Electrical engineer, programmer and founder of. The disadvantages of the larger number of insulators are that both the polluted and the impulse flashover voltages increase. It is also the cause of most flashovers in MV metal clad electrical equipment. But when the load is increased to the point that the series overpowers the shunt fields, catastrophe occurs. Flashover voltage characteristics of contaminated station insulators under temporary ac overvoltages in the ac system connected with a frequency converter station. 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. Do you know any predictive maintanance system for it? BEST REGARDS. Electrical failure follows a puncture through the porcelain or by ‘flash-over’ round its surface, which produces an arc short-circuiting the line. The resistive glaze is exceptionally effective near the ocean. Replacement of porcelain insulators with non-ceramic insulators. Tell us what you're thinking... we care about your opinion! Otherwise, the shunt fields might overheat and fail prematurely. Vasily V. Petrov, a Russian scientist who discovered it in 1802, first described the phenomenon. PROBLEMS WITH FLASHOVER FIRE IN APRIL, 1998 VEST/GATION, 65758 The second problem is the speed of the spread of the 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. 18 great presentations in all! It has long been known that, at the moment a flashover begins, the field polarity reverses. (And the customer might not admit having done so until you press the issue.) This 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors. (The percent compounding describes the percentage of total field flux contributed by the series fields, at full load.) hello sir; I have question, What is water /Solvent use for cleaning insulator ? Earlier this year vegetation management workers were pruning nature strip trees on behalf of a municipal council. 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. Fortunately, drives ramp up the armature voltage, rather than applying it instantly. Fig. No word to tell about your transparency, i am also one of the electrical lover. We are using glass insulators. I have been interested with your points on how to reduce insulator flash over in TL. 9 presents the flashover voltage from the test with the quasi-homogeneous setup with all kinds of voltage stress. The glaze shunts the dry bands and reduces or eliminates surface arcing. Flashover definition, a disruptive discharge around or over the surface of a solid or liquid insulator. !” The purpose of this article is to help you answer those questions. High-pressure nozzles are attached to the towers and water is supplied from a central pumping station. In addition, the resistive glaze provides an alternative path when dry bands are formed. Cleaning by hand is very labor intensive. Back Flashover (BFO) is one of the several phenomenon which decreases power transmission lines reliability. If a customer has chronic issues with flashover, take a lesson from the traction motor industry and add flashover protection. Routine tests Let's have a discussion one by one-Flashover Test. 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 first of these is to simply chamfer the end of the commutator bars. The causes of a flashover can be partially explained by the insulating properties of air, and Ohm’s Law. Those compensating windings, just like interpoles, must be connected correctly so as to yield the correct interpole strength. Flashover on polluted surfaces of hydrophilic insulators often is performed in some steps [2]:. 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? Several countermeasures have been proposed to improve insulator performance. Reference: The electric power engineering handbook – L.L. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes. As puncture destroys the insulator, it is more serious than flash-over. An unintended electric arc, as between two pieces of apparatus. The latter jeopardizes the effectiveness of insulation coordination because of the increased strike distance, which increases the overvoltages at substations. Are you agree, please explain. Grease provides a hydrophobic surface and absorbs the pollution particles. Discounted Training OpportunityLooking for cost-effective education? 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. 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. Periodic washing of the insulators with high-pressure water. Study specialized technical articles and papers. 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. 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. 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, … Mechanical Stresses on Insulator 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. Flashover detection is commercially available and reliable. This calculator also shows how using a Helium atmosphere can help your test be more stringent. Since this is a newly rebuilt motor, there is a very good chance that your customer will blame you. 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. This is a must-have guide to the repair of rotating electrical machines. Revisit — or watch for the first time — all the sessions from EASA 2020 Reimagined! When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Tests have proven that when a flashover occurs … Fast washing prevents the formation of dry bands and pollution-caused flashover. 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. Covering the insulators with a thin layer of petroleum or silicon grease. Thank you. Automated instrumentation, by monitoring the polarity of the field current, can shut the motor down before the fault current causes damage. This calculator also shows how using a Helium atmosphere can help your Test be more stringent of! Electrical insulator must undergo the following tests 1 as between two pieces of apparatus 2020... Code for Pro plan: EEP2020 are we Still Friends shunt motors conductor and flashover 2020! 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