Transformers and AC Circuits

Lesson 1 - Principles of Alternating Current

Topics:

AC and DC electricity; AC waveform; Peak-to-peak, average, effective values; Energy storage; Faraday's Law; Basic circuit concepts

Learning Objectives:

– State of definition of a waveform.
– Demonstrate how to calculate the frequency of an alternator's output.
– Explain how to calculate an effective value.
– Name the kinds of values that must be used when applying the dc rules and laws to ac circuits.

Lesson 2 - Mathematics in AC Circuits

Topics:

Potential difference; Angles and degrees; Vectors applied to AC circuits; Graphic and math solutions; Calculating instantaneous values

Learning Objectives:

– Describe a triangle.
– State the definition of a vector.
– Identify the vector representing resistance in a vector diagram.
– Demonstrate how to calculate the total impedance in an ac circuit.

Lesson 3 - Inductance and Inductive Reactance

Topics:

Factors affecting inductance; CEMF; Inductive reactance and time delay; Phase angles; Impedance; Mutual induction; Inductors

Learning Objectives:

– Name the property of a coil that makes it resist changes in current.
– List the factors that determine inductance in a coil.
– State the definition of counter electromotive force.
– Demonstrate how to convert a frequency in Hz to a frequency in radians per second.

Lesson 4 - Capacitance and Capacitive Reactance

Topics:

How a capacitor works; Factors controlling capacitance; Kinds of capacitors; Time constants; Capacitive reactance; Phase angle

Learning Objectives:

– Name the parts of a capacitor.
– List the factors that affect the amount of charge stored in a capacitor at a given potential difference.– Demonstrate how to install a multisection electrolytic capacitor.– State the definition of capacitive reactance.

Lesson 5 - Impedance

Topics:

Impedance in series circuits; Phase angles; Resonance in series circuits; Impedance in parallel circuits

Learning Objectives:

– State the definition of impedance
– Explain how to calculate the impedance in a series ac circuit.
– Demonstrate how to find the value of a phase angle for a circuit.
– Explain how to calculate the impedance in a parallel circuit.

Lesson 6 - Power and Energy in AC Circuits

Topics:

Work and energy; Power in resistive, inductive, and capacitive circuits; Power factor correction; Power capacitors; Capacitor installation

Learning Objectives:

– State the definition of power.
– Demonstrate how to calculate power in an inductive circuit.
– State the reason why capacitors are added to circuits to increase the power factor.
– Explain how to install capacitors correctly.

Lesson 7 - Three-Phase Circuits

Topics:

Three-phase alternators; Y- and delta-connected alternators; Power in three-phase circuits; Load connections; Measuring power

Learning Objectives:

– List the main advantages of the three-phase ac system.
– State the definition of phase sequence.
– Demonstrate how to calculate the RMS power in a single-phase circuit.
– Explain how to measure the total power consumed by the load in a three-phase circuit.

Lesson 8 - Principles of Transformers

Topics:

Magnetic field; No-load operation; Transformer construction, losses, and efficiency; Autotransformers; Instrument transformers

Learning Objectives:

– Explain the difference between the primary winding and the secondary winding in a transformer.
– Explain how the windings are positioned in a core-type transformer.
– List the kinds of losses that occur in transformers.
– State the definition of a current transformer.
– List the functions of an instrument transformer.

Lesson 9 - Transformer Applications

Topics:

Transformer designation, insulation, cooling, and polarity; Single- and three-phase transformer connections; Installing transformers

Learning Objectives:

– Name general kinds of transformers.
– List the temperature limits for each class of transformer insulation.
– Explain how oil-immersed transformers are cooled.
– Name the common methods of connecting three single-phase transformers for three-phase operation.
– Explain how to select the correct location for a transformer.

Lesson 10 - Maintaining Transformers

Topics:

Preventive maintenance; Inspection; Transformer liquids; Transformer failure; Testing; Disassembly and inspection

Learning Objectives:

– Explain what to look for during an inspection of sealed transformers.
– List problems that are indicated by an increase in transformer operating temperature.
– Demonstrate how to perform a breakdown test.
– Explain how to locate the exact point of a leak in a welded joint below the liquid level.
– List the steps in inspecting a transformer when a winding fails.