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Second Sem > Apparatus > Flashcards

Apparatus Flashcards

1
Q

A static electrical machine which transforms electrical power from
one circuit to another circuit, without changing the frequency.

A

ELECTRICAL TRANSFORMER

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2
Q

WORKING PRINCIPLE OF TRANSFORMER

A

The basic principle behind working of a transformer is the
phenomenon of mutual induction between two windings linked by
common magnetic flux.

consists of two inductive coils; primary
winding and secondary winding. The coils are electrically separated
but magnetically linked to each other.

Flux produced is alternating (the direction of it is continuously
changing), EMF gets induced in the secondary winding according to
Faraday’s law of electromagnetic induction.

If the secondary winding is closed circuit, then mutually induced
current flows through it, and hence the electrical energy is
transferred from one circuit (primary) to another circuit (secondary)

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3
Q

BASIC CONSTRUCTION OF TRANSFORMER

A

-conservator tank
-breather
-low voltage bushes
-cooling tubes
-drain off
-tank cover
-main tank

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4
Q

Depending on the voltage level, the transformer has three categories

A

a. Step Down
b. Step Up and
c. Isolation Transformer.
NOTE: For the Isolation transformer, the voltage level is the same for
both sides

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5
Q

STEP – DOWN TRANSFORMER

A

A step-down transformer converts the primary voltage level to a
lower voltage across the secondary output.

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6
Q

increase the low primary voltage to a high
secondary voltage.

A

STEP – UP TRANSFORMER

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6
Q

does not convert any voltage levels. This is because the primary and the secondary winding ratio is always
equal to the 1.

A

ISOLATION TRANSFORMER

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7
Q

uses multiple soft iron plates as the core material.
Due to the excellent magnetic properties of iron, the flux linkage of the
iron core transformer is very high. Thus, the efficiency of the iron core
transformer is also high

A

Iron Core

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7
Q

TYPES BASED ON CORE MATERIAL

A

Iron Core
* Ferrite Core
* Toroidal Core
* Air Core

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8
Q

FERRITE CORE TRANSFORMER

A

A ferrite core transformer uses a ferrite core due to high magnetic
permeability.
* This type of transformer offers very low losses in the high-frequency
application

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9
Q

TOROIDAL CORE TRANSFORMER

A

Due to the ring shape, the leakage inductance is very low and offers
very high inductance and Q factors. The windings are relatively short,
and weight is much less than traditional, same rating transformers

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10
Q

does not use any physical magnetic core as the
core material.

A

AIR CORE TRANSFORMER

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11
Q

Power Domain

A
  • Power Transformer
  • Measurement Transformer
  • Distribution Transformer
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12
Q
  • Pulse Transformer
  • Audio Output Transformer
A

Electronics Domain

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13
Q

deals with the power generation, measurement
distribution

A

Power Domain

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14
Q

The rating can be more than 30KVA to the 500-700KVA or in some cases
that can be equal to or more than 7000KVA for small rated power
transformer

A

Power Transformer

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15
Q

Used to isolate the main power and convert the
current and voltage in a smaller ratio to its
secondary output.

A

Measurement Transformer

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16
Q

are step down transformer, which converts
High grid voltage to the end customer required voltage, 110V or 230V.
It can also be single phase or three phases

A

Distribution Transformer

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17
Q

It is used in various digital circuits where pulse generation is needed
in an isolated environment.

A

Pulse Transformer

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18
Q

It is specially used in Audio related application where impedance
matching is required

A

Audio Output Transformer

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19
Q

s related to the conductivity of the material and the induced currents that flow within it due to the changing magnetic field

A

Eddy current loss

20
Q

is related to the magnetic properties of the material and the energy required to repeatedly magnetize and demagnetize it.

A

hysteresis loss

21
Q

A voltmeter, wattmeter, and an ammeter are
connected in LV side of the transformer as shown. The voltage at
rated frequency is applied to that LV side with the help of a VARIAC of
variable ratio auto transformer

A

OPEN CIRCUIT TEST

22
Q

voltmeter, wattmeter, and an ammeter are connected in HV side
of the transformer as shown. A low voltage of around 5-10% is
applied to that HV side with the help of a VARIAC (i.e., a variable
ratio auto transformer)

A

SHORT CIRCUIT TEST

23
Q

TRANSFORMER TESTS

A
  1. Test done at factory
    a) Type tests
    b)Routine tests
    c) Special tests
  2. Test done at site
    a) Pre-commissioning tests
    b)Periodic / condition
    monitoring tests
    c) Emergency tests
24
Q

is mainly for confirming the operational
performance of the individual unit in a production lot

A

Routine tests of transformer

25
Q

Special Tests of Transformer

A

as per customer requirement to
obtain information useful to the user during operation or
maintenance of the transformer

26
Q

8 Common Testing Procedures for Electrical Transformers

A
  1. Turn Ratio Testing
  2. Insulation Resistance Testing
  3. Power Factor Testing
  4. Resistance Testing
  5. Polarity Testing
  6. Phase Relation Testing
  7. Oil Tests
  8. Visual Inspection
27
Q

TURN RATIO TESTING

A

the ratio
between the windings of the primary and secondary coils follow the
proper specifications

28
Q

known as the Megger test, insulation resistance testing
measures the quality of insulation within the transformer.

A

INSULATION RESISTANCE TESTING

29
Q

power loss of the transformer’s
insulation system by measuring the power angle between an applied
AC voltage and the resultant current

A

POWER FACTOR TESTING

30
Q

is conducted several hours after a transformer has
stopped conducting current when it reaches the same temperature
as its surroundings

A

RESISTANCE TESTING

31
Q

POLARITY TESTING

A

direction of current flow in a transformer

32
Q

PHASE RELATION TESTING

A

This test will detect if two or more transformers have been connected
in a correct phase relationship

33
Q

provides insulation and cooling properties

A

OIL TESTS

34
Q

A standard procedure must be established to perform the visual test,
identifying the elements to be viewed and criteria for pass/fail
judgments

A

VISUAL INSPECTION

35
Q

voltage regulation of the transformer IS THE

A

percentage change in the output voltage from no-load to full-load
dynamic, load-dependent number

36
Q

variation in secondary terminal voltage

A

if these losses are high and the secondary voltage becomes too low

37
Q

Most of the transformers have full load efficiency between

A

95% to 98.5%

38
Q

The maximum efficiency occurs when the

A

core loss and the copper loss
are equal.

39
Q

autotransformer are linked together

A

both electrically and magnetically

40
Q

An autotransformer required ________ than an ordinary transformer
of a similar rating.

A

less copper

41
Q

An autotransformer required ________ than an ordinary transformer
of a similar rating.

A

less copper

42
Q

It has __________ and operates at a __________ than a 2-winding transformer of the same rating.

A

better voltage regulation, higher efficiency

43
Q

An autotransformer requires a __________ than a 2- winding transformer of the same rating.

A

smaller exciting current

44
Q

It has a __________ than an ordinary transformer of the same rating

A

smaller size

45
Q

The main disadvantage of an autotransformer is that it

A

does not have the primary to secondary winding isolation

46
Q

If the secondary side winding becomes open-circuited

A

load current stops flowing through the primary winding

47
Q

the all-day efficiency of a transformer is calculated using the _____ done in a whole day.

A

work

48
Q

if the autotransformer becomes _____-circuited, full primary voltage is being applied to the load

A

open

49
Q

____ are sometimes used to isolate equipment from earth

A

double wound transformer

Second Sem (10 decks)

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