ESP Unit1 Overview of Substation
Q1) Classify substations based on constructional features. S22
Ans:
Classification of Substations Based on Constructional Features:
1. Indoor Substation. 2. Outdoor Substation.
3. Gas insulated Substation. 4. Underground Substation.
5. Pole mounted substation. 6. Plinth mounted Substation.
7. Compact/prefabricated substation.
Q2) Compare indoor & outdoor substation on the basis of the following points:W22
(i) Installation cost
(ii) Lightning protection
Ans:
Q3) Explain any four factors to decide the selection of site for the sub-station. S23
Ans:
1) The site should be as near the load center as possible.
2) The site should be far away from obstructions, to permit easy and safe approach/termination
of high voltage overhead transmission lines.
3) The Site should have sufficient land area.
4) The site should have Necessary clearances for electrical safety.
5) Access to maintain large apparatus such as transformers.
6) The site must have room for expansion due to load growth or planned transmission additions.
7) Environmental effects like drainage, noise and road traffic effects should be taken into account.
8) Grounding must be taken into account to protect passers-by during a short circuit in the
transmission system.
9) The substation site must be reasonably central to the distribution area to be served.
Q4) Justify the following factors governing the selection of the site of the electrical substation:
(i) Type of substation (ii) Atmospheric pollution. W22
Ans:
Factors governing the selection of the site of the electrical substation:
(i) Type of Substation:
The type of substation is important for its location. For example a step-up substation, which is point
where power from various sources (generators or generating stations) is pooled and stepped up for
long distance transmission, should be located as close to the generating stations as possible to
minimize the transmission losses.
Similarly a step-down substation should be located nearer to the load centre to reduce transmission
losses, cost of distribution system and better reliability of supply.
(ii) Atmospheric Pollution:
Atmosphere around factories, which may produce metal corroding gases, air fumes, conductive
dust etc., and nearer to sea coasts, where air may be more humid and may be salt laden, is
detrimental to the proper running of power system and therefore substations should not be located
near factories or sea coast.
Q5) Write any four advantages of neutral grounding. S22
Ans:
Advantages of Neutral Grounding:
1. In this system the neutral point is not shifted and thus the voltages of the healthy phases remain
nearly constant.
2. The high voltages due to arcing grounds are eliminated.
3. The earth fault relays can be installed to isolate the faulty portion for earthed neutral grounding
system.
4. It provides greater safety to personnel and equipment.
5. It provides improved service reliability.
6. Operation and maintenance expenditures are reduced.
7. The neutral grounding stabilizes the neutral point.
8. Neutral grounding is useful in discharging over-voltages due to lightning to the earth.
9. The neutral grounded systems require relatively lower insulation levels as compared with
ungrounded systems.
10. Discriminative type protective gear can be installed in a neutral grounded system.
11. Due to elimination / reduction of the arcing grounds, unnecessary tripping of circuit
breakers is prevented.
12. Improved life of equipment, machines and installation is achieved.
13. The induced static charges do not produce any disturbance in the circuit / system as they are
conducted to earth immediately.
14. Overall economy is achieved by providing more safety, reducing faults and accurate type of
protection arrangements
Q6) Describe general safety rules to be followed to minimize the risk of electrical hazards in
substation. W22
Ans:
General safety rules to be followed to minimize the risk of electrical hazards in substation:
i) Permits to be issued / cancelled while carrying out any electrical work.
ii) Use of PPEs, danger boards while working on line.
iii) SOP, SMP to be followed while carrying out maintenance activities.
iv) Understand the safety threats that abound in the work environment.
v) Know how each equipment functions, what parts are energized and what voltages, clearance
requirements, risk involved and levels of protection are required to work on the equipment.
vi) Be cautious even when around de-energized equipment.
vii) Conduct routine inspections to ensure that the area and equipment are safe for use prior to each
task.
viii) Maintain the prescribed clearance from each type of equipment, and handle operations remotely
if the option is available.
ix) Securing Battery Stores, Securing Perimeter Area, Restricting or Prohibiting Visitor Access to
such areas.
x) Enough Clearance from energized parts should be provided to avoid accidental contact with them.
If that can’t be met, live parts should be guarded or enclosed.
Q7) State the value of earth resistance as per IE rule S23
for:
1. 11 kV substation (small) 2. Power station (32, 220kV)
Ans:
Values of earth resistance as per IE rules:
1. 11 kV substation (small): 2 ohm
2. Power station (32,220kV): 0.5 ohm
Q8.) Define tower footing resistance of steel structure and write its significance in
protection. S24
Ans:
Tower footing resistance of steel structure:
Tower footing resistance is the resistance offered by the tower footing to the dissipation of
ground. OR
Tower footing resistance is the resistance offered by the tower footing to the discharge current
during lightning surges to ground.
Significance of Tower footing resistance in protection:
Tower footing resistance acts as a shield, protecting not only the steel structure itself but also
the intricate systems within, from the potential havoc wreaked by electrical events.
