Power Systems MCQ Quiz - Objective Question with Answer for Power Systems - Download Free PDF

Explanation:

Francis Turbine Components and Flow Regulation

Definition: A Francis turbine is a type of reaction turbine used for hydropower generation, designed to operate efficiently under a wide range of head and flow conditions. It converts the potential energy of water into mechanical energy, which is then used to generate electricity through a connected generator. A key feature of the Francis turbine is its ability to dynamically regulate flow and optimize power output under varying load conditions.

Correct Option Analysis:

The correct answer is:

Option 1: Guide Vanes

The guide vanes play a critical role in regulating the flow rate and optimizing the power output of a Francis turbine. They are adjustable components located just before the turbine runner. By dynamically altering their angle, guide vanes control the amount of water entering the runner and the direction of the flow. This ensures that the turbine operates at peak efficiency under varying load conditions.

Working Principle of Guide Vanes:

• Flow Regulation: The guide vanes adjust their position to regulate the flow of water entering the runner. When the load on the turbine decreases, the guide vanes close slightly to reduce the flow rate, and when the load increases, they open to allow more water to flow through.
• Flow Direction: The guide vanes direct the water flow at an optimal angle to the runner blades. This ensures that the kinetic energy of the water is effectively transferred to the runner, maximizing the turbine's efficiency.
• Dynamic Response: Modern Francis turbines are equipped with servo mechanisms that allow the guide vanes to respond quickly to changes in load or flow conditions, maintaining stable operation and consistent power output.

Advantages of Guide Vanes:

• Enable precise control over the turbine's power output by dynamically adjusting the water flow.
• Improve the overall efficiency of the turbine by ensuring optimal flow direction and velocity.
• Help in maintaining stable operation during fluctuating load conditions.
• Reduce the risk of cavitation and mechanical stress on the turbine components by controlling flow conditions.

Conclusion: The guide vanes are essential components in a Francis turbine that dynamically adjust to regulate the flow rate and optimize power output under varying load conditions. Their ability to control both the quantity and direction of water entering the runner ensures efficient and reliable operation of the turbine.

Important Information

To further understand the analysis, let’s evaluate the other options:

Option 2: Spiral Casing

The spiral casing is the outer component of a Francis turbine that distributes the incoming water evenly to the guide vanes. It is designed to maintain a constant velocity of water around its circumference. However, it does not dynamically adjust to regulate the flow rate or optimize power output. Its primary function is to ensure uniform distribution of water, which is critical for the efficient operation of the turbine, but it does not have a direct role in dynamic regulation under varying load conditions.

Option 3: Draft Tube

The draft tube is a diverging passage located at the exit of the turbine runner. Its purpose is to recover the kinetic energy of the water leaving the runner and convert it into pressure energy, thereby increasing the overall efficiency of the turbine. While the draft tube plays a significant role in energy recovery, it does not dynamically adjust to regulate the flow rate or power output. Its function is passive rather than active in the context of flow regulation.

Option 4: Runner Blades

The runner blades are the primary moving components of a Francis turbine that convert the kinetic and potential energy of water into mechanical energy. While the shape and design of the runner blades are crucial for the turbine's efficiency, they do not dynamically adjust during operation. The runner blades are fixed in position and rely on the guide vanes to control the flow of water entering the runner.

Conclusion:

In a Francis turbine, the only component that dynamically adjusts to regulate the flow rate and optimize power output under varying load conditions is the guide vanes (Option 1). The spiral casing, draft tube, and runner blades, while essential for the turbine's operation, do not have the capability to dynamically adjust during operation. Understanding the distinct roles of these components is crucial for comprehending the operation and design of Francis turbines.

Explanation:

Solar Panels (Photovoltaic - PV) vs. Concentrating Solar Power (CSP):

Definition: Solar Panels (PV) and Concentrating Solar Power (CSP) are two prominent technologies used to harness solar energy. PV panels directly convert sunlight into electricity using semiconductor materials, while CSP systems use mirrors or lenses to concentrate sunlight onto a receiver to produce heat, which is then converted into electricity using a turbine or engine.

Correct Option Analysis:

The correct option is:

Option 2: They need costly batteries to store power for nighttime use.

This statement highlights one of the major challenges associated with Solar Panels (PV) compared to CSP systems. Solar Panels generate electricity during the daytime when sunlight is available, but they do not inherently have storage capabilities. To ensure a continuous power supply during nighttime or cloudy periods, it is necessary to pair PV systems with energy storage solutions, typically batteries.

