Abstract: In recent years, the electro-magnetic effect of underground power cables in cities on the environment and the public has caused widespread concern. The 2-D finite element analysis on magnetic field was used to set up simulation models for typical cable tunnels and to calculate the power frequency magnetic field inside and outside the tunnel, and the space distribution law and influence factors were discussed. It is found that the more the circuit number is, the denser cables are laid, or the higher the current is transmitted, the stronger the power frequency magnetic field inside and outside the tunnel will be. The distance from the cables is the key factor to determine the magnitude of the power frequency magnetic field. Magnetic cable brackets will cause the accumulation of magnetic field, so as to reduce the economy and safety of cable lines. In-site measurements of power frequency magnetic field were carried out in several cable tunnels, and the test data were in good agreement with the calculated values. The magnetic field strength levels at the pavement and ground surface of the cable tunnels discussed are lower than the exposure limits recommended by current standards.

Key words: AC power cables, tunnel laying, power frequency magnetic field, safety limit