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Transformers > Transformers > Flashcards

Transformers Flashcards

1
Q

What are two types of core losses associated with a transformer?

A

Hysteresis

Eddy currents

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2
Q

Describe induction

A

The process of by which a voltage is produced by the interaction of a conductor and a magnetic field

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3
Q

What is inductance

A

The property of a circuit that opposes change in current

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4
Q

What is mutual induction

A

When a change of current in one circuit causes a voltage to be induced into another circuit

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5
Q

True or false

The primary coil is always connected to the source

A

True

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6
Q

True or false

The primary side of a transformer is the high side (H1,H2)

A

False

The primary side is the supply side. It can be high or low

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7
Q

What are the three basic types of transformers (construction)

A

Core type
H type
She’ll type

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8
Q

True or false

The core type xmer has the most leakage flux

A

True

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9
Q

True or false the shell type transformer construction has the least leakage flux

A

True

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10
Q

True or false

Transformers are rated in true power

A

False
They are rated in apparent power.
kVa input = kVa output

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11
Q

Why is a short circuit test performed on a transformer immediately after it is manufactured?

A

To determine the %IZ

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12
Q

What is impedance voltage

A

The primary voltage required to circulate the rated full load secondary current when the secondary winding is short circuited at the terminals.

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13
Q

True or false

The secondary coil of a transformer is not always connected to the load

A

False

The secondary IS ALWAYS connected to the load.

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14
Q

If the turns of the secondary coil are decreased what will happen to the induced voltage

A

It will decrease

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15
Q

What are three types of transformer losses

A

Eddy currents
Hysteresis
I2R Losses

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16
Q

What type of test is performed to find out the core losses of an xmer

A

An open circuit test

17
Q

Why are xmer ratios so important ?

A

They can be used to determine voltage, current and apparent power in the primary and secondary turns.

18
Q

What is the purpose of transformer taps in the primary side door

A

To obtain proper secondary voltage.

19
Q

Why are taps used on the secondary of a transformer

A

To supply more than one voltage

20
Q

What is another name for mutual induction

A

Transformer action

21
Q

The small current that flows in the primary winding of a transformer while connected to and ac supply is known as what?

A

Exciting current

22
Q 
The overall magnetic flux from no load to full load will:
A   stay nearly the same
B   Vary proportional to load
C   Vary inversely proportional to load
D.   Is always zero
A

Stay nearly the same. Within in a few %

23
Q

What type of test is used to determine core losses

A

Open circuit test

24
Q

What are the three main parts of a transformer

A

Core
Primary windings
Secondary windings

25
Q

What does the va or the kVa rating of a transformer represent

A

Full load output

26
Q

What is the formula to calculate the power factor

A

Pf = P/S

True power over apparent power
W/VA

27
Q

A transformer can operate up to what percent of its its rated voltage

A

110%

28
Q

What is the formula for calculating the number of turns in a xmer winding

A

Number of turns = primary turns / volts per turns

29
Q

What is the formula to find voltage regulation

A

Vreg = v no load - full load / V full load

30
Q

What is the main component that limits exciting current

A

Primary induced voltage aka counter emf (XL)

31
Q

True or false

Under load conditions the secondary current flux opposes primary current flux

A

True

32
Q

When load is added toe an xmer, what will happen to the overall magnetic flux?

A

It will increase

33
Q

What is the formula for efficiency of an xmer

A 
%eff = Pin / Pout
Pin = Pout + losses
34
Q

When paralleling transformers what must be identical on the transformers

A

Secondary volages
Same %IZ within 5%
Same tap settings

35
Q

The current in the series winding of an auto transformer is also known as

A

The primary line current

36
Q

The series coil current in a step down auto transformer is the same as the primary line current
True or false

A

True

37
Q

Compared to a mutual induction transformer, the auto transformer will have a higher short circuit current
Tue or false

A

True

38
Q

What is the transformed apparent power rating of for an auto transformer a product of

A

The product of of the rated common winding voltage times the rated common winding current of an autotransformer

39
Q

Describe conducted power of an autotransformer

A

The product of the rated common winding g voltage times the rated series winding current of an autotransformer

Transformers (1 decks)

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