Q1.
State any four factors by which locations and spacing of substations are
decided.
Ans:
Factors by which locations and spacing of substations are decided:
1.
System voltage: For identical percentage voltage drops, system voltage is
greater and
hence allowable resistance is more and hence the substations can be placed at
higher distances.
2. Availability of HT
grid lines: If easily available, nearby voltage fluctuations are less and hence
distances between
substations can be increased.
3.
Availability of land: Proximity of land to stations or railway owned lands.
4.
Losses in track conductor system: Higher distances lead to higher losses.
5.
Maximum permissible voltage drop: Greater spacing leads to higher drops.
6.
Overload current setting of track feeder: For large spacing, the resistance of
feeder is large and the tripping may not occur due to insufficient current even
though fault has occurred.
Q2. What are various supply
arrangements of feeding AC traction substation?
Ans:
Supply arrangement of feeding AC traction sub-station:
1)
Supply authorities are responsible for following:
*Operation
and Maintenance of 132/110 kV transmission line.
*Operation
and Maintenance of Grid substations upto 25 kV outgoing terminals.
*The
traction power controller controls 25 kV feeder circuit breaker from remote
control centre.
2)
Supply authorities are responsible for following
*All
132 kV and 25 kV equipment are owned, installed operated and maintained.
*Railway
authorities own, install, operate and maintain 25 kV CBs.
3)
Supply authorities give only 132/110 kV supply at substation.
*Railway
authorities install, operate and maintain all 132/110 kV equipment at
substations.
4)
Supply authorities provide 3 phase supply at 132 kV at a point.
*The
railway authorities distribute to the traction substations through own
transmission lines.
Q 3. Draw a
neat Labeled diagram of feeding post and write any four points related to it.
Ans:
Feeding
post:
1)
Each feeder has two conductors one insulated for 25 kV (connected to bus-bar)
and other for 3 kV (connected to track for return current).
2)
Located as near as possible to substation with maximum distance being 2 km.
3)
Feeders connected to two sets of bus-bars which are used to maintain supply to
OHE in case of failure of one of them or when under maintenance.
4)
The 25 kV CB of FP are controlled from RCC of railway.
5)
Interlocked double pole isolators provided on both side of CB.
6)
The interrupters which are remotely controlled are supposed to operate only
under normal current as they are not provided with protection for the same.
Q 4. Draw neat labeled layout of traction substation.
Ans: Layout of Traction Substation
Purpose of sectioning arrangements:
-Power to the consecutive substations
is fed from different phases in rotation as shown in figure to balance the
energy load on the three phases. Avoid phase shifts.
-Zones fed by adjacent substations are
acting as a separate independent unit.
-Neutral section is provided in
between two adjacent substations.
Q 6) State the necessity of feeding and
sectioning arrangement in traction SS. Draw its sketch also.
Ans:
Need of
feeding arrangement:
Feed
the supply properly to the traction arrangement of over head lines &
transformers (132 kV/25 kV) of each phase which in turn feed the up and down
lines as shown in the figure.
Need of sectioning
arrangements:
Power to the
consecutive substations is fed from different phases in rotation as shown in
figure to balance the energy load on the three phases. Avoid phase shifts.
Zones fed by adjacent substations are acting as a separate independent unit.
Neutral
section is provided in between two adjacent substations.
Q 7. State
any two miscellaneous equipment at control post with their functions.
Ans:
Miscellaneous equipment at control post:
Lightening
arrestor: provides
protection against voltage surges
Auxiliary
transformer: provides
230 V, 50 Hz, supply to operate battery charger, remote control equipment,
signally and lighting.
PT: provides continuous indication
regarding the condition of supply.
Battery: for operation of remote control
equipment and interrupter.
Battery
charging equipment: charge
batteries at the control post.
Q 8. List
four special features of traction transformer.
Ans:
1. Specially
designed to withstand severe operating conditions.
2. Have high
short time peak capacity.
3. Class A
insulation specially reinforced to withstand stresses of frequent short
circuits.
4. Can take
overloads as- 50 % for 15 min , 100 % for 5 min , 120 % for instantaneous
5. Impulse
withstand voltage nearly 5 times higher
6. To limits
the effect of SC , impedance not less than 8.5 % for 10 MVA and 10 % for 12.5
MVA.
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