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

Explanation:

• Tapings are connected to the high voltage winding side, because of low current. If we connect tapings to the low voltage side, sparks will produce due to high current.
• The number of turns in the High voltage winging is large and hence a fine voltage variation can be obtained.
• LV winding is placed nearer to the core and HV winding is placed outside. Therefore providing taps on the HV winding is comparatively easier than that of the LV winding.

Explanation:

• In constant voltage transmission, a constant voltage drop is maintained along the line with the help of the phase modifiers (synchronous motor running without mechanical load) at the receiving end.
• With the change in load, the power factor of the system is changed by the synchronous motors and thus voltage drop along the line remains constant.

The main disadvantage of constant power transmission is

1. Increased the risk of interruption of supply due to falling of synchronous motors
2. Short-circuit current in the system is increased.

Explanation:

Skin effect depends upon the following factor.

• Frequency: Skin effect increases with the increase in frequency.
• Diameter: It increases with the increase in diameter of the conductor.
• The shape of the conductor: Skin effect is more in the solid conductor and less in the stranded conductor because the surface area of the solid conductor is more.
• Type of material: Skin effect increase with the increase in the permeability of the material
• The resistivity of the conductor: When resistivity increases its conductivity decrease, therefore, the skin effect also increases. 

Explanation:

• Many alternators are connected to an infinite busbar and they are synchronized at the same frequency, so removing one of them doesn’t change the frequency.
• It can be said that the power capabilities of the infinite bus bar are very much large as compared to an individual alternator connected to it thus when any alternator is removed no significant impact is made on the bus bar voltage or frequency and hence they don’t change. 

Explanation:

Interconnected station

• In an interconnected station to transfer large load between the stations, it is required that the load on the line must be shared equally.

• Consider the 2 generating stations S-1 and S-2 supplying a Receiving station RS through line 1 and line 2.
• To deliver equal power through line 1 and line 2 the phase and active component of line current I₁ and I₂ must be equal.
• To compensate for Impedance drop the regulating components (RE) are installed at the sending end of each transmission line.
• The parallel operation and load sharing between two alternators are possible because of alternator internal reactance which limits the short circuit current and allows angular displacement between two stations.

Explanation:

Electromechanical regulators

• The voltage of an AC generator is controlled by the electromechanical voltage regulator.
• The magnetic field produced by the current attracts a moving ferrous core held back under spring tension.

• The magnetic field produced by the current attracts a moving ferrous core held back under spring tension.
• As voltage increases, so does the current, strengthening the magnetic field produced by the coil and pulling the core towards the field.
• When voltage decreases, so do the current, releasing spring tension or the weight of the core and causing it to retract. This closes the switch and allows the power to flow once more.
• The magnet is physically connected to a mechanical power switch, which opens as the magnet moves into the field.

Explanation:

• Series capacitor is the method of improving the system voltage and impedance by injecting the reactive power in the transmission line.
• If the voltage drop is the limiting factor then the series capacitor is very effective. Voltage fluctuations due to the arc furnace can also be compensated by series capacitors.
• Series capacitor is also very effective when the total line reactance is high.
• It is mostly used in extra and ultra high voltage line but if the load vAR requirement is small series capacitor are of little use.
• The shunt capacitor is used for lightly loaded cables or lines.

Explanation:

Magnetic amplifier

• Magnetic amplifier voltage regulators work on the principle of the saturable magnetic core.
• Two dc windings are arranged on the core of the opposite magnetic field which is fed through the rectifier.
• The combination of the ampere-turns of the D.C signal coil and the series rectifying coil will produce the varying degree of reactance in the series circuit.
• Any small change in the voltage will change the resultant ampere-turns on the control winding which is used to control the field current of the exciter of the alternator.

Explanation:

• In skin effect the eddy current causes the electron to be repelled towards the outermost surface of the conductor.
• Repelling the electron towards the outer surface of the conductor increase the conductor resistance.

Explanation:

• The electrical current travels by means of ions dissolved in the moisture in the ground. In dry soil, this may not work as but in wet ground, current can flow easily because water is a good conductor of electricity.
• The key point is that the current flows from one point of the circuit, through the ground, then back into the circuit. With only one connection to the ground, there is no circuit for the current to flow through.
• If there is a second connection to ground elsewhere in the circuit (usually at the sub-station) which forms the circuit.