PARTS OF TRANSFORMERS & FUNCTIONS

Transformer parts are:-
1)BUCHHOLZ RELAY: it is avery sensitive gas and oil
operated instrument which safely detect the formation of
gas or sudden prssure inside the oil transformer.
2)CONSERVATOR: it is used to provide adequate space for the
expansion of oil when transformer is loaded or when ambient
temprature changes.
3)SILICA GEL BREATHER: it sucks the moisture from the air
which is taken by transformer so that dry air is taken by
transformer.
4)DOUBLE DIAPHRAGM EXPLOSION VENT: it is used to discharge
excess pressure in the atmosphere when excess pressure is
developed inside the transformer during loading.
5)OIL LEVEL INDICATOR: it is used to show the oil level in
the transformer.
6) Winding temperature indicator: used to show the
temperature of transformer winding.
7) RADIATORS: these are used for cooling of the transformer
oil.

The supply voltage is connected to the primary
winding, the load is connected to the secondary winding and
in the transformer core only the magnetic flux path will be
established..
In power transformers(used for transmit the heavy
voltages to the grid) on load tap changers used.. but in
distribution transformers off circuit tap changers are
used.

USE OF NEUTRAL IN 3P SYSTEM

In most of the 3-ph systems neutral is provided just to take care of the unbalanced current. Unbalanced current are nothing but when any of the phase is slightly overloaded or in case of phase failure, balanced currents will produced and neutral will carry these currents safely to earth without disturbing the other phases and other connected equipment to the distribution board neutral is generally provided and all the neutrals of the db's (Distribution boards) are interconnected and at the transformer this neutral will solidly grounded.

During any disturbances ,ie: during short circuit condition neutral is used to ground the surge flowing through the lines.

S.F.U

It is Switched Fuse Unit. It has one switch unit and one
fuse unit. When we operate the breaker, the contacts will
get closed through switch and then the supply will pass
through the fuse unit to the output.

Whereas in Fuse Switch Unit there is no separte switch and
fuse unit. There is only fuse unit which act itself as a
switch. When we operate the fuse unit will close the input
and output of the breaker.
SFU has been used to trip the circuit,particularly for high capacity tripping.
. Where as MCB&MCCB are used for low capacity tripping.

GRID

Grid means interconnection of different generating stations
and load centres which are all tuned to constant voltage
and frequency.
A Grid can be a NATIONAL GRID OR A REGIONAL GRID depending
on whether we are connecting to nations or two regions.

3.5 CORE CABLES

In 3.5 core cables, the neutral conductor will be half the size of the phase conductors.If the load is fairly balanced ,the unbalanced current in
the neutral of 3ph 4w system will be very less and hence
the smaller sectional area for the neutral cable to save
money.

DYN11 & DYN5

In DYN 11, HV voltage is lagging from LV by angle of 30 degree and in DYN 5, HV voltage leads LV voltage by 150 degree.we can change vector group from DYN 11 to DYN 5 by change primary winding connection of transformer.

ELR & CBCT

ELR Earth Leakage Relays along with CBCT are used to detect
leakage current in the earhing. If the earthing is not
proper a small amount of current will appear (in the order
of mA). ELR will continuously monitor the leakage current
if it exceeds the set threshold an output electromechanical
relay (which is inside the ELR) will operate. The output
relay contact can be connected to circuit breakers /
contactor to isolate power supply or alarms.

CBCT Core Balance Current Transformers these will come in
different sizes. the core material will be either nickel or
alloy of nickel, copper wire will be wounded on the core
and properly insulated. The 3-phase line along with neutral
are passed in this core and secondary is connected to ELR.
Idealy the leakage current should be zero if any earth
leakage happen the leakage current will appear at CBCT
secondary it will be detected by ELR.