129. Define sag of a line.
The
difference in level between the points of supports and the lowest point of the
conductor is called as sag.
130.Mention the factors that affect sag in the
transmission line.
Weight of
the conductor, length of the span , working tensile strength and the
temperature.
131. What is the reason for the sag in the
transmission line?
While
erecting the line , if the conductors are stretched too much between supports
then there prevails an excessive tension on the line which may break the
conductor. In order to have safe tension in the conductor a sag in the line is
allowed.
132. How the capacitance effect is taken into
account in a long line?
They have
sufficient length and operate at voltage higher than 100 kv the effects of
capacitance cannot be neglected. Therefore in order to obtain reasonable
accuracy in long lines , the capacitance effects are taken.
137. Mention the limitations of nominal T and pi
methods in the line problems.
Generally
the capacitance is uniformly distributed over the entire length of the line.
But for easy calculations the capacitance is concentrated at one or two points
.Due to these effects there are error in the calculations.
138. What are limitations of end condenser method.
There is
considerable error in calculations because the distributed capacitance has been
assumed to be lumped or concentrated. This method over estimates the effects of
the line capacitance.
139. What is end condenser method?
It is a
method used for obtaining the performance calculations of medium lines. Here
the capacitance of the line is lumped or concentrated at the receiving end.
140. What is power circle diagram?
It is a
diagram drawm for the transmission lines network involving the generalized
circuit constants and the sending end and receiving end voltage.
141. What are the voltage regulating equipments
used in transmission system?
Synchronous
motors, tap changing transformers , series and shunt capacitors booster
transformers , compound generators and induction regulator.
142.Mention the methods used for voltage control of
lines
Tap
changing auto- transformer, booster transformer , excitation control and
induction regulator.
143.What is sending end power circle diagram?
The
circle drawn with sending end true and reactive power as the horizontal and
vertical co-ordinates are called sending end power circle diagram.
144.What is receiving end power circle diagram?
The
circle drawn with receiving end values are called receiving end power circle
diagram
145.Mention 2 significance of neutral grounding
the
system voltage during the earth fault depends on neutral earthing.
is
provided for the protection against arcing grounds , unbalanced voltages with
respect to earth, protection from lightning.
146. What is neutral grounding.
Connecting
the neutral or star point of any electrical equipment(generator ,transformer
etc) to earth.
147. Define resonant frequency
is a
reactance earthing with selected value of reactance to match with the line to
ground capacitance.
is
earthing through a reactance of such a value that power frequency current in
neutral to ground connection is almost opposite to the power frequency
capacitive current between un faulted line to earth.
148. Mention 2 disadvantages of ungrounded neutral
occurrence of insulation breakdown leading to the heavy phase to phase fault
condition.
system
cannot be protected from earth fault.
voltages
due to lightning surges do not find path to earth.
149. Mention two advantages of neutral grounding.
arcing
grounds are eliminated.
voltages
of healthy phases with respect to earth do not increase to 3^0.5 times with
normal values.
150.
Name the
various types of grounding.
solid grounding
resistance
grounding
reactance
grounding
resonant
grounding
151.
Define
screening coefficient.
Screening
coefficient for ‘n’ electrodes in parallel is = (resistance of one
electrode)/(resistance of n electrodes in parallel * n) substation
152.What is a substation.
The
assembly of apparatus used to change some characteristic ( eg: voltage , A.C to
D.C frequency power factor etc) of electric supply is called a substation.
153.Mention any two layouts of laying out a substation.
location
should be at the center of the load should provide safe and reliable
arrangement .
154.How substations are classified .
-according
to service requirement constructional feature.
155.
State the various types of substation according to its service requirements. transformer
substation
switching
substation
power
factor correction substation
frequency
changer substation
converting
substation
industrial
substation
156.List the types of substations classified
according to its construction.
indoor
substation
outdoor
substation pole mounted substation
157.Mention any two comparisons between indoor and
outdoor substations.
INDOOR:
-space required and clearances between the conductors are less. -time required
for erection and possibility of faults are more.
OUTDOOR:
-space required and clearances between conductors are more. -time required for
erection and possibility of faults are less.
158.List the various substation equipments.
Transformer
, busbars , insulators , isolators , circuit breaker , relays , lightening
arresters.
159.Define step potential.
It is the
voltage between the feet of a person standing on the floor of the substation
with 0.5m spacing between two feet during the flow of earth fault current
through the earthing system.
160.Define touch potential.
It is the
voltage between the fingers of raised hand touching the faulted structure and
the feet of the person standing on the substation floor. the person should not
get shocked even if the earth structure is carrying faulted current .i.e touch
potential should be very very low.
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