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Third 6 Month (Elect.) > PHEP 23 > Flashcards

PHEP 23 Flashcards

1
Q

Transformers permit the transfer of electric energy between two circuits which are…

A

Completely insulated from each other

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2
Q

The winding of a transformer which receives its energy inductively, is called the…

A

Secondary winding

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3
Q

When the number of turns or voltage on the secondary of a transformer is greater than that of the primary, it is known as…

A

A step-up transformer

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4
Q

In transformers, a ______ must always exist between the primary and secondary field to maintain the required primary current to supply the transformer losses and the secondary load.

A

Balanced condition

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5
Q

What is the induced secondary voltage of a transformer having a primary winding of 3000 turns, and a secondary winding of 300 turns, when connected to a 2400V AC source?

A

E1/E2 = T1/T2
2400/E2 = 3000/300
2400 = 10 (E2)
E2 = 240V

PHEP 23 pg.7

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6
Q

A transformer developed 120 V in its secondary when a 2400 V source was connected across its primary. Assuming a primary current of 0.25A, the secondary current is…

A

E1 x I1 = E2 x I2

(0.25 A)(2400V) = (120V) I2
I2 = 5A

PHEP 23 pg.7

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7
Q

The power transformer, transfers electric power from one circuit, at a certain frequency and voltage, to a secondary circuit at…

A

A different voltage, and the same frequency

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8
Q

True or false:

Transformers are classed as static AC systems

A

True

PHEP 23 pg.9

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9
Q

Current transformers are instrument transformers used to…

A

Step down current

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10
Q

The secondary terminals of a potential transformer should never be…

A

Short-circuited to remove the device it operates from service

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11
Q

The secondary of a current transformer should never be…

A

Opened to remove the device and operates from service

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12
Q

Transformers having only one winding are called

A

Auto transformers

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13
Q

In the core type transformer, how are the windings wound?

A

A section of both the primary and secondary windings are wound on each leg of the core

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14
Q

Hysteresis can be explained as…

A

Friction of the molecules due to alternating current

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15
Q

True or false:

In an energized transformer, iron losses are present, even if there is no load on the secondary .

A

True

PHEP 23 pg.13

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16
Q

The rating of a transformer is usually given in…

A

Volt-Amperes (VA), in KVA, or in MVA

17
Q

The conservator system is used in transformers to…

A

Preserve the dielectric strength of the transformer oil

18
Q

Bushings are used on transformers to…

A

Serve as entrances into transformers for the main leads

19
Q

Series Street lighting systems require what type of transformer?

A

Constant current transformer

20
Q

When transformer windings are connected in WYE, the line current will be ______ the phase current.

A

the same as

Third 6 Month (Elect.) (8 decks)

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