Transformer Testing & Applications Quiz
Three-Phase Transformers
1. The common three-phase transformer connections are:
Explanation: The common three-phase transformer connections are Star-Star, Delta-Delta, and Star-Delta configurations.
2. A Delta-Star transformer is used for:
Explanation: Delta-Star transformers are commonly used for step-down distribution as they provide a neutral point for grounding on the secondary side.
3. In a three-phase transformer, a 30° phase shift occurs in:
Explanation: A 30° phase shift occurs in Star-Delta connections due to the different winding configurations between primary and secondary.
4. The main advantage of a three-phase transformer over three single-phase units is:
Explanation: Three-phase transformers are more economical, require less space, and have fewer external connections compared to three single-phase units.
5. Scott connection is used to convert:
Explanation: Scott connection is a method of connecting transformers to convert three-phase power to two-phase power or vice versa.
Special Transformers & Applications
6. A current transformer (CT) secondary should never be open-circuited because:
Explanation: Open-circuiting a CT secondary can cause core saturation, dangerous high voltage spikes, and insulation damage due to the high voltage produced.
7. Potential transformers (PT) are used for:
Explanation: Potential transformers step down high voltages to measurable levels for metering and protection purposes.
8. An isolation transformer provides:
Explanation: Isolation transformers provide galvanic isolation between primary and secondary circuits for safety and noise reduction.
9. Pulse transformers are used in:
Explanation: Pulse transformers are designed to transmit rectangular electrical pulses and are commonly used in digital circuits and communication systems.
10. A welding transformer has:
Explanation: Welding transformers are designed with high leakage reactance for current limiting, operate at low power factor, and provide variable output current for different welding applications.
Faults & Protection
11. The most common transformer fault is:
Explanation: Overheating is the most common transformer fault, often caused by overloading, poor cooling, or insulation degradation.
12. Differential protection is used for:
Explanation: Differential protection compares currents entering and leaving the transformer to detect internal faults (winding short-circuits, turn-to-turn faults).
13. Surge arresters protect transformers from:
Explanation: Surge arresters protect transformers from voltage surges caused by lightning strikes or switching operations.
14. The purpose of a breather in a transformer is to:
Explanation: The breather contains silica gel to absorb moisture from the air entering the transformer, preventing moisture contamination of the oil.
15. Overfluxing in a transformer occurs due to:
Explanation: Overfluxing occurs when the voltage-to-frequency ratio (V/f) is too high, which can saturate the core and cause excessive heating.
Summary
The purpose of a conservator tank is to: (Expansion space for oil)
Buchholz relay operates on: (Gas accumulation from faults)
Transformer oil must have: (High dielectric strength)
The kVA rating of a transformer depends on: (Temperature rise limits)
A step-down transformer has: (More primary turns than secondary)
Leakage flux causes: (Voltage drop & regulation issues)
The main advantage of zigzag windings is: (Harmonic suppression)
Neutral grounding is done to: (Limit fault currents)
A CT’s secondary must always be: (Short-circuited if not in use)
The future of transformers includes: (Smart grids & renewable integration)
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