transformers




1).
What kVA rating is required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV?
A   4 kVA   
B   0.25 kVA   
C   16 kVA   
D   8 kVA   
ANS: C - 16 kVA

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2).
The turns ratio required to match an 80  source to a 320  load is
A   80   
B   20   
C   4   
D   2   
ANS: D - 2

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3).
When the turns ratio of a transformer is 20 and the primary ac voltage is 12 V, the secondary voltage is
A   12 V   
B   120 V   
C   240 V   
D   2,400 V   
ANS: C - 240 V

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4).
If a transformer has 50 turns in the primary winding and 10 turns in the secondary winding, what is the reflective resistance if the secondary load resistance is 250 
A   250    
B   25    
C   6,250    
D   62,500    
ANS: D - 62,500 

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5).
A certain transformer has 400 turns in the primary winding and 2,000 turns in the secondary winding. The turns ratio is
A   0.2   
B   0.4   
C   5   
D   25   
ANS: C - 5

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6).
The primary winding of a transformer has 110 V ac across it. What is the secondary voltage if the turns ratio is 8?
A   8.8 V   
B   88 V   
C   880 V   
D   8,800 V   
ANS: C - 880 V

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7).
To step 110 V ac down to 20 V ac, the turns ratio must be
A   5.5   
B   18   
C   0.18   
D   0.018   
ANS: C - 0.18

Vp/Vs = Np/Ns 

Vs = (Ns/Np)Vp 

We required turns ratio i.e., (Ns/Np) 

= Vs/Vp 

= 20/110 

= 0.181818182 

8).
The mutual inductance when k = 0.65, L1 = 2 H, and L2 = 5 H is
A   2 mH   
B  H   
C  H   
D  H   
ANS: B - H

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9).
A transformer with a 110 V primary has a 15:1 turns ratio. The load resistance, RL, is 120 . What is the approximate voltage across the load?
A   7.3 V   
B   73 V   
C   88 V   
D   880 V   
ANS: A - 7.3 V

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