According to the equipment affected by stray current, the maximum allowable anode potential change of metro tunnel or new special tram is 0.1 V in big cities, and the single power supply part or the whole tunnel within the limit value of voltage drop is 0.1 v. The following conditions must be met for concrete walls or steel or cast iron walls or wall and steel concrete composite structures:
¢Ù Continuous electrical connections should be aware of each part of the tunnel or structural component over the entire length of the tunnel;
¢Ú Good electrical insulation should be aware of propagation tracking and tunnel structure;
¢Û Electrical insulation should be aware of the tunnel, all metal equipment outside the tunnel itself and the railway.
The first two requirements are mainly to ensure a voltage drop of 0.1V in the tunnel and to limit the amount of current leaking into the soil. The third requirement is to prevent stray current from leaking directly to external devices. There are no special regulations for electrical insulation of soil in tunnels. Tests on existing and under construction equipment show that the leakage load of tunnel can be reduced economically by using insulating layer.
In order to reduce stray current, external equipment shall not have electrical contact with track or tunnel structure. There should be plastic pipe and cable with plastic pipe sheath in the tunnel. All power supply lines shall be electrically insulated at the tunnel entrance. Insulated joints shall be installed on pipes outside the tunnel. The current from the public grid must be fed through an isolation transformer. It is necessary to install shangjiazhuang insulating joint on the pipeline or metal shielded cable.
Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing cathodic protection technology, engineering design, installation and technical services. Tel: 0539 3712117, 15588026668.