The following chapters address routine maintenance, some processes area unit typically higher than and on the far side routine maintenance work to stay the transformer operational.
Transformer medical specialty needs specialized instrumentation and coaching. This experience isn’t expected to be maintained in each workplace. In some cases, it should be necessary to contact medical specialty specialists, either within or outside Reclamation, World Health Organization have the most recent instrumentation and up to date expertise. Shows the transformer condition assessment methodology, linking routine maintenance and diagnostics
1 Introduction to Reclamation Transformers
Standards organizations like American National Standards Institute/Institute of Electrical and Electronic Engineers (ANSI/IEEE) think about average GSU transformer life to be 20 to 25 years. This estimate relies on continuous operation at rated load and repair conditions with a mean close temperature of 40 ºC (104 degrees Fahrenheit [ºF]) and a temperature rise of 65 ºC. This estimate is additionally supported the idea that transformers receive adequate maintenance over their service life . Reclamation, Bonneville Power Administration, and Western space Power Administration conduct regular studies to work out applied mathematics instrumentation life.
These studies show that average lifetime of a Reclamation transformer is 40 years. Reclamation gets longer service than IEEE estimates due to operational at lower close temperatures and with lower masses.
A big variety of transformers were purchased within the 1940s, 1950s, and into the 1970. Many are replaced, however Reclamation has several transformers
That area unit nearing, or area unit already well past, their anticipated service life. We must always expect transformer replacement and failures to extend, because of this age issue.
Current minimum replacement time is around 14 months; a lot of realistic time is also 18 months to 2 years. Within the future, lead times might extend well on the far side what they’re nowadays. Therefore, high-quality maintenance and correct medical specialty area unit vital for all transformers, however it’s fully essential for older ones—especially for essential transformers that will cause loss of generation. It’s to contemplate providing spares for essential transformers.
2. Transformer Cooling strategies Introduction
Heat is one in every of the foremost common destroyers of transformers. Operation at solely 8 ºC higher than the transformer rating can cut transformer life by 50%. Heat is caused by internal losses, because of loading, high close temperature, and radiation. It’s vital to know however your specific transformers area unit cooled and the way to sight issues within the cooling systems. ANSI and IEEE need the cooling class of every transformer to seem on its plate. Cooling classifications, with short explanations, seem the letters of the class designate within atmosphere and sort or varieties of cooling.
In some transformers, quite one class of cooling and load rating is indicated. At every step of extra cooling, the rating will increase to correspond with redoubled cooling. Note that the letter “A” indicates air, “FA” indicates forced air (fans), “O” indicates oil, “FO” indicates forced oil (pumps), “G” indicates some form of gas, and “W” indicates there’s a water/oil device.
3. Dry-Type Transformers
1. Class AA transformers area unit ventilated and self-cooled. This suggests there area unit ventilation ports situated in outside walls of the transformer enclosure. There are not any fans to force air into and out of the enclosure, with usually no external fins or radiators. Cooler air enters the lower ports, is heated because it rises past windings, and exits the higher ventilation ports. (Although it’s not perennial below; it’s obvious that, in each cooling class, some heat is additionally removed by natural circulation of air round the outside of the enclosure.)
2. Class AFA transformers area unit self-cooled (A) and in addition cooled by forced circulation of air (FA). This suggests that there area unit ventilation ports for fan inlets and outlet. (Inlets area unit typically filtered.) Usually, there are not any extra ventilation ports for natural air circulation.
3. Class AA/FA transformers area unit ventilated and self-cooled (same as Class AA in item 1). Additionally, they need a lover or fans providing extra forced-air cooling. Fans is also wired to begin mechanically once the temperature reaches a pre-set worth. These transformers usually have a twin load rating— one for AA (self-cooling natural air flow) and a bigger load rating for FA (forced air flow).
4. Class ANV transformers area unit self-cooled (A), non-ventilated (NV) units. The enclosure has no ventilation ports or fans and isn’t sealed to exclude migration of out of doors air, however there are not any provisions to purposely permit outside air to enter and exit. Cooling is by natural circulation of air round the enclosure. This transformer may have some form of fins hooked up outside the enclosure to extend area for added cooling.
