Electrical Objective Questions:Transmission and Distribution (Set 2)

Electrical Objective Questions With Answers:

1) In a transmission line the distributed constants are:

a) Resistance and Capacitance

b) Capacitance and Inductance

c) Resistance, Inductance, and Capacitance only

d) Resistance, Inductance, Capacitance and Shunt Capacitance

2) If the frequency of the transmission line increases then:

a) Line resistance increases

b) Line resistance decreases

c) Shunt rectance increases

d) Shunt reactance decreases

3) The phenomenon in which the conductor surface carries more current compared to core when alternative voltage is applied is

a) Corona 

b) Skin Effect

c) Ferranti Effect

d) Lenz's Law

4) On what factors does Skin Effect depends:

a) Cross section of the conductors

b) Supply Frequency

c) Permeability of the conductor material

d) all the above

5) The Skin Effect of a conductor reduces with increase in the:

a) Cross section of the conductor

b) Supply frequency

c) permeability of the conductor

d) Resistivity of the conductor material

6) Skin effect of the conductor results in the:

a) decrease in the dc resistance

b) Increase in the dc resistance

c) decrease in the ac resistance

d) Increase in the ac resistance

7) Which of the following is correct:

a) with increase in the frequency skin effect decreases

b) skin effect decrease with decrease in the conductor diameter

c) with increase in the conductor permeabilty skin effect decreases

d) with increase in resistivity of the material skin effect increases

8) With the presence of earth in case of overhead lines:

a) Capacitance of the line decreases and Inductance increases

b) Capacitance of the line increases and Inductance increases

c) Capacitance and Inductance of the line increases

d) Only Capacitance of the line Increases

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Answers:  

(1) d (2) d (3) a (4) d 
(5) d (6) d (7) b (8) d

Explanation for Objective Questions: 

1. Answer (d). For simulating a transmission lines, equivalent circuit can be represented as resistance and inductance in series and capacitance and shunt conductance parallel to the circuit. Hence a transmission line can be represented as equivalent circuit of these parameters.

2. Answer (d). If the frequency of the line increases, then shunt reactance = 1/(2 x pi x f x c). So when frequency (f) inceases shunt reactance decreases.

3. Answer (a). This phenomeon is called Skin Effect

4. Answer (d). Skin Effect depends on all the above said factors

5. Answer (d). The Skin effect reduces with increase in the resistivity of the conductor

6. Answer (d). When an alternating current is passed through the conductor, then due to the high inductance of the inner part of the conductor compared to external all the current will tend to flow on the outer surface of the conductor, this phenomenon is called skin effect. As there is resistance for the ac current flow, therefore the effective conductor resistance for ac is higher than dc

7. Answer (b). Skin effect increases with the increase in the conductor diameter (size), increase in the frequency and increase in the permeability and skin effect decrease with the increase in the resistivity of the material.

8. Answer (d). With the presence of the earth, charging currents phenomenon will come in to picture which increases the shunt capacitance of the transmission line. However Inductance do not have any effect on the presence of earth.