Urja Khabar
Kathmandu: In the knowledge-enhancing column "Urja Gyan" published every Friday in Energy News, this week we have focused on transmission (transmission) lines. Last week, we provided information on the issues and solutions related to MCB (Miniature Circuit Breaker) and MCCB (Molded Case Circuit Breaker) used in electrical circuits.
1. What is an Electric Transmission Line?
Answer: A transmission line is a specially designed structure for transferring electrical energy or signals from one location to another. It is one of the key components of electrical power systems and telecommunications networks. Transmission lines are designed to carry high-voltage electrical energy or high-frequency signals over long distances most efficiently.
2. Classification of Transmission Lines
Transmission lines are classified into three categories based on length:
Short Transmission Line (STL): A length of transmission line up to 50 km is treated as a short transmission line. In such lines, normally voltages up to 33 kV are transmitted. Moreover, in such lines, the effect of capacity is negligible, while the effect of inductance (reactance) is considerable. Thus, in STL, only resistance and inductance are considered as parameters, and these are in series connection.
Medium Transmission Line (MTL): Those transmission lines which are in the range of 50 to 150 kilometers come in the category of medium transmission lines. In such lines, voltage transmitted is within 33 kV to 66 kV. As these lines are relatively long, the effect of capacity becomes predominant; hence capacitance also becomes the part of the parameters of the MTL.
Long Transmission Line: A transmission line greater than 150 km is known as a long transmission line, and it transmits voltages greater than 132 kV. In these long lines, the effect of capacitance is more dominating, and transmission lines are divided into several segments for accurate calculation.
Multiple-Choice Questions
(1) Which voltage is known as transmission voltage?
(a) 11 kV
(b) 33 kV
(c) 132 kV
(d) 400 volts
Answer: 132 kV
(2) In order to reduce the loss of electric power in the lines of transmission, the voltage ________.
(a) should be increased
(b) should be decreased
(c) inductance should be increased
(d) more capacity should be added
Answer: should be increased
(3) The electric power lost is ________ to the voltage of transmission.
(a) inversely proportional to the square of voltage
(b) directly proportional to voltage
(c) equal to voltage.
(d) It is inversely proportional to current.
Answer: It is inversely proportional to the square of voltage.
(4) What is the resistance of a conductor?
(a) It is proportional to specific resistance.
(b) It is proportional to the length of the conductor.
(c) It is inversely proportional to the cross-sectional area.
(d) All of the above.
Answer: All of the above
(5) For customers, which regulation is considered good from a comparative point of view?
(a) 5 percent
(b) 2 percent
(a) 2%
(b) 4%
(c) 7 percent
(d) 10 percent
Answer: 2 percent
(6) Number of capacitance locations are to be normally considered in the calculations of medium transmission line,
(a) 0
(b) 1-2
(c) 4 to 5
(d) 6 - 7
Answer: 1-2
(7) Number of capacitance location, to be usually considered for long transmission lines:
(a) 0
(b) 12
(c) 67
(d) more than two location
Answer: more than two location
Last week's article, which discussed issues and solutions relating to MCB and MCCB in electrical circuits, can be viewed here : Application Problems and Solutions for MCB and MCCB in Electrical Circuits
