Abstract: The neutral point of the generator often grounded through a blowout coil. In system operation process of a power plant, the highvoltage fuse of potential transformer may blow and make negative influence on the system sometimes. The operation features of the power plants were analyzed ,in which the neutral point of the generator is grounded through a blowout coil，and it is an important reason that the drift voltage of the neutral point will be amplified by the blowout coil. A preventive scheme was proposed, in which a resistor is connected in series with the blowout coil to restrain the amplifying effect of the drift voltage of the neutral point and to prevent the PT fuse blow; an electronic switch is connected in parallel with the resistor to control the resistor. Taking a hydropower plant as example, the effectiveness of this scheme was verified.

Key words: voltage transformer (PT), fuse blow, drift voltage of neutral point, damping resistor, electronic switch