Substation MCQ Quiz - Objective Question with Answer for Substation - Download Free PDF

The correct answer is option 4.

Explanation

• Outdoor substations are usually cheaper than indoor substations because they do not require expensive building enclosures or as much insulation. Indoor substations require additional space, construction, and ventilation, making them more costly.
• No substation is completely maintenance-free. Indoor substations require regular maintenance to ensure safe and reliable operation, including cleaning, checking insulation, and monitoring equipment conditions.

Difference between Indoor and Outdoor Substations:

Parameters	Indoor Substation	Outdoor Substation
Construction	The construction of the indoor substation is complicated.	The construction of the outdoor substation is not more complicated.
Voltage	These substations install up to the 66kV voltage level.	These substations install for beyond the 66kV voltage level.
Location	Generally, the indoor substations place inside the building.	The outdoor substations place outside the building.
Space Required	There is required a small space.	There is required plenty of space.
Installation	Cannot easily expand the installation of indoor substations.	Can easily expand the installation of outdoor substations.
Cost	The cost of the indoor substation is low.	The cost of the outdoor substation is high.
Fault Condition	Very easy to clear the fault.	Very difficult to clear the fault.
Maintenance	Indoor substation requires high maintenance.	Outdoor substation requires less maintenance.
Safety	Indoor substations are much safer.	Outdoor substations are not much safer.

 

Classification of switchgear

Switchgear is broadly classified based on the voltage levels and the environment in which it is installed. The two main types are:

Indoor Switchgear

• Used for low and medium voltage applications (typically up to 36 kV).
• Installed inside buildings or enclosures to protect from environmental factors like rain, dust, and extreme temperatures.
• Example: Metal-clad switchgear used in industrial plants.

Outdoor Switchgear

• Used for high voltage applications (above 36 kV).
• Designed to withstand environmental conditions like storms, humidity, and temperature variations.
• Example: Air-insulated or gas-insulated switchgear in substations.

Indoor substations are generally superior to outdoor substations in terms of safety and fault location, while outdoor substations may be cheaper and require less maintenance. 

Safety: 

• Indoor substations provide better protection from environmental hazards (e.g., storms, dust, pollution).
• They reduce the risk of electrocution and accidental contact compared to outdoor substations, which are more exposed.
• They are usually enclosed, making them safer for personnel.

Cost:

• Outdoor substations are often cheaper to build and require less space, especially for lower voltage applications. 

Maintenance requirement:

• Indoor substations require higher maintenance because of the need for cooling, ventilation, and insulation protection.

Fault location:

• Fault location in indoor substations can be easier due to the enclosed environment and centralized equipment. 

 The neutral section plays a vital role in the overall safety and reliability of the electrical distribution network, ensuring that areas fed by different substations can function independently.

Explanation:

• Separation of Areas: The neutral section serves to clearly delineate the electrical boundaries between two different sections of the power supply, which are typically fed by different substations. This separation is crucial for operational integrity and safety.
• Operational Control: It allows for the independent operation of each substation, meaning that maintenance or faults in one section do not affect the other. Each section can be controlled and managed separately.
• Avoiding Short Circuits: By having a neutral section, you prevent the risk of short circuits between the different supply phases or sections, which could occur if the two adjacent substations were connected without a neutral gap.

Explanation:

• Distribution substations play a crucial role in the power grid by facilitating the transfer of electricity from the high-voltage transmission system to the lower-voltage distribution system within a specific area.
• These substations step down the voltage for local distribution, making it suitable for homes, businesses, and other end-users.
• Distribution substations often include transformers to adjust voltage levels, switchgear for circuit protection, and other equipment for control and monitoring.
• This transition from the transmission to the distribution system ensures efficient and reliable power supply to consumers in a given locality.

Isolator:

• An isolator is a manually operated mechanical switch which separates a part of the electrical power.
• Isolators are used to open a circuit under no load.
• Its main purpose is to isolate one portion of the circuit from the other and is not intended to be opened while the current is flowing in the line.
• Isolators are generally used on both ends of the breaker so that repair or replacement of a circuit breaker can be done without any danger.

 

Rewireable fuse:

• A fuse is a part of the circuit that consists of a conductor that melts easily and breaks the connection when the current exceeds the predetermined value.
• The function of fuse wire is to carry the normal current without excessive heating but more than normal current when passes through fuse wire, it rapidly heats up and melts.
• The materials used for fuse wires are mainly tin, lead, zinc, silver, antimony, copper, aluminum, etc.
• Rewireable fuses are used to open a circuit under loaded conditions.

