Transformers are protected against faults and overloads through various protective devices and mechanisms. Here are some of the common methods used to ensure the safety and reliable operation of transformers:

  1. Overcurrent Protection: Transformers are equipped with overcurrent protection devices, such as fuses or circuit breakers, to safeguard against excessive current flow. These devices detect the overcurrent condition and interrupt the circuit to prevent damage to the transformer.

  2. Overload Protection: Thermal overload protection is provided to prevent the transformer from overheating due to prolonged high-current conditions. Typically, a bimetallic strip or a thermal relay is used to monitor the temperature rise. If the temperature exceeds a pre-set threshold, the protection device trips, disconnecting the transformer from the power source.

  3. Short-Circuit Protection: Short-circuit currents can cause severe damage to transformers. To protect against short circuits, fast-acting protective devices like high rupturing capacity (HRC) fuses or current-limiting circuit breakers are installed. These devices detect the abnormal current flow and quickly disconnect the transformer from the fault.

  4. Buchholz Relay Protection: Buchholz relay is a gas and oil-operated relay installed in larger transformers. It detects internal faults such as insulation failure or incipient short circuits. When faults occur, gas bubbles are generated, causing the relay to operate and disconnect the transformer from the system.

  5. Differential Protection: Differential relays are commonly used to protect transformers against phase-to-phase and phase-to-ground faults. These relays continuously monitor and compare the current flowing into the transformer with the current flowing out of the transformer. If an imbalance is detected, indicating a fault, the differential relay operates and isolates the transformer.

  6. Ground fault protection: Transformers are also equipped with ground fault relays to detect current leaks to the ground. Such faults may occur due to insulation breakdown or accidental contact with a grounded object. The relay operates when an imbalance is detected between the current flowing in the phase conductors and the return current through the grounding system.

  7. Voltage Protection: Voltage monitoring relays are used to protect transformers from overvoltage and undervoltage conditions. These relays monitor the transformer's input and output voltage levels and trip the circuit if the voltage exceeds or drops below acceptable limits.

  It's essential to note that the protection scheme for transformers may vary depending on the specific application, size, and voltage rating of the transformer. Designers and engineers consider various factors to ensure adequate protection and reliable operation of transformers.