Question { HP, 3481 }

IS it possible for a feedbacksurge to travel over a
wireless connection?

Answer

Not at all possible if it is frequency,VSB and phase
modulated.
Amplitude modulated signals can be distorted during such
surges.

Question { 21394 }

How is a 100 MVA transformer cooled?

Answer

Yes there r such methods of liquid nitrogen and Hydrogen
cooling of transformer. These methods are costlier and
efficient, and requires sofisticated instruments.
This is the only method for high capacity transformers,
alternators engines etc.

Question { NTPC, 16686 }

what is the difference b/w winding insulation class and
winding temperature class?

Answer

winding insulation classification is nothing but a group of
materials arranged in the order of insulation resistivity
in terms of Kv per mm.

winding temp. class is related to temperature withstand
capability of winding insulation.

Question { SCS, 5662 }

How to increase the specific gravity of DG batteries?

Answer

for the clear understanding, the DG batteries are always
lead acid. The specific gravities can be increased by
charging with a dc source. If the specific gravity is not
getting enough, change the electrolite,ie: sulphuric acid
and do the task again.

Question { 8169 }

diagram for soft stater ?

Answer

No one can give u such diagram, unless there is some commercial implications. For your kind understanding,
softstarter is nothing but a variable transformer, can be
of conventional type, or modern triac based. The
requirement is to vary the supply voltage applying to a
high capacity motor.

Question { 4292 }

Do I need a special Transformer to put 240 VAC 3 phase into
it and and get 480 VAC 3 phase out of it to run a machine?
Or, do I just use an ordinary step down transformer and step
up the voltage? Thanks

Answer

Transformer can change the voltage levels, but do consider
the current ratings also.

Question { CFCL, 6465 }

if any leas acid battery is having low or high sp.gravity
taen what will be effect of battery and why

Answer

Specific gravity of electrolyte is an indication of charge
stored on the battery.
spe.gravity low means battery having less charge and need
to be charged with a DC source.

Question { GAIL, 24113 }

In step down transformer (415/200V),mistakenly secondary
side is connected to 415V for some hours, what would be
result of this condition?

Answer

The current at 200v side will be more than what designed
for the transformer and core loss will be more. So
ultimately,transformer will be heated up more faster than
ordinary condition. Depends upon the insulation used for
core construction, and how long u are connected the supply,
there r chances of insulation failiure.

Question { L&T, 48381 }

WHY THE FREQUENCY IS 50 HZ IN INDIA.CAN WE USE SOME OTHER
FREQUENCY.IF SO WHAT IS THE RANGE AND WHAT WILL BE THE
EFFECT IN PRESENT POWER SYSTEM IF WE CHANGE THE FREQUENCY
AS YOU SUGGEST ?

Answer

Question :

WHY THE FREQUENCY IS 50 HZ IN INDIA

Ans: The material properties of ferromagnetic substances
having great importance in selecting frequency. Frequency
range from 45 Hz to 70 Hz is useable region.
Another consideration is the core and copper loss. In core
loss, the power loss is proportional to frequency, and for
copper loss, is proportional to sq.of frequency.
Developing countries like India, defenitely select the
chepest option, thats 50 HZ.
Another consideration is equipment availablity.
Equipment availibility is only in the range of 50 Hz and 60
Hz. If we chose some other frq. say 70 Hz, Indian
manufactures has to produce accordingly, and that will
create less utilization of ferro magnetic materials.

From above, the conclusion is 50Hz is most suitable and
economical option.

Question { Bhel, 17042 }

Why current flows in nutral? As per theory there should be
no current in 3 ph explain.

Answer

if the three phase load is unbalanced, there will be a
voltage between the common point (star system) and earthed
ground( system ground), known as Neutral shift voltage. So
if you are short circuiting these, there will be a current.

Ir+Iy+Ib=Io not Zero for unbalanced loads.

Question { Essar, 44866 }

what is saturation in transformer

Answer

Transformer saturation means its core get saturated due to
higher flux linkages than designed.simply we can say, the
feromagnetic substance acquired some residual magnetism due
to the application of higher level flux( about 4 to 5 times
normal designed flux). due to this, the transformer core
cannot act as a good flux linkage media.

Question { Roverco, 10260 }

how winding temperature detects in power transformer...?

Answer

power transformer directly not detecting any winding temp.
but detects the cooling oil temperature, using a Buckoltz
relay.

Question { TCS, 19711 }

Explain types soft starters?

Answer

Soft starters are used for reducing starting currents of
high capacity motors( above 60 HP ). Ofcourse, these are now
a days used with SCR's.

Question { 3125 }

Slow acting fuses are most often used for which application
a) Lighting circuit b) heating circuit c) Motor D) Radar
circuit

Answer

motors, since the motor consumes more current during
starting.

Question { 15438 }

how does relay works?

Answer

Relays are electro-mechanical switches, and it needs some
power either AC/DC to operate the activation coil.
As soon as the coil gets magnetised, the contact attached
will make/break.