Transformer winding resistance issues

The resistance of the transformer’s primary winding is indeed very low, but to understand why it does not burn out when the rated AC voltage is applied, it is necessary to consider the principles of how transformers operate and the characteristics of alternating current. 1. When an alternating current supply is connected to the primary winding of a transformer, since both the voltage and current of the alternating current vary over time, its average power is not simply determined by the DC resistance. The primary winding of the transformer generates an alternating magnetic flux under AC voltage; this flux is coupled to the secondary winding through the core, and according to Faraday’s law of electromagnetic induction, an induced voltage is generated in the secondary winding. Under no-load or loaded conditions, the current in the primary winding does not exceed its rated value; therefore, no sufficient heat is generated to cause burning. 2. If a DC voltage equal in magnitude to the AC voltage is applied to one winding, the situation is completely different. Since the operation of a transformer relies on an alternating magnetic field, direct current cannot generate a changing magnetic field; this means that a DC power supply will not enable the transformer to function properly. Due to the very low DC resistance, the DC voltage will cause a large current to flow through the primary winding, and this current can be much higher than the rated current under AC conditions. Therefore, the windings generate a large amount of heat, which can lead to damage to the insulating materials or even burnout of the windings. 3. Under direct current voltage, since no alternating magnetic field is generated, no induced voltage is produced in the secondary winding; therefore, no voltage is output. However, at the moment of activation, direct current may cause a brief instantaneous voltage to appear in the secondary winding, but this is due to an instantaneous change in magnetic field resulting from the change in direct current voltage (from zero to a certain value). After this instantaneous response, the secondary winding will not produce any voltage output. In practical applications, to prevent the transformer from being overloaded or misused, it is usually equipped with protection circuits and safety measures to avoid damage caused by such operations. .

When a rated AC voltage is applied to the primary side of the transformer, a high back EMF will be induced in the primary winding; however, since the resistance of the transformer’s primary winding is low, the coil will not burn out. When the same direct current is applied to the primary winding, since the voltage does not vary, there is no induced electromotive force within the winding, and no voltage is output on the secondary side. Over a long period of time, the transformer will overheat and get damaged.