. A text-book of electrical engineering;. tant, quite irrespective of theload on the transformer. If an unloaded transformer be suddenly loaded,the sudden rush of secondary current exerts a powerful demagnetisingeffect. The magnetic flux and back are momentarily decreased, but• the primary current instantly rises to such a value that the demagnetisingeffect is neutralised, and the magnetic flux maintained at its no-load other words, the combined magnetic effect of the primary ampere-turnsZiTi and the secondary ampere-turns I^T^ is equal to the effect of the no-loadampere-turns
. A text-book of electrical engineering;. tant, quite irrespective of theload on the transformer. If an unloaded transformer be suddenly loaded,the sudden rush of secondary current exerts a powerful demagnetisingeffect. The magnetic flux and back are momentarily decreased, but• the primary current instantly rises to such a value that the demagnetisingeffect is neutralised, and the magnetic flux maintained at its no-load other words, the combined magnetic effect of the primary ampere-turnsZiTi and the secondary ampere-turns I^T^ is equal to the effect of the no-loadampere-turns I^T^. The vector IJ^ in the diagram is the resultant of thevectors J^Tj and I^T^. If the no-load ampere-turns I^^T^ are very small compared with theampere-turns when loaded, l-JT-^^ is approximately equal to 1.^7^. This is also true in the case of the series transformer (Fig. 268) in whichthe primary winding is inserted in one of the leads connecting the alter-nator with the external circuit. Its secondary winding can be closed through. Fig. 268 an adjustable resistance R^. When the secondary circuit is open, the pri-mary winding acts as a choking coil, but if the number of primary turns issmall, the potential drop will be small compared with the terminal ofthe alternator; it will, however, have its maximum value under this con-dition. On closing the secondary circuit through a large resistance as shownin the figure, current flows in this circuit, which will be unaltered on reducingi?2- Assuming a constant primary current, the secondary current is alsoconstant, being dependent namely on the transformation ratio. As R^ isdecreased, the secondary terminal , which is equal to I^R.^, decreases,and consequently also the primary Hence the primary acts as achoking coil of adjustable inductance; the across it will be zero when thesecondary winding is short-circuited. We shall now consider the vector diagram of a transformer on non-inductive load, taking into accoun
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