Top Interview Questions with answer
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What is Fusion and fission?
Answer: Fusion and fission are both nuclear processes that release enormous amounts of energy, Fusion and fission are two types of nuclear reactions that release energy, but they work in different ways:
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Nuclear Fusion:
- Definition: Fusion is the process where two light atomic nuclei combine to form a heavier nucleus. During this process, a large amount of energy is released.
- How It Works: In fusion, when two hydrogen nuclei (or isotopes like deuterium and tritium) come close enough, they combine to form helium, releasing energy in the form of heat and light.
- Example: The Sun and other stars generate energy through fusion. The Sun primarily fuses hydrogen atoms to form helium.
- Energy Production: Fusion releases a large amount of energy, much more than fission. However, achieving controlled fusion on Earth for power generation is a significant challenge due to the extremely high temperatures and pressures required.
When light nuclei fuse to form a heavier nucleus, the mass of the product nucleus is slightly less than the sum of the masses of the original nuclei. This “missing” mass is converted into a tremendous amount of energy, as described by Einstein’s famous equation, .
- Waste Products: Fusion reactions generally produce less radioactive waste compared to fission, and the byproducts are often stable or have short half-lives (e.g., helium).
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Nuclear Fission:
- Definition: Fission is the process in which a heavy atomic nucleus splits into two lighter nuclei, releasing energy.
- How It Works: In fission, a heavy atom (like uranium-235 or plutonium-239) absorbs a neutron, becomes unstable, and splits into smaller nuclei, releasing more neutrons and a large amount of energy.
- Example: Nuclear reactors use fission to generate energy. The fission of uranium-235 in a nuclear power plant releases energy that heats water to produce steam and drive turbines.
- Energy Production: Fission also releases a lot of energy, but not as much as fusion. It is easier to control compared to fusion, which is why fission is used in current nuclear reactors and weapons.
- Waste Products: Fission produces radioactive waste products, which can have long half-lives and pose environmental challenges.
Here’s a table summarizing the key differences:
| Feature | Nuclear Fission | Nuclear Fusion |
| Process | Splitting of a heavy nucleus | Combining of light nuclei |
| Starting Material | Heavy, unstable nuclei (e.g., Uranium, Plutonium) | Light nuclei (e.g., Hydrogen isotopes) |
| Initiation | Often initiated by a neutron | Requires extremely high temperatures and pressures |
| Energy Release | Large amount of energy released | Even larger amount of energy released |
| Chain Reaction | Possible and utilized | Not naturally self-sustaining on Earth (currently) |
| Natural Occurrence | Does not occur naturally (except some rare spontaneous fission) | Powers stars (e.g., the Sun) |
| Waste Products | Radioactive waste products with long half-lives | Generally produces less radioactive waste |
| Current Use | Nuclear power plants, atomic bombs | Primarily in research and experimental stages for power generation, thermonuclear weapons |
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What is unity power factor?
Answer: Unity power factor (power factor = 1) occurs when the current and voltage are in phase, meaning all the apparent power is converted to real power. This is the ideal situation.
3. What are the causes of a low power factor?
Answer:
A low power factor is often caused by inductive loads, such as motors, transformers, and fluorescent lights. These devices cause the current to lag behind the voltage, leading to a low power factor. The major causes of low power factor include:
- Inductive loads: These loads consume reactive power, which causes the current to lag.
- Overloaded equipment: When electrical devices are operating inefficiently, the power factor can decrease.
- Poorly maintained equipment: Faulty or old equipment can also lead to a decrease in power factor.
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What is the role of a Star-Delta starter?
Answer:
A Star-Delta starter is a device used to reduce the inrush current during the starting of an induction motor. The starter initially connects the motor windings in Star to reduce the voltage and starting current. After a preset time delay or when the motor reaches a certain speed, the connection is changed to Delta to allow the motor to run at full capacity.
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Tell us Different parts of Electrical Substation.
Answer:
An electrical substation is a critical part of the electrical power system that is responsible for transforming voltage levels, ensuring the safe distribution of electricity, and providing protection to the system. There are several key components in a substation, each playing an important role in the overall operation. Here are the main parts of an electrical substation:
1. Transformers
- Function: Transformers are used to step up (increase) or step down (decrease) the voltage levels. They are essential for ensuring that electricity is transmitted efficiently over long distances and then converted to usable levels for distribution to homes and businesses.
- Types: There are typically step-up transformers (raise voltage) and step-down transformers (reduce voltage).
