Best 10 EEE Viva Question & Answer

EEE Viva Question & Answer

1. Why use vibration damper in Electrical transmission line?

Answer: Vibration dampers are used in electrical transmission lines to reduce the mechanical stresses caused by wind-induced vibrations, such as Aeolian vibrations or galloping. These vibrations can lead to wear and fatigue on the conductors, insulators, and other components, potentially causing damage or failure. By absorbing and dissipating vibrational energy, dampers help prevent conductor breakage, reduce maintenance costs, and increase the lifespan and reliability of the transmission system.

Types of Vibration Dampers:

• Stockbridge Dampers: These are the most common type used in transmission lines. They are designed to reduce high-frequency vibrations, such as those caused by wind. Stockbridge dampers consist of a mass-spring system that absorbs and dissipates the vibrational energy.
• Helical Dampers: These are spiral-shaped dampers that are also used to reduce vibrations. They work by increasing the resistance to movement through torsional and flexural forces.

2. Why use ACSR cable instead of copper in electrical transmission line?

Answer:  ACSR (Aluminum Conductor Steel Reinforced) cables are preferred over copper in electrical transmission lines primarily due to their lower cost, lighter weight, and greater strength. Aluminum is significantly cheaper and lighter than copper, reducing both material and installation costs. The steel core in ACSR provides mechanical strength, allowing for longer spans between towers without sagging. While aluminum has lower electrical conductivity than copper, it still offers sufficient performance for high-voltage transmission when designed with larger diameters, making ACSR a cost-effective and durable solution for long-distance power transmission.

3. What is the difference DCS, PLC and SCADA?

Answer:  DCS (Distributed Control System), PLC (Programmable Logic Controller), and SCADA (Supervisory Control and Data Acquisition) are all industrial control systems used in automation, but they serve different purposes and are used in different contexts. Here’s a concise breakdown of the differences:

1. DCS (Distributed Control System):

• Purpose: Primarily used for complex, continuous, and large-scale industrial processes like chemical plants, power plants, or refineries.
• Structure: Involves a network of controllers distributed across the plant or process, where control and monitoring are spread across many devices rather than centralized.
• Functionality: Provides real-time control of process variables (e.g., temperature, pressure, flow) and ensures smooth, continuous operations. It’s designed for complex and highly integrated control tasks.
• Key Feature: Integration of control and monitoring at various levels, with a focus on process optimization and stability.
• Example: A power plant where multiple process variables (boilers, turbines, generators) need continuous, fine-tuned control.

2. PLC (Programmable Logic Controller):

• Purpose: Designed for discrete control tasks, typically used in manufacturing, assembly lines, or automated machinery.
• Structure: A single, centralized controller (though can be networked) that executes pre-programmed logic to control machines or systems based on input/output signals.
• Functionality: Handles digital and analog input/output operations, managing sequences, timing, counting, and logic decisions for automation systems.
• Key Feature: High-speed processing for discrete tasks, with ease of programming and reprogramming.
• Example: Controlling a conveyor belt system or managing the operation of a robotic arm on an assembly line.

3. SCADA (Supervisory Control and Data Acquisition):

• Purpose: Used for supervisory control and monitoring of large-scale industrial operations, typically across geographically distributed locations.
• Structure: A centralized system that gathers data from remote field devices (sensors, PLCs, RTUs) and provides operators with a high-level view of the entire system.
• Functionality: SCADA systems provide real-time data collection, visualization, alarm management, reporting, and the ability to remotely control processes. It’s used for supervisory monitoring rather than direct control.
• Key Feature: Integration of data from various sources, remote monitoring, and control with emphasis on process visibility, trending, and alarms.
• Example: Monitoring and controlling a water treatment plant or an electrical grid across a large geographical area.

Summary of Key Differences:

• DCS: Focuses on continuous, integrated control of complex processes (e.g., chemical, power plants).
• PLC: Best for discrete, high-speed control of machines or automated processes in manufacturing or machinery.
• SCADA: Primarily for supervisory monitoring and control, often over large, distributed systems with remote access to data and operations.

Each system serves a specific role depending on the scale, complexity, and nature of the industrial process being managed.

4. What is optical ground wire in electrical transmission line?

Answer:  An Optical Ground Wire (OPGW) has two primary purposes:

1. Grounding and Lightning Protection:

Like conventional ground wires, OPGW provides electrical grounding and protection against lightning strikes. It serves as a protective shield for the transmission lines by directing lightning strikes safely to the ground, preventing damage to the conductors, insulators, and equipment.

2. Communication and Data Transmission:

Answer:  The key differentiator of OPGW is that it incorporates fiber optic cables within its design, allowing for high-speed, reliable communication between substations and other control centers. This enables the transmission of data such as operational status, monitoring, and control signals, facilitating SCADA systems (Supervisory Control and Data Acquisition), telemetry, and real-time monitoring of the transmission network.

Key Features of OPGW:

• Dual Functionality: It serves both as a grounding conductor and a communication medium.
• Fiber Optic Core: The cable contains optical fibers inside, typically within the metallic wire or as part of the wire’s construction, enabling data transmission over long distances.
• Corrosion Resistance: OPGW cables are designed to be durable, resistant to environmental factors like corrosion, and to withstand high mechanical stresses due to wind or vibration.
• Long-Distance Communication: Because of the fiber optic technology, OPGW allows for very high bandwidth and minimal signal degradation over long distances.