 

Circuit breaker:

• An electrical circuit breaker is a switching device which can be operated manually and automatically for controlling and protecting an electrical power system.
• During a short circuit fault or any other type of electrical fault, a high fault current will flow through this equipment as well as the power network itself.
• So a circuit breaker is needed to break the circuit and quenching the arc produced by the potential energy stored during braking.
• It is operated under loaded conditions.

 

Air-break switch:

• The switch whose contacts open in the air and quenching of an arc achieves by compressed air, such type of switch is called an air break switch.
• The air acts as a dielectric medium for the air-break switch.
• It is more effective and reliable as compared to another switch.
•  The maximum voltage for the switches is up to 35 kV.
• The air-break switches are classified into two types. They are Single-Pole Air-Break Switch and the Gang Operated Air-Break Switch.

The correct answer is option 4):(The cost of outdoor substation is higher than indoor substation.)

Concept:

Indoor Substation:

• The substation which installs for low voltage requirements inside the building construction is called an indoor substation.
• The construction of the indoor substation is complicated.
• These substations install up to the 66kV voltage level.
• Generally, the indoor substations place inside the building.
• You cannot easily visualize the equipment of the indoor substation.
• There is required a small space.
• You cannot easily expand the installation of indoor substations.
• The cost of the indoor substation is high.Hence option 4 is wrong
• Fault location is easier.
• Indoor substation requires high maintenance.
• The equipment of the indoor substation cannot easily repair and replace.
• Indoor substations are much safer.
• The distribution substation is an example of an indoor-type substation.

Outdoor substation:

• The substation which installs for high voltage requirements outside the building construction is called an outdoor substation.
• The construction of the outdoor substation is not more complicated.
• These substations install beyond the 66kV voltage level.
• There is required plenty of space.

Concept:

When a fault occurs, the fault current flows to the ground due to which the potential gradient near the electrical equipment developed.

This potential gradient may affect a person in two ways, either by step-to-step contact or by touch contact.

Step-Potential:

Step potential is the potential difference between the feet of a person standing on the floor of the substation, with 0.5 m spacing between the one-step, during the flow of fault current through the ground system.

Touch-Potential:

Touch potential is a potential difference between the fingers of a raising hand touching the faulted structure and the feet of the person standing on the substation floor.

To eliminate these and protect from the faults we are using earthing for the operating personnel.

Pole Mounted Substation:

• Pole Mounted Substation is an outdoor step-down distribution substation that is placed on an overhead pole.
• It is the cheapest, smallest and simplest substation. This type of substation does not have any building works.
• The transformer is mounted on an H-Type pole or Four Pole Structure.
• The electrical power supply comes into our house mostly from this pole-mounted substation.
   

Use of Pole Mounted Substation:

• Pole mounted substation is used for the low voltage power distribution.
• It generally supplies the electrical power supply to domestic consumers.
• It steps up the voltage from three-phase three-wire 11KV into three-phase four-wire 400V and single-phase 230V power supply.
• The main advantage of this substation is it provides output in both three-phases and single phases. So it can be used to provide power supply to both the single-phase and three-phase consumers.
   

​Diagram of Pole mounted Substation:

Classification of Sub-station according to Application:

1. High Voltage Substation (HV Substation): Involving voltage between 11 kV and 66kV.

2. Extra-High Voltage Substation (EHV Substation): Involving voltage between 132 kV and 400kV.

3. Ultra-High Voltage Substation (UHV Substation): Operating on voltage above 400 kV.

4. Indoor Substation:

• In such a substation, the apparatus is installed within the substation building.
• They are usually mounted up to 11 kV because of space requirements.
• It also can be erected up to 66 kV when the surrounding atmosphere is contaminated with impurities such as metal corroding gases, fumes, conductive dust, etc.

5. Outdoor Substation:

• These are either Pole Mounted or Foundation Mounted type.
• Pole Mounted type is used for distribution of power in localities by using Single Pole or H Pole or 4-Pole structure.
• Foundation Mounted type Substation used above 250 kVA and 33 kV
   

6. Step-Up and Step-Down Type Substation:

• This type of substation is placed at various points in an electrical power system.
• This type of substation can change the transmission voltage or distribution voltage from one voltage level to another voltage level.
• Generally at the supply end step-up substation is installed and at the load end step-down substation is installed by means of a Transformer and other equipment.
   

7. Mobile Substation or, Portable Substation:

• The mobile substation or portable substation is fully equipped with different power system equipment and must be able to be shipped from one place to another with fully assembled mode during the requirement of power supply for various work.
• The overall height and width of the total substation unit should be such that it is able to transport by Road or Railway.
• It is used in Emergency services, New services, or Temporary Services.

