AC Electrics - Practical Aircraft Systems — Page 231, Lesson 245

We've just moved into a new chapter — Chapter 14, AC Electrics – Transformers. Before we dive into the theory, the book gives us a real-world example to set the stage. It mentions the Boeing 747-400 as an aircraft that uses the kind of paralleled AC generator system we were just discussing. On the flight deck, the electrical system is managed through two key displays: the electrical control panel, shown in Figure 13.6, and the EICAS electrical display, shown in Figure 13.7. EICAS stands for Engine Indication and Crew Alerting System — that's the primary screen the crew uses to monitor engine and system parameters, including the electrical bus status. So the 747-400 gives us a concrete picture of how a paralleled AC system looks from the pilot's seat. Now, turning to Chapter 14, we're going to start with the fundamental component that makes AC power distribution practical: the transformer. The chapter outline lists the topics we'll cover in order: first, what a transformer is and how it works; then the transformation ratio, which tells us how voltage is stepped up or down; next, power in a transformer — because ideal transformers conserve power, so current changes inversely with voltage. After that, we'll look at three-phase transformers, which are essential for aircraft AC systems, and autotransformers, a special type that shares a single winding. Then we move into rectification of alternating current — converting AC into DC — starting with half-wave rectification, then full-wave rectification, and then three-phase rectifiers. That leads us to Transformer Rectifier Units, or TRUs, which are the actual units in an aircraft that take AC from the generators and produce DC for the battery and DC buses. Finally, we'll cover inverters, which do the opposite — they convert DC back into AC. The chapter ends with questions and answers for self-study. So, to begin: a transformer is a device that transfers electrical energy between two or more circuits through electromagnetic induction. It has no moving parts, and it works only with alternating current — because a changing magnetic field is required to induce voltage in the secondary winding. We'll start with the basic construction and the transformation ratio next.