FERRITE CORE TRANSFORMER

 FERRITE CORE  TRANSFORMER

Ferrite core power transformers are widely used in switched-mode power supplies (SMPSs). The powder core enables high-frequency operation, and hence much smaller size-to-power ratio than laminated-iron transformers.

Ferrite transformers are not used as power transformers at mains frequency since laminated iron cores cost less than an equivalent ferrite core.

Constant voltage transformer

Constant voltage transformer

 Voltage regulator § Constant-voltage transformer

By arranging particular magnetic properties of a transformer core, and installing a ferro-resonant tank circuit (a capacitor and an additional winding), a transformer can be arranged to automatically keep the secondary winding voltage relatively constant for varying primary supply without additional circuitry or manual adjustment. Ferro-resonant transformers run hotter than standard power transformers, because regulating action depends on core saturation, which reduces efficiency. The output waveform is heavily distorted unless careful measures are taken to prevent this. Saturating transformers provide a simple rugged method to stabilize an AC power supply.

Resonant transformer

Resonant transformer 

                                

For more details on this topic, see Resonant inductive coupling.

For more details on this topic, see Tesla coil § Resonant transformer.

A resonant transformer is a transformer in which one or both winding has a capacitor across it and functions as a tuned circuit. Used at radio frequencies, resonant transformers can function as high Q factor bandmpass filters. The transformer winding have either air or ferrite cores and the bandwidth can be adjusted by varying the coupling (mutual inductance). One common form is the IF (intermediate frequency) transformer, used in super heterodyne radio receivers. They are also used in radio transmitters.

Resonant transformers are also used in electronic ballasts for gas discharge lamps, and high voltage power supplies. They are also used in some types of switching power supplies. Here the short-circuit inductance value is an important parameter that determines the resonance frequency of the resonant transformer. Often only secondary winding has a resonant capacitor (or stray capacitance) and acts as a serial resonant tank circuit. When the short-circuit inductance of the secondary side of the transformer is L sc and the resonant capacitor (or stray capacitance) of the secondary side is C_r' The resonance frequency ω_s of 1' is as follows

{\displaystyle \omega _{s}={\frac {1}{\sqrt {L_{sc}C_{r}}}}={\frac {1}{\sqrt {(1-k^{2})L_{s}C_{r}}}}}

The transformer is driven by a pulse or square wave for efficiency, generated by an electronic oscillator circuit. Each pulse serves to drive resonant sinusoidal oscillations in the tuned winding, and due to resonance a high voltage can be developed across the secondary.

Applications:

·        Intermediate frequency (IF) transformer in super heterodyne radio receiver

·        Tank transformers in radio transmitters

·        Tesla coil

·        CCFL inverter

·        Oudin coil (or Oudin resonator; named after its inventor Paul Oudin)

·        D'Arsonval apparatus

·        Ignition coil or induction coil used in the ignition system of a petrol engine

·        Electrical breakdown and insulation testing of high voltage equipment and cables. In the latter case, the transformer's secondary is resonated with the cable's capacitance.

STRAY-FIELD TRANSFORMER

STRAY-FIELD TRANSFORMER 

A leakage transformer, also called a stray-field transformer, has a significantly higher leakage inductance than other transformers, sometimes increased by a magnetic bypass or shunt in its core between primary and secondary, which is sometimes adjustable with a set screw. This provides a transformer with an inherent current limitation due to the loose coupling between its primary and the secondary winding. In this case, it is short-circuit inductance which is actually acting as a current limiting parameter. The output and input currents are low enough to prevent thermal overload under all load conditions—even if the secondary is shorted.

Uses

Leakage transformers are used for arc welding and high voltage discharge lamps (neon lights and cold cathode fluorescent lamps, which are series connected up to 7.5 kV AC). It acts then both as a voltage transformer and as a magnetic ballast.

Other applications are short-circuit-proof extra-low voltage transformers for toys or doorbell installations.

Variable-frequency transformer

Variable-frequency transformer

Variable-frequency transformer

A variable-frequency transformer is a specialized three-phase power transformer which allows the phase relationship between the input and output winding to be continuously adjusted by rotating one half. They are used to interconnect electrical grids with the same nominal frequency but without synchronous phase coordination.

Phase-shifting transformer

Phase-shifting transformer

This is a specialized type of transformer which can be configured to adjust the phase relationship between input and output. This allows power flow in an electric grid to be controlled, e.g. to steer power flows away from a shorter (but overloaded) link to a longer path with excess capacity.

POWER TRANSFORMER ,GROUNDING TRANSFORMER

Grounding transformer

 

Earthing transformer

Grounding or earthing transformers let three wire (delta) poly phase system supplies accommodate phase to neutral loads by providing a return path for current to a neutral. Grounding transformers most commonly incorporate a single winding transformer with a zigzag winding configuration but may also be created with a wye-delta isolated winding transformer connection.