Top EEE Viva Question & Answer

1. What is LT panel? Describe it details.

Answer: An LT (Low Tension) panel is an electrical distribution panel used in low-voltage electrical systems, typically in the range of 230V to 415V, for distributing electrical power in commercial, industrial, and residential buildings. It serves as a important component in managing and distributing electricity to various parts of a building or facility, ensuring safe operation and protecting the electrical system.

Key Features of an LT Panel:

1. Power Distribution: It distributes electrical power from the main source (like a transformer or electrical substation) to various circuits or loads within a facility.
2. Protection: LT panels incorporate protection devices such as circuit breakers, fuses, or relays to safeguard the system from faults, short circuits, and overloads.
3. Control: The LT panel often contains control mechanisms such as switches, meters, and indicators for monitoring and controlling the electrical system’s operation.
4. Metering: It may include provisions for metering electricity usage, which helps in managing energy consumption and billing.

Types of LT Panels:

• • Main LT Panel: Directly connected to the main power supply, controlling power distribution to sub-panels.
  • Feeder Panels: Distribute power to different areas or departments.
  • Sub-Distribution Panels: Used to supply smaller units or areas with specific electrical needs.

Applications of LT Panels:

• Residential Buildings: For distributing power to lighting, air conditioning, and appliances.
• Commercial Buildings: To manage and distribute power to offices, elevators, lighting, HVAC systems, etc.
• Industrial Plants: In factories or plants for distributing power to machinery, lighting, and other equipment.

Overall, LT panels are essential for efficient and safe electrical distribution and protection in low-voltage electrical systems.

2. Deference between clip on meter and multi meter

Answer: The clip-on meter and the multi meter are both electrical measurement devices, but they are designed for different purposes and offer distinct functionalities.

Clip-on Meter:

It also called Clamp Meter or Clamp-on Ammeter. Primarily used for measuring current in a circuit, without the need to disconnect or break the circuit. It Works by clamping around a conductor (wire) to measure the current flowing through it using electromagnetic induction and Can measure AC current (and some models can measure DC current) by detecting the magnetic field generated by the current. Clamp meters can also measure voltage, resistance, and frequency. Clip-on Meter Generally provides less accuracy compared to a multi meter, especially for low current or DC current measurements. It Very useful for quick and non-invasive current measurements in live circuits.

Multi meter:

Multi meter is a versatile tool that can measure multiple electrical parameters, including voltage (AC/DC), current (AC/DC), resistance, and sometimes capacitance, frequency, and diode testing. Requires the circuit to be open for current measurements (i.e., you need to place the multi meter in series with the circuit), but it can also measure voltage by connecting across two points in parallel. Multi meter Measures a wider range of electrical quantities such as voltage (both AC and DC), current (AC and DC), and resistance. It usually used for smaller-scale current measurements (milli ampere to ampere range), but can handle more precise measurements for voltage and resistance. Current measurements are taken by connecting the multi meter in series with the load, requiring the circuit to be opened. Multimeter Provides high accuracy for all types of measurements, especially in low current, voltage, and resistance applications. Ideal for precise measurements of small components or low-voltage circuits.

Typically both are compact and portable, fitting easily in a tool bag and is convenient for carrying around for various types of electrical tests.

Usage and Application:

• Clip-on Meter:
  • Ideal for measuring current in live circuits without interrupting the system.
  • Commonly used by electricians and technicians when troubleshooting or monitoring electrical systems.
  • Provides a non-invasive method to check current, which is particularly useful when you want to measure current in large wires or circuits where it’s difficult or unsafe to disconnect the wires.
• Multimeter:
  • Ideal for a wide range of measurements, especially for voltage and resistance testing in both AC and DC circuits.
  • Used for testing and diagnosing electrical circuits, checking battery voltages, resistance in components, and checking the health of circuits.
  • Commonly used in electronics, household appliances, and low-voltage circuits.

3. How do we determine whether a transmission line will be 132kv or 230kv or 400kv?

Answer: The voltage rating of a transmission line whether it’s 132 kV, 230 kV, or 400 kV is determined by several factors, all of which are related to the power transmission requirements, distance, and the characteristics of the network it serves.