2. Circuit Breakers
- Function: Circuit breakers are safety devices that protect the electrical circuits from overloads or short circuits. They automatically disconnect parts of the system in case of faults, preventing damage to equipment and ensuring safety.
- Types: Air circuit breakers (ACBs), vacuum circuit breakers, and SF6 circuit breakers.
3. Switchgear
- Function: Switchgear refers to a collection of electrical disconnects, circuit breakers, and fuses that can be manually or automatically operated to isolate parts of the system. It is used to protect, control, and switch the power flow in the substation.
- Types: High-voltage and low-voltage switchgear.
4. Busbars
- Function: Busbars are metallic bars (usually made of copper or aluminum) that act as a common connection point for multiple circuits within the substation. They help distribute power from the incoming transmission lines to different outgoing feeders.
- Types: Single busbar, double busbar, and ring busbar configurations, depending on the complexity and reliability needs.
5. Disconnectors (Isolators)
- Function: Disconnectors (also known as isolators) are used to isolate parts of the circuit when necessary, particularly during maintenance. They are typically operated when the system is de-energized.
- Difference from Circuit Breakers: Disconnectors cannot break current under load, unlike circuit breakers, which can interrupt the current under fault conditions.
6. Lightning Arresters
- Function: Lightning arresters are used to protect the substation’s equipment from damage caused by lightning strikes. They divert the high-voltage surge (from a lightning strike) safely to the ground.
- Types: Metal oxide varistor (MOV) type, and gap type.
7. Current Transformers (CTs)
- Function: Current transformers are used for measuring and monitoring current in the system. They convert high currents to lower, manageable levels for measurement and protection purposes.
- Application: Used in metering and in protective relaying schemes.
8. Voltage Transformers (VTs) or Potential Transformers (PTs)
- Function: Voltage transformers step down high voltages to safe, measurable levels, typically used for voltage measurement and protection purposes.
- Application: Used in metering, protection, and control systems.
9. Protection Relays
- Function: Protection relays are devices that monitor the electrical parameters (like current, voltage, and frequency) of the substation and the distribution system. If any fault occurs, relays send a signal to the circuit breaker to isolate the faulty section.
- Types: Overcurrent relays, differential relays, distance relays, etc.
10. Control Panels
- Function: The control panels are used for monitoring and controlling the operation of the substation. Operators can view data, adjust settings, and manage the various components of the substation from these panels.
11. Batteries and Battery Charger
- Function: The battery system ensures an uninterrupted power supply to critical equipment like protection relays, control systems, and communication devices in case of a power outage or failure of the main power source.
- Application: The battery charger keeps the batteries charged, and the batteries provide power during emergencies.
12. Earthing System
- Function: The earthing (or grounding) system is crucial for safety. It ensures that electrical currents are safely directed to the ground in case of faults or system malfunctions.
- Purpose: Prevents electrocution and damage to equipment by stabilizing the voltage levels.
13. Shunt Capacitors
- Function: Shunt capacitors are used to improve the power factor in the system by providing reactive power compensation. They help in reducing losses and improving the efficiency of power transmission.
- Application: Common in long-distance transmission systems to improve voltage stability and reduce reactive power.
14. Surge Arresters
- Function: Surge arresters are designed to protect electrical equipment from transient overvoltages (such as those caused by lightning strikes or switching operations). They absorb and dissipate excess voltage.
15. Power Distribution Panels
- Function: These panels help manage and distribute electricity to various parts of the grid or the facility served by the substation. They are used to control and monitor the power flows within the substation.
16. Cooling Systems
- Function: Many components of the substation, especially transformers, generate a lot of heat. Cooling systems (e.g., fans, oil-based cooling) are used to dissipate this heat to prevent damage to equipment.
17. Communication Systems
- Function: Communication equipment like telecommunication systems, SCADA (Supervisory Control and Data Acquisition) systems, and remote terminal units (RTUs) enable operators to monitor and control substations from remote locations.
18. Fuses
- Function: Fuses are protective devices that automatically disconnect a part of the system in the event of excessive current. They are typically used in low-voltage circuits.
Conclusion:
An electrical substation integrates several components designed to ensure the smooth, safe, and efficient transmission and distribution of electrical power. These parts work together to regulate voltage levels, prevent system failures, and protect against electrical faults.
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What is HVDC? Where and why it used?
HVDC stands for High Voltage Direct Current. It is a technology used to transmit electricity over long distances using direct current (DC) rather than alternating current (AC). HVDC systems are used when long-distance power transmission is required, and they offer advantages over traditional AC systems in certain situations.
