Tappings of transformer.

Terminology related Tappings of transformer.

·        Tapping — In a transformer having a tapped winding, a specific connection of that winding, representing a definite effective number of turns in the tapped winding and, consequently, a definite turns ratio between this winding and any other winding with fixed number of turns.

NOTE — One of the tappings is the principal tapping, andother  tappings are described in relation to the principal tapping by their respective tapping factors. See definitions of these terms below.

·         Principal Tapping — The tapping to which the rated quantities are related.

·        Tapping Factor (corresponding to a giventapping)
                                          The ratio:
                                  Ud  / Ur    - (tapping factor) or

                                100*Ud / Ur (tapping factor expressed as a percentage)

Ur = rated voltage of the winding ; and
Ud = voltage which would be developed at no load at the terminals of the winding, at the tapping concerned, by applying rated voltage to an untapped winding.
NOTE — This definition is not appropriate in relation to a series winding of a booster transformer (see 3.1.3), and in that case the percentage notation would be referred to the voltage of the energizing winding or of the winding of an associated system transformer.

·        Plus Tapping — A tapping whose tapping factor is higher than 1.

·        Minus Tapping — A tapping whose tapping factor is lower than 1.

·        Tapping Step — The difference between the tapping factors, expressed as a percentage, of two adjacent tappings.

·        Tapping Range — The variation range of the tapping factor, expressed as a percentage, compared with the value ‘100’.
NOTE — If this factor ranges from 100 + a to 100 – b, the tapping range is said to be: +a percent, – b percent or ± a percent, if a = b.

·        Tapping Voltage Ratio (of a pair of windings) —The ratio which is equal to the rated voltage ratio:
a)     multiplied by the tapping factor of the tapped winding, if this is the high-voltage       
b)     divided by the tapping factor of the tapped winding, if this is the low-voltage     

NOTE — While the rated voltage ratio is, by definition, at least equal to 1, the tapping voltage ratio can be lower than 1 for certain tappings when the rated voltage ratio is close to 1.

·        Tapping Duty — The numerical values assigne to the quantities, analogous to rated quantities, which refer to tappings other than the principal tapping.

·        Tapping Quantities — Those quantities the numerical values of which define the tapping duty of a particular tapping (other than the principal tapping). The tapping quantities are:
                           a) Tapping voltage 
                           b) Tapping power  and
                           c) Tapping current .
NOTE — Tapping quantities exist for any winding in the transformer, not only for the tapped winding .

·        Full-Power Tapping — A tapping whose tapping power is equal to the rated power.

·        Reduced-Power Tapping — A tapping whose tapping power is lower than the rated power.

·        On-load Tap-changer — A device for changing the tapping connections of a winding, suitable for operation while the transformer is energized or on load.
                                                                                                                source-REC T.S
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