When a transformer has stomach pain and wants to…http://electrical- engineering- portal.com/when- transformer- has- a- stomach- pain- and- wants- to May 13, 2013 Edvard T ransf ormer windings f orces due to the magnetic f orces (photo by ALST OM) About stomach pain During normal operation, transformer internal structures and windings are subjected to mechanical forces due to the magnetic forces. These forces are illustrated in Figure 1. By designing the internal structure very strong to withstand these forces over a long period of time, service life can be extended. However, in a large transformer during a “through fault” (fault current passing through a transformer), forces can reach millions of pounds, pulling the coils up and down and pulling them apart 60/50 times per second. Notice in Figure 1 that the internal low-voltage coil is being pulled downward, while the highvoltage winding is pulled up, in the opposite direction. At the same time, the right-hand part of the figure shows that the high- and low-voltage coils are being forced apart. Keep in mind that these forces are Figure 1 . Design of the windings and bracing must consider the magnitude of these forces and provide adequate strength to withstand them without significant mechanical deformation which could result in a dielectric failure. Many times. How to prevent pain Through Fault – Short Circuit withstand considerations The windings are subject to both radial and axial forces related to the current and flux interactions. although explosive failures do occur occasionally. The picture below is an example ofa free bucking mechanical failure of an inner winding resulting from radial forces in compression on the winding. if fault currents are high. There are protective relaying systems to protect against this possibility. throwing flaming oil over a wide area. there wasn’t a dielectric failure of this winding. Radial forces in the inner winding (normally the LV winding) are in compression while the outer winding (normally the HV winding) forces are in tension. It is obvious why internal structures of transformers must be built incredibly strong. even though there is mechanical failure. . Note.T ransf ormer Internal Forces reversing 50/60 times each second. these forces can rip a transformer apart and cause electrical faults inside the transformer itself. This normally results in arcing inside the transformer that can result in explosive failure of the tank. DETC taps (De Energized Tap Changer) in the HV windings and LTC (Load Tap Changer) operation result in changes in the ampere turn distribution resulting in axial forces. If the HV and LV windings are not aligned axially or one winding is physically shorter than the other. When the ampere turns of the HV and LV windings are equal and balanced. ampere turn balance is significantly affected and axial forces are magnified.Flux Free bucking mechanical f ailure of an inner winding resulting f rom radial f orces in compression on the winding fields are dependent of the balance of the ampere turn distribution of the HV and LV windings. . the only forces are radial. low impedance. Helical and Layer Windings for Power Transformer Applications . motor starting duty.Autotransformers. three winding transformers with dual secondary windings for start up or unit auxiliary service at power plants – all can result in increased axial and radial forces during a short circuit and require special consideration. CTO of SPX-Waukesha Transformers Basics.S. P. Jin Sim. Maintenance and Diagnostics – U. EEP recommends . Harris.E. transformers with multiple voltages by reconnecting the transformer windings in series and parallel configurations. T ransf omer core f orce and f lux R e f e re nce s: Presentation on Short-circuit Forces by H.David L. Construction of power transf ormer (VIDEO) Cant see this video? Click here to watch it on Youtube. Primary and assembly process (VIDEO) Cant see this video? Click here to watch it on Youtube. of the Interior Bureau of Reclamation The Design and Performance of Circular Disc. Dpt.