63.What is corona?
The
phenomenon of violet glow, hissing noise and production of ozone gas in an
overhead line is called corona.
64.Mention the factors affecting corona.
Atmosphere,
conductor size, spacing between conductors and line voltage.
65.Define critical disruptive voltage.
It is
defined as the minimum phase voltage at which corona occurs.
66.Define visual critical voltage.
It is the
minimum phase voltage at which corona appears all along the line conductors.
67.State any two merits of corona.
Reduces
the effects of transients produced by surges .System performance is improved.
68.Give the two demerits of corona.
The
transmission efficiency is affected. Corrosion occurs.
69.Mention the methods of reducing corona effect.
By increasing
the conductor size and conductor spacing.
70.Why ACSR conductors are used in lines?
If the
size of the conductor is larger corona effects are reduced and reduces the
proximity effect .Hence they are used in lines.
71.Define medium lines.
Lines having
length between 60 and 150 km and line voltages between 20 and 100kv are called
medium lines.
72.Define short lines.
Lines
having lengths below 60km and voltages below 20kv are called short lines.
73.Explain the term voltage stability.
The
ability of the system to maintain the voltage level within its acceptable
limits is called as voltage stability.
74.Differentiate between voltage stability and
rotor angle stability.
Voltage
stability: -It means load stability. -It is mainly related to reactive power
transfer. -Here problems arise mainly in the event of faults.
Rotor
angle stability: -It means basically generator stability. -It is mainly
interlinked to real power transfer. -Here problems arise during and after
faults.
75.What is shunt compensation ?
Shunt
compensation is the use of shunt capacitors and shunt reactors is the line to
avoid voltage instability.
76.Define a synchronous compensator (condenser)?
Synchronous
compensator is a synchronous motor with no mechanical output .When it is under
exited it operates at lagging p.f (ie it delivers vars ) .Thus it operates both
as a shunt capacitor and as a shunt reactor .
77.Mention any two advantages of series
compensation
improves
system stability .
are generally self regulatory and requires
little or no control equipment
78.
State any
two comparisons between series compensation and shunt compensation
Series
compensation is cheaper than SVS .
Losses are lower than in SVS .
79.
Why
series compensation is used in long series ?
to
increase transmission capacity
to
improve system stability .
to obtain
correct load division between parallel circuits .
80.Mention any two advantages of SVS .(Static Var
System )
Provides
fast control over temporary over voltages. Provides a better control of voltage
profile .
81.Mention the components used in series
compensation ?
Series
capacitors Spark gap protection Metal oxide resistor (for protection ) Current
limiting reactor Bypass switch Control & protection equipment .
82.Mention the components used in static var
compensator .
Saturated
reactor Thyristor controlled reactor –fired capacitor (TCR –FC )
Thyristor
switched capacitor – thyristor controlled reactor (TSC –TCR )
Harmonic
filters.
83.Give any two reasons to minimize the reactive
power transfer in lines .
leads to
voltage stability.
results
in greater real and reactive losses
84.List the four parameters by which the
performance of transmission lines are governed.
Series
resistance Series inductance Series capacitance Series conductance.
85.Define Ferranti effect .
Under no
load or lightly loaded conditions ,the capacitance associated with the line
generates more reactive power than the reactive power which is absorbed &
hence thevoltage at the receiving end is found to be greater than at the sending
end . This is called as Ferranti effect
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