Your question is really deep, and it is the theme of many doctoral and master's papers at present and for a long time to come. In the 29 years that our company has been engaged in the production and sales of R&D and reactive power compensation equipment, we often see novices asking similar questions. Like this:

Briefly talk about my understanding: the confusion faced by railway traction substation is:

1, the load fluctuates greatly, and the train is heavy near, light far away, and the time is very short. The load gap is very large, which leads to the need of fast speed and large capacity for power factor measurement and reactive power compensation.

2, the harmonic is too large. The locomotive uses single-phase direct current, which brings great harmonics. We used to measure the power of the substation with various meters, but the data of the two meters can't be consistent, which shows that the interference of harmonics to the meters is huge, and it is very difficult to measure the harmonics of locomotives. However, the power factor of harmonics itself is still controversial in theory.

Therefore, to improve the power factor of train substation, the most effective way in theory is to use high-capacity and high-speed dynamic active filter! The filter can not only suppress harmonics but also compensate reactive power. However, the price is too high! It is estimated that this is the biggest obstacle at present.

More information about reactive power compensation and power factor can be found and discussed here: /uteam/view? teamId=36954