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Drying time for transformer core

Drying time for transformer core

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The transformer is a fixed electrical machine used to transfer power from one circuit to another. The voltage can be changed anytime as per the need of the owner or according to the situation. Usually, the transformer had four-component terminals or more to transfer current or voltage into a device. It has two sides, i.e., Primary and Secondary, with two terminals at each side. A straightforward two-winding transformer development constitutes each winding being twisted on a different delicate iron attachment or at the center, giving the essential attractive circuit. It is also known as the transformer core. Having a dry transformer core is all you need to enhance your manufacturing effectively because the wet transformer is neither easy to use nor causes you any benefits except a lot of damage.

 In today’s era, everyone is very much aware of using a transformer in specific fields, especially our mechanical engineers. It also acts as an ITD (Impedance Transferring Device). As it is used to supply power in Ac, not in Dc, and apart from it, they also know the several other uses of the transformer and the pros and cons of it. They know that using a dry transformer is much better than using a wet transformer as a wet transformer only increases the manufacturer’s problems. Usually, the drying time of the transformer depends on the rating of the voltage. If you have a high power voltage rating, then it takes less time and vice versa. Most transformers are kept inside the oven for a better drying process. In transformer manufacturing industries, drying the transformer regularly is still a very common practice that is done as an important part of the management process.

 It needs lots of effort to maintain endless deportment for managing precipitation for large units. The drying process is used at the initial stage, i.e., manufacturing and endless attempts to keep the dryness stable. According to the IEEE (Institute of Electrical and Electronics Engineers), Std 62 – 1995(1) states that the moisture content in solid insulation was defined as follows.

  • Dry Insulation: 0 – 2%
  • Wet Insulation: 2 – 4%
  • Very Wet Insulation: 4.5%+

 Drying the transformer is practiced by generating the force between water vapor all over the insulation and water vapor in that same insulation. Moisture weight in the insulation is increased by heating the compact insulation, and moisture force near the insulation is reduced by creating the vacuum. The insulation’s drying time expands continuously according to the performing voltage and the transformer’s capacity. The higher the drying time, the higher the limited discharge commencement voltage.

 To make the moisture disappear from the tough insulation of high capacity transformer, heat and vacuum amalgamation is necessary. Being a modern human-robot, technologies are beneficial for the advancement of tough insulation. There are infinite numbers of technologies that can be used for drying the transformer core. Some of the common technologies are as follow:

 • HAC (Hot Air Circulation):                    

  HAC is used to eliminate the precipitation from the transformer. To start with clearing out the precipitation, the transformer core coil accumulation installs into the oven minimum of one and a half ` days, i.e., 36 hours. The oven’s heat is set to 120 degrees Celsius to swelter the transformer’s core coil assembly. During this process, the temperature of the oven should be stick fixed. For a distribution transformer, this method is usually preferable.  

 • HOS (Hot Oil Spry) / AC (Auto Craving):

                                                  HOS method is mainly prevalent for drying power transformers in the field. This method is very time-consuming because the construction of the core system transformers and uniform warmth of the whole transformer is very tough due to press plates and shielding. When the core coil cluster is heated, the precipitation fades away.

   • HOL (Hot Oil Circulation):

                          HOL is when the tough insulation is drying up with the circular movement of hot oil. This method is usually completed either by oil purification or reclamation. The oil treatment plant raises the level of oil temperature to a certain level; then it passes through the transformer tank. After that, the vacuum is generated so that the circulation movement’s oil movement precipitates the water. 

   • VD (Vacuum Drying):

                      VD is a process in which the core coil is put in a vacuum chamber for heating with the help of electrical heaters, and then the vacuum is removed with the help of the vacuum pump. In the vacuum drying process, the water in the tough insulation is a vanishing form of vapor due to a vacuum pump’s utilization and compile through a condenser in the water form. This water capacity is noted down at the regular interval.

 Apart from all these techniques, the oven is also used for drying the transformer core. The changing temperature inside the oven is set up with temperature sensors’ help, which is kept inside the oven. In the whole drying process, resistances are kept checking with the help of the Megger test set. With the help of this test set, the test was performing on two types of transformers. Meanwhile, the basic manufacturing process was carried on. The outcome shows that insulation resistance has elevated with time, and after reaching its top point, it starts dropping down. When the test is going on, the oven was unplugged for almost 15 to 16 hours to bring another transformer set for tanking, and then the temperature in the oven decreases very rapidly.

   The rapid increment in resistance of both the transformers caused almost parallel. So, it is evident that rapid increment in insulation resistance happens because of the oven’s opening.

 Apparently, the insulation resistance hikes up to the peak value, and then it should stay at that peak value for further drying.

   After obtaining the results, we can say that the time for drying the tested transformer lies in the range of 15 to 20 hours.

 According to the IEC 60076 standard, the results were up to the desired will; therefore, it must be said that drying time for the transformer core can be decreased by a cogent time.

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