Question { 6433 }

How to conduct Magnetic Balance Test, Measurement of
Excitation Current (both on HV- and LV-side) and vector
group on a 1000 KVA distribution transformer. There is a
neutral on HV side.

Answer

for magnetic balance test apply the 415 v volt to R phase
then measure Y phase voltage it must be 60 to 80 % of i/p
voltage and B phase should measure around 40 to 20 % of i/p
volatge and when voltage applied to Y phase R & B phase
should read 40 to 60 % of i/p reading. For voltage applied
to B pahse reading should be reverse of first case.

and for measuring excitaation current just give 415 V to
either side H.V or L.V but H.V side prefer and measure
current with clamp meter of all phases.

and for vector group just short the R phase of H.V with r
Phase of L.V
measure voltage as
1R-1Y =
1Y-1B =
1B-1R =
1Y-2y =
1Y-2b =
1B-2b =
1B-2y =

then e.g Dyn11

these condition to fullfill
1Y-2y = 1Y-2b
1B-2y > 1B-2b

Question { CSS, 25436 }

1.Whats the use of GNAC(Generator Neutral Accessory
Compartment)

2. why generator or any other system require Neutral
Grounding and not Phase grounding

3. what happens if any one of the phase is grounded.

4. if 15kv is grounded directly what will happen, why it
should not be grounded like that

5. use of of NGTR(Neutral Grounding Transformer and
Resistor) for grounding is helpfull and how

Answer

1. for connecting equipments like ct, pt's.
2. neutral grounding is for flowing of third harmonic
component present in system to ground and it is grounding
at only one side either supply side or recieving side of
one level voltage like 220kv line or 33kv.. mostly on
sending side.
3 earth fault occur.
4 short cicuit current flow. depends on the impedance of
the generator.
5 NGTR is used for lowering fault current which flows
through neutral to the safe value to dissipated to ground
safely.

Question { 6738 }

what is fault level in 66kV system?

Answer

it depends on p.u impeadeance of supply transformer

Question { ITC Infotech, 26073 }

HOW VFD USED IN ENERGY SAVING

Answer

vfd drive works almost t unity pf. so this mainly it saves
energy. if u connect motor directly it works on .8 of pf.
but vfd mainly used for better speed and torque control not
for power saving purpose

Question { ITC Infotech, 26073 }

HOW VFD USED IN ENERGY SAVING

Answer

have anybody checked the input and out current of drive if
yes then he knows that ipput current of drive is less than
that of out put current that is because of power factor

Question { Reliance, 4025 }

what is slip resistance?
how much its value in 110 kw motor?
why voltage is varied in vvvf drive ?

Answer

i think there is slip value. and it is around 1% that is
Ns-n/ns *100 =
voltage varied for keeping V/F ratio constant

Question { 6762 }

Using 11000V/433V,3 ph,50Hz,500 KVA, what is the maximum
capacity of motor in KW that can be connected and started at
a single moment? Also explain about any calculations and
formulas used in deriving the same.

Answer

500x.8 = 400 kw

Question { Pepsi, 11462 }

How do you select a cable size(cu and Al) for a particular load

Answer

it depends upon length. but you can take it as for al cable
1 sqmm = 1a and for cu 1sqmm = 2.5 a

Question { Jindal, 41479 }

What happen if LV supply is fed to a HT motor?

Answer

if LT applied to HT motor then motor winding will burn out.
because motor current is inversely propotional to voltage.
i f applied less voltage the motor current will increase.
e.g.
1500 kw motor supply voltage 6.6 kV current 155 A.
if applied 415 V then current is around 2000A .

Question { 8142 }

Hi,
We facing one similar problem in our computers i.e we are
newly constructed our design department after that shifted
our computers but our computer desktop screen is vibrating.
we are conducted our electrical maintainance person he told
that is UPS problem, then we changed the UPS also again we
are facing that problem in that room only. then we put lcd
monitors that problem is solved. But in other monitors why
the computer desktop screen is vibrating please give a
suggestion to me.

Regards,

Raju.N.G

Answer

it is due to magnetic field. that may be produced by
inductor presnt somewhere around monitor.

Question { Reliance, 20146 }

What are difference between earthing switch and earthing
truck ?
What is the operation philoshopy of earthing truck ? Wht
are the component of earthing truck ?

Answer

earthing switch permanent connected in cicuit where as
eathing truck is movable you can use it where ever you need.
suppose you have to work on portion of power line you can
permanet connect the earthing truck to that portion of line
after repairing you disconnect it

Question { L&T, 7316 }

Why size of HT cable is less then LT cable inspite of the
fact that voltage is higher in HT cable?

Answer

size that is the cross sectional area of cable that is in
Sq mm. mainly depends on current carrying capacity of cable
and second on voltage if voltage increases than the
current decreases. so in HT that high tension above 1.1 Kv
current carring capacity decrease for transferring the same
amont of power. so is the size reduced . yes it has extra
insulation for this high voltage.

Question { HP, 4773 }

What is expand formation of AYFY cable

Answer

so we read as AYFY AS
A ALUMINUM CONDUCTOR
Y PVC SHEATH
F FLAT STEEL STRIP ARMOUR
Y PVC OUTER SHEATH

IF _Y_Y
COPPER CONDUCTOR
NO ARMOUR AND OUTER PVC SHEATH

Question { 8586 }

If Two Generators are working parellel in a network and
suddenly the field of one Generator get weakened What will
happened if there is no reverse power relay fixed in that
Generator panel????

Answer

field weakened generator will run as induction motor

Question { 37461 }

What will Happened if the polarity of CT is changed?

Answer

ammeter reading change. i means needle move from right to left