Transformers

A transformer is an electrical component used to transfer energy between circuits through electromagnetic induction. A transformer is made up of a core, a primary and a secondary side. The primary side is connected to the input and the secondary side is connected to the load. The primary and secondary are windings of conductive wires around the core. An AC current going through the primary winding creates a varying magnetic flux in the core, which in turn generates a magnetic field that induces a voltage in the secondary winding. The voltage induced on the secondary is proportional to the ratio of the number of turns of wire between the primary and the secondary.

 

EP and ES are the induced voltages on the primary and secondary windings, respectively. RP and RS are the resistances of the wires that make up the windings. LP and LS represent the leakage flux that is not able to be contained within the core. RC represents the loss due to hysteresis and eddy currents and Lm is the inductance associated with the magnetic flux generated by the AC current. CP and CS are the capacitances of the primary and secondary circuits, respectively, and CW is the combined capacitance between the windings of the transformer. NP and NS represent the number of turns on the primary and secondary windings, respectively, and RL represents the load.

Transformers are designed based on many specifications, but one of the most important design considerations is operating frequency. Practical transformers have losses due to different factors and frequency is an important design element. The impedances of capacitors (ZC) and inductors (ZL) can be modeled using the following equations.

It can be observed that as frequency increases, a capacitor begins to resemble a short circuit, an inductor begins to resemble an open circuit, and vice-versa as frequency decreases.
Real transformer energy losses include: (1) winding resistance joule losses; (2) core losses; (3) stray losses; (4) magnetostriction related transformer hum; (5) mechanical vibration and audible noise transmission. They are dominated by winding resistance joule and core losses. Another way to categorize transformer losses is by load (no-load loss, full-load loss, half-load loss, etc.).

The core losses include eddy current and hysteresis losses. They are constant at all load levels and dominate overwhelmingly without load, while variable winding joule losses dominate increasingly as load increases. The no-load loss can be significant, so that even an idle transformer constitutes a drain on the electrical supply. Eddy currents are induced within conductors by a changing magnetic field and generate magnetic fields opposing the field that created them. They are a source of energy loss as they cause the current flowing through the conductor to dissipate energy as heat. Hysteresis in transformers is shown by the magnetization not returning to zero when the magnetic field is removed. AC currents cause the magnetic field to alternate directions and the hysteresis effect causes energy loss every time the field is reversed.

In high frequency transformers, two additional significant causes of energy loss are the skin effect and the proximity effect. As frequency increases, the induced eddy currents block and limit current flow in a conductor to a certain depth known as the “skin depth” (effectively increasing the resistance of the conductor). The proximity effect is also due to eddy currents which causes current to be concentrated in areas of the conductor furthest away from nearby conductors carrying current in the same direction, also effectively increasing resistance. The additional resistance that is generated by these two effects causes power loss and undesirable heating which complicates transformer designs for high frequencies.
Energy efficient transformers require suitable cores, appropriate wire size and type, and good construction methods to reduce the above mentioned losses.
Amp Line Corp. (ALC) specializes in proficiently designed high frequency transformers for operating frequencies of up to 1M Hz. Some of the noteworthy characteristics of ALC’s transformers include low leakage inductance, low stray capacitance and high voltage output capability. ALC manufactures transformers custom designed for a wide range of applications.

Click here to get custom designed transformers.

 

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