While CSP systems often use thermal storage methods (e.g., molten salt) to store heat energy for later use, PV systems rely on batteries, which are expensive and can significantly increase the overall cost of the system. The integration of batteries into PV setups also presents challenges related to scalability, efficiency, and environmental concerns due to the mining and disposal of battery materials.

Detailed Explanation:

1. The Need for Energy Storage:

• Solar Panels (PV) produce electricity only when sunlight is available, meaning their output is intermittent and depends on the weather and time of day.
• To achieve a stable and reliable energy supply, PV systems often require batteries to store excess energy generated during the day for use during nighttime or cloudy periods.
• The cost of batteries, such as lithium-ion batteries, is a significant factor in the overall expense of a PV system. Additionally, battery lifespan and efficiency can impact the long-term viability of the system.

2. Cost Implications:

• Batteries are one of the most expensive components of a PV system. Their cost can rival or even exceed the cost of the solar panels themselves.
• The maintenance and replacement of batteries add to the operational costs, making PV systems less economically competitive compared to CSP in some cases.
• The environmental impact of battery production and disposal is another concern, as the extraction of materials like lithium and cobalt can cause ecological harm.

3. Comparison with CSP:

• CSP systems typically use thermal storage techniques, such as molten salt storage, which are more cost-effective and environmentally friendly compared to batteries.
• Thermal storage allows CSP systems to generate power even after sunset, providing a more consistent and reliable energy output.

4. Advances in Battery Technology:

• Research and development in battery technology, including solid-state batteries and flow batteries, aim to reduce costs and improve efficiency, which could make PV systems more competitive in the future.
• Despite these advancements, the current reliance on costly batteries remains a significant challenge for PV systems.

Conclusion:

Option 2 correctly identifies the major challenge of Solar Panels (PV) needing costly batteries for nighttime energy storage. This reliance on batteries increases the cost and complexity of PV systems compared to CSP systems, which often utilize more efficient and cost-effective thermal storage solutions.

Additional Information

Analysis of Other Options:

Option 1: They have lots of moving parts, making maintenance costly.

This statement is incorrect for Solar Panels (PV). PV systems have no moving parts, which is one of their advantages over CSP systems. CSP systems involve components like mirrors, tracking systems, and turbines, which require regular maintenance and have higher operational costs due to their mechanical complexity.

Option 3: They completely stop working on cloudy days.

This statement is misleading. While the efficiency of PV systems decreases on cloudy days due to reduced sunlight, they do not "completely stop working." Advanced PV panels can still generate some electricity under diffuse light conditions, although at a lower output. CSP systems, on the other hand, rely on direct sunlight for optimal performance and are more affected by cloudy weather.

Option 4: They need high-tech factories to be made.

This statement is partially correct but not unique to PV systems. Both PV and CSP technologies require specialized manufacturing facilities. PV panels involve semiconductor fabrication, which necessitates high-tech factories, but CSP systems also require precision engineering for mirrors, receivers, and tracking systems. Therefore, this challenge is not exclusive to PV systems.

Conclusion:

While all the options highlight challenges related to solar technologies, Option 2 accurately identifies the significant issue of costly batteries for energy storage in PV systems, making it the correct choice. Understanding these challenges is essential for selecting the appropriate solar technology based on specific needs and conditions.

Explanation:

Hydropower Plant Categories

Definition: Hydropower plants are categorized based on their installed capacity, which is the maximum amount of electricity they can generate under ideal conditions. These categories help classify hydropower projects for planning, design, and regulatory purposes. The primary classifications are Small hydro, Mini hydro, Medium hydro, and Large hydro. Each category is defined by specific capacity ranges, which can vary slightly depending on the country or organization.

Correct Option Analysis:

The correct option is:

Option 1: Small hydro

Why is this correct?

In most international classifications, a hydropower plant with an installed capacity between 1 MW and 25 MW is categorized as a Small hydro project. Since the given hydropower plant has an installed capacity of 10 MW, it falls squarely within this range. Small hydro projects are typically used to supply power to local communities or industries and often have a minimal environmental impact compared to larger projects.

Characteristics of Small Hydro Projects:

• Capacity Range: Typically between 1 MW and 25 MW.
• Applications: Often used for rural electrification, decentralized power generation, or small industrial purposes.
• Environmental Impact: Generally lower than larger hydropower projects due to their smaller scale and less invasive construction requirements.
• Advantages:
  • Can be developed in remote areas to provide localized power solutions.
  • Lower initial investment and shorter construction times compared to large hydropower projects.
  • Can often operate without the need for large dams, preserving local ecosystems.
• Disadvantages:
  • Limited capacity means it may not be suitable for regions with high power demands.
  • May be less efficient in terms of energy production compared to larger hydropower plants.

