What is a tap changer? What does it mean if tap position is set to zero?
Answer:
*A device used to increase or decrease a transformer's voltage to alter the level of current it can draw (tap) from the circuit supplying electricity. Changing the tap of a transformer or regulator serves the same function in an electrical circuit as turning the tap handle of a water faucet serves to adjust water flow.
*Tap points are usually made on the high voltage, or low current, side of the winding in order to minimise the current handling requirements of the contacts. To minimise the number of windings and thus reduce the physical size of a transformer, use may be made of a 'reversing' winding, which is a portion of the main winding able to be connected in its opposite direction and thus oppose the voltage. Insulation requirements place the tap points at the low voltage end of the winding. This is near the star point in a star connected winding. In delta connected windings, the tappings are usually at the centre of the winding. In an autotransformer, the taps are usually made between the series and common windings, or as a series 'buck-boost' section of the common winding.
*Tap changer are set at minimum and maximum level.
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A tap changer is a switching system that is used to change the primary or secondary connections to the voltage adjustment taps of a transformer. For example, assume that you have a 13,600V:480V 3-phase transformer that has two 2-1/2% taps above and below the nominal transformer voltage. That transformer could be connected to deliver the nominal 480V secondary voltage with an actual primary voltage of 13,600V when connected to the nominal primary voltage taps or it could be connected to deliver 480V with a 12,928, 13,260, 13,940 or 14,288 volts. A tap changer would change all the necessary connections to set the primary voltage to any of the 5 alternatives. I would assume that the zero position would select the tap for the nominal 13,600V primary.
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