Partial discharge (corona) extinction voltage — the rms voltage at which partial discharge above the specified intensity level is no longer observed as the voltage is decreased from a level above the corona inception voltage.
Partial discharge (corona) inception voltage – the lowest rms voltage at which partial discharge above the specified intensity level is observed to occur as the voltage is increased.
Regulation of a transformer — the change in secondary voltage, expressed as a percentage of rated secondary voltage, that occurs when the rated kV.A output at a specified power factor is reduced to zero, the primary impressed terminal voltage being held constant.
Note: In the case of mulciwinding transformers, the loads on all windings are to be reduced from rated kV.A to zero simultaneously.
Relative lead polarity of a transformer a designation of the relative instantaneous directions of current in the leads of a transformer.
Notes:
1) Primal)’ and secondary leads are said to hove the some polarity when, during most of each halt cycle, at a given instant, the current enters on identified or marked primary lead and leaves the similarly identified or marked secondary lead in the same direction as though the two leads fanned a continuous circuit
2) The relative lead polarity of a single-phase trans former may be either additive or subtractive. When the lowest numbered H and the lowest numbered X terminations are connected together (H, and X, in Figure 2), and voltage is applied across one of the windings (H, and H, or X, and X?.),
a) polarity is additive if voltage between the highest numbered H and highest numbered X (between H, and X,) is greater than the voltage between the highest and lowest numbered H winding (H, and H,); and
b) polarity is subtractive if voltage between the highest numbered H and highest numbered X (between H, and X is less than the voltage between the highest and lowest numbered H winding (H, and H1.). When more than two windings ore used, the same relationship applies between any set of windings.
3) The relative lead polarity is indicated by identification marks on primary and secondary leads of like polarity or by other
appropriate identification.
4) The polarity of a pot yphase transformer is fixed by the internal connections between phases as well as by the relative
location of leads; it is usually designated by means of a vector diagram showing the angular displacement of windings and
o sketch showing the marking of the leads. The vector lines of the diagram represent induced voltages, and the recognized
counter-clockwise direction of rotation is used. The vector representing any phase voltage of a given winding is drawn
parallel to that representing the corresponding phase voltage of any other winding under consideration.
Series winding of an autotransformer — that portion of the autotransformer winding that is not common to both the primary and secondary circuits, but is connected in series between the input and output circuits.
System, effectively grounded — a system in which the highest rms line-to-ground power frequency voltage on a sound phase, at a selected location, during a fault-to-ground affecting one or more phases, does not exceed 80% of the line-to-line power frequency voltage that would be obtained, at the selected location, with the fault removed.CSA C9-02 pdf free download.