I. Transformer Working Principle
A transformer utilizes the phenomenon of electromagnetic induction, using two or more mutually insulated windings (i.e., coils) wound on an iron core (or magnetic core) to achieve the transmission of electrical energy and the transformation of voltage. When one of the windings (called the primary winding) is connected to an AC power source, an alternating magnetic flux is generated in the iron core. This alternating magnetic flux passes through one or more other windings (called the secondary windings), thereby inducing an electromotive force in the secondary winding and achieving voltage transformation.
When the primary winding is connected to an AC power source, current flows through the winding, generating an alternating magnetic flux in the iron core according to Ampere's circuital law. This magnetic flux varies with time, and its frequency of change is the same as the frequency of the primary current.
When alternating magnetic flux passes through the secondary winding, an electromotive force (EMF) is induced in the secondary winding according to Faraday's law of electromagnetic induction. The magnitude of this EMF is proportional to the primary voltage, the number of turns in the secondary winding, and the rate of change of the magnetic flux.
Since the number of turns in the secondary winding can be different from the number of turns in the primary winding, the induced electromotive force can be higher or lower than the primary voltage, thereby realizing voltage boosting or bucking.
When a load is connected to the secondary winding, a secondary current begins to flow, which also generates its own magnetic flux. However, since the applied voltage remains constant, the primary magnetic flux tends to remain constant. To maintain magnetic flux balance, the primary current increases accordingly to generate sufficient magnetomotive force to counteract the magnetic flux effect generated by the secondary current. In this way, energy is transferred between the primary and secondary windings through electromagnetic induction.
II. What are the protection methods for transformers?
1. Overload protection
When the load current on a transformer exceeds its rated value, the temperature of the transformer windings will rise, exceeding the insulation temperature limit, leading to equipment damage and even danger. Therefore, overload protection for transformers must be considered in the design and operation. During the protection process, the transformer winding temperature needs to be checked regularly to identify overload faults and take appropriate protective measures to prevent them from occurring.
2. Short circuit protection
When a transformer experiences a short-circuit fault, the current within the transformer surges dramatically, exceeding its design capacity. This can easily lead to damage to the windings and insulation, or damage to other equipment in the vicinity. To ensure the safety of certain equipment, automatic protection devices need to be installed. Short-circuit protection can be categorized into several types, including overcurrent protection, differential protection, and grounding protection.
3. Undervoltage protection
When a transformer loses power or the power supply voltage drops to a certain level, it will be insufficient for the transformer to operate normally, potentially leading to equipment failure. Undervoltage protection is a protective device designed to address this situation. It primarily works by detecting a drop in transformer voltage. Once undervoltage is detected, the equipment can automatically disconnect to prevent damage.
4. Overvoltage protection
In some cases, due to sudden power supply malfunctions or other reasons, transformers may be subjected to excessively high voltages, i.e., overvoltage. In such situations, protection systems are needed to prevent this. The principle of overvoltage protection is that an overvoltage protection device is installed at the high-voltage end of the transformer. When an overvoltage is detected, the overvoltage protection device will immediately cut off the power supply, thereby protecting the transformer from damage due to excessive voltage.
