A: At this time, it is assumed that the excitation current of the generator is unchanged, and the voltage of the system is also unchanged. According to the power angle characteristics of the motor, we will talk about the process of adjusting the active load.
(1) Load-increasing process: when the large valve is opened, the main torque on the rotor shaft of the generator increases. At this time, since the electric power has not started to change, that is, the magnitude of the resistance torque has not changed, the rotor must be accelerated, so that the rotor and the stator According to the power angle characteristics of the motor itself, as the power angle increases, the output power of the motor will increase, that is, more load. Whether the rotor will keep accelerating, normally it will not, because the motor has more load, the resistance torque will increase. When the resistance torque is large enough to balance with the main torque, the rotor speed will stabilize. At this time, the power generation The output of the machine will rise to a new value.
(2) Load reduction process: when the valve is closed, the main torque on the rotor shaft of the generator decreases, so the rotor decelerates and the power angle becomes smaller. When the power angle becomes smaller, the electromagnetic power decreases, and the corresponding resistance torque also becomes smaller. When the resistance torque is reduced to be as large as the new main torque, a new balance is reached, and the motor is less loaded at this time.
Two points should be paid attention to when adjusting the active load:
(1) The force rate should be kept within the range specified in the regulations as much as possible, and should not be greater than 0.95 of the delayed phase. Because the high force rate means that the excitation current corresponding to the active power at that time is small, that is, the generator is stationary and the magnetic field lines between the rotor poles are small, which is easy to lose stability. From the perspective of the power angle characteristics, the active power sent increases. , the power angle will be close to 90 degrees, so it is easy to lose stability.
(2) It should be noted that the load should be adjusted slowly. When the output of the unit is increased, its overload capacity is generally reduced.