Transformers are power devices and used to increase or decrease of power supply. They are used for electrical isolation, power distribution and control and instrumentation applications. Power transformers convert power-level voltages from one level or phase configuration to another. They are used for power distribution, control and instrumentation applications. RF transformers transfer energy from one circuit to another by electromagnetic induction. Audio transformers are involved in the transmission of voice or sound signals; they often require wide frequency bandwidth with low distortion and noise suppression. Toroidal transformers are typically copper wires wrapped around a cylindrical core so the magnetic flux that occurs within the coil doesn't leak out. Signal transformers transfer information from one circuit to another by electromagnetic induction and have wide railway applications. Various types of transformers available are oil cooled transformer, electrical transformer, fluid filled transformer, automatic voltage controller, high voltage transformer, amorphous and fluid filled power & distribution transformers, induction and arc furnace transformers, mobile transformers etc.