Applications:

• Utility Networks: OPGW is used in overhead power transmission lines to enable communication between remote substations and control centers, while also providing lightning protection.
• Smart Grids: OPGW plays a key role in smart grid systems by facilitating real-time data exchange and monitoring between grid components.

5. Why used capacitor bank in in electrical distribution line?

Answer:  A capacitor bank is used in electrical distribution systems primarily to improve power quality and efficiency. Here are the key reasons why capacitor banks are employed in these systems:

1. Power Factor Correction:

Capacitor banks help correct poor power factor by providing reactive power (leading reactive power) to the system. A low power factor (often caused by inductive loads like motors and transformers) leads to inefficient use of electrical power, resulting in higher losses and increased demand on the power generation and distribution system.

Capacitors generate reactive power (or “leading current”) to counterbalance the lagging reactive power from inductive loads, thereby improving the overall power factor closer to 1 (or unity). This reduces the burden on the generator and improves the efficiency of the system.

2. Voltage Support and Regulation:

Capacitor banks help maintain or raise the voltage in distribution lines, especially under conditions of heavy load.  When reactive power is supplied by the capacitor bank, it compensates for the voltage drop across long distribution lines and helps to maintain stable voltage levels, ensuring consistent power quality for end-users.

3. Reduced Losses in the System:

By improving the power factor and reducing the amount of reactive power flowing in the transmission and distribution lines, capacitor banks help reduce line losses. which in turn reduces I²R losses (resistive losses in the conductors). This makes the system more efficient and reduces energy losses.

4. Increased System Capacity:

With improved power factor and reduced reactive power demand, the distribution system can handle a larger real power load without overloading the equipment.

5. Reduction in Utility Charges:

Many utilities impose penalties for low power factor (typically below 0.9), as it results in less efficient use of their infrastructure. By improving the power factor, capacitor banks can help consumers avoid penalties and reduce their electricity costs.

6. Improved System Reliability:

Capacitor banks contribute to the overall stability and reliability of the power system, especially during peak demand periods or in areas with highly fluctuating loads. Capacitors help to balance the reactive power in the network, preventing excessive voltage fluctuations and potential voltage sags or swells, which can cause equipment malfunctions or disruptions.

 

6. What is the technique to identify 11kv line and 33kv line in electrical system?

Answer:

1. Physical Characteristics:

1. • Conductor Size: 33kV lines typically use larger conductors compared to 11kV lines, as they carry higher currents due to the higher voltage. The conductor diameter and insulation size can give a clue about the voltage.
   • Insulation: 33kV lines often have more insulation (e.g., thicker or more layers) around the conductors to handle higher voltages safely, while 11kV lines have comparatively less insulation.

2. Line Configuration:

1. • Pole Structures: The supporting structures may differ. For example, 33kV lines might use taller, stronger poles or towers to accommodate the heavier conductors and higher voltage levels.
   • Spacing between Conductors: 33kV lines generally have greater spacing between conductors compared to 11kV lines to reduce the risk of flashovers and ensure proper electrical clearance.

3. Equipment Labels and Markings:

1. • Electrical equipment like transformers, switches, and circuit breakers connected to 11kV and 33kV lines are typically labeled with their voltage ratings. These markings can help in identifying the line voltage.

4. Voltage Measurement (Using a Volt Meter or Tester):

1. • Volt meters or voltage testers can be used to measure the potential difference between the conductors. An 11kV line will show a voltage around 11,000 volts, and a 33kV line will show a voltage near 33,000 volts.

5. Local Utility Identification:

1. • In many regions, local utility companies have specific color coding or labeling conventions that help distinguish different voltage levels. For example, certain regions may color-code insulators, transformer housings, or identification plates to denote whether the line is 11kV or 33kV

6. What is the function of anti-pumping in circuit breaker?

Answer: The function of anti-pumping in a circuit breaker is to prevent the breaker from automatically re-closing after it has been tripped and opened. Without anti-pumping, a malfunction or failure in the control circuit could cause the breaker to continuously close and open, which could lead to equipment damage or further electrical faults. Anti-pumping ensures that once the breaker is opened due to a fault, it stays open until manually reset, ensuring safety and preventing unwanted operations.

7. There are a Transformer and an induction machine. Those two have the same supply. For which device the load current will be maximum? And why?

Answer: The motor has max load current compare to that of transformer because the motor consumes real power and the transformer is only producing the working flux and it’s not consuming. Hence the load current in the transformer is because of core loss so it is minimum.

8. Why we do 2 types of earthing on transformer (i.e. 🙂 body earthing & neutral earthing, what is function?

Answer: The two types of earthing are Familiar as Equipment earthing and system earthing. In Equipment earthing: body (non-conducting part) of the equipment should be earthed to safeguard the human beings. System Earthing: In this neutral of the supply source (Transformer or Generator) should be grounded. With this, in case of unbalanced loading neutral will not be shifted.so that unbalanced voltages will not arise. We can protect the equipment also. With size of the equipment (transformer or alternator) and selection of relying system earthing will be further classified into directly earthed, Impedance earthing, resistive (NGRs) earthing.

9. What is the difference between MCB & MCCB, Where it can be used?

Answer: MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit. MCCB is moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition. Under voltage and under frequency may be inbuilt. Normally it is used where normal current is more than 100A.

10. What is Automatic Voltage regulator (AVR)?

Answer: AVR is an abbreviation for Automatic Voltage Regulator. It is important part in Synchronous Generators, it controls the output voltage of the generator by controlling its excitation current. Thus it can control the output Reactive Power of the Generator.