Closed-type transformers generate extremely low-frequency (ELF) electromagnetic fields during operation, which are distinct from the high-energy ionizing radiation (such as X-rays or γ-rays) commonly associated with radiation concerns. The electromagnetic field levels they produce are typically far below the limits set by international and national safety standards, posing negligible health risks to humans. Below is a detailed analysis:

　　Nature of Electromagnetic Radiation

　　Transformers operate based on the principle of electromagnetic induction, where a time-varying magnetic field induces a voltage in the windings. This process inevitably generates electromagnetic fields, but they are of an extremely low frequency (50Hz/60Hz) and classified as non-ionizing radiation. This fundamentally differs from the radiofrequency (RF) radiation (MHz-GHz) emitted by devices like mobile phones and microwave ovens.

　　Electromagnetic Shielding Design of Closed-Type Transformers

　　The metal enclosure of closed-type transformers not only provides physical protection but also serves as an electromagnetic shield:

　　Faraday Cage Effect: The metal enclosure reflects and absorbs internal electromagnetic fields, significantly reducing the external electromagnetic radiation intensity.

　　Structural Optimization: The iron core is made of high-permeability materials (such as silicon steel sheets or amorphous alloys), which further confine the magnetic field path and minimize leakage flux.

　　International Safety Standards and Limits

　　The International Commission on Non-Ionizing Radiation Protection (ICNIRP) and national standards (e.g., China's GB 8702-2014) stipulate the following limits for public exposure:

　　Electric Field Strength Limit: 4 kV/m (at 50Hz).

　　Magnetic Flux Density Limit: 100 μT (at 50Hz).

　　Actual measurements indicate that the electromagnetic field levels around closed-type transformers are typically only a fraction (a few percent to a thousandth) of these limits.

　　Actual Measurement Data

　　Electric Field Strength: At a distance of 1 meter from the transformer, the electric field strength is usually below 0.1 kV/m.

　　Magnetic Flux Density: At a distance of 1 meter from the transformer, the magnetic flux density is typically below 1 μT.

　　Expert Opinions and Conclusions

　　World Health Organization (WHO): It has been clearly stated that ELF electromagnetic fields have no substantive impact on health, and the current evidence does not support a correlation between "electromagnetic hypersensitivity" and electromagnetic field exposure.

　　Chinese Center for Disease Control and Prevention (China CDC): The electromagnetic radiation levels from transformers and other power equipment are far below safety limits and do not pose a threat to human health.

　　Usage Recommendations

　　Although there is no need for concern regarding the electromagnetic radiation from closed-type transformers, it is advisable to adhere to the following safety guidelines:

　　Maintain a Safe Distance: Avoid prolonged stays near the transformer (typically, a distance of 1 meter is considered safe).

　　Avoid Direct Contact: Do not touch the transformer enclosure or climb on the equipment.

　　Heed Warning Signs: Stay away from areas marked with "High Voltage" warnings.