# Transformers Flashcards

## Transformers stuff

Induction is described as the property of a circuit that _____

Opposes change in current

Mutual Induction occurs when a change of _____ in one circuit causes _____ to be induced into another circuit

Current, voltage

Mutual induction is also called

Transformer action

The coil of a transformer which is connected to a source of potential difference is the _____ (Primary or Secondary)

Primary

Once primary current in a DC connected transformer reaches a steady value, what happens in the secondary coil?

No voltage is induced.

A self or mutually induced voltage only occurs when the current is _____.

Changing (as with AC)

What does reluctance do? What does it have to do with transformers?

Opposes magnetic flux on a magnetic circuit.

The soft iron core is low-relunctance.

Is the efficiency of a transformer high or low?

High. 95-98%

Which type of core has the most leakage flux? And the least?

Core type - most

H TYPE - least

An H type center is commonly found on what type of transformers?

High voltage distribution

Hysteresis losses are _____ to the frequency of the source voltage

Proportional

Power losses due to eddy currents and hysteresis losses are also called _____

Core losses

How do you determine %Z of a transformer?

A short circuit test

What is a common use for a step up transformer?

To transfer power over long distances, such as power station switchyard for transmission.

What happens to a transformer beyond 110% of rated voltage?

Primary current increase and transformer burns out.

If the secondary voltage on a transformer doubles, what does the current do?

Reduces to half

If the current on a secondary winding is halved, what happens to the voltage?

Doubles

Transformer polarity is the relative direction of _____ voltage to the direction of _____

Primary voltage, Secondary voltage

With power or distribution transformer, polarity is important when _____

Paralleled

A tap labelled -5% would go on the primary if the supply voltage is _____

5% lower than rated

A transformer whose capacity is reduced in proportion to the reduction of primary voltage has a _____

Reduced capacity tap

A full capacity tap transformer has higher overall capacity so that ____

Rated kVA is available at any tap setting

FCBN taps would be used when primary supply voltage is _____

5% lower than rated

How does an automatic tap changer work?

Feedback control circuit that changes taps when secondary V is above or below a preset value.

What is % Voltage Regulation?

Change of the secondary output Voltage from no-load to full-load.