1. The efficiency of a Transformer is usually in the range of
Answer : 95 to 99 %
Explanation:-
2. Transformer zero voltage regulation occurs at
Answer : leading power factor
Explanation:-
3. The efficiency of a transformer at full load 0.8 pf lagging is 95% then its efficiency at full load 0.8 pf leading will be
Answer : 95%
Explanation:- The efficiency of transformer does not depend on type of power factor(lead/lag)
4. At full load the iron loss in a transformer is 600 watts. At half load the iron loss will be
Answer : 600 watts
Explanation:- Iron loss does not depend on load
5. The function of a breather in a Transformer is
Answer : To arrest flow of moisture into the tank
Explanation:-
6. An auto transformer having a transformation ratio of 0.8 supplies a load of 10 kw. The power transferred inductively from the primary to the secondary is
Answer : 2kw
Explanation:-
The power transfer inductively=input(1-K)
=10(1-0.8)
=2 Kw
7. A 3-phase star-delta transformer has secondary to primary turns ratio per phase of 5. For a primary voltage of 400 v, the secondary voltage would be nearly
Answer : 1154.7 v
Explanation:-
Given V1(line)=400 V and N2/N1=5 which is equal to K
K=5
V1(phase)=400/√3=230.9V
K=V2/V1
V2=K*V1=5*230.9=1154.7 V
8. The form factor of a sinusoidal alternating voltage wave form is
Answer : 1.11
Explanation:-
9. A balanced three phase star connected load of (8+j6) Ohm per phase is connected to a balanced three phase 400√3 V supply. Then the phase current in amperes is
Answer : 40
Explanation:- In star connection I line=I phase and Vph=Vl/√3
Given Vl=400√3 V Z=(8+j6) Ohm/ph
Phase current = Vph/zph
Zph=√(64+36)=10 ohm
Vph=Vl/√3=400√3/(√3)=400V
Iph=Vph/Zph=400/10=40 A
10. A 50 HZ, 20 V AC sinusoidal voltage source is connected across a series RC circuit. If the Voltage across resistor is 12 Volts, then the voltage across capacitor is
Answer : 16V
Explanation:-
Vc=√((V^2)-(Vr^2))
=√((20*20)-(12*12))
==√(400-144)=√256=
16 V
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