The J & P Transformer Book docx

[...]... clear that these industry changes can and will go further, so that there will undoubtedly be a need for further revision to this work in the not so distant future, but it is hoped that the changes introduced in this edition will prove helpful, will not disappoint readers, and neither will they detract from the appeal of The J & P Transformer Book to a wide international readership MJH This page intentionally... current I2 although these do not, in fact, occur simultaneously and, in the case of polyphase transformers, by multiplying by the appropriate phase factor and the appropriate constant depending on the magnitude of the units employed It should be noted that rated primary and secondary voltages do occur simultaneously at no load Single-phase transformers Output ϭ E2I2 with the multiplier 10Ϫ3 for kVA... dependent upon the magnitude of that current and the resistance of the system Transformer windings are no exception and these give rise to the load loss or copper loss of the transformer Load loss is present only when the transformer is loaded, since the magnitude of the no-load current is so small as to produce negligible resistive loss in the windings Load loss is proportional to the square of the. .. terminals of the transformer The constant ͙3 is a multiplier for the phase voltage in the case of star-connected windings, and for the phase current in the case of Transformer theory 11 delta-connected windings, and takes account of the angular displacement of the phases Alternatively expressed, the rated output is the product of the rated secondary (no-load) voltage E2 and the rated full-load output current... working for a major US utility with technical responsibility for the health and well-being of a fleet of over 1000 power transformers, and in participating during that same period in the standards development and maintenance work of the IEEE/PES Transformers Committee, a group for which I am privileged to presently serve as Chair The J& P Transformer Book has served well to educate prior and present generations,... Three-phase transformers Output ϭ 4.44 f ΦmNI ϫ ͙3 with the multiplier 10Ϫ3 for kVA and 10Ϫ6 for MVA In the expression for single-phase transformers, I is the full-load current in the transformer windings and also in the line; for three-phase transformers, I is the full-load current in each line connected to the transformer That part of the expression representing the voltage refers to the voltage... other words the percentage voltage drops considered as occurring in either winding remain the same To transfer primary resistance values R1 or leakage reactance values X1 to the secondary side, R1 and X1 are divided by the square of the ratio of transformation n in the case of both step-up and step-down transformers Transformer theory 7 Figure 1.3 Phasor diagram for a single-phase transformer supplying... diagram corresponding to a transformer on no-load (neglecting for the moment the fact that the transformer has reactance) and the symbols have the significance shown on the diagram Usually in the practical design of transformer, the small drop in voltage due to the flow of the no-load current in the primary winding is neglected Figure 1.1 Phasor diagram for a single-phase transformer on open circuit Assumed... (1.1) and, in view of the need for ampere-turns balance: I1/N2 ϭ I2/N2 (1.2) where E, I and N are the induced voltages, the currents and number of turns respectively in the windings identified by the appropriate subscripts Hence, the voltage is transformed in proportion to the number of turns in the respective windings and the currents are in inverse proportion (and the relationship holds true for both... 0.80, the resistance and leakage reactance drops being allocated to their respective windings In fact the sum total effect is a reduction in the secondary terminal voltage The resistance and reactance voltage drops allocated to the primary winding appear on the diagram as additions to the e.m.f induced in the primary windings Figure 1.2 Phasor diagram for a single-phase transformer supplying a unity power . The J & P Transformer Book Prelims-H8164.indd iPrelims-H8164.indd i 8/1/07 2:52:50 PM8/1/07 2:52:50 PM This page intentionally left blank The J &. neither will they detract from the appeal of The J & P Transformer Book to a wide international readership. M J H Prelims-H8164.indd xiPrelims-H8164.indd