Practice Test: Question Set - 09
1. Star/star transformers work satisfactorily when
- (A) Load is unbalanced only
- (B) Load is balanced only
- (C) On balanced as well as unbalanced loads
- (D) None of the above
2. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in
- (A) Short-circuiting of the secondaries
- (B) Power factor of one of the transformers is
leading while that of the other lagging
- (C) Transformers having higher copper losses will
have negligible core losses
- (D) Loading of the transformers not in
proportion to their kVA ratings
3. During open circuit test of a transformer
- (A) Primary is supplied rated voltage
- (B) Primary is supplied full-load current
- (C) Primary is supplied current at reduced
voltage
- (D) Primary is supplied rated kVA
4. Reduction in core losses and increase in permeability are obtained with transformer employing
- (A) Core built-up of laminations of cold rolled
grain oriented steel
- (B) Core built-up of laminations of hot rolled
sheet
- (C) Either of the above
- (D) None of the above
5. To step 120 V ac up to 900 V ac, the turns ratio must be
- (A) 75
- (B) 750
- (C) 7.5
- (D) 0.13
6. Which of the following acts as a protection against high voltage surges due to lightning and switching?
- (A) Horn gaps
- (B) Thermal overload relays
- (C) Breather
- (D) Conservator
7. An open-circuit test on a transformer is conducted primarily to measure
- (A) Insulation resistance
- (B) Copper loss
- (C) Core loss
- (D) Total loss
8. 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
9. Minimum voltage regulation occurs when the power factor of the load is
- (A) Unity
- (B) Lagging
- (C) Leading
- (D) Zero
10. In a transformer the energy is conveyed from primary to secondary
- (A) Through cooling coil
- (B) Through air
- (C) By the flux
- (D) None of the above
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