Conclusion: Since the given hydropower plant has an installed capacity of 10 MW, it falls into the category of Small hydro. This classification is widely recognized and aligns with international standards for hydropower categorization.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 2: Mini hydro

Mini hydro projects typically have an installed capacity of less than 1 MW (or sometimes up to 2 MW, depending on specific definitions). These systems are smaller than small hydro projects and are often used for localized, off-grid power generation in rural or isolated areas. Since the given plant has a capacity of 10 MW, it does not fall under this category.

Option 3: Medium hydro

Medium hydro projects generally have capacities ranging from 25 MW to 100 MW. These plants are larger than small hydro projects and are used to supply power to larger grids or industrial facilities. The 10 MW capacity of the given plant is significantly below this range, so it does not qualify as a medium hydro project.

Option 4: Large hydro

Large hydro projects have an installed capacity exceeding 100 MW. These are massive infrastructure projects that often involve significant dam construction and reservoir creation. They are used for large-scale power generation and contribute to national or regional grids. Since the given plant has a capacity of only 10 MW, it does not fall under this category.

Conclusion:

The classification of hydropower plants is essential for understanding their scale, applications, and potential impacts. The given plant, with an installed capacity of 10 MW, clearly falls under the category of Small hydro, as defined by widely accepted standards. This classification highlights the plant's suitability for localized power generation with minimal environmental disruption compared to larger hydropower projects.

Explanation:

The Maximum Fault Current and Cut-off Current

Definition: The maximum fault current reached before a fuse melts is referred to as the cut-off current. It represents the peak current value that the fuse allows to pass during a fault condition before it interrupts the circuit. This parameter is crucial in designing protective devices and ensuring the safety of electrical systems.

Working Principle: Fuses are protective devices designed to safeguard electrical circuits from overcurrent conditions. When a fault occurs (e.g., a short circuit or an overload), the current in the circuit rises rapidly. If this current exceeds the rated capacity of the fuse, the fuse element heats up and melts, breaking the circuit and preventing further damage to the system.

However, before the fuse melts, the current often reaches a peak value. This peak value is called the cut-off current. The time required for the fuse to melt depends on the current's magnitude and the fuse's characteristics, such as its material and design. The cut-off current is an essential parameter because it determines the maximum stress imposed on the electrical system during a fault.

Advantages of Considering Cut-off Current:

• Protects electrical components from thermal and mechanical damage caused by excessive current.
• Helps in designing robust and reliable protective devices for electrical systems.
• Ensures the safety of both the equipment and personnel by interrupting fault currents swiftly.

Applications: The concept of cut-off current is widely used in electrical engineering, particularly in the design and selection of protective devices like fuses and circuit breakers. It is also crucial in determining the withstand capability of electrical components during fault conditions.

Correct Option Analysis:

The correct option is:

Option 3: Cut-off current

This option accurately describes the phenomenon where the maximum fault current is reached before a fuse melts. The term "cut-off current" is used to denote this peak value, which is a critical parameter in the functioning of fuses and other protective devices. The fuse interrupts the circuit as soon as this current is reached, protecting the system from further damage.

Important Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Rupturing Current

Rupturing current refers to the maximum current that a protective device, such as a fuse or circuit breaker, can safely interrupt without causing damage to itself or the system. While related to the concept of cut-off current, rupturing current is not the same. The cut-off current pertains to the peak current value just before the fuse melts, whereas rupturing current is the maximum current the device can handle while breaking the circuit.

Option 2: Holding Current

Holding current is a term commonly associated with devices like thyristors or SCRs (Silicon Controlled Rectifiers). It represents the minimum current required to keep the device in a conducting state. If the current falls below this value, the device turns off. This term is unrelated to the operation of fuses and fault currents.

Option 4: Peak Current

Peak current refers to the highest instantaneous current value in an electrical circuit during its normal operation or under fault conditions. While the cut-off current is a type of peak current specific to fault conditions in fuses, not all peak currents are cut-off currents. Therefore, this option is not precise in the context of the given question.

Option 5: Not Provided

This option is not relevant as it does not describe any specific phenomenon related to the operation of fuses or fault currents.

