Introduction to Transformers Flashcards
By what principle(s) is voltage induced in a single phase transformer?
Mutual induction.
Self induction.
What is transformer action?
Mutual induction.
When changing current in one circuit causes voltage to be produced in another magnetically linked circuit.
What is the primary coil of a transformer?
The coil which is connected to a source of voltage.
If the turns on a secondary coil are increased, how is secondary voltage affected?
It would increase as well.
Is the reluctance of iron high or low?
Low.
Iron has a high permeability and magnetic fields are easily established.
Which lamination method has the least amount of reluctance?
A long iron sheet that is spiralled around the core.
What are the three basic types of transformer construction? Which has the most leakage flux?
Core, Shell and H type.
Core type has the most leakage flux and is the least efficient.
Where are H type transformers commonly found?
High voltage distribution.
Which losses are roughly static? Which vary with loading?
Hysteresis losses, as they are proportional to frequency.
Since a transformer has a net flux which is nearly constant, eddy current loss should be static as well.
Copper losses, because the load changes the current which will change I2R.
What is typically the efficiency range of transformers?
95-98%.
The VA rating of a transformer is always the __________?
Output capacity.
What properties affect %IZ of a transformer? How is it determined?
- Amount and type of core material.
- Winding wire size.
- # of winding turns.
- Degree of magnetic coupling.
A short circuit test is performed with a very low primary voltage. The voltage is increased until rated secondary current flows. Impedance voltage is a percentage of rated voltage, and that percentage is %IZ.
What are the three main functions of transformers?
- To step up Voltage.
- To step down Voltage.
- To Isolate a circuit from ground.
The H markings on a transformer always refer to the ________winding.
High voltage.
What will happen if a transformer is overvoltaged (>110% of rated V)?
Primary current will increase to dangerous levels and burn out the coil.
Is the transformer turns ratio the same as the current ratio?
No, the turns ratio is the same as the voltage ratio, the current ratio is the inverse of those two.
Which ratio is always 1:1 across the primary and secondary coils?
The volts/turn ratio.
When looking at a transformer from the low voltage side ANSI standards dictate the H1 terminal goes where?
The upper left hand corner.
In most transformers, which winding is wrapped around the other?
The high voltage winding is usually wrapped around the low voltage winding.
How is relative polarity indicated in transformer windings?
It is indicated through subscript.
At any instant and odd numbers will have the same polarity, and any even numbers will have the same polarity.
When H1 is directly opposite X1 the trasformer is said to have _________.
Subtractive polarity.
Why would a primary voltage tap be used?
To maintain rated secondary voltage, It would be used if the supply voltage was higher or lower than rated primary voltage.
When referring to taps what does RCBN mean?
Reduced capacity below normal.
Would a transformer with full capacity taps be larger or smaller than one with reduced capacity taps?
Larger.
This is because extra heat would need to be dissipated.
