electrical-power-transmission-mcqs

Electrical Power Transmission MCQs

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Electrical Engineering XYZ MCQs on Topic: Electrical Power Transmission. The electrical power transmission system involves the transmission lines which carry the bulk power from generation plants to the distribution networks. At present, the primary source of transmission is alternating current (AC). The primary power transmission levels are 138-765kV, whereas the secondary transmission levels are between 34.5-115 kV. In this section, you’ll learn about Electrical Power Transmission MCQs that are very important for competitive tests such and university exams. While they are vital for concept development you get the technical insight of subject. Let’s start our learning.

Sort the EHV class of voltages

Which of following belongs to EHV class of voltages:

  1. 66 kV-120 kV
  2. 345 kV-765 kV
  3. 120 kV-245 kV
  4. 245 kV-345 kV

Correct answer: 2. 345 kV-765 kV

Explanation: EHV stands for Extra High Voltage, which refers to voltage levels higher than the standard high voltage levels used in power transmission and distribution systems. In general, EHV class of voltages starts from around 345 kV and goes up to several hundred kilovolts.

Looking at the options provided:

  • 66 kV-120 kV: This range falls within the high voltage (HV) class, not EHV.
  • 345 kV-765 kV: This range falls within the EHV class as it starts from 345 kV, which is the minimum voltage mentioned, and goes up to 765 kV, which is well within the EHV range.
  • 120 kV-245 kV: This range falls within the high voltage (HV) class, not EHV.
  • 245 kV-345 kV: This range also falls within the high voltage (HV) class, not EHV.

Therefore, the only range that belongs to the EHV class of voltages among the given options is 345 kV-765 kV.

Recommended reading: https://en.wikipedia.org/wiki/High_voltage#:~:text=In%20electric%20power%20transmission%20engineering,used%20in%20experiments%20in%20physics.

The surge impedance of a transmission line is defined as

The surge impedance of a transmission line is defined as:

  1. √(L/C)
  2. √LC
  3. √(L + C)
  4. √(C – L)

Correct answer: 1. √(L/C)

Explanation: The surge impedance of the line is ration between L and C and it explains that if a purely resistive load is connected to the load side of any line, then the voltage surge introduced at input will be completely absorbed on the output.

The surge impedance of a transmission line represents the characteristic impedance of the line, which is the ratio of voltage to current in a traveling wave on the line. It is an important parameter in understanding and analyzing the behavior of transmission lines.

In general, the surge impedance is given by the square root of the ratio of inductance (L) to capacitance (C) per unit length of the transmission line. Therefore, the correct formula is √(L/C).

Option 2 (√LC) is not correct because it doesn’t take into account the division of L by C.

Option 3 (√(L + C)) is incorrect because it adds L and C together, which is not the correct relationship for calculating the surge impedance.

Option 4 (√(C – L)) is also incorrect because it subtracts L from C, which is not the correct relationship for calculating the surge impedance.

In summary, the correct formula for the surge impedance of a transmission line is √(L/C), where L represents inductance and C represents capacitance per unit length of the line.

Voltage regulation of a well-designed transmission line is expected to be

Voltage regulation of a well-designed transmission line is expected to be:

  1. Low
  2. Medium
  3. High
  4. Very high

Correct answer: 1. Low

Explanation: In the context of a transmission line, voltage regulation refers to the percentage change in voltage between the sending end and the receiving end. It is typically calculated by comparing the voltage at the sending end with the voltage at the receiving end and expressing the difference as a percentage of the sending end voltage.

A lower voltage regulation indicates that the transmission line is better able to maintain the desired voltage level along its length, resulting in less voltage drop. Conversely, a higher voltage regulation implies that there is a significant voltage drop along the transmission line, resulting in a larger deviation from the desired voltage at the receiving end.

Therefore, based on this understanding, the correct answer to the MCQ would be “Low” because a well-designed transmission line aims to have low voltage regulation, indicating minimal voltage drop and a better ability to maintain a stable voltage level from the sending end to the receiving end.

Compare to solid transmission conductor, the stranded conductor has _________ skin effect

As compared to solid transmission conductor, the stranded conductor has _________ skin effect:

  1. Greater
  2. Smaller
  3. Same
  4. Negligible

Correct Answer: 1. Greater skin effect

Explanation: Skin effect refers to the tendency of alternating current (AC) to concentrate near the surface of a conductor, resulting in a non-uniform distribution of current. This phenomenon occurs because the magnetic field produced by the current induces an opposing current in the conductor, which is stronger near the surface.

In a solid transmission conductor, the current flows through a single solid piece of metal, and therefore, the skin effect is more pronounced. The current tends to concentrate near the outer surface of the conductor, and the deeper regions of the conductor carry less current.

On the other hand, a stranded conductor consists of multiple smaller strands or wires bundled together. These strands increase the surface area of the conductor, allowing the current to distribute more evenly across the surface. Consequently, the skin effect in a stranded conductor is smaller compared to a solid conductor.

Therefore, the statement “As compared to solid transmission conductor, the stranded conductor has greater skin effect” is incorrect. The correct statement would be: “As compared to solid transmission conductor, the stranded conductor has smaller skin effect.”

