Transformers Flashcards
(36 cards)
What is a transformer?
It is a magnetically operated machine that can change values of voltage, current, and impedance without changing frequency.
What are the three classifications of transformers?
Isolation transformer, autotransformer, and current transformer
All values of a transformer are proportional to its ________
Turn ratio
How do you calculate the turns ratio of a transformer?
Divide the number of turns of the primary wire by the number of turns of the secondary wire
What is primary winding?
The winding that is connected to the incoming power supply
What is secondary wiring?
It is the winding that is connected to the driven load.
What are isolation transformers?
Transformers that have secondary wiring that is physically and electrically separated from primary wiring.
Why is isolation desirable in a transformer?
It reduces voltage spikes that originate on the supply side.
What is the excitation current?
The amount of current required to magnetize the core of a transformer. It remains constant from no load to full load.
How is mutual induction formed?
The magnetic field produced by the primary winding cuts the windings of the secondary which then produces a voltage.
What is mutual induction?
The ability of one coil to induce a voltage in another coil.
The amount of voltage induced in the secondary is determined by _________
The ratio of the number of turns of wire in the secondary to those in the primary.
Multiple tapped windings
Isolation transformers that have more than one set of lead wires connected to the primary and secondary.
What is a distribution transformer?
Type of transformer that changes the high voltage of a power company to the standard 240/120 volts that runs most homes and businesses.
If you measured the voltage across the entire secondary of a 240/120-volt line, what would the voltage be? What would it be if you measured each line to the center tap?
240 volts. 120 volts.
What is a control transformer?
A transformer that is used to reduce the line voltage to the value needed to operate control circuits.
The most common type of control circuit contains ________ and __________.
Two primary windings and one secondary winding
Why are laminated cores preferred in transformers?
A thin layer of oxide forms on the surface of each lamination which insulates the core and reduces the formation of eddy currents.
The magnetic coupling between the windings and the efficiency of the transformer is determined by the ________ and _______ of the core
Type and shape
How are the windings arranged in a core-type transformer?
Windings are placed around each end of the core material. Low voltage winding is closest to the core and high voltage winding is over the low voltage winding.
How are the windings arranged in a shell-type transformer?
Primary and secondary windings are wound around a centerpiece of the core (there is a window in the core).
How are the windings arranged in a H-type transformer?
Similar to shell-type core in which windings are wound around a centerpiece; however, the core surrounds the windings on four sides instead of two.
How are the windings arranged in a tape-wound core transformer?
Winding is one long continuous steel tape that is wound into a spiral. Flux leakage is kept to a minimum with this design.
What is inrush current?
The amount of current that flows when power is initially applied to the circuit.
