1) Why is AC transmission preferred over DC transmission?
Answer.
- Loss of power during transmission of current from the power generation plant to the grid is less in AC than in DC.
- AC can be easily transformed to DC with the help of rectifiers whereas in DC it is not possible.
- AC can be easily stepped up or stepped down by transformers whereas in DC it is not possible because transformers work on a changing EMF principle.
- Generation of AC is cheaper than DC power.
2) What is the difference between the Transmission line and distribution line?
Answer. Transmission lines are used for carrying electric power from power stations to the substations.
Distribution lines are used for carrying the electricity from substations to load points such as home, businesses, industries, etc.
3) What is the material used for overhead transmission lines?
Answer. The most common conductor in use for transmission today is aluminum conductor steel reinforced (ACSR).
4) What are the factors that limit the maximum power transfer capability in a transmission line?
Answer. Some of the factors which limit the maximum power transfer are:
- Electrical phase shift
- Voltage drops.
- Thermal effects in the line
5) What Is Corona in overhead power transmission lines?
Answer. The phenomenon of violet glow, hissing noise and production of ozone gas in an overhead transmission line is known as Corona.
6) What Is Skin Effect in power Transmission lines?
Answer. The non-uniform distribution of electric current over the surface or skin of the conductor carrying a.c is called the skin effect.
7) Why Is Voltage Stepped Up Before Transmission?
Answer. Voltage is stepped up earlier than transmission due to the subsequent motives:
- Reduces volume of conductor thickness.
- Increases transmission performance.
- Decreases percent line drop (losses).
8) What Are Standard Transmission and Distribution Voltages?
Answer.
Primary Transmission: 66 kV, 132 KV, 220 kV and 400 kV
Secondary Transmission: 33 kV
Primary Distribution: 11 kV, 3-section, 3-twine
Secondary Distribution: 400 V between stages (three-phase, 4-wire) and 230 V between any individual segment and impartial
9) What Are Lightning Arrestors?
Answer. Lightning Arrester is a device used for the protection of electrical equipment against lightning stroke. The lightning stroke is the high voltage transients caused by the traveling waves during lightning.
We install lightning protection devices to protect the transformer, transmission line, and the major electrical equipment
10) What is wavelength of a line?
Answer. The distance the wave travels along the line while the phase angle is changing through 2 radians is called a wavelength
11) What are the types of line distortions?
Answer. The distortions occurring in the transmission line are called waveform distortion or line distortion. Waveform distortion is of two types:
- Frequency distortion
- Phase or Delay Distortion.
12) What is 3-Phase supply?
Answer. It is a type of poly phase system and is the most common method used by grids worldwide to transfer power. In a three-phase system, three circuit conductors carry three alternating currents (of the same frequency) which reach their instantaneous peak values at different times
13) What is a Sub-station?
Answer. The assembly of apparatus used to change some characteristics (e.g. voltage, AC to DC, frequency, power factor) of the electric supply is called a sub-station
14) Which are preferred – Underground or Overhead cables?
Answer. Although many low voltage, local electric distribution lines are buried underground, almost all high-voltage electric transmission lines are tried to be placed as overhead cables due to the cost difference.
15) What will happen when the power factor is leading in the distribution of power?
Answer.
If there is a high power factor, i.e. if the power factor is close to one.
- Losses in the form of heat will be reduced.
- Cable becomes less bulky and easy to carry, and very cheap to afford.
- It also reduces overheating of transformers.
16) Why Delta Star Transformers are used for Lighting Loads?
Answer. For lighting loads, the neutral conductor is must and hence the secondary must be star winding and this lighting load is always unbalanced in all three phases.
To minimize the current unbalance in the primary we use delta winding in the primary. So delta/star transformer is used for lighting loads.
17) What are the various components of overhead lines?
Answer. The main components of an overhead line are supports or towers, cross arms, clamps, insulators, conductors, guys and stays, lightning arresters, earth wires, V-guards, guard wires, phase plates, bird guards, danger plates, anti-climbing devices, vibration dampers.
18) What are the factors on which conductor spacing and ground clearance depend?
Answer. Factors affecting conductor spacing are voltage while factors affecting ground clearance are voltage and area (living or non-living, urban or suburban, along the streets or across the streets, river crossings/hill crossings, railway track/bridge, etc.
19) What types of insulators are used for overhead transmission and distribution lines?
Answer. The insulators used for overhead lines are pin type, suspension type, strain type, and shackle insulators.
20) What do you mean by sag in transmission line?
Answer. The transmission line is not fully stretched but it is allowed to sag down. The difference in levels between point of support and the lowest point on the conductor is called sag.
21) Which type of connection is employed for current transformers for the protection of star-delta connected 3-phase transformer?
Answer. Delta-star. In case of star-delta transformer, the current on the two sides differ in phase by 30 degree. This is compensated by connecting current transformer in delta on the star side and in star on the delta side of the transformer.
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