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The correct answer is option 1):(large and narrow)

Concept:

The hysteresis loop depicts the relation between the magnetic flux density and the magnetizing field strength.

The hysteresis loop for the material of the core of a transformer should be Tall and narrow 

The loop is produced by measuring the magnetic flux coming out from the ferromagnetic substance while changing the external magnetizing field.

Soft magnetic materials have narrow hysteresis shapes. these materials are easily magnetized and demagnetized. They typically have intrinsic coercivity less than 1000 Am-1. They are used primarily to enhance the flux produced by an electric current.

Advantages of Hysteresis Loop

1. A smaller region of the hysteresis loop is indicative of less loss of hysteresis.  2. Hysteresis loop provides a substance with the importance of retentivity and coercivity. Therefore the way to select the right material to make a permanent magnet is made simpler by  the heart of machines. 3. Residual magnetism can be calculated from the B-H graph and it is, therefore, simple to choose material for electromagnets.

The correct answer is option 4

Concept:

Sag is defined as the difference in level between points of support and the lowest point on the conductor.

Sag of conductor’s between two poles can be determined by

\(S = \frac{{W{L^2}}}{{8T}}\)

Where, S is the sag of conductors

W is the weight per unit length of the conductor

L is the length of span

T is the tension in the conductor

Explanation:

Length of span - The horizontal distance between two consecutive supports of an overhead line.

Observations:

• The SAG is directly proportional to the weight of the conductor.
• The SAG is directly proportional to the span length.
• The SAG is inversely proportional to the working tensile strength of the conductor at constant temperature.

When the temperature rises:

• As the temperature rises, the tension in the transmission line decreases
• As temperature rises, the sag in transmission lines increases
• Tension and sag in transmission lines are complementary to each other

Important Points:

• Stringing chart is useful in knowing the sag and tension at any temperature
• Stringing chart gives the data per sag to be allowed and the tension to be allowed for a particular temperature
• Stringing chart prepared by calculating the sag and tension on the conductor under worst conditions such as maximum wind pressure and minimum temperature by assuming a suitable safety factor

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The correct answer is option 2):(harmonics)

Concept:

• The crawling in the induction motor is caused by harmonics developed in motor.
• Crawling is the tendency of particularly squirrel cage rotor to run at speeds as low as one-seventh of their synchronous speed. This phenomenon is known as the crawling of an induction motor.
• When the no. of rotor slots is equal to the number of stator slots, the speed of all the harmonics by the stator slotting coincide with the speed of corresponding rotor harmonics.
• Thus harmonics of every order would try to exert synchronous torques at their synchronous speeds and the machine would refuse to start.
• This is known as cogging or magnetic locking.
• Therefore the no. of stator slots should never equal to the rotor slots. Cogging can be easily overcome by making no. of rotor slots prime to no. of stator slots.

The correct answer is option 1):(A = 1, B = 0, C = Y, D = 1)

Concept:

• The shunt admittance of a line consists of the conductance and the capacitive susceptance.
• The conductance is usually ignored because it is very small compared to the capacitive susceptance.
• For a short transmission line
• A short transmission line can be modelled as a series impedance z = R + jωL
• The ABCD constants of this series impedance are

\(\left[ \begin{matrix} 1 & Z \ 0 & 1 \ \end{matrix} \right] \)   A = D = 1, B = z, C = 0​

• The ABCD constants of   Shunt admittance

  is  \(\left[ \begin{matrix} 1 & 0 \ Y & 1 \ \end{matrix} \right]\) A = 1, B = 0, C = Y, D = 1

The correct answer is option 4): (remove the moisture of steam coming out of boiler)

Concept:

• A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry steam Superheated steam is used in steam turbines for electricity generation, steam engines, and in processes such as steam reforming
• The superheater is used to remove  the moisture of steam coming out of the boiler
• While the temperature of the steam in the superheater rises, the pressure remains the same as that of the boiler Superheaters:
• It is used to dry the wet steam and raise the temperature of the steam above its saturation temperature.
• It is generally placed in the path of the furnace gases so as to utilize the heat from the hot flue gases.
• Heat is added on a constant pressure process, thus the pressure remains the same whereas the temperature increases.