Bundled conductors are used in

Bundled conductors are used in:

  1. HVDC lines
  2. HVAC lines
  3. Both of these
  4. None of these

Correct answer: 3. Both of these

Explanation: Bundled conductors are used in both HVDC (High-Voltage Direct Current) lines and HVAC (High-Voltage Alternating Current) lines.

HVDC lines are used to transmit electricity over long distances with lower losses compared to HVAC lines. In HVDC systems, the electrical current flows in one direction, eliminating the need for constant conversion between AC and DC. Bundled conductors are commonly used in HVDC lines to enhance the transmission capacity and improve the efficiency of power transmission.

On the other hand, HVAC lines are the traditional method of transmitting electricity, where the current alternates direction periodically. Bundled conductors are also used in HVAC lines to increase the transmission capacity and enhance the system’s reliability.

Therefore, bundled conductors find applications in both HVDC and HVAC lines, making the correct answer “Both of these.”

The transmission line conductors are made of

The transmission line conductors are made of:

  1. Copper
  2. Gold
  3. ACSR
  4. Aluminium

Correct answer: 3. ACSR

Explanation: Transmission line conductors are the cables or wires used to carry electric power over long distances. They are designed to have low resistance and high conductivity to minimize power loss during transmission. While copper and gold are excellent conductors of electricity, they are not commonly used as conductors in transmission lines due to their high cost.

ACSR stands for Aluminium Conductor Steel Reinforced and it is a specific type of transmission line conductor that consists of a central core made of one or more steel wires surrounded by multiple layers of aluminium strands. The steel core provides mechanical strength and improves the overall tensile strength of the conductor, while the aluminium strands offer electrical conductivity.

The combination of aluminium and steel in ACSR conductors provides a balance of mechanical and electrical properties. The steel core adds strength, allowing the conductor to withstand the tension and mechanical stresses that occur during installation and while the transmission lines are in service. Meanwhile, the outer aluminium strands provide the desired electrical conductivity.

ACSR conductors are commonly used in overhead power transmission lines because they offer several advantages. The steel core enhances the mechanical stability of the conductor, making it suitable for long-span applications. The aluminium strands provide a good balance of electrical conductivity and weight, making ACSR conductors cost-effective compared to using solid copper or gold conductors.

Furthermore, ACSR conductors have good resistance to corrosion due to the protective properties of the aluminium strands. The aluminium strands form an oxide layer that helps prevent corrosion and maintain the conductor’s performance over time, even in harsh environmental conditions.

In summary, ACSR (Aluminium Conductor Steel Reinforced) is a specific type of transmission line conductor that combines the mechanical strength of steel with the electrical conductivity of aluminium. It is widely used in overhead power transmission lines due to its balance of mechanical stability, electrical conductivity, cost-effectiveness, and corrosion resistance.

The major advantage associated with the high voltages

The major advantage associated with the high voltages:

  1. The losses are reduced to a negligible extent
  2. Power transfer capability is improved
  3. Area of cross-section is reduced
  4. All of these

Correct answer: 4. All of these

Explanation: High voltages offer several advantages in electrical power systems. Let’s examine each option in this Electrical Engineering MCQs on Electric Power Transmission:

  1. The losses are reduced to a negligible extent: One advantage of high voltages is that they allow for reduced power losses in electrical transmission and distribution systems. According to Ohm’s law (V = IR), when the voltage (V) is high, the current (I) can be lower to transmit the same amount of power (P). Since power losses are directly proportional to the square of the current (P_loss = I^2R), reducing the current can significantly decrease the power losses. Therefore, high voltages help to minimize losses and improve overall system efficiency.
  2. Power transfer capability is improved: Another advantage of high voltages is an increased power transfer capability. As mentioned above, when the voltage is high, the current can be reduced to transmit the same amount of power. This reduction in current allows for more power to be transmitted through the same transmission lines and equipment. Higher power transfer capability is essential for meeting the increasing demand for electricity and ensuring reliable supply.
  3. Area of cross-section is reduced: High voltages also enable the reduction of the cross-sectional area of conductors used in power transmission. As per Ohm’s law (V = IR), when the voltage (V) is high, the current (I) can be lower to transmit the same amount of power (P). Since the current is directly proportional to the cross-sectional area of the conductor (I = A * J, where A is the cross-sectional area and J is the current density), reducing the current allows for a smaller cross-sectional area of the conductor. This reduction in the cross-sectional area has practical benefits, such as cost savings in conductor material and reduced weight of transmission lines.

Therefore, all of the given options are correct. High voltages contribute to reducing losses, improving power transfer capability, and reducing the required area of the conductor cross-section.

The correct statement about corona and surge transients

The correct statement about corona and surge transients:

  1. Corona increases the transients
  2. Corona reduces the transients
  3. Both are not related

Correct answer: 2. Corona reduces the transients

The ________ the cross arms of pylon, the _________ is the efficiency

The ________ the cross arms of pylon, the _________ is the efficiency.

  1. Shorter, Greater
  2. Longer, Greater

Correct answer: 2. Longer, greater

Long transmission lines are modeled using

Long transmission lines are modelled using:

  1. Rigorous Method
  2. Nominal T Method
  3. Nominal Pi Method
  4. End condenser method

Correct answer: 1. Rigorous method

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