Conclusion:

The concept of cut-off current is pivotal in understanding the operation of fuses and other protective devices in electrical systems. It represents the peak fault current that occurs just before a fuse melts, safeguarding the circuit from further damage. By analyzing the other options, it is evident that the term "cut-off current" provides the most accurate description of the phenomenon in question. Electrical engineers must carefully consider this parameter when designing and selecting protective devices to ensure the safety and reliability of electrical systems.

Explanation:

Underground vs. Overhead Power Systems

Definition: Power distribution systems can be broadly classified into overhead and underground systems. An overhead system involves power lines that are installed above ground, typically using poles or towers. An underground system, on the other hand, involves cables that are laid below the surface of the ground. Each system has its own advantages and disadvantages, and the choice between them depends on factors such as cost, safety, reliability, and aesthetics.

Correct Option Analysis:

The correct option for the given question is:

Option 4: Tapping for loads and service mains is easier.

This option is NOT an advantage of the underground system over the overhead system. In fact, this is one of the main disadvantages of underground systems. The process of tapping into underground cables for additional loads or service mains is significantly more challenging compared to overhead systems. Here's why:

• Complex Installation: Underground cables are buried beneath the surface, often encased in protective conduits or ducts. To tap into these cables, excavation work is required, which can be time-consuming, labor-intensive, and costly.
• Specialized Equipment: Unlike overhead lines, where tapping can be done relatively easily using basic tools, underground systems require specialized equipment and skilled personnel to access and modify the cables.
• Disruption: Excavation work for tapping into underground cables can cause significant disruption to traffic, pedestrians, and the surrounding environment. It may also require obtaining permits from local authorities.
• Risk of Damage: During the process of tapping, there is a risk of damaging the existing underground cables, which can lead to power outages and expensive repairs.

In contrast, tapping for loads and service mains is much easier in overhead systems. The lines are easily accessible, and modifications can be made without the need for excavation or specialized equipment. This accessibility is one of the key advantages of overhead systems over underground systems.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Reduced voltage drops.

This is an advantage of underground systems over overhead systems. Underground cables are typically shorter and have better insulation, which reduces resistance and minimizes voltage drops. Additionally, underground systems are less affected by environmental factors such as temperature and weather conditions, which can impact the resistance and efficiency of overhead lines.

Option 2: Better aesthetics and safety.

Underground systems offer significant advantages in terms of aesthetics and safety. Since the cables are buried, they do not obstruct the visual landscape, making them ideal for urban areas, residential neighborhoods, and locations with strict aesthetic requirements. From a safety perspective, underground systems eliminate the risk of accidental contact with live wires and are less prone to damage from storms, falling trees, or other external factors.

Option 3: Lower chances of power failures.

Underground systems are generally more reliable than overhead systems. They are less susceptible to power failures caused by environmental factors such as high winds, lightning, and snowstorms. Additionally, underground cables are protected from physical damage caused by animals or human activities, further reducing the likelihood of power outages.

Option 4: Tapping for loads and service mains is easier.

As previously explained, this is NOT an advantage of underground systems. Tapping into underground cables is more complex, costly, and disruptive compared to overhead systems.

Conclusion:

While underground power systems offer numerous advantages, such as reduced voltage drops, better aesthetics, enhanced safety, and lower chances of power failures, they are not without their drawbacks. One of the significant disadvantages is the difficulty in tapping for loads and service mains, which is why Option 4 is the correct answer to the question. Understanding the trade-offs between underground and overhead systems is crucial for making informed decisions in power distribution planning and infrastructure development.

Tarapur Atomic Power Station:

• Tarapur Atomic Power station is located in Tarapur, Maharashtra.
• It was the first commercial atomic power station of India commissioned on 28th October 1969.
• It was commissioned under 123 agreements signed between India, the United States and International Atomic Energy Agency. 
• The station is operated by the National power corporation of India.

 

Power plant	Type of reactor
Kudankulam Nuclear Power Plant	WWER (Water-Water Energetic Reactor)
Tarapur Atomic Power Station	BWR (Boiling Water Reactor)
Narora Atomic Power Station	PHWR (Pressurised Heavy Water Reactor)
Kaiga Atomic Power Station	PHWR (Pressurised Heavy Water Reactor)

About Tarapur Atomic Power Station:

• Tarapur Atomic Power station is located in Tarapur, Maharashtra.
• It was the first commercial atomic power station of India commissioned on 28th October 1969.
• It was commissioned under 123 agreements signed between India, the United States, and International Atomic Energy Agency. 
• The station is operated by the National power corporation of India.

