Talking about the Power System of Domestic Generator Sets
1 generator grounding carbon brush problem
Since the stator magnetic field of the generator cannot be absolutely uniform, a potential difference of several volts or more is generated on the rotor of the generator. Since the loop resistance of the generator rotor and the bearing and the earth is small, a large shaft current may be formed. In order to prevent the formation of this current, the manufacturer placed an insulating sheet under all the bearings on the exciter side of the generator to block the shaft current path. At the same time, in order to ensure the same potential of the large shaft and the ground, a large shaft grounding carbon brush should be installed on the generator turbine side. Chinese manufacturers provide a grounded carbon brush device (two of the foreign manufacturers provide two), and the design department on the design drawings according to the requirements of the rotor grounding protection, the secondary protection wiring is connected to the large shaft through the carbon brush, so many construction units The grounded carbon brush supplied by the manufacturer was used as the "connecting shaft" for the rotor grounding protection, and the carbon brush was not grounded. It is harmful that the generator shaft is not grounded on the turbine side. Due to the potential difference between the large shaft of the generator and the ground, the large shaft may be discharged to the ground through the oil gap of the bearing bush, resulting in electrical burn of the bearing bush. In some accident situations, the damage is even greater. If the grounding insulation of the generator exciter side bearing housing (including the oil pipe connecting the bearing to the ground) is damaged, it may cause a large shaft current, especially if the stator coil In the event of a turn-to-turn short circuit, the shaft current will be larger, not only damaging the bearing pads, but also may cause magnetization of the turbine-related components due to large shaft currents flowing through the turbine shaft. For this reason, the generator set must be grounded to the grounding carbon brush (or grounded via a small resistor) during the installation phase, and care should be taken to maintain the grounding insulation of the bearings at the exciter end of the generator during operation, paying particular attention to preventing generator excitation. The metal sheath of each temperature measuring and vibration measuring cable on the machine side short-circuits the bearing to ground insulation.
