Page 544 - Basic Electrical Engineering

I can be resolved into two components I and I , where I is in phase with ϕ
c
m
m
0
and is responsible for producing ϕ. This I is also called the magnetizing
m
current because this current magnetizes the core, i.e., produces the required
flux in the core. I is equal to I sin ϕ . I is equal to I cos ϕ . Therefore,
0
0
m
0
0
c
. The no-load power input W is equal to V I cos ϕ which
0
1 0
0
equals V I . The induced EMF in the secondary winding, i.e., E has been
2
1 c
shown lagging flux ϕ by 90°. It has been assumed that N > N , and hence E 2
2
1
> E .
1

Figure 6.7 Transformer on no-load: (a) core and the windings; (b) no-load phasor diagram

Here, cos ϕ is the no-load power factor which is very low (may be 0.1 or
0
so).