Transformers In AC

Question 1

What is a transformer?

Answer 1

Device which raises or lowers voltage in ac circuits through mutual induction. Transformers can increase or decrease voltage or current but NOT both simultaneously

Question 2

Relation between voltages, number of turns and, current, (primary and secondary) in transformer

Answer 2

Vs/Vp = Ns/Np = Is/Ip
V- voltage
N- no of turns
I- current
P, S - primary and secondary

Question 3

Efficiency of a transformer

Answer 3

Π = P out/P in = = VsIs/VpIp

Question 4

Condition for ideal transformer

Answer 4

Efficiency= Π = 1

Question 5

Difference between step up transformer and step down transformer

Answer 5

STEP UP TRANSFORMER-
Np < Ns
Vp < Vs
Ip > Is
Rp < Rs

STEP DOWN TRANSFORMER-

Np > Ns
Vp > Vs
Ip < Is
Rp > Rs

Question 6

What is done to minimise I²R loss(Cu loss) in transformer

Answer 6

Windings are made of thick Cu wires (high resistance)

Question 7

What is done to minimise eddy current loss in transformer

Answer 7

Cores are laminated

Question 8

What is done to minimise hysteresis loss in transformer

Answer 8

Select material of narrow hyst. Loop
Cores of transformer made of soft iron

Question 9

What is done to minimise magnetic flux linkage loss in transformer

Answer 9

Secondary winding is kept inside the primary winding