What are the differences in operating characteristics between synchronous generator sets and asynchronous generator sets?

There are many differences in the operating characteristics between synchronous generator sets and asynchronous generator sets, mainly reflected in the following aspects:

Relationship between frequency and rotational speed

Synchronous generator set: Its speed and frequency strictly maintain a synchronous relationship, that is, (where is speed, is frequency, and is logarithmic). As long as the grid frequency is stable, the speed of the generator remains constant and can output electrical energy at a stable frequency.

Asynchronous generator set: There is no fixed synchronous relationship between speed and frequency, and its speed is always slightly higher or lower than the synchronous speed, with a slip rate (where is the synchronous speed and is the actual speed).

Voltage regulation characteristics

Synchronous generator set: By adjusting the excitation current, the output voltage can be conveniently regulated. When the load changes, the excitation can be adjusted in a timely manner to maintain voltage stability, and the voltage regulation performance is good.

Asynchronous generator set: It does not have an independent excitation device to directly regulate the voltage. The terminal voltage is greatly affected by load and grid parameters, and the voltage stability is relatively poor. It usually requires the use of external reactive power compensation devices to stabilize the voltage.

Power factor characteristics

Synchronous generator set: The power factor can be adjusted within a certain range by adjusting the excitation current. It can operate in both lagging and leading power factor states, and can flexibly provide reactive power according to the needs of the power grid.

Asynchronous generator set: It needs to absorb lagging reactive power from the power grid to establish a magnetic field during operation, and its power factor is generally lagging, which is difficult to adjust flexibly like synchronous generators.

Grid connected operation characteristics

Synchronous generator set: When connected to the grid, strict conditions must be met, such as voltage amplitude, frequency, phase, and phase sequence, which must be consistent with the grid. After grid connection, it can operate accurately according to the frequency and phase of the power grid, with good synchronization with the power grid.

Asynchronous generator set: Grid connection is relatively simple, as long as the voltage and phase sequence are correct, it can generally be connected to the grid. It can automatically track the grid frequency, but there may be significant surge currents at the moment of grid connection.

stability

Synchronous generator set: During stable operation, as long as the input power of the prime mover and the load power are balanced, the generator can maintain stable operation. But in some cases of malfunction or disturbance, unstable phenomena such as out of step may occur.

Asynchronous generator set: It has a certain degree of self-regulation ability. When the load changes, the speed will automatically adjust to adapt to the load changes. However, in extreme cases, instability problems such as overload and locked rotor may also occur.