5. Class GA transformers area unit sealed with a gas within (G) and area unit self-cooled (A). The enclosure is hermetically sealed to stop run. These transformers usually have a gas, like element or Freon, to produce high non conductor and smart heat removal. Cooling happens by natural circulation of air round the outside of the enclosure. There are not any fans to flow into cooling air; but, there is also fins hooked up to the surface to assist in cooling.
4. Liquid-Immersed Transformers
4.1 Liquid-Immersed, Air-Cooled
There area unit three categories during this class
1. class OA: Oil-immersed, self-cooled. Transformer windings and core area unit immersed in some sort of oil and area unit self-cooled by natural circulation of air round the outside enclosure. Fins or a radiator is also hooked up to the enclosure to help in cooling.
2. class OA/FA: Liquid-immersed, self-cooled/forced cool. Same as OA, with the addition of fans. Fans area unit sometimes mounted on radiators. The transformer generally has Two load ratings: one with the fans off (OA) and a bigger rating with fans operative (FA). A fan is also wired to begin mechanically at a pre-set temperature.
3. class OA/FA/FA: Liquid-immersed, self-cooled/forced cool/forced air-cooled. Same as OA/FA, with an extra set of fans. There generally are going to be three load rating cherish every increment of cooling. Magnified ratings area unit obtained by increasing cooling air over parts of the cooling surfaces. Typically, there area unit radiators hooked up to the tank to help in cooling. The two teams of fans is also wired to begin mechanically at pre-set levels as temperature will increase. There aren’t any oil pumps. Oil flows through the transformer windings by the natural principle of convection (heat rising).
4.2 Liquid-Immersed, Air-Cooled/Forced Liquid-Cooled
There area unit two categories during this cluster.
1. class OA/FA/FOA: Liquid-immersed, self-cooled/forced air-cooled/forced liquid, and compelled cool. Windings and core area unit immersed in some sort of oil. This transformer generally has radiators hooked up to the enclosure. The transformer has self-cooling (OA) natural ventilation, forced air-cooling (fans), and compelled oil-cooling (pumps) with extra forced air-cooling (FOA) (more fans).
The transformer has three load ratings cherish every cooling step. Fans and pumps is also wired to begin mechanically at pre-set levels as temperature will increase
2. class OA/FOA/FOA: Liquid-immersed, self-cooled/forced oil, and compelled air-cooled/forced oil, and compelled cool. Cooling controls area unit organized to begin solely a part of} the oil pumps and part of the fans for the primary load rating/temperature increase, and also the remaining pumps and fans for the second load rating increase. The plate can show a minimum of 3 load ratings.
4.3 Liquid-Immersed, cool
This class has two classes:
1. class OW: transformer coil and core area unit immersed in oil. Typically, an oil/water heat exchanger device (radiator) is attached to the surface of the tank. Cooling water is pumped through the heat exchanger; however the oil flows solely by natural circulation. As oil is heated by the windings, it rises to the highest and exits through piping to the radiator. As oil is cooled, it descends through the radiator and re-enters the transformer tank at all-time low.
2. class OW/A: transformer coil and core area unit immersed in oil. This transformer has two ratings. Cooling for one rating (OW) is obtained as in item one. Above The self-cooled rating (A) is obtained by natural circulation of air over the tank and cooling surfaces.
4.4 Liquid-Immersed, Forced Liquid-Cooled
This class has two classes:
1. class FOA: Liquid-immersed, forced liquid-cooled with forced cool. This transformer commonly has just one rating. The transformer is cooled by pumping oil (forced oil) through a radiator commonly hooked up to the surface of the tank. Also, air is forced by fans over the cooling surface.
2. class FOW: Liquid-immersed, forced liquid-cooled, water cooled. This transformer is cooled by AN oil/water device commonly mounted one by one from the tank. Each the transformer oil and also the cooling water area unit pumped-up (forced) through the heat exchanger to accomplish cooling.