**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:

**U**

**d**

*/*

**U**

**r -**(tapping factor) or

*100*U**d*

*/ U**r*(tapping factor expressed as a percentage)

where

*U*r = rated voltage of the winding ; and

*U*d = 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

winding;and

b)
divided
by the tapping factor of the tapped winding, if this is the low-voltage

winding.

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.
·

source-REC T.S

*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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