Talk about the reverse operation of generators

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Let’s talk about the reverse operation of generators. 1. What is the reverse operation of generators? The reverse operation of a generator, also known as the operation of a generator in motor mode, refers to a situation where, when the unit is connected to the grid, there is insufficient steam supply to the turbine or the steam supply is interrupted; in such cases, the generator must absorb active power from the grid in order to keep the unit operating at the grid frequency. Second, will reverse operation of the generator cause a change in direction? I thought of this question while discussing knowledge with colleagues today; when a generator operates as a motor and draws power from the power grid, does its direction of rotation change at that time? The answer is no, because during reverse operation of the generator as an electric motor, it is merely due to the interruption of steam supply to the turbine that the generator shifts from supplying power to the grid to absorbing power from the system in order to drive the turbine. Whether the generator is supplying power or absorbing power from the grid, its phase sequence remains unchanged; therefore, its direction of rotation does not change, and the generator will not reverse direction. Third, what are the hazards of operating a generator in reverse? Operating a generator in reverse mode does not cause any harm to the generator itself; it simply means that the power output is replaced by power absorption. However, since the load on the power grid remains constant, when a generator shifts from emitting power to absorbing power from the grid, it can cause the frequency of the entire grid to drop. This is especially true for power plants operating in small grids, and it can even affect the stability of the power grid. On the other hand, under this approach, the turbine exhaust cylinder and the final stage blades will overheat rapidly. Since no steam or only a small amount of steam reaches the turbine, this causes aerodynamic friction on the last stage of the turbine blades, resulting in overheating of the low-pressure cylinder and damage to those blades. Therefore, the generator is equipped with reverse power protection to prevent it from operating in reverse. IV. What is the asymmetric operation and partial-phase operation of a generator? Any condition that causes a disruption in the three-phase symmetry of an electrical power system, such as a disruption in the symmetry of the impedance across the phases, a disruption in load symmetry, or a disruption in voltage symmetry, is referred to as asymmetric operation. Non-full-phase operation is a special case of asymmetric operation. During asymmetric operation, negative-sequence currents occur in the generators; when the transformer’s neutral point is grounded, zero-sequence currents also appear. This leads to rotor heating, increased vibration of the unit, and overheating of certain phase stator windings. V. Phenomena and handling of generator operation in reverse drive 1. Phenomena 1.1. The active power indication of the generator is negative. 1.2. A “valve closed” signal appears. 1.3. The reactive power reading of the generator increases, while the current reading decreases. 1.4. The stator voltage and excitation system parameters are normal. 1.5. The system frequency may decrease slightly. 2. Handling 2.1. If the generator trips due to reverse power or the shutdown of the main steam valve, it shall be treated as an accident trip. 2.2. If the reverse power protection does not activate, the generator should be disconnected manually (it is important to note that the active power meter reading of the generator should be negative before disconnection).