Generator and motor are known as two different kinds of mechanical equipment. One is to convert other energy into electrical energy for power generation, while the motor converts electrical energy into mechanical energy to drag other objects. However, the two can not be installed and replaced with each other. Some kinds of generators and motors can be interchanged after design and modification. However, in case of a fault, the generator is also converted to motor operation, which is the reverse protection under the reverse power of the generator we want to talk about today.
What is reverse power?
As we all know, the power direction of the generator should flow from the generator direction to the system direction. However, for some reason, when the turbine loses motive power and the generator outlet switch fails to trip, the power direction changes from the system to the generator, that is, the generator changes to the motor in operation. At this time, the generator absorbs active power from the system, which is called reverse power.
Harm of reverse power
Generator reverse power protection is that when the main throttle valve of the steam turbine is closed due to some reason and the original power is lost, the generator turns into a motor to drive the steam turbine to rotate. The high-speed rotation of the steam turbine blade without steam will cause blast friction, especially in the last stage blade, it may cause overheating and lead to the damage accident of the rotor blade.
Therefore, reverse power protection is actually the protection of steam turbine without steam operation.
Programmed reverse power protection of generator
The generator program reverse power protection is mainly to prevent the generator from suddenly tripping the generator outlet switch under a certain load and the main throttle valve of the steam turbine is not fully closed. In this case, the steam turbine generator unit is prone to overspeed and even speeding. In order to avoid this situation, for some protections without short-circuit fault, after the action signal is sent, it will first act on closing the main steam valve of the steam turbine. After the reverse power * * * of the generator acts, it will form and valve with the signal closing the main steam valve, form program reverse power protection after a short time, and the action will act on full stop.
Difference between reverse power protection and program reverse power protection
Reverse power protection is to prevent the generator from turning into a motor after reverse power, driving the steam turbine to rotate and causing damage to the steam turbine. In the final analysis, I’m afraid that the prime mover will be driven by the system if it lacks power!
The program reverse power protection is to prevent the turbine overspeed caused by the main throttle valve not fully closed after the generator unit is suddenly disconnected, so the reverse power is used to avoid. In the final analysis, I’m afraid that too much power of the prime mover will lead to overspeed of the unit.
Therefore, strictly speaking, reverse power protection is a kind of generator relay protection, but it mainly protects steam turbine. The program reverse power protection is not a protection, but an action process set to realize program tripping, also known as program tripping, which is generally applied to shutdown mode.
The key is that as long as the reverse power reaches the set value, it will trip. In addition to reaching the set value, the program reverse power also requires the main throttle valve of the steam turbine to be closed. Therefore, the reverse power action must be avoided at the moment of grid connection during unit startup.
These are the functions of generator reverse protection and the explanation of generator reverse power. For the steam turbine generator in grid connected operation, it will operate as a synchronous motor after the main throttle valve of the steam turbine is closed: absorb active power and drag the steam turbine to rotate, which can send reactive power to the system. As the main throttle valve of the steam turbine has been closed, the tail blade of the steam turbine has friction with the residual steam to form blast loss, which is damaged by overheating during long-term operation. At this time, the reverse protection can protect the steam turbine from damage.
Post time: Jan-10-2022
