IEEE C57.12.80-1978 pdf free.An American National Standard IEEE Standard Terminology forPower and Distribution Transformers.
Polarity，Angular Displacement,and PhaseSequence.
Lead Polarity. A designation of therelative instantaneous direction of the currentsin the leads of a transformer. Primary and secondary leads are said to have the same polar-ity when,at a given instant,the current entersthe primary lead in question and leaves thesecondary lead in question in the same direction as though the two leads formed a continuous circuit.
The lead polarity of a single-phase distribution or power transformer may be eitheradditive or subtractive. If adjacent leads fromeach of the two windings in question are con-nected together and voltage applied to one ofthe windings: (1) the lead polarity is additiveif the voltage across the other two leads of thewindings in question is greater than that of thehigher voltage winding alone;(2) the leadpolarity is subtractive if the voltage across theother two leads of the windings in question isless than that of the higher voltage windingalone.
The polarity of a polyphase transformer isfixed by the internal connections betweenphases; it is usually designated by means of aphasor diagram showing the angular displacements of the voltages in the windings and asketch showing the marking of the leads.Thephasorsofthe phasor diagrams representinduced voltages.The standard rotation ofphasors is counterclockwise.
Angular Displacement of a PolyphaseTransformer.The phase angle expressed indegrees between the line-to-neutral voltageof the reference identified high-voltage terminaland the line-to-neutral voltage of the corresponding identified lowvoltage terminal.
Definition of Phase Sequence. Theorder in which the voltages successively reachtheir positive maximum values.
Direction of Rotation of Phasors. Phasordiagrams should be drawn so that an advance inphase of one phasor with respect to another isin the counterclockwise direction. In the fol-lowing figure,phasor 1 is 120 degrees in ad-vance of phasor 2,and the phase sequence is1,2,3.
No-Load (Excitation) Losses.Thoselosses which are incident to the excitation ofthe transformer. No-load (excitation) losses include core loss，dielectric loss，conductor lossin the winding due to exciting current，andconductor loss due to circulating current inparallel windings.These losses change with theexcitation voltage.Load Losses.Those losses whichare incident to the carrying of a specified load.Load losses include I2 R loss in the windingsdue to load and eddy currents; stray loss dueto leakage fluxes in the windings,core clamps,and other parts,and the loss due to circulatingcurrents (if any) in parallel windings，or inparallel winding strands.IEEE C57.12.80 pdf download.