Dec. 29, 2021
The increase speed of the load after the generator is connected to the grid should be determined according to the capacity of the unit, the cooling and heating conditions and the actual operating conditions. If the temperature of the stator winding and stator core of the generator exceeds 50% of the rated temperature, the generator can be considered to be in a hot state. If the temperature of the stator winding and stator core is lower than 50% of the rated temperature, the generator can be considered to be in a hot state. Cold state. After the turbo generator is integrated into the power system from the cold state, usually the stator can immediately carry 50% of the rated current, and then rise to the rated value at a uniform speed within 30 minutes. According to relevant data, it takes about 37 minutes for the stator current of a 1MW generator set to reach the rated value from 50%.
The reason for limiting the increase speed of the generator load is to prevent residual deformation of the rotor windings. Because the rotor rotates at high speed, the huge centrifugal force presses the rotor windings on the slot wedge and the ferrule of the rotor core, forming an immovable one. overall. After the rotor is heated, the expansion of the winding copper rod is greater than the expansion of the iron core and it cannot move freely. The copper rod is relatively compressed and deformed. When the compression stress exceeds the elastic limit, residual deformation will occur. When the generator is shut down to cool down, copper shrinks more than steel, which will cause insulation damage, and the bottom of the tank is the most severe. This phenomenon repeats every time it starts and stops, and the residual deformation gradually accumulates, which may cause a short circuit between turns or a ground fault. Therefore, the "Regulations" stipulates the time required for the stator current to increase from 50% (according to calculations, when the sudden increase in load does not exceed 50% of the rated current, the rotor winding will not produce residual deformation) to 100% of the rated current. In addition, when When the generator is in a hot state or in an accident, the speed at which the load can be increased after being integrated into the power system is not limited.
The power factor cosΦ of the generator, also known as the force rate, is the cosine of the phase angle between the stator voltage and the stator current. It shows the relationship between the active power, reactive power and apparent power emitted by the generator. Its size reflects the generator's output of reactive load to the system. The reactive load sent by the generator is usually inductive. Generally, the rated power factor of the generator is 0.8.
When the power factor of the generator changes from the rated value to 1.0, the rated output can be maintained. But in order to maintain the stable operation of the generator, the power factor should not exceed 0.95 in the late phase, generally running at 0.85.
When the power factor is lower than the rated value, the generator output should be reduced. Because the lower the power factor, the greater the reactive component of the stator current, and the stronger the demagnetization armature response. At this time, in order to maintain the generator's terminal voltage unchanged, the rotor current must be increased, and the generator stator current is also Increased by the increase in reactive components. At this time, if the output of the generator is to be kept constant, the generator rotor current and stator current will exceed the rated value, and the rotor temperature and stator temperature will exceed the allowable value and overheat. Therefore, when the generator is running, if the power factor is lower than the rated value, care must be taken to adjust the load so that the rotor current does not exceed the allowable value.
The above content was compiled by the editor of the diesel generator set manufacturer Guangxi Dingbo Power. For more questions about diesel generator sets, please inquire through email email@example.com.
Jun. 24, 2022
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