When the synchronous generator operates normally, the connection between the stator magnetic poles and the rotor magnetic poles can be regarded as elastic magnetic lines of force. As the load increases, the power angle increases, which is equivalent to lengthening the magnetic field lines; when the charge decreases, the power angle decreases, which is equivalent to shortening the magnetic field lines. When the load changes suddenly, due to rotor inertia, the rotor power angle cannot stabilize at the new value immediately, but must oscillate several times around the new stable value. This phenomenon is called synchronous generator oscillation.
There are two types of oscillation: one is that the amplitude of the oscillation becomes smaller and smaller, and the power angle oscillation gradually attenuates, and finally stabilizes at a new power angle, and fonstill works stably. at synchronous speed, called synchronous oscillation; the other is that the oscillation amplitude becomes larger and larger, and the power angle continues to increase until it goes out of the stable range, resulting in generator loss of synchronization and the generator enters asynchronous operation, called asynchronous oscillation.
Phenomena when the generator oscillates or loses synchronization
a) The stator ammeter indicates that it exceeds the normal value and it moves violently back and forth. This is because the angle between the parallel potentials changes and a difference in electromotive force occurs, causing a current to flow between the generators. Due to the oscillation of the rotor speed, the angle between the electromotive force becomes smaller and smaller, and the torque and power are also smaller and smaller, resulting in a circulating current of moresmaller, so that the stator current pointer swings back and forth. . This circulating current plus the original charging current may exceed the normal value.
b) The pointer readings of the stator voltmeter and other bus voltmeters are lower than the normal value and oscillate back and forth. In fact, the angle between the potential of the out-of-phase generator and that of the other generators changes, causing voltage oscillations. Since the current is higher than normal, the voltage drop is also large, making the voltage low.
c) The active charge and the reactive charge oscillate considerably and violently. This is because the power sent by the generator during the oscillation process when it is not out of phase is sometimes large and sometimes small, and when it is out of phase it sometimes sends active power and sometimes absorbs power active.
d) The indicator ofthe voltage of the rotor and the ammeter is in the normal state oscillates around the value. When the generator oscillates or loses pitch, an alternating current is induced in the rotor winding and fluctuates with the fluctuation of the stator current. This current is superimposed on the original excitation current, causing the rotor ammeter needle to oscillate near the normal value.
) The frequency table oscillates up and down. In case of oscillation or offset, the power output of the generator changes continuously and the torque acting on the rotor also changes accordingly, so the rotational speed also changes accordingly. .
What is the oscillation and offset of the generator?
The diesel generator vibrates during operation, except that the fuel injection of the engine machinery is incorrect and each cylinder is not working properly. Besides factors such as wear and loosening of diFor parts of the machine, this is mainly due to improper support. Let's look at the following specific reasons.
1. The engine mount is broken.
2. The engine mount mounting bolts are loose.
3. The motor mounting buffer block fails or falls off.
4. The motor mounting position is incorrect, causing the transmission part to have different axle centers.
When the load changes suddenly, due to rotor inertia, the rotor power angle cannot be stabilized immediately at the new value, but must oscillate several times around the new stable value. This phenomenon is called synchronous generator oscillation.
For stepper motors, there are certain requirements regarding the power frequency of the windings. If the power-on frequency is too high and exceeds the maximum stepper speed of the stepper motor, lag will occurwill go. In addition, in a synchronous motor, when the load torque of the motor is greater than the torque that the motor can provide, the speed of the motor cannot keep up with the synchronization speed of the motor, which will also cause lag.
Detailed information
There are two types of oscillation: one is that the amplitude of the oscillation becomes smaller and smaller, and the power angle oscillation gradually attenuates and finally stabilizes under a certain new power angle, it always works stably at a synchronous speed, called synchronous oscillation; the other is that the oscillation amplitude becomes larger and larger and the power angle continues to increase until it is out of the stable range, causing the generator to lose synchronization and the electricity production. The machine enters asynchronous operation, called asynchronous oscillation.
Protectionn against generator offsets reflects the change trajectory of the impedance measured at the generator end, which can reliably avoid system short circuits and stable oscillations, and can distinguish out-of-synchronous accelerations and decelerations. offset during the offset swing process.
Baidu Encyclopedia - Out of Pace Protection
Baidu Encyclopedia - Out of Pace Protection