Europe was the first region to develop railways, so it makes sense that the international standards related to railways in that region also have been perfected.
Trains experience long-term exposure in harsh environments, with extreme temperature variations, dust, and vibration, as well as voltage fluctuations and transients of electrical equipment. Thus, EN50155, the most commonly used specification in Europe, not only lists the working condition of electrical equipment and the voltage range of power supplies, but also conditions of reliability.
In particular, electrically powered trains absolutely need good power-density designs. The following sections will demonstrate why this is necessary.