​

 

Nuclear Power Plant	State of location	Opened in
Kudankulam	Tamil Nadu	1998
Tarapore	Maharashtra	1969
Kaiga	Karnataka	2000
Narora	Uttar Pradesh	1991

 

Nuclear power plant	State	Capacity
Tarapur Nuclear power plant	Maharashtra	1400 MW
Rawatbhata Nuclear power plant	Rajasthan	1180 MW
Kudankulam Nuclear power plant	Tamil Nadu	2000 MW
Kaiga Nuclear power plant	Karnataka	880 MW

The minimum clearance distance that equipment should be kept away from power lines of different voltage levels is shown in below table.

Voltage	Minimum clearance distance (feet)
Up to 50 kV	10
50 to 200 kV	15
200 to 350 kV	20
350 to 500 kV	25
500 to 750 kV	35
750 to 1000 kV	45
Over 1000 kV	50

Transmission lines are classified based on three criteria.

a) Length of transmission line

b) Operating voltage

c) Effect of capacitance

The table below summarizes the classification of transmission lines.

Transmission Lines	Length of transmission line	Operating voltage	Effect of capacitance
Short transmission line	(0 - 80) km	(0 - 20) kV	'C' is not considered
Medium transmission line	(80 - 200) km	(20 - 100) kV	'C' is lumped.
Long transmission line	(> 200) km	(> 100) kV	'C' is distributed

Concept:

Load factor:

The load factor is the ratio of average energy consumed to maximum demand.

Load factor = average energy consumed / maximimum energy consumed

Calculation:

Given load factor = 0.5

Average energy consumed at 0.5 load factor = 600 kWh

Maximum energy consumed = \(\frac{{600}}{{0.5}}\) = 1200 kWh

Now maximum energy consumed is constant and load factor is increased to 0.8

Average energy consumed = load factor × maximum energy consumed

= 0.8 × 1200

= 960 kWh

Load factor \(=\frac{average~demand}{maximum~demand}\)

Average demand = (50) (0.6) = 30 MW

Plant capacity factor \(=\frac{average~demand~}{plant~capacity}\)

Plant capacity \(=\frac{30}{0.5}=60~MW\)

Reserve capacity = Plant Capacity – Maximum Demand = 60 - 50 = 10 MW

BIS Symbol	Equipment
	Distribution fuse board without switches
	Distribution fuse board with switches
	Main fuse board without switches
	Main fuse board with switches

 

CONCEPT:

Nuclear reactor:

• It is a device in which a nuclear reaction is initiated, maintained, and controlled.
• It works on the principle of controlled chain reaction and provides energy at a constant rate.

EXPLANATION:

• The moderator's function is to slow down the fast-moving secondary neutrons produced during the fission.
• The material of the moderator should be light and it should not absorb neutrons.
• Usually, heavy water, graphite, deuterium, and paraffin, etc. can act as moderators.
• These moderators are rich in protons. When fast-moving neutrons collide head-on with the protons of moderator substances, their energies are interchanged and thus the neutrons are slowed down.
• Such neutrons are called thermal neutrons which cause fission of U235 in the fuel. 

The following types of cables are generally used for 3-phase service:

1. Belted cables - up to 11 kV

2. Screened cables - from 22 kV to 66 kV

3. Pressure cables - beyond 66 kV

Belted cables:

• These cables are used for voltages up to 11 kV but in extraordinary cases, their use may be extended up to 22 kV
• The belted type construction is suitable only for low and medium voltages as the electrostatic stresses developed in the cables for these voltages are more or less radial i.e., across the insulation
• For high voltages (beyond 22 kV), the tangential stresses also become important
• These stresses act along the layers of paper insulation
• As the insulation resistance of paper is quite small along the layers, therefore, tangential stresses set up leakage current along the layers of paper insulation
• The leakage current causes local heating, resulting in the risk of breakdown of insulation at any moment

Recovery Voltage:

The RMS voltage that appears across the circuit breaker contacts after final arc interruption (when breaker opens) is called “recovery voltage”

Restriking Voltage:

It may be defined as the voltages that appears across the breaking contact at the instant of arc extinction

Active Recovery Voltage:

It may be defined as the instantaneous recovery voltage at the instant of arc extinction

Arc Voltage:

It may be defined as the voltages that appears across the contact during the arcing period, when the current flow is maintained in the form of an arc. It assumes low value except for the point at which the voltage rises rapidly to a peak value and current reaches to zero.