Chapter 7: DC generators, AC generators and Transformers
Chapter Overview
Chapter 7 will cover DC generators, AC generators and transformers. Most electrical systems contain both AC and DC voltages, so it is important to understand how both types are generated and utilized in the field. Worksheet information link.
Key points to remember:
Transformers are also covered in this section. Because of the extensive use of transformers throughout the industry, it is important to understand their operating principles and usages, especially when designing, installing, or troubleshooting an electrical system.
- Electromagnetism is the basic property behind the operation of DC/AC generators and transformers.
- In the “War of Currents” Tesla’s AC system was proven to be the best because AC systems can be transformed and distributed over longer distances.
- The cores of transformers are laminated for the same reason the magnetic assembly in a solenoid is: To confine the eddy currents in the individual laminations.
DC and AC Generator Basics
A generator converts mechanical energy into electrical energy using electromagnetic induction. Generators are designed to either produce DC or AC power, and both use electromagnetism in slightly different ways to accomplish the same goal of electrical power generation. Electricity produced from generators is widely used in modern-day power distribution. The modern-day reliance on electricity has continued to increase the need for qualified electricians to build and maintain these systems integral to society. As an electrician it is important to understand how they work and the critical role they play in modern electrical systems.
DC generators operate through the rotation of a coil of wire spinning in a magnetic field, which induces a voltage into the coils as it cuts through the magnetic force lines of the associated magnetic field. The amount of voltage produced depends on the rate at which the coil is rotated and the strength of the associated magnetic field. The alternating current generated from this process is converted to direct current (DC) by a segmented commutator that establishes the negative and positive polarity. AC generators operate very similarly to DC generators with the main difference being that the generated current is delivered to the outside circuit using slip rings, which produces the alternating wave form that defines AC systems.
Transformers Basics
Transformers also rely on electromagnetic induction but differ from generators as they do not produce electricity but simply step up or down voltage and current levels respectively. All transformers contain a primary and secondary winding which is comprised of many turns of wire surrounding a steel core. The primary and secondary windings are in close proximity but are isolated from each other. The ratio of the primary to secondary windings will determine the amount of reduction or increase of the associated voltage and current levels, known as “buck” or boost” transformers.
Transformer losses are always present due to inherent inefficiencies within the system. Not all the energy that is delivered to the primary coil is effectively transferred to the secondary or load circuit. Most of this loss is materialized as heat, and is a sign of the inefficiencies inherent to the transformers’ operation. These inefficiencies can be described as resistive, eddy current, and hysteresis type losses. Resistive losses are directly affected by whatever material the transformer is constructed from. Eddy currents that form perpendicular to the natural flow of current also contribute to this inefficiency as they effectively impede current flow. Hysteresis is the final transformer type loss that can be described as magnetic friction. At the associated AC magnetic field fluctuates, this causes the affected atoms to realign constantly thereby causing even further losses in the system.
Looking Deeper
The prevalence of AC electrical distribution systems is largely due to the “War of Currents” waged between Nikola Tesla’s alternating current (AC) system and Thomas Edison’s direct current (DC) system. Tesla’s AC systems were simply better as AC can easily be stepped up and down for transmission over longer distances.
Keep in mind
Generators and transformers are essential components of modern electrical generation and distribution systems, and they will likely be a constant presence in many if not all, electrical systems encountered throughout your career.
Machine that uses electromagnetic induction to convert mechanical energy into electrical energy.
An assembly consisting of many turns of wire wound together with the purpose of creating an electric magnet strong enough to be used to open and close sets of contacts. Referred to as the “heart” of a contactor or motor starter.
An electrical device common to most AC electrical systems that steps up or down voltage and current through a primary and secondary coil using electromagnetic induction.