01․ Galvanised steel is generally used as
If the wires are made up with some other ordinary steels, rust and corrosion attacked the wire after some time due to the environmental wet conditions. A layer of zinc oxide can be provided on the steel wire by some chemical process. This zinc oxide layer protects the steel wire from the rust and corrosion effects. That’s why galvanized steel is used in many places.
02․ Plug setting of a relay can be altered by varying
The minimum pick up value of the deflecting force of an electrical relay is constant. Again the deflecting force of the coil is proportional to its number of turns and electric current flowing through the coil. Now, if we change the number of active turns of any coil, the required electric current to reach at minimum pick value of the deflecting force, in the coil also changes. That means if active turns of the relay coil is reduced, then proportionately more electric current is required to produce desired relay actuating force.
03․ Objectives of power system is/are
Objectives of power system are
1. Cost of electrical energy per KWh is to be minimum
2. Rated voltage and frequency has to be supplied to the consumers
3. Reliable power has to be available
4. Effective protection system has to be used for isolating the faulty section and keeping other sections healthy.
5. More stable generators are to be used, so that it should not lose synchronism under faulty condition.
6. Flexible power has to be available.
04․ Objectives of power system is/are
Objectives of power system are
1. Cost of electrical energy per KWh is to be minimum
2. Rated voltage and frequency has to be supplied to the consumers
3. Reliable power has to be available
4. Effective protection system has to be used for isolating the faulty section and keeping other sections healthy.
5. More stable generators are to be used, so that it should not lose synchronism under faulty condition.
6. Flexible power has to be available.
05․ The main objectives of electrical power transmission is/are
Objectives of electrical power transmission are
1.Transmission system must be more efficient with minimum line losses and maximum power transfer capability
2. Voltage regulation of the transmission line must be zero or minimum
06․ Advantages of higher transmission voltage is/are
Advantages of higher transmission voltage are
1. Power transfer capability of the transmission line is increased
Pmax = Vs*Vr/Xs
Where, Vs = Supply voltage
Vr = Receiving end voltage
If Vs = Vr,
Pmax ∝ Vs²
2. Transmission line losses are reduced
Power P = VI cosφ
I = P/(V cosφ)
Transmission line losses Pl = I²R
Therefore, Transmission line losses Pl∝ 1/V²
3. Area of cross section and volume of the conductor is reduced
Resistance R = ρl/A
Where, ρ= resistivity
l = length of the conductor
A = Area of cross section
Therefore area A ∝ 1/V²
07․ Which of the following statement is true
At higher voltage, volume of conductor is reduced.
Area of conductor A ∝ 1/Vs²
Where Vs = Supply voltage
So that material requirement is reduced and hence cost of the material and transmission is reduced.
08․ Maximum power transfer capability of transmission line can be increased by
Maximum power Pmax ∝ Vs²/Xs
Maximum power transfer capability of transmission line can be increased by either increasing voltage level or reducing the line reactance value.
Methods of reducing line reactance are
1. Parallel transmission lines
2. Using series capacitance
3. Using bundled conductors
09․ For flat voltage profile system, voltage regulation is
% Voltage regulation = (Vs-Vr)/Vr*100
Where,
Vs = Supply voltage
Vr = Receiving end voltage
For flat voltage profile system Vs = Vr
Therefore, voltage regulation for flat voltage profile system is 0%.
10․ Maximum power transfer in a transmission line can be obtained by
Maximum power Pmax ∝ Vs²/X
Where
Vs = supply voltage
X = reactance
Maximum power transfer capability of transmission line can be increased by either increasing voltage level or reducing the line reactance value.
Methods of reducing line reactance are
1. Parallel transmission lines
2. Using series capacitance
3. Using bundled conductors
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