• 132 kV: Typically used for local or regional transmission in areas or sub-transmission networks with moderate power demands and shorter distances.
• 230 kV: Used for larger regions, medium to long distances, and higher power requirements.
• 400 kV: Used for long-distance, high-capacity transmission over large areas or between major power grids.

1. Power Transmission Capacity

• 132 kV: Often used for regional or sub-transmission networks where the distance is moderate, and power requirements are not extremely high.
• 230 kV: Typically used for larger regional transmission systems, especially when the distance is greater or the power demand is higher.
• 400 kV: Used for long-distance, high-power transmission, especially when the demand is very high, and efficiency is crucial.

2. Distance

• 132 kV: Suitable for shorter distances or less densely populated areas where the power demand is lower.
• 230 kV: Used for medium to long distances, but typically within a more localized network or regional grid.
• 400 kV: For very long distances, often crossing states or countries, requiring high capacity to minimize losses over the transmission path.

3. Load Requirements (Power Demand)

• 132 kV: Suitable for lower power demands, often for distribution to smaller urban areas or towns.
• 230 kV: Typically used when there is a moderate demand, often used for interconnecting power grids at regional levels.
• 400 kV: Used for high-demand areas or for major power stations that need to transmit large amounts of power across long distances.

4. Grid Integration

• 132 kV and 230 kV: Typically operate at regional or sub-regional levels, interconnecting power stations within a particular area.
• 400 kV: Often part of a national or cross-border grid, used to balance supply and demand over larger regions.

5. Economic Factors

While higher voltages can transmit more power with fewer losses, they also require more expensive infrastructure. The cost of building and maintaining transmission lines increases with the voltage, so economic considerations play a role in determining the voltage level.

4. What is an Ideal Transformer?

Answer:  An ideal transformer is an imaginary transformer in which no losses occur at all. An ideal transformer assumes that there are no hysteresis or eddy current losses in the magnetic core and No Copper Losses (There is no resistance in the windings). In other words, the transformer Input power is equal to the output power of the transformer i.e. they have 100% efficiency. It is just a theoretical transformer because there must be some losses in a real transformer.

The ideal transformer operates by stepping up or stepping down the voltage according to the turns ratio of the primary and secondary windings. If V₁ is the voltage on the primary coil and V₂ is the voltage on the secondary coil, the relationship is: V1/V2=N1/N2.  Where N1 and N2​ are the number of turns on the primary and secondary coils, respectively.

Power Conservation: P_primary ​= P_secondary​

The frequency of the AC voltage remains the same on both the primary and secondary sides. An ideal transformer does not alter the frequency of the electrical signal.

5. What is of Ohm’s Law? What are the limitations of ohm’s law? Where are Applications of Ohm’s Law?

Ohm’s Law states that, the current (I) flowing through a conductor is directly proportional to the voltage (V) applied across the conductor and inversely proportional to the resistance (R) of the conductor.

Mathematically, it is expressed as: V=I×R

Where:

• V is the voltage (in volts, V),
• I is the current (in amperes, A),
• R is the resistance (in ohms, Ω).

Limitations of Ohm’s Law:

1. Non-linearity: Does not apply to non-linear materials such as semiconductors, diodes, and transistors.
2. Temperature effects: Resistance varies with temperature, making Ohm’s Law inaccurate under temperature variations.
3. Frequency effects: In AC circuits, impedance (not resistance) must be used, as the relationship between current and voltage is frequency-dependent.
4. High electric fields: At extremely high voltages or electric fields, Ohm’s Law may not apply due to breakdown or non-ohmic behavior.
5. Superconductivity: In superconductors, where resistance is zero, Ohm’s Law does not apply.
6. Complex materials: Materials with in homogeneities or varying resistance do not follow Ohm’s Law.
7. Voltage-dependent resistance: Some materials have resistance that changes with voltage, causing deviations from the law.

Practical Applications of Ohm’s Law:

1. Designing Electrical Circuits: Ohm’s Law helps engineers and electricians design circuits by calculating the required voltage, current, or resistance for safe operation.
2. Troubleshooting: By measuring voltage and current, Ohm’s Law can be used to identify problems in circuits, such as faulty components or unexpected resistance.
3. Power Calculations: Ohm’s Law also relates to electrical power. Power (P) can be calculated as: P = V×I = I²×R = V² /R

Where P is the power (in watts).