Answer / n.r.biswas

In a long transmission line, there is a rise of voltage at
the receiving end due to no load or light loads. In long
transmission line having large capacitance which causes
large charging current in the line, occurs voltage drp in
the line, accordingly, receiving end voltage becomes
greater than the sending end voltage, the phenomenan is
called ferranti effec
Line drop = Ic(R+jX) Ic - Charging current at no load
Vr=Vs+Ic(R+jX) Ic leads Vr by an angle 90 Deg.

Answer / ashli

receiving end voltage becomes greater than sending end only
at light load or noload condn. most of our loads are
inductive, so power factor corecting equipments(say
capacitors) are connected in parallel to the line so that
the reactive power consumed by the load s supplied by the
capacitor. even though the loads are removed these
capacitive equipments are there. now the reactive power
supplied by the capacitor get added up. this s why the
receiving voltage becomes greater than supply end..

Answer / larry

An answer to this one is not easy. First, there is a
difference between active power (the power that actually
does work) and reactive power (VARs, for Volts-Amperes
Reactive), which is power that does not itself produce
effective work, yet at the same time it is absolutely
necessary in power systems. Sounds like a contradiction, I
know. Alternating current (and voltage for that matter)
swings from positive to negative values, and the phase
relationship between voltage and current gets shifted
slightly due to inductance (i.e., magnetic field issues)
and capacitance (essentially a charge buildup that in its
most basic form is somewhat similar to battery effect).

Reactive power (VARs) that is required is affected by the
combined inductive reactance and capacitive reactance for
any given system. Long transmission lines therefore
amplify these factors, since there is logically more
inductance and more capacitance over longer distances.
Heavy motor loads (and transformer loads) on power systems
introduce large inductive loads (loads that require
generation of magnetic fields to operate). Consequently,
power systems must compensate for this inductance which
forces a phase shift between current and voltage. This is
accomplished by adding extra capacitance to bring things
closer to being phase for a more efficient power factor
(ratio of active power to apparent power). Inductive loads
cause the current to lag and voltage to lead, while
capacitive loads cause the current to lead and the voltage
to lag. So, the two are “combined” to get the most
efficient results and the targeted power factor.

When a power grid experiences interruption by distant loads
dropping off line, if the transmission line is still
charged the capacitance in the system that is always being
generated by the potential between transmission lines and
ground (or even with other lines) tends to build up much
like when you walk across a carpet and develop voltage that
is not being used. Then, when you touch a grounded object
the unusually high voltage discharges. This might be a
poor example, but the principle proves that devices—
including wires—can “float” up to charges even when a
generator is not directly causing this. This situation is
compounded in major transmission lines where separate
installations by the power company and even certain
customers’ installations specifically add capacitance to
counter what is normally heavier inductive loading.

Why is reactive power necessary and yet it technically
performs no effective work? It is what creates the
magnetic field that allows motors and transformers to do
their work. The magnetic fields are not collapsing and
consuming constant power to re-energize them—instead, they
use reactive power in what is essentially a closed circuit,
two-way street, give-and-take, with the power plant. A
full study of reactive power would be required to
understand this. As a powerplant operator (a new hire), I
have to adjust reactive power on my generators to
compensate for situations electrically downstream. On one
hand the system produces megawatts which is billable
electric power, and on the other hand we provide megavars
(billed to no one) which is something akin to priming a
pump but it is not the work produced for or by the pump.

By the way, buried cables have much higher capacitance than
overhead lines, and these systems introduce special
reactive power considerations. Consequently, the Ferranti
Effect is much more an issue with lengthy underground
transmission lines.

Answer / urnav bagchi

Receiving end voltage being greater than sending end voltage in a transmission line is known as ferranti effect. All electrical loads are inductive in nature and hence they consume lot of reactive power from the transmission lines. Hence there is voltage drop in the lines. Capacitors which supply reactive power are connected parallel to the transmission lines at the receiving end so as to compensate the reactive power consumed by the inductive loads. As the inductive load increases more of the capacitors are connected parallel via electronic switching. Thus reactive power consumed by inductive loads is supplied by the capacitors thereby reducing the consumption of reactive power from trans line. However when the inductive loads are switched off the capacitors may still be in ON condition. The reactive power supplied by the capacitors add on to the transmission lines due to the absence of inductance. As a result voltage at the receiving end or consumer end increases and is more than the voltage at the supply end.This is known as ferranti effect.

Answer / shekhar

It occurs under light load condition.It is the capacitor
which raises the receiving end voltage.generally capacitors
are near to the load side to compensate reactive power.we
know that reactive power is directly proportional to
voltage so under light load or non inductive load voltage
increased cause reactive power is just increasing the
voltage at that time

Answer / kiranmayee

The charging current produces drop in the reactance in the
transmission line which is in phase opposition to the
receiving end voltage.hence sending end voltage is smaller
than receiving end voltage

Answer / thompson

Ferranti effect,is as a result of long transmisson line
which is not heavily loaded.Since the lines are connected
parallel there is capacitance along the transmisson line as
such the receiving end voltage will eventually be more than
sending voltage.Mostly reactors are used to correct this
effect.

Answer / pushparaj

the receiving end voltage greater than the sending voltage during the lightload or no load condition and no load or light load the capacitance associated with the light load generate more reactive power which is obserb hence vR>vs

Answer / pinjari imran

in case of no load or light load condition the capacitance
between line and earth is very much accountable thats why
reseiving end vtg is more than sending end vtg.

Answer / ullas

Vr= Vs(1+WCLl2)
Vr= receiving end voltage.
Vs= sending end voltage
W= 2*3.14*frequency
C= line capacitance
L= line inductance
l2= l square
l= line length.

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