Question

A 400v/100v transformer takes a no load current of 5A at 0.2 lagging pt.secondary winding supplies a load of 100 A at p.f of 0.8 lagging .find the primary input current.​

Answer 1

Answer:

Explanation:

Let the additional primary current beI2′.It is known asloadcomponent of primary current.This current is antiphase withI2′.Theadditional primary m.m.f.N1I2sets up its own fluxΦ2′which is inopposition toΦ2(but is in the same direction asΦ) and is equal to it inmagnitude.Hence, the two cancel each other out.So, we find that themagnetic effects of secondary currentI2are immediately neutralized bythe additional primary currentI2′which is brought into existence exactlyat the same instant asI2.The whole process is illustrated in Fig. 32.17.Hence, whatever the load conditions,the net flux passing throughthe core is approximately the same as at no-load.An important deduction is that due to the constancyof core flux at all loads,the core loss is also practically the same under all load conditions.AsΦ2=Φ2′∴N2I2=N1I2′∴I2′=2221NIKIN×=Hence, when transformer is on load, the primary winding has two currents in it; one isI0and the otherisI2′which is anti-phase withI2andKtimes in magnitude.The total primary current is the vector sumof I0and I2′