Transformer MCQs Part 17
Contents
- 1 Assuming a maximum flux density of 1.3 Wb/m^2 and induced voltage per turn of 40 V, the core area required for 1600 kVA, 5500/220 V, 60 Hz single phase core type power transformer is:
- 2 A transformer has full load copper losses of 400 W. The copper loss at half of full-load will be
- 3 Short circuit test helps us to determine
- 4 If there is break in 220/110 V autotransformer in winding that is common to both HV and LV sides, then the output voltage on LV side will be:
- 5 Which of following transformer should never had its secondary open circuited when its primary is energized:
Assuming a maximum flux density of 1.3 Wb/m^2 and induced voltage per turn of 40 V, the core area required for 1600 kVA, 5500/220 V, 60 Hz single phase core type power transformer is:
Assuming a maximum flux density of 1.3 Wb/m^2 and induced voltage per turn of 40 V, the core area required for 1600 kVA, 5500/220 V, 60 Hz single phase core type power transformer is:
- 1025 cm^2
- 1100 cm^2
- 1155 cm^2
- 1200 cm^2
Correct answer: 3. 1155 cm^2
From formula: E = 4.44 * f * N * Φm
E/N = 4.44 * f * Φm
40 = 4.44 * 60 * Φm
Φm = 0.15015 Wb
Formula for area is: a = Φm/Bm
a = 0.1501/1.3 = 0.1155 m^2 = 1155 cm^2
A transformer has full load copper losses of 400 W. The copper loss at half of full-load will be
A transformer has full load copper losses of 400 W. The copper loss at half of full-load will be:
- 400 W
- 200 W
- 100 W
- 50 W
Correct answer: 1. 400 W
Soution:
Copper losses vary as square of current
At half-full load = (1/2)^2 * Full load Cu loss = ¼ * 400 = 100 W
Short circuit test helps us to determine
Short circuit test helps us to determine:
- Iron losses at no load
- Cu losses at no load
- Both of these
- None of these
Correct answer: 2. Cu losses at no laod
If there is break in 220/110 V autotransformer in winding that is common to both HV and LV sides, then the output voltage on LV side will be:
If there is break in 220/110 V autotransformer in winding that is common to both HV and LV sides, then the output voltage on LV side will be:
- 110 V
- 220 V
- Zero
- None of these
Correct answer: 2. 220 V
Which of following transformer should never had its secondary open circuited when its primary is energized:
Which of following transformer should never had its secondary open circuited when its primary is energized:
- Autotransformer
- Power transformer
- Voltage transformer
- Current transformer
Correct answer: 4. Current transformer
Explanation: In a current transformer, the primary current depends entirely upon the load on system. It doesn’t depend on load of secondary. If the secondary is open circuited while primary is carrying heavy load, the demagnetizing effect of secondary current will no longer exist and flux in core will be increased. Increased flux will induce high voltage in secondary which can puncture the insulation or can give dangerous shock to anyone coming in contact.