If flash over occurs, the insulator may be over heated which may ultimately results into shuttering of it. Need an Accredited service center?Find a service center that has proven they repair electric motors in accordance with ANSI/EASA's AR100. 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 can occur when the surface of an insulator has become compromised by pollutants or water, causing failure under normal operating voltages. This 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors. Grease provides a hydrophobic surface and absorbs the pollution particles. Suresh Duggal Technical Advisor BEST REGARDS. VIEW THE LISTLEARN MORE ABOUT THE PROGRAM, Thank You!For Making EASA 2020 Reimagined a Success. This coating has a hydrophobic and dirt-repellent surface, with pollution performance similar to non-ceramic insulators. Voltage stress varies exponentially to the inverse of the radius. Tell us what you're thinking... we care about your opinion! 2. 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. Members can also download PDFs of the entire manual or individual sections. If so, a competent drive technician should be able to adjust that to reduce the chance of flashover. Discounted Training OpportunityLooking for cost-effective education? 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. 1. The transmission lines are washed by a large truck carrying water and pumping equipment. It has long been known that, at the moment a flashover begins, the field polarity reverses. If not rectified a flashover is imminent, possibly causing enormous damage and injury to personal. When an electrical flashover occurs, conductors can vaporize, expanding to thousands of times their original volume. Safe washing requires spraying large amounts of water at the insulators in a short period of time. As the flash over distance is reduced, the chance of failure of insulator due to flash over becomes more. Lines closer to the ocean are in more danger of becoming contaminated. As a verb arc is to move following a curved path. Mechanical Stresses on Insulator Solvent-free silicone coating for insulators As a result the flash over distance of the insulator is reduced. This requires cleaning of the insulator and application of the grease, both by hand. That shortcut has worked in the past — on straight shunt motors. Electrical engineer, programmer and founder of. When an electrical flashover occurs, conductors can vaporize, expanding to thousands of times their original volume. Automated instrumentation, by monitoring the polarity of the field current, can shut the motor down before the fault current causes damage. Earlier this year vegetation management workers were pruning nature strip trees on behalf of a municipal council. 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 most advanced method is cleaning with high pressure driven abrasive materials like ground corn cobs or walnut shells. ♦ 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. Thank you. See more. With a compound-wound machine, this time-saving shortcut changed the motor from a cumulative connection to differential. The coating is sprayed on the surface using standard painting techniques. The motor runs fine unloaded, and even with a moderate load. Introducing New Services: Are Customers Interested? The causes of a flashover can be partially explained by the insulating properties of air, and Ohm’s Law. Replacement of porcelain insulators with non-ceramic insulators. !” The purpose of this article is to help you answer those questions. After all, you just rebuilt the motor. 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. Improving Sales Call Success: Are You Asking the Right Questions? A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. 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. If not prevented, flashover can cause enormous damage and injury to personnel. Regard, Greg. 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. Visit our co-branded website to order your products online. They check rotation and discover that the motor needs to be reversed. Are you agree, please explain. The latter jeopardizes the effectiveness of insulation coordination because of the increased strike distance, which increases the overvoltages at substations. 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. LEARN MORE AND DOWNLOAD MÁS INFORMACIÓN Y DESCARGAR, READ MORE ABOUT THE FEATURES AND BENEFITS. 18 great presentations in all! Bhutan Sir, We are experincing frequent flashover and snapping of twin moose conductor in a 400kV tension line at the same location. Flashover detection is commercially available and reliable. Several countermeasures have been proposed to improve insulator performance. However, insulator aging may affect the long-term performance. One example would be a compound wound motor driving a roller coaster. Thank you. Substations are equipped with permanent washing systems. A flashover is an electric discharge over or around the surface of an insulator. When the cars are coasting downhill, the regenerative mode is used to prevent dangerous over-acceleration. This current heats the insulator’s surface and reduces the moisture of the pollution. The fundamental cause of this phenomenon is an electrical breakdown of air caused by electrical stress and poor air quality within the switchgear. Flashover usually means widespread and uniform destruction. 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. Takashi Yamazaki. Rewind Study ResultsTests prove proper repair/rewind practices maintain the efficiency/reliability of Premium Efficiency/IE3 motors. 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. 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. Covering the insulators with a thin layer of petroleum or silicon grease. (The percent compounding describes the percentage of total field flux contributed by the series fields, at full load.) Flashover and snapping of twin moose conductor in a 400kV tension line at insulators... Article is to move following a curved path motor down before the fault causes. Undergo thermal decomposition and release flammable gases roller coaster help you understand how a Dielectric Withstand Test your... Yes, i have question, What is water /Solvent use for cleaning?. 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