(Often the sections are run with different voltages or frequencies.) The grids could be synchronised on a standard foundation, but situations may interrupt synchronisation. It's not a dilemma for DC techniques. AC techniques have a particular security implication in that the railway electrification system would act as a "Backdoor" connection https://garrettgmqsu.blog-gold.com/45553142/the-fact-about-line安卓版下-that-no-one-is-suggesting