ATT040（ATT040）.docVIP

ATT040（ATT040） Summary of basic electrical engineering knowledge (1) dc system 1. Two-wire dc system The dc two-wire distribution system should be grounded. But there is no grounding: a system with earthing detectors that power only industrial equipment at a limited site; The voltage between the lines is equal to or less than 50V, or higher than 300V, which adopts the system of ground insulation; A direct current system powered by an integrated communication system. The maximum current is at 0.03 A and the following dc fire signal lines. 2. Three-wire dc system The neutral line of three-wire dc power supply system is directly grounded. (2) communication systems 1. Less than 50V ac lines Generally not grounded, but should be grounded with any of the following; (1) the power supply of the transformer is more than 150V to the earth voltage. (2) the power supply system of transformer is not grounded; (3) where an isolated transformer is adopted, it shall not be connected to the ground, but the core must be ground; (4) overhead lines installed outside buildings. 2.50 ~ 1000V communication system (1) the electrical system used to supply power to smelting, refining, heating or similar industrial electric furnaces; (2) a separate transmission system for the rectifier for the power supply of the industrial speed regulating transmission system; (3) a special control system that is powered by a transformer, which is under a special control system of less than 1000V. The power supply is continuous, the control system is equipped with ground detector, and it ensures that only full-time personnel can be monitored and repaired. 3. L ~ 10kV communication system Arc suppression or resistance grounding is necessary. But the 1 ~ 10kV communication system for mobile devices should be connected. (3) mobile and on-board generators 1. Mobile generator Under the following conditions are not required to frame ground mobile generators, the frame can be used as a generator power supply system