1. Isolation Transformer:
- Isolation Transformer are used for other purposes like breaking a circuit into a primary and a secondary, so direct current noise can’t get through.
- It can prevent capacitance build-up by high-frequency noise.
- It also prevents unconditional ground connection between the primary and secondary and thus prevents high voltage discharge.
- It is used mostly in sensitive equipment as power supply.
- It can be used to protect people against the dangers of electric shocks.
2. Ferro-resonant Transformers:
- Ferro-resonance is a non-linear resonance phenomenon that can affect power networks.
- The abnormal rates of harmonics and transient or steady state over voltages and over currents that it causes are often dangerous for electrical equipment.
- Ferro-resonance is different from resonance in linear system element. In linear system, resonance results in high sinusoidal voltage and current of the resonant frequency. Ferro-resonant is also result in high voltage and current but the resultant waveform is not in sinusoidal shape, they are of irregular shape.
- Some unexplained breakdowns can be ascribed to this rare, non-linear phenomenon.
- Ferro-resonant transformer is also called as Constant-Voltage Transformer (CVT).
- It can handle voltage sags, and mostly used for constant, low-power loads.
- Variable loads, especially with high inrush currents, are problem for CVTs, because of the tuned circuit on the output.
- Ferro-resonant transformers are basically 1:1 transformer which are excited high on their saturation curves, thereby providing an output voltage which is not significantly affected by input voltage variations.
- The CVT will output over 90 percent normal voltage as long as the input voltage is above 30 percent.
- If CVT is overloaded, the voltage will collapse to zero.
Page No. 10