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36 Cards in this Set
- Front
- Back
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What is meant by "transformer action?"
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The transfer of energy from one circuit to another circuit by electromagnetic induction.
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What are, the three basic parts of a transformer?
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Primary winding; secondary winding; core.
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What are three materials commonly used as the core of a transformer?
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Air; soft iron; steel.
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What are the two main types of cores used in transformers?
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Hollow-core type; shell-core type.
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Which transformer windings are connected to an ac source voltage and to a load, respectively?
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Primary to source; secondary to load.
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A transformer designed for high-voltage applications differs in construction in what way from a
transformer designed for low-voltage applications? |
Additional insulation is provided between the layers of windings in the high-voltage transformer.
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What is meant by a "no-load condition" in a transformer circuit?
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A voltage is applied to the primary, but no load is connected to the secondary.
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What is meant by "exciting current" in a transformer?
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Exciting current is the current that flows in the primary of a transformer with the secondary
open (no load attached). |
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What is meant by "exciting current" in a transformer?
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Self-induced or counter emf.
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What causes a voltage to be developed across the secondary winding of a transformer?
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The magnetic lines generated by the current in the primary cut the secondary windings and
induce a voltage into them. |
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What is the phase relationship between the voltage induced in the secondary of an unlike-wound
transformer and the counter emf of the primary winding? |
In phase. Remember, the cemf of the primary is 180 degrees out of phase with the applied
voltage. The induced voltage of the secondary of an unlike-wound transformer is also 180 degrees out of phase with the primary voltage. |
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What is "leakage flux?"
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Lines of flux generated by one winding which do not link the other winding.
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Name the three power losses in a transformer.
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Copper loss, eddy-current loss, and hysteresis loss.
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List five different types of transformers according to their applications.
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a. Power transformer
b. Autotransformer c. Impedance-matching transformer d. Audio-frequency transformer e. Radio-frequency transformer |
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The leads to the primary and to the high-voltage secondary windings of a power transformer
usually are of what color? |
Primary leads-black; secondary leads-red.
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What is the cause of most accidents?
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Carelessness.
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Before working on electrical equipment containing capacitors, what should you do to the
capacitors? |
Discharge them by shorting them to ground.
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When working on electrical equipment, why should you use only one hand?
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To minimize the possibility of providing a path for current through your body.
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The amplitude of the voltage induced in the secondary is dependent upon the efficiency of the transformer and the turns ratio. The efficiency of a transformer is
related to the power losses in the windings and core of the transformer. Efficiency (in percent) equals Pout/Pin × 100. A perfect transformer would have an efficiency of 1.0 or 100%. |
TRANSFORMER EFFICIENCY
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A transformer with two or more windings wound on a laminated iron core. The transformer is used to supply stepped up and stepped down values of voltage to the various circuits in electrical equipment.
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POWER TRANSFORMER
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A transformer with a single winding in which the entire winding can be used as the primary and part of the winding as the secondary, or part of the winding can be used as the primary and the entire winding can be used as the secondary.
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AUTOTRANSFORMER
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A transformer used in audio-frequency circuits to
transfer af signals from one circuit to another. |
AUDIO-FREQUENCY TRANSFORMER
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A transformer used in a radio-frequency circuit to
transfer rf signals from one circuit to another |
RADIO-FREQUENCY TRANSFORMER
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A transformer used to match the impedance of
the source and the impedance of the load. The mathematical relationship of the turns and impedance of the transformer is expressed by the equation: |
IMPEDANCE-MATCHING TRANSFORMER
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The current which appears to flow through a capacitor?
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DISPLACEMENT CURRENT
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Induced circulating currents in a conducting material that are caused by a varying magnetic field.
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EDDY CURRENT
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Losses caused by random current flowing in the core of a transformer.Power is lost in the form of heat.
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EDDY CURRENT LOSS
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The generation of a magnetic field around a current carrying conductor
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ELECTROMAGNETISM
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The field of influence between two charged bodies
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ELECTROSTATIC FIELD
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The basic unit of capacitance. A capacitor has a capacitance of 1 farad when a voltage change
of 1 volt per second across it produces a current of 1 ampere. |
FARAD
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The basic unit of frequency equal to one cycle per second.
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HERTZ (Hz)
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Any material that affords a path for magnetic flux lines in a coil.
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CORE
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An inductive device created by looping turns of wire around a core.
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COIL
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An insulator; a term applied to the insulating material between the plates of a capacitor.
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DIELECTRIC
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The property of a circuit which tends to oppose a change in the existing current flow. The symbol for inductance is L.
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INDUCTANCE
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The current induced in a circuit due to its motion in a magnetic field or to a change in its magnetic flux in such a direction as to exert a mechanical force opposing the motion or to oppose the change in flux.
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LENZ'S LAW
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