Thread Content
What is generator reverse power protection? I. What is reverse power? As is well known, the power direction of a generator should be from the generator to the system. But for some reason, when the turbine loses its driving force and the generator’s output switch fails to trip, the power flow direction changes from the system to the generator; in other words, the generator operates as a motor. At this point, the generator draws active power from the system, which is known as reverse power. II. Hazards of reverse power: Generator reverse power protection is necessary in cases where, for some reason, the main steam valve of a turbine closes and it loses its driving force; in such situations, the generator functions as a motor to rotate the turbine. The high-speed rotation of the turbine blades without steam present can cause aerodynamic friction, and especially in the last stage of the blades, this may lead to overheating and damage to the rotor blades. Therefore, reverse power protection is essentially a safeguard against the turbine operating without steam. III. Programmed reverse power protection for generators: The programmed reverse power protection for generators is designed to prevent the generator outlet switch from suddenly closing off when the generator is under load, in situations where the main steam valve of the turbine cannot be fully closed. Under these conditions, the steam turbine generator set is highly prone to overspeeding, or even runaway. To avoid such a situation, for certain protections against non-short-circuit faults, after the actuation signal is sent, it first operates to close the main steam valve of the turbine; once the generator’s reverse power relay activates, this signal together with the signal indicating that the main steam valve has been closed forms an AND gate, and after a short time delay, this constitutes a programmed reverse power protection mechanism that triggers a full shutdown. IV. Difference between reverse power protection and programmatic reverse power protection. Reverse power protection is designed to prevent the generator from functioning as a motor after reverse power occurs, thereby causing the turbine to rotate and resulting in damage to the turbine. Ultimately, it is to prevent the prime mover from having insufficient power and thus being driven by the system! The reverse power protection in the program serves to prevent the turbine from speeding up due to the main steam valve not closing fully after the generator set is suddenly disconnected, and it does this by utilizing reverse power. Ultimately, it is to prevent the unit from speeding up due to excessive power from the prime mover! Therefore, strictly speaking, reverse power protection is a type of relay protection for generators, but its main purpose is to protect the steam turbine. Program reverse power protection is not a form of protection; rather, it is a mechanism designed to trigger a program-based trip, also known as program trip, and it is generally used in shutdown scenarios. The most crucial point is that tripping occurs as soon as the reverse power reaches a certain set value; whereas for programmed reverse power, in addition to reaching that set value, it is also required that the main steam valve of the turbine be closed. Therefore, at the moment of grid connection during unit startup, it is essential to avoid reverse power triggering.