Question { Cipla, 30825 }

Wht is the meaning of floating neutral

Answer

If the supply source in star connection and the obtained
neutral is not grounded then in case of the unbalnced load
neutral point will shift causing unequal phase voltages.

Question { L&T, 113149 }

3. What is Impedance Voltage in Transformer?

Answer

Impedance voltage of a transformer is the voltage required
to

short circuit the secondary winding terminals of the
transformer and apply voltage gradually from zero at
primary winding.increase the voltage gradullay till the
full load current flows in the secondary.The voltage at
which full load current flows that voltage is the impedance
voltage of the transformer.This is required for short
circuit calculations.You can find on the transformer name
plate as Impedance voltage or percentage impedance.

Question { 29374 }

What is the difference between body earthing and neutral
earthing?

Answer

Body Earthing is also termed as Equipment earthing,which
safegaurds human beings in the event of any leakage
currents from the eqipments.And all equipments should be
earthed at different places.

Neutral Earthing is also termed as System Earthing.It is so
essantial to keep the neutral at stable point in the event
of unbalances loads.Without system earthing neutral point
will shift its position causing unbalnced voltages,... .All
transformers where secondary windings are connected in STAR
( Power and Distribution) and generators, neutrals should
be earthed either solidly grounded or through impedance or
resistance earthed

Question { ABB, 35019 }

What is the difference between AMF panel and DG
Synchronization panel? please define the working of both
the panels?

Answer

AMF Panel: is Auto Mains failure panel. When the EB power
goes off with a time delay signal will go to DG self
starter to start the DG. And when the EB power
resumes,after definite time delay stop signal goes to DG
and EB supply contactor will become ON.For a fraction of
time power will not be there for the utilities.

In synchronization, there is no outage of supply to the
utilities.When the incoming genset is to synchrinize with
the existing set,we've to match the magnitude of the
voltage, phase angle and the frequency and then only we've
to switch on the incoming set's breaker.

Question { Exide, 50171 }

how to calculate AH of a battery?

Answer

AH capacity of the battery is the current required to
discharge the battery from its full charge voltage to full
discharge voltage and the time taken to do so.FCV of a cell
is : 2.2 or 2.3 volts , FDV is :1.9v.
If we know the no plates of a battery then can calculate
the capacity as above. Otherwise full charge it and the
discharge it to full discharge voltage.mutiply the time
taken to get fully discharged in hours and the current
drawn in amps.

Question { 7317 }

In a Dyn11 transformer, how are the 3 windings of the delta
connected? Assume that R1-R2, Y1-Y2, B1-B2 are the 3
windings on the HV side.

Answer

In a Dyn11 transformer,Hv windings in delta conection and
LV in star only as the vector symbol represents in first
and second letters. numeral 11 indicates that when we super
impose the secondary voltage vector on to the primary one
secondary voltage vector leads the primary vector by 30
degrees.when we superimpose and make a study on delta side
imagine the neutral.

By connecting R1-Y2,Y1-B2,B1-Y2 and taking R1, Y1 and B1 to
terminals DYn11 will be achived. The same transfomer can be
changed to Dyn1 by interchanging the connections in delta.
i.e, R2-Y1;Y2-B1;C2-R1.

Question { Ecil, 23800 }

keeping in view of parallel operation which of the 3 phase
transformer connection are possible?
a)delta-delta to delta-star b) delta-delta to star-delta c)
star-star to delta-delta d) delta-star to star-delta

Answer

For parallel operation of transformers as you know the
requirements, 1. magnitude of the voltage, 2. phase angle
difference between the i/p and o/p voltages, 3. equal
percentage impedance of the transformers.

I don't think that whatever you are asked configurations
same vector symbol will get. So we can't do paralleling.
if you get the same phase angle difference ypu can go ahead
with paralleling.

Question { 14249 }

What is the recommended voltage gap between Live and Earth
and ,Earth and Neutral.If these are exceded what is the
solution.

Answer

If the neutral of the system is earthed then the voltage
between Live condutor and earth is line voltage/ squre root
of 3.i.e, 415 volts is L-L voltage then the voltage L - E
is 239 volts.

Voltage between Neutral and earth should not exceed 5
volts.if it exceeds the earthing was not proper. needs
attention on earthing.

Question { 3293 }

why we connect dg neutral with ground?

Answer

To keep the neutral steady in unbalanced loads. Else neutral will shift in unbalanced loads and with neutral shifting phase to neutral voltages will vary in all three phases.

To avoid that situation we will ground the neutral of DG and distribution trafos. This is called as System earthing.