A Flashcards

1
Q

Current rating formula

A

VA ÷ V

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2
Q

KVA (apparent power) formula

A

V X A ÷ 1000

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3
Q

Watts in a transformer formula

A

VA X PF

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4
Q

Volts per turn of wire formula

A

V/turn = V ÷N

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5
Q

Actual primary voltage % tap formula

A

Actual primary voltage - rated primary voltage ÷ rated primary voltage

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6
Q

KVA (apparent power) formula

A

KVA = V X A ÷ 1000

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7
Q

Watts formula

A

VA X pf

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8
Q

Taps - actual prime voltage formula

A

Actual prime voltage - rate prime voltage ÷ rated prime voltage

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9
Q

Number of turns formula

A

V ÷ V / per turn

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10
Q

Each winding lead that is marked with an even number

A

Should have the same polarity

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11
Q

The relative direction of the transformer prime voltage compared to the direction of its induced secondary voltage

A

Transformer polarity

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12
Q

If a transformer is constructed so terminal X1 is diaganal from terminal H1

A

Additive polarity transformer

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13
Q

Transformer constructed so X1 is directly opposite H1

A

Subtractive polarity transformer

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14
Q

Ways taps can be changed

A
  • manually changing the leads
  • moving connecting bars
  • installing a mechanical device
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15
Q

5% Full capacity below normal (FCBN)

A

Used when primary supply voltage is 5% lower than rated voltage

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16
Q

5% Full capacity above normal (FCAN)

A

Supply voltage is 5% higher than rated voltage

17
Q

Taps
2.5% reduced capacity below normal RCBN

A

Supply voltage is 2.5% lower than rated voltage

18
Q

Additive or subtractive.
Same polarity =

A

Subtractive

19
Q

Different polarities

Are they additive or subtractive?

A

Additive

20
Q

Explain secondary winding taps

A

Transformers have taps arranged in the primary (high voltage) winding so that the proper secondary voltage is obtained

21
Q

The process where an EMF is produced in a conductor from the interaction of the conductor and magnetic field is called

A

Induction

22
Q

The property of a coil that apposes a change in current is called

A

Inductance

23
Q

When a change of current in one curcuit causes a voltage to be induced into another circuit it is called?

A

Mutual induction. Also called transformer action

24
Q

A basic mutual induction transformer has at least how many coils

A

2

25
Q

The opposition offered to the establishment of magnetic flux in a circuit is called

A

Reluctance.
Air has high reluctance
Iron has low

26
Q

Eddie currents are produced by

A

Heat

27
Q

Two types of core losses are

A

Eddie current and hysteresis

28
Q

What do transformer name plates list

A

Primary voltage
Secondary voltage
KVA rating

29
Q

Name a transformers 3 functions

A

Step up voltage
Step down voltage
Isolate one curcuit from another

30
Q

What isolates the conductors on the output side from the ground

A

Isolation transformer

31
Q

What test is performed to get impedence

A

Short circuit test

32
Q

Opposition to a change of current in a coil is?

A

Inductance

33
Q

A change in current in one curcuit causes a voltage to be induced in another is called?

A

Mutual induction

34
Q

A change in current in a circuit induces a voltage into itself

A

Self induction

35
Q

Name 3 construction types of transformers

A

Core type
Shell type
H type

They have 95% - 98% efficiency

36
Q

Copper losses are measured with what test?

A

Short circuit test