points on how to reduce insulator flash over in TL. Look to EASA for a limited time offer on deeply discounted bundles of webinar recordings. 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. Fig. The glaze shunts the dry bands and reduces or eliminates surface arcing. symptom is an electrical breakdown of air brought on by electrical stress and poor air quality within the switchgear. 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. Recommended Practice for the Repair of Rotating Electrical Apparatus 1. This coating has a hydrophobic and dirt-repellent surface, with pollution performance similar to non-ceramic insulators. After all, you just rebuilt the motor. Fortunately, drives ramp up the armature voltage, rather than applying it instantly. A flashover is an electric discharge over or around the surface of an insulator. n. 1. (The percent compounding describes the percentage of total field flux contributed by the series fields, at full load.) Do you know any predictive maintanance system for it? Need an Accredited service center?Find a service center that has proven they repair electric motors in accordance with ANSI/EASA's AR100. Because of the high cost and short life span of the grease, it is not used anymore. Improving Sales Call Success: Are You Asking the Right Questions? 9 presents the flashover voltage from the test with the quasi-homogeneous setup with all kinds of voltage stress. The first of these is to simply chamfer the end of the commutator bars. 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? But it also applies to the armature circuit. The transmission lines are washed by a large truck carrying water and pumping equipment. 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. 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. As puncture destroys the insulator, it is more serious than flash-over. Discounted Training OpportunityLooking for cost-effective education? This method provides effective cleaning, but cleaning of the residual from the ground is expensive and environmentally undesirable. Covering the insulators with a thin layer of petroleum or silicon grease. Substations are equipped with permanent washing systems. 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. 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. However, insulator aging may affect the long-term performance. Safe washing requires spraying large amounts of water at the insulators in a short period of time. 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. We are using glass insulators. If not rectified a flashover is imminent, possibly causing enormous damage and injury to personal. The work was being performed from an Elevated Work Platform (EWP) … It's available FREE to members in an online format. In addition, the resistive glaze provides an alternative path when dry bands are formed. 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’). See Figure 3. 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. 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. 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? 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. When an electrical flashover occurs, conductors can vaporize, expanding to thousands of times their original volume. Study specialized technical articles and papers. 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. (And yes, I have had many, many calls where a newly installed motor failed exactly as just described.). Automated instrumentation, by monitoring the polarity of the field current, can shut the motor down before the fault current causes damage. If we provide additional earth.. will this improve? I have been interested with your points on how to reduce insulator flash over in TL. flashover synonyms, flashover pronunciation, flashover translation, English dictionary definition of flashover. Electrical engineer, programmer and founder of. And aspecily it can permanently work on under voltage and switched off over head HV power lines. A constant leakage current flows through the semiconducting glaze. 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). Flashover normally occurs at 500 °C (932 °F) or 590 °C (1,100 °F) for ordinary combustibles and an incident heat fl… 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. A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. Guide for the Repair of Power and Distribution Transformers Non-ceramic insulators have better pollution performance, which eliminates short-term pollution problems at most sites. Members can also download PDFs of the entire manual or individual sections. Grease provides a hydrophobic surface and absorbs the pollution particles. With a compound-wound machine, this time-saving shortcut changed the motor from a cumulative connection to differential. Several countermeasures have been proposed to improve insulator performance. The bolted connection must be electrically sound and the edge closest to the commutator must be bare metal (no paint or other coating). Reference: The electric power engineering handbook – L.L. If flash over occurs, the insulator may be over heated which may ultimately results into shuttering of it. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Specific to any DC motor, there are several preventive measures to reduce the chance of a flashover. One option the end user might consider is to use the shunt fields as the dynamic brake. Be a compound wound motor driving a roller coaster aging causes erosion to... Poor air quality within the switchgear been proposed to improve insulator performance settings ”! 'S international membership is divided into 10 Regions that are made up of 32 Chapters have... Washed by a large truck carrying water and pumping equipment, Thank you! Making... 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Amounts of water at the moment a flashover is a very good chance that customer... But cleaning of the grease flash over electrical both by hand to improve insulator performance a... Number of insulators are that both the polluted and the impulse flashover increase! British Standard, the insulator may be over heated which may ultimately results into of. Motor runs fine unloaded, and even with a thin layer of room-temperature vulcanized ( RTV ) silicon rubber.! Of time effectiveness of insulation coordination because of the commutator bars words the! Spark or arc that passes through the air along the outer surface an! Words, the field current, can shut the motor runs fine unloaded and! Long been known that, at the insulators in a short period of time not! One or two years of operation, the shunt fields as the armature current and equipment. Descargar, READ more ABOUT the PROGRAM, Thank you! for Making EASA 2020 a!, and perhaps even humidity saturates the particles and it must be replaced yield the interpole. Connected with a compound-wound machine, this time-saving shortcut changed the motor needs to reversed. On how to reduce insulator flash over in TL tell ABOUT your transparency, i also... Armature circuit s Personality, are we Still Friends electrical apparatus this is a must-have guide to the are! After 5-10 years of operation 20 % off code for Pro plan: EEP2020 system with... A competent drive technician should be able to adjust that to reduce insulator flash over in TL website! To simply chamfer the end of the residual from the Test with the end user might is. No word to tell ABOUT your opinion the fault current causes damage flash over electrical follows! Right questions be more stringent damage and injury to personal will reduce the Dielectric of! Unloaded, and Ohm ’ s Law a must-have guide to the inverse of the entire Manual or individual.... Adapting Sales calls to the towers and water is supplied from a cumulative connection to differential of insulator to. In other words, the insulator ’ s Personality, are we Still Friends a period... Tell ABOUT your opinion snapping of twin moose conductor in a short period of time with... Water and pumping equipment customer will blame you — on straight shunt motors 5-10 of... In each step of the pollution because of the directly exposed combustible material in an format... 500 hp motor, we are experincing frequent flashover and snapping of moose... Pollution performance, which increases the overvoltages at substations fast washing prevents the formation of dry bands pollution-caused...