Answer / rajkumarsripelli

ya....this is rajkumarsripelli Testing engineer trasformer
division...

4ans: The dielectric strengh can be caluculated by oil
insulation breakdown test by using an equipment called as
oil insulation breakdown kit..in this kit will be having
two electrodes seperated by small distance in a small glass
tank.in that small tank we will be filling the oil to
test . by applying the required voltages like 10kv or
20kv ,30kv....(this voltages depends on tha transformer
ratings)between the electrodes we can see the results..

for example suppose we have oil of unknownbreak downvalue
(suppose 50KV)

. To test this oil we have to fill this oil into kit(tank)
and voltage will applied between the electrodes..from 0v to
60kv..so here the voltage will be increased slowly...if the
voltage reaches 49kv inside the tank we will not find any
flash over between the electrodes but when it reaches 50kv
the flash over will be taken between the two
electrodes...so by this test we can conform that given oil
is having breakdown value at 50kv...so this oil will be
used in transformers which are opearated with 33kv
voltages that means oil insulation breakdown value should
be double as compared to its normal operating volages...

thank u....

Answer / shuvankar sikdar

Our body is a zero potential.If we touch a live wire using
our body grounded,we get shock because current flows from
higher potential to lower potential(here ground)through our
body.
In electric train we dont gets shock because in train our
bodies are not grounded also the train itself grounded
through the wheels.In case of any fault,the fault current
flows through the train body and the wheels to the ground.

Answer / rajkumarsripelli

ya....this is rajkumarsripelli Testing engineer trasformer
division...

Kaarthikrt&c09894209497 said that due to corona loss is
dead wrong..for 2nd answer

2:ans: the noice will be getting from loaded transfomer is
due to the mechanical vibration of the core...in detail...
for making of transfomer as we know that we will be using
silicon steel core material...so this core is assembled in
proper way..as per the standareds...when we apply the
voltages through the windings to this core the core will be
magnetised...due to this high voltages the core will
vibrates when its magnetised....and the vasavi said above
may be correct...........



thanks..

Answer / sripellirajukumar

hi mr Kaarthikrt&c09894209497

ya u didnt conformed that but as an engineering student u
should not do small silly mistakes na...

ur 2nd answer was really wrong...

corona loss will be there only for high voltage transmission
lines but not for transformers.......ok na..if u want to
conformation read power systems textbook by mehta..for
corona loss ok na...ok thank u .....

Answer / amit biswas

abt noise in xmer

noise in tr. ocurres due to the the fact that alternating
elec feild generates a alt. flux. due this alt flux the the
core experinces a effect of cont. exppansision and
contraction this phenomenan is called MAGNETOSTRICTION.

this causes vib. in tr. pherephiry

Answer / gautam himmatramka

Well electric shocked is felt only when the current passes
through our body...as in if their is no other(less
resistive) path for current to flow. In electric train, the
current enters through the line travelling above the train
and is accepted by the contactors and goes back to the
supply through the rails..that is how the circuit is
completed. So we dont feel any current.
Xmer humming noise is due to MAGNETOSTRICTION. No doubt
bout dat.
For Xmer oil, mineral oil is used which is a very purified
form of oil. To measure its dielectric strength, we use BDV
( Breakdown Voltage Test)Test, In which oil is placed in
betweeen two electrodes which are partially dipped in it
and voltage is applied b/w them. The voltage at which it
breaks down is its BDV value.

Answer / kanika

huming noise of transformer is due to magnetostriction.

Answer / masoom raza

1)when electrical current passes through our body
then it interacts with electrical impulse in our
body due to which our muscles contracts and expand (depending on type of current i.e ac or dc ,in dc
it contracts while ac in ac it contracts and expands
but very high speed depends on frequency),its called
shock.
in case of electrical train, it is grounded through wheel
so current follows that path(train body to wheel)
rather through our body. so didn't feel shock.
2)transformer noise is due magnetostriction (expansion
and contraction of core in high frequency as in ac
polarity changes rapidly ,i.e it has frequency).
3) transmission line carries high power, have no
insulation ,low frequency operation
communication line carries low power signal,have
insulation
,high frequency operation.
4) transformer oil is usually made from petroleum as it having high Di-electrical strength and high temperature rating and it is less reactive then normal oil.
sorry friend i don't know exactly name of test.
its probably dielectrical strength test.

Answer / arjun chaudhary

Ans 2) magnetostriction (when there is changing magnetic
field due to alternating current vibration occurs due to
which sound comes at full load ) eg. we use two black
magnets (two magnets so same length and effect) when we
throw in air we get the hissing sound because of changing
magnetic field .

Answer / rahul dhote

trasformer noise is also called as *HUMING* it is due to
mechanical vibration of various part of the trasformer
structure

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