Overview
A transformer is an electrical device that transfers energy from one circuit to another purely by magnetic coupling. Transformers are often used to convert between high and low voltages, to change impedance, and to provide electrical isolation between circuits.
A basic transformer consists of two sets of coils or windings close to each other (sometimes wrapped around an iron or ferrite "core"). Each set of windings is simply an inductor. Power is fed into one coil (the "primary"), which creates a magnetic field. The magnetic field causes current to flow in the other coil (the "secondary"). The alternating current that flows through the primary winding establishes a time-varying magnetic flux, some of which links to the secondary winding and induces a voltage across it. The number of times the wires are wrapped around the core ("turns") is very important and determines how the transformer changes the voltage:
- If the primary has fewer turns than the secondary, you have a step-up transformer that increases the voltage
- If the primary has more turns than the secondary, you have a step-down transformer that reduces the voltage
- If the primary has the same number of turns as the secondary, the outgoing voltage will be the same as what comes in. This is the case for an isolation transformer
- In certain exceptional cases, one large coil of wire can serve as both primary and secondary. This is the case with variable auto-transformers.
A transformer doesn't change power levels. If you put 100 Watts into a transformer, 100 Watts come out the other end. Actually, there are minor losses in the transformer because nothing in the real world is 100% perfect. But transformers come pretty darn close; perhaps 95% efficient.
This 3-hour course provides a basic overview of transformers and is based entirely on Naval Education and Training Materials (NAVEDTRA 14174), Electricity and Electronic Training Series; Module-2 and covers Chapter 5, titled “Transformers”.
The student must take a multiple-choice quiz consisting of fifteen (15) questions at the end of this course to obtain PDH credits.
Specific Knowledge or Skill Obtained
This course teaches the following specific knowledge and skills:
- Understand transformer action and its physical characteristics
- The difference in construction between a high and a low voltage transformer
- The meaning of a “no-load condition” and “exciting current”
- The meaning of leakage flux and its effect on the coefficient of coupling
- Be able to identify a transformer as step up or step down and state the current ratio of a transformer when given the turns ratio
- The mathematical relationship between the power in the primary and the power in the secondary of a transformer
- The three power losses in a transformer
- The five different types of transformers according to their applications
- The general safety precautions when working with transformers
Course
Click on the following link to the PDF document to review the course material before taking the quiz for credit.
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