Ferro resonant transformers additionally referred to as constant-voltage transformers (CVTs), will handle most voltage sag conditions. CVTs are particularly engaging for constant, low-power masses. Variable loads, particularly with high inflow currents, gift a lot of a drawback for CVTs as a result of the tuned circuit on the output. Ferro resonant transformers are primarily 1:1 transformers that are excited high on their saturation curves, thereby providing associate output voltage that isn't significantly suffering from input voltage variations. A typical Ferro resonant electrical device schematic circuit diagram is shown above.
From the above figure shows the voltage sag ride-through improvement of a method controller fed from a 120-VA Ferro resonant electrical device. With the CVT, the method controller will ride through voltage sag down to 30% of nominal, as opposition 82% while not one. Notice however the ride-through capability is command constant at a precise level. The rationale for this can be the tiny power demand of the method controller, only 15 VA. Ferro resonant transformers ought to be sized considerably larger than the load.
From this figure the allowable voltage sag as a share of nominal voltage (that can lead to a minimum of 90% voltage on the CVT output) versus Ferro resonant electrical device loading, as nominal by one manufacturer. At 25 % of loading, the allowable voltage sag is 30% of nominal, which means the CVT can output over 90% traditional voltage as long because the input voltage is higher than 30%. This is vital since the plant voltage seldom falls below 30% of nominal throughout voltage sag conditions. Because the loading is magnified, the corresponding ride-through capability is reduced, and once the Ferro resonant electrical device is full (e.g., 150% loading), the voltage can collapse to zero.