Apparatus Flashcards
A static electrical machine which transforms electrical power from
one circuit to another circuit, without changing the frequency.
ELECTRICAL TRANSFORMER
WORKING PRINCIPLE OF TRANSFORMER
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)
BASIC CONSTRUCTION OF TRANSFORMER
-conservator tank
-breather
-low voltage bushes
-cooling tubes
-drain off
-tank cover
-main tank
Depending on the voltage level, the transformer has three categories
a. Step Down
b. Step Up and
c. Isolation Transformer.
NOTE: For the Isolation transformer, the voltage level is the same for
both sides
STEP – DOWN TRANSFORMER
A step-down transformer converts the primary voltage level to a
lower voltage across the secondary output.
increase the low primary voltage to a high
secondary voltage.
STEP – UP TRANSFORMER
does not convert any voltage levels. This is because the primary and the secondary winding ratio is always
equal to the 1.
ISOLATION TRANSFORMER
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
Iron Core
TYPES BASED ON CORE MATERIAL
Iron Core
* Ferrite Core
* Toroidal Core
* Air Core
FERRITE CORE TRANSFORMER
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
TOROIDAL CORE TRANSFORMER
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
does not use any physical magnetic core as the
core material.
AIR CORE TRANSFORMER
Power Domain
- Power Transformer
- Measurement Transformer
- Distribution Transformer
- Pulse Transformer
- Audio Output Transformer
Electronics Domain
deals with the power generation, measurement
distribution
Power Domain
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
Power Transformer
Used to isolate the main power and convert the
current and voltage in a smaller ratio to its
secondary output.
Measurement Transformer
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
Distribution Transformer
It is used in various digital circuits where pulse generation is needed
in an isolated environment.
Pulse Transformer
It is specially used in Audio related application where impedance
matching is required
Audio Output Transformer
s related to the conductivity of the material and the induced currents that flow within it due to the changing magnetic field
Eddy current loss
is related to the magnetic properties of the material and the energy required to repeatedly magnetize and demagnetize it.
hysteresis loss
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
OPEN CIRCUIT TEST
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)
SHORT CIRCUIT TEST
TRANSFORMER TESTS
- Test done at factory
a) Type tests
b)Routine tests
c) Special tests - Test done at site
a) Pre-commissioning tests
b)Periodic / condition
monitoring tests
c) Emergency tests
is mainly for confirming the operational
performance of the individual unit in a production lot
Routine tests of transformer
Special Tests of Transformer
as per customer requirement to
obtain information useful to the user during operation or
maintenance of the transformer
8 Common Testing Procedures for Electrical Transformers
- Turn Ratio Testing
- Insulation Resistance Testing
- Power Factor Testing
- Resistance Testing
- Polarity Testing
- Phase Relation Testing
- Oil Tests
- Visual Inspection
TURN RATIO TESTING
the ratio
between the windings of the primary and secondary coils follow the
proper specifications
known as the Megger test, insulation resistance testing
measures the quality of insulation within the transformer.
INSULATION RESISTANCE TESTING
power loss of the transformer’s
insulation system by measuring the power angle between an applied
AC voltage and the resultant current
POWER FACTOR TESTING
is conducted several hours after a transformer has
stopped conducting current when it reaches the same temperature
as its surroundings
RESISTANCE TESTING
POLARITY TESTING
direction of current flow in a transformer
PHASE RELATION TESTING
This test will detect if two or more transformers have been connected
in a correct phase relationship
provides insulation and cooling properties
OIL TESTS
A standard procedure must be established to perform the visual test,
identifying the elements to be viewed and criteria for pass/fail
judgments
VISUAL INSPECTION
voltage regulation of the transformer IS THE
percentage change in the output voltage from no-load to full-load
dynamic, load-dependent number
variation in secondary terminal voltage
if these losses are high and the secondary voltage becomes too low
Most of the transformers have full load efficiency between
95% to 98.5%
The maximum efficiency occurs when the
core loss and the copper loss
are equal.
autotransformer are linked together
both electrically and magnetically
An autotransformer required ________ than an ordinary transformer
of a similar rating.
less copper
An autotransformer required ________ than an ordinary transformer
of a similar rating.
less copper
It has __________ and operates at a __________ than a 2-winding transformer of the same rating.
better voltage regulation, higher efficiency
An autotransformer requires a __________ than a 2- winding transformer of the same rating.
smaller exciting current
It has a __________ than an ordinary transformer of the same rating
smaller size
The main disadvantage of an autotransformer is that it
does not have the primary to secondary winding isolation
If the secondary side winding becomes open-circuited
load current stops flowing through the primary winding
the all-day efficiency of a transformer is calculated using the _____ done in a whole day.
work
if the autotransformer becomes _____-circuited, full primary voltage is being applied to the load
open
____ are sometimes used to isolate equipment from earth
double wound transformer
