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Transformers > Transformers > Flashcards

Transformers Flashcards

1
Q

State the clause number that outlines the requirements and restrictions for transformers

A

4.14 , 4.2.2.3

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2
Q

State the two methods used to insulate transformers one for high and low voltage

A

Oxide or powder

Oil or Myer film

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3
Q

Name two pieces of information that can be found on a nameplate

A

Kva rating and voltage rating

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4
Q

Name the two basic core types for transformers

A

Shell and Core

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5
Q

What material is commonly used to laminate the core

A

Staloy

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6
Q

According to appendix

A

61558 ASNZ

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7
Q

Name 3 applications for transformers

A

Distribute power

Stepping down voltage

Stepping up voltage

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8
Q

State the functions of the following transformers

Transmission

Distribution

A

Transmission - they step down the high voltage for use

Distribution - send high voltages for supply power

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9
Q

State the 2 different transformer windings

A

Primary

Secondary

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10
Q

What is the term used for transformers rating

A

Kilovolt amps

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11
Q

State two advantages and disadvantages for auto transfromers

A

Advantage - cost effective and size effective

Disadvantage - dangerous if open circuit, can’t be used to supply electrical equipment

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12
Q

What would be the consequence of making closing a connection where a significant voltage was indicated

A

Transformer will get damaged

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13
Q

State the condition required before connecting or disconnecting

A

De energised and no open circuit

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14
Q

State one application for each of thre following

A

Auto transformer - starting motors

Potential transformer - operating high voltage machines

Current transformer - operating high current machines

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15
Q

Which transformer can have a primary winding which is not part of the current transformer itself

A

Toroidal

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16
Q

What ratio defines the rating of a current transformer

A

Rated by the ratio of primary current to secondary current

17
Q

State the two main factors that determine the value of induced voltage in the secondary winding of a double wound transformer

A

Applied voltage and number of turns

18
Q

State the main principles of mutual inductions

A

Inducing an emf on a winding which creates magnetic flux in the secondary winding

19
Q

If a double wound transformer has a turns ratio of 5 - 1

And applied voltage of 200v

And an applied current of 10 amps state the secondary voltage and current

A

Voltage - 200 ÷ 5 = 40v

Current - 10 × 5 = 50A

20
Q

What components is placed between the windings of an isolating transformer as a safety precaution

A

Insulated Bar

21
Q

State how to operate transformer at maximum efficiency

A

On full load

22
Q

State a cooling method for each of the following transformers

Small low voltage transformer

Large distribution transformer

A

Small low voltage transformer - air

Large distribution transformer - Oil

23
Q

State the losses that occur in transformers

A

Iron losses, copper losses

24
Q

State why type of transformer loss that will occur during

Open circui

Short circuit

A

Open circuit - iron loss

Short circuit - copper loss

25
Q

What effect does cooling have on Kva rating

A

Increase

26
Q

State two factors responsible for voltage variation

A

Copper loss, iron loss

27
Q

Calculate the voltage regulation of a transformer with no load secondary voltage of 40 volts and a full load secondary voltage of 38

A

(40 -38)÷38 x 100 = 5.26%

28
Q

Define transformer impedence percentage

A

The percentage of primary voltage needed to cause the full load current to flow in secondary when Short circuited

29
Q

Calculate transformer impedence %

A

10 ÷ 400 = 0.025 x 100 = 2.5%

30
Q

Which output value of transformers can be increased by connecting transformers in parallel

A

Secondary current can be increased

31
Q

What should a reading be on a voltmeter across terminal’s of a closing connection prior to connection

A

OL

32
Q

Which two nameplate values should be checked before paralleling

A

Kva rating, resistance frequency

33
Q

What value of voltage would be measured across the closing terminal’s of two transformers in parallel if polarity was reversed and rated output was 24v

A

48v

Transformers (1 decks)

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