Transmission and Distribution MCQ [Free PDF] – Objective Question Answer for Transmission and Distribution Quiz

Explanation:

1. Stranded Conductors are widely used over solid conductors. Although there seems to be more expensive than a solid conductor but offers many advantages too, over the solid conductor.
2. The stranded conductor offers much surface area for the flow of current that results in the reduced diameter of the conductor for the same current carrying capacity.
3. As the Stranded conductor offers much surface area so the overall resistance of the conductor is lesser than the same size solid conductor.
4. Eddy’s current losses are very much lesser than the solid conductor.
5. Stranded conductors are very suitable for an external environment and reduce the risk of loose connection.
6. Stranded Conductors offer much flexibility hence have a longer life than the solid conductor.

Explanation:

Suspension Type Insulator

• With an increase in the line voltage (above 33 kV) the pin insulator becomes heavy and complicated.
• Suspension type Insulator consists of a Number of porcelain discs connected in series with the metallic links to form a chain and the line conductor is carried by the bottom-most insulator.\

Advantages of Suspension Type Insulator

1. Each disc is designed for low voltage i.e for 11 kV. Therefore by connecting the number of an individual disc in series, the insulator can be designed for any system voltage. For e.g 33 kV working voltage will require 3 individual discs.
2. Mechanical stress on the string is very low.
3. Line conductors are less affected by lightning.
4. If anyone of the insulators fails it can be replaced easily and at a very low cost.
5. It is more economical than pin type insulator for high operating voltage.

Explanation:

Sector-shaped conductors

A sector conductor is a stranded conductor whose cross-section is approximately the shape of a sector of a circle. A multiple conductor insulated cable with sector conductors has a smaller diameter than the corresponding cable with round conductors.

Explanation:

• Cables for power distribution of 10 kV or higher may be insulated with oil and paper, and are run in a rigid steel pipe, semi-rigid aluminum, or lead sheath.
• An extruded lead sheath over the paper cable was required to ensure that the paper remained absolutely dry.

Explanation:

Aluminum-conductor steel-reinforced cable(A.C.S.R. conductors)

• Aluminum conductor steel-reinforced cable (ACSR) is a type of high-capacity, high-strength stranded conductor typically used in overhead power lines.
• The outer strands are high-purity aluminum and the center strand is the steel for additional strength to help support the weight of the conductor.
• Steel has higher strength than aluminum which can allow increased mechanical tension to be applied on the conductor.

Explanation: 

Generally industrial loads include inductive motor coil,

• Industrial wiring systems are very inductive because they contain many inductive machines and circuits., such as electric motors, transformers, welding plants, and discharge lighting.
• The inductive nature of the industrial load causes the current to lag behind the voltage and creates a lagging power factor.
• The power factor is the percentage of current in an alternating current circuit that can be used as energy for the intended purpose. A power factor of say 0.7 indicates that 70% of the current supplied is usefully employed by the industrial equipment.
• An inductive circuit, such as that produced by an electric motor, induces an electromagnetic force that opposes the applied voltage and causes the current wave to lag the voltage wave, therefore, they have a lagging power factor.

Explanation:

• Steel wire armored cable, commonly abbreviated as SWA, is a hard-wearing power cable designed for the supply of mains electricity.
• It is one of a number of armored electrical cables – which include 11 kV Cable and 33 kV Cable – and is found in underground systems, power networks, and cable ducting.
• Armour Steel wire armor provides mechanical protection, which means the cable can withstand higher stresses, be buried directly, and used in external or underground projects.

Explanation:

• Cross arms are either made up of wood or steel angle sections.
• Cross arms are installed at the top of the pole for holding the insulator on which the conductors are fastened.
• If the cross arms are fixed in the center of the pole then it is simply called cross arms.
• If the cross arms are fixed on the side of the pole then it is termed as side cross arms.
• For the three-phase line, U-shaped Cross arms are used.

Explanation:

• Insulators used for high-voltage power transmission are made from glass, porcelain or composite polymer materials.
• Porcelain insulators are made from clay, quartz, or alumina and feldspar, and are covered with a smooth glaze to shed water.
• Porcelain has a dielectric strength of about 4–10 kV/mm.
• Glass has higher dielectric strength, but it attracts condensation and the thick irregular shapes needed for insulators are difficult to cast without internal strains.

Explanation:

• The insulator conductors are covered with the lead sheath. This provides additional mechanical strength and also protects the cable from moisture.
• Note: The most common material used as the sheath in today’s cables is Poly-Vinyl-Chloride or PVC. In earlier days, the lead was used as the sheath.