Indoor sub-stations:

For voltages up to 11 kV, the equipment of the sub-station is installed indoor because of economic considerations. However, when the atmosphere is contaminated with impurities, these sub-stations can be erected for voltages up to 66 kV.

Outdoor sub-stations:

For voltages beyond 66 kV, equipment is invariably installed outdoor. It is because for such voltages, the clearances between conductors and the space required for switches, circuit breakers and other equipment becomes so great that it is not economical to install the equipment indoor.

Underground sub-stations:

In thickly populated areas, the space available for equipment and building is limited and the cost of land is high. Under such situations, the sub-station is created underground.

Pole-mounted sub-stations:

This is an outdoor sub-station with equipment installed overhead on H-pole or 4-pole structure. It is the cheapest form of sub-station for voltages not exceeding 11kV (or 33 kV in some cases). Electric power is almost distributed in localities through such substations.

Classification of substation according to Constructional features:

Indoor Switchgear:

• For voltages, up to 11 kV, the equipment of the sub-station is installed indoors because of economic considerations.
• When the atmosphere is contaminated with impurities, this switchgear can be erected for voltages up to 33 kV.

Outdoor Switchgear:

• For voltages beyond 33 kV or 66 kV, equipment is invariably installed outdoor.
• It is because for such voltages, the clearances between conductors and the space required for switches, circuit breakers, and other equipment becomes so great that it is not economical to install the equipment indoors.

Underground Switchgear:

• In thickly populated areas, the space available for equipment and building is limited and the cost of land is high.
• Under such situations, the sub-station is created underground.
   

Pole-mounted Switchgear:

• This is an outdoor sub-station with equipment installed overhead on H-pole or 4-pole structure.
• It is the cheapest form of sub-station for voltages not exceeding 11kV (or 33 kV in some cases).

Gas-insulated substation:

A gas-insulated substation (GIS) is a high voltage substation in which the major conducting structures are contained within a sealed environment with a dielectric gas known as SF₆, or sulfur hexafluoride gas as the insulating medium.

The total space required for a GIS is roughly one-tenth of that needed for a conventional substation.

The gas-insulated substation is smaller than the conventional substation because of:

1. The high insulation property of SF₆ gas
2. The high dielectric property of SF₆ gas
3. The high electronegative property of SF₆ gas

Primary distribution system:

• It is that part of the AC distribution system which operates at voltages somewhat higher than general utilization and handles large blocks of electrical energy than the average low-voltage consumer uses
• The voltage used for primary distribution depends upon the amount of power to be conveyed and the distance of the substation required to be fed
• The most commonly used primary distribution voltages are 11 kV, 6.6 kV, and 3.3 kV; Due to economic considerations, primary distribution is carried out by 3-phase, 3-wire system
• Electric power from the generating station is transmitted at high voltage to the substation located in or near the city; At this substation, voltage is stepped down to 11 kV with the help of a step-down transformer
• Power is supplied to various substations for distribution or to big consumers at this voltage; This forms the high voltage distribution or primary distribution

Transformer substation employed for the changing of the voltage level of electric supply.

Additional Information

Classification of Sub-station according to Application:

1. High Voltage Substation (HV Substation): Involving voltage between 11 kV and 66kV.

2. Extra-High Voltage Substation (EHV Substation): Involving voltage between 132 kV and 400kV.

3. Ultra-High Voltage Substation (UHV Substation): Operating on voltage above 400 kV.

4. Indoor Substation:

• In such a substation, the apparatus is installed within the substation building.
• They are usually mounted up to 11 kV because of space requirements.
• It also can be erected up to 66 kV when the surrounding atmosphere is contaminated with impurities such as metal corroding gases, fumes, conductive dust, etc.

5. Outdoor Substation:

• These are either Pole Mounted or Foundation Mounted type.
• Pole Mounted type is used for distribution of power in localities by using Single Pole or H Pole or 4-Pole structure.
• Foundation Mounted type Substation used above 250 kVA and 33 kV
   

6. Step-Up and Step-Down Type Substation:

• This type of substation is placed at various points in an electrical power system.
• This type of substation can change the transmission voltage or distribution voltage from one voltage level to another voltage level.
• Generally at the supply end step-up substation is installed and at the load end step-down substation is installed by means of a Transformer and other equipment.
   

7. Mobile Substation or, Portable Substation:

• The mobile substation or portable substation is fully equipped with different power system equipment and must be able to be shipped from one place to another with fully assembled mode during the requirement of power supply for various work.
• The overall height and width of the total substation unit should be such that it is able to transport by Road or Railway.
• It is used in Emergency services, New services, or Temporary Services.