Key Features of HVDC:
- Direct Current Transmission: Unlike traditional AC systems where current alternates direction, HVDC systems use a unidirectional flow of current.
- High Voltage: The electricity is transmitted at a very high voltage (hundreds of kilovolts) to reduce energy losses during transmission.
- Conversion Stations: HVDC requires conversion stations at both ends of the transmission line — one to convert AC to DC (rectifier station) and one to convert DC back to AC (inverter station).
Where HVDC is used:
- Long-Distance Power Transmission: HVDC is especially useful for transmitting electricity over long distances, particularly when the distance is greater than 600 km (or 400 miles).
- Example: HVDC lines are often used for underwater or underground cables that connect grids in different regions or even different countries (e.g., the NorNed link between Norway and the Netherlands).
- Interconnection of Power Grids: HVDC is used to link two separate power grids, which may operate at different frequencies (e.g., connecting an AC grid operating at 50 Hz with one at 60 Hz).
- Example: HVDC is used in the China-Siberia interconnection, where it connects the electrical grids of China and Russia.
- Integration of Renewable Energy: HVDC is increasingly being used to transmit electricity from renewable energy sources (such as offshore wind farms) to land-based grids. Offshore wind farms, for instance, generate DC power, so it is more efficient to transmit it as HVDC before converting it to AC for distribution.
- Example: The Hornsea One offshore wind farm in the UK connects to the grid using an HVDC system.
- Underground or Underwater Cables: HVDC is often used for subsea or underground cables, where AC transmission would face significant losses due to the capacitive reactance of the cables over long distances.
- Example: The Baltic Cable connecting Sweden and Germany uses HVDC for underwater transmission.
- Urban or Remote Area Supply: HVDC can be used in densely populated or remote areas to avoid the complexities and cost of AC distribution systems.
Why HVDC is used:
- Reduced Transmission Losses: HVDC transmission lines have lower losses over long distances compared to AC transmission. The reason is that AC transmission faces reactive power losses due to inductive and capacitive effects, whereas DC transmission doesn’t have these effects.
- More Efficient for Long Distances: When transmitting electricity over very long distances (over 600-800 km), HVDC systems are more efficient in terms of energy loss. The ability to use HVDC is a significant advantage, especially when connecting far-flung regions.
- Cost-Effective Over Long Distances: While the initial cost of converting stations for HVDC can be higher, the reduced energy losses and maintenance costs over long distances make it cost-effective in the long run.
- Stability and Control: HVDC systems provide better control over power flow compared to AC systems. HVDC can control the direction of power flow, which helps in stabilizing grids and preventing large-scale blackouts or fluctuations.
- Interconnecting Different Power Grids: Since AC grids operate at different frequencies (50 Hz in most parts of the world, 60 Hz in others), HVDC allows the connection of grids with different frequencies, offering more flexibility and reliability in global electricity networks.
- Power Transfer in Weak Grids: HVDC is particularly useful when connecting weak grids or regions with less robust infrastructure. It helps in stabilizing the overall power network.
- Minimal Electromagnetic Interference (EMI): HVDC systems generate less electromagnetic interference compared to high-voltage AC systems. This is especially important in urban areas or in sensitive environments.
- Control over Power Flow: HVDC systems allow operators to have better control over the flow of electricity, which is particularly beneficial for stabilizing grids and for energy trading between different regions.
- Integration of Renewable Energy: HVDC is well-suited for integrating renewable energy sources like wind and solar, especially from remote locations (offshore or rural). These sources often generate DC power, and HVDC transmission minimizes conversion losses when transporting energy to the grid.
Challenges of HVDC:
- High Initial Cost: The installation of HVDC systems, especially the converter stations, can be more expensive than AC systems. However, as mentioned, the operational savings can outweigh this initial investment over time.
- Complex Conversion Stations: The need for AC-to-DC and DC-to-AC conversion stations makes the system more complex than traditional AC transmission.
- Limited to Point-to-Point Transmission: While HVDC is excellent for point-to-point transmission, it is not as flexible as AC in terms of branching and connecting multiple points in a network.
Conclusion:
HVDC is a powerful and efficient method for long-distance electricity transmission, especially in applications involving large-scale energy transfers, interconnections between different power grids, and renewable energy integration. While it involves higher initial costs, the benefits of lower energy losses, stability, and control make it an increasingly important technology in modern power transmission systems.
