Question { ABB, 178126 }

Do you know how to measure the earth resistance? if so
explain it

Answer

Earth resistance can be measured using Megger instrument.

Question { Bhel, 25032 }

differance b|w ground, neutral&earth

Answer

Ground and earth are same.the current flow in earth/ground
when fault occurs.

Neutral is used as a return path. current flow only when
closed path is there.
current flow in neutral under normal conditions.

Question { ST Micro, 43385 }

What is the power ratio between power in Star and Delta
circuit?

Answer

power = 3vicos

in delta Iphase = Iline/rt3.
Vphase = Vline

ie in delta connected ckt P= rt3VphaseIphasecos

IIly in star connected vphase=Vline/rt3,
Iline=Iphase
ie Power = rt3 vpahseIphaseCos
ie. in both star and delta power remain same
therefore the Power ratio = 1.

Question { HCL, 44259 }

why earth hole size is biggest in plug point?

Answer

hi

the property of the current is that it takes low resistance
path.
if two resistance is conected in IIel, the current flow
will be more in low resistance.

and Resistance is inversly proportional to area.
when area is more the reistance is low.
if any shock occurs current will flow thro the low
resistance instead of the human(human reistance is more
than earth resistance) that is the concept of having lare
earth pin.

Question { 11657 }

Explain Clearly Pahase and Neutral?

Answer

current passes only when a closed circuit is present.
here neutral is act as a return path. ie why neutral
conductor is half of the phase conductor value.

another information is that.

phase only have the fuse. neutral having neutral link.bcoz,
the equipment should protect before the fault current
reaches it. if we provide fuse in neutral fuse blows after
gone thro the equipment to be protected. bcoz neutral is a
return path

Question { 15874 }

How the starter control the starting current in three
phase AC Motor?(In DC apply the reistance).

Answer

types of starters in ac motor
1. Rotor resitance starter-it is used only for Slip ring
in squirrel cage IM is wound rotor so we cant add external
resistance.in starting resistances are included to limit
the starting current.
2. star delta starter-at the time starting the rotor is
connected as star and in running itis connected as delta.
it can be used for both slip and Squirrel cabe IM.
3. Auto transformer starter- at the time starting by using
auto transforme the voltage is reduced.
4. DOL starter - it doesnt reduce any staring current. it
is used only for small rating of motor

Question { 17963 }

Is voltage & potential transformer are the same? Are they
used for same application ?

Answer

Yes VT and PT are same.

it is mainly used for Protection and metering.

the Tx.line have high voltage. if you want to measure the
voltage it should also designed with HV. it leads more cost.
therfore we are steping down the voltage to a low level. it
is usally 110V.

also it is used for distance protection. the distance
protection is based on Impedance. Impedance can be
calculated by using the formula Z= Voltage/Current.

Question { Bhel, 20965 }

it is clear that volts equal to the current as per ohms law.
is it appliable to the AC power or only for DC. if it is
appliacable to AC in transformers when voltage increases
the voltage decreases ????? why??????????????

Answer

i think its applicabe for both Ac and DC.

in transformer N1/N2=V1/V2 = I2/I1.
ie when no.of turns in primary increased voltage in primary
increased bcoz its direct propotional. and current is
inversly proportional hence the current will reduced.

i am not sure the above ans.
if correct ans known to anybody inform me too.