Hysteresis Vs. Copper Loss Vs. Induction LossFitness Gear & Equipment
Hysteresis Vs. Copper Loss Vs. Induction Loss
Another type of loss which occurs in the core of the transformer is called hysteresis. When iron is magnetized, its magnetic domains are arranged in a random pattern. However, if a magnetic force is applied, the domains line up with the magnetic field. In a transformer, the magnetic field will reverse direction many times each second in step with the applied AC signal.
Thus, the domains must reverse their direction many times each second with applied AC signal. When reversing direction, the domains must overcome friction and inertia. In doing this a certain amount of power is dissipated in the form of heat. This power loss is referred to as a hysteresis loss. Soft iron has higher hysteresis loss whereas in steel it is lower. Some large power transformers use a special type of metal called silicon steel because it has a low hysteresis loss. The amount of hysteresis loss increases with frequency.
This loss is caused by the AC resistance of the copper wire in the primary and secondary windings. A transformer winding can consist of hundreds of turns of fine copper wire. Because of the length of the wire and its tiny cross sectional area, the AC resistance can be quite high. As current flows through this resistance, some power is dissipated in the form of heat. The amount of power can be determined by the formula. P = l2 x R
For this reason another name for copper loss is l2R loss. The amount of copper loss is proportional to the square of current. The copper loss can be reduced by increasing the size of the copper wire in the windings. Larger wire has less resistance and thus the l2R loss can be reduced. It can be also reduced by keeping the current in the transformer as low as possible.
As the magnetic field expands and contracts around the transformer, it cuts an external conductor of some kind. If current is induced into the conductor, some power is lost from the transformer circuit. In most cases the power lost by external induction is so small that it can be ignored, however voltage induced into outside circuit can be bothersome. Interference caused by induction from a transformer can be reduced by shielding. Often, sensitive circuits are placed inside a metal shield which will prevent stray magnetic fields reaching the circuits.