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When a sudden short circuit occurs at the line terminals of a device with windings, such as a transformer or an electric motor, the following happens to the current in the windings:
1. Immediate Increase in Current Flow: The short circuit provides a path with very low resistance, causing a sudden and drastic increase in the current flowing through the windings. This phenomenon is due to Ohm’s Law, where current is inversely proportional to resistance. Since the resistance has dropped significantly, the current increases sharply.
2. Thermal Stress: The sudden surge in current generates significant heat within the windings. This can cause thermal stress on the insulation and the materials of the windings, potentially leading to immediate damage or degradation over time.
3. Electromagnetic Stress: Along with thermal stress, the windings also experience electromagnetic stress due to the high magnetic fields generated by the increased current. This can lead to mechanical damage such as deformation of the windings.
4. Protection Mechanisms Activation: To protect the device and the electrical system, protection mechanisms such as fuses or circuit breakers will activate to interrupt the circuit. This happens very quickly, often within milliseconds, to minimize the damage.
5. Risk of Arcing: The abrupt increase in current can cause arcing across contacts or insulating materials, leading to further damage and potentially causing fires or explosions in extreme cases.
6. Potential System Destabilization: Beyond the immediate physical effects on the windings,
Answer: b
Explanation: The current in the windings during short circuit at the line terminals increases to about 15 times the full load current. It can also increase to higher level depending on the direct axis sub-transient reactance.