Additional Information

​The correct path of flue gases from boiler furnace to chimney is:

Correct option 2

Concept:

Synchroscope

• A Synchroscope is a device designed specifically to indicate if two power networks or generators (or any other AC electrical power system) are synchronized with one another.
• This device checks the operation of both systems to make sure they are working at the same frequency.
• To be synchronized, the phase angle of these two systems should be 0 as well as The phase sequence between two poly-phase systems, too, should be the same.

Synchroscope structure and working principles

• The relative frequency difference, as well as the phase angle between two AC power systems, are measured with the help of these principles.
• A Synchroscope consists of a stator, a two-phase one, and a rotor. The two-phase supply to the Synchroscope is provided by the alternators.
• When two of the phases are synchronized together, the third one automatically follows the process and will sync with the other two phases.
• The Synchroscope’s stator receives the supply from the existing alternator. The incoming alternator, then, provides the supply for the rotor. This phase shifting between the above-mentioned supplies is a sign of the difference in both frequency and phase to the connected alternators that are parallel to one another.

Type of Synchroscope :

1. Electrodynamic type
2. Moving Iron type

Electrodynamic type: 

• This Synchroscope type is also known as the western Synchroscope type and includes an electrodynamic device as well as a three-limb transformer.
• The static and dynamic methods of synchronization have been brought together in this Synchroscope type to achieve the correct synchronization instant.
• In the dynamic method, an electrodynamometer-type Synchroscope will be used while in the static method, the system will need a lamp.

Moving Iron Synchroscope :

• This Synchroscope type consists of a static coil. These static coils are tailored for minimal current and are connected throughout the busbars’ phases.
• Two iron cylinders are located on a shaft and are apart from each other with the help of spacers.

The correct answer is option 4): (extremely good)

Concept:

The conduit wiring is two types

1. Surface conduit wiring
2. Concealed conduit wiring

​Surface conduit wiring:

• If the conduits are installed on the roof or wall, it is known as surface conduit wiring.
• In this wiring method, they make holes on the surface of the wall on equal distances and conduit is installed then with the help of Rawal plugs.

Concealed conduit wiring:

• If the conduit is hidden inside the wall slots with the help of plastering, it is called Concealed conduit wiring. It is the most popular, beautiful, stronger, and common wiring system nowadays.
• In this, steel tubes known as conduits are buried in the walls under the plaster, and VIR or PVC cables are afterward drawn by means of a GI wire of size about 18SWG. Mostly PVC conduits are used in domestic wiring.

​Advantages of conduit wiring:

• It is the safest wiring system, and its appearance is very beautiful.
• No risk of mechanical wear and tear and fire in the case of metallic pipes.
• It is a reliable and long-lasting wiring system

The correct answer is option 2): (operating voltage)

Concept:

• The thickness of the insulation layer on the conductor in cables is dependent upon voltage.
• In a conductor, the voltage gradient is developed along the length of the conductor which decreases radially outwards from the conductor.
• If no insulation is being used then air behaves as dielectric to absorb that voltage gradient and may take a few meters to completely absorb the voltage gradient.
• For example overhead bare conductors, that's why they have separated apart with a certain distance. In distance between the bare conductor increases with the increase in voltage.
• But in the case of underground cables insulation covers the bare conductor.
• The material used in insulation has greater dielectric strength and absorbs all the voltage gradients just within a few mm or cm distance. As the voltage increases the thickness of insulation increases.
• Thus insulation absorbs the voltage gradient
• The insulation is made of such material so that it can dissipate the heat generated in the conductor inside.
• Thus insulation is independent of current and depends only on voltage.

The correct answer is option 3):(Long lasting reduction of load on the motor)

Concept:

• The primary function of a motor starter is to start and stop the motor to which it is connected.
• These are specially designed electromechanical switches similar to relays.
• The main difference between a relay and a starter is that a starter contains overload protection for the motor.
• So the purpose of the starter is twofold, i.e., to switch the power automatically or manually to a motor and at the same time protect the motor from overload or faults
• The Causes for the failure of the starter may include a large change in load e.g., a scrap grinder is fed reduced load for a long time, missalignment, a broken drive gear, or improper motor drive. Power problems also may cause an overload condition.

The correct answer is option 2):by sinusoidal water waves

Concept:

wave power, also called ocean wave energy, electrical energy generated by harnessing the up-and-down motion of ocean waves.

Wave power is typically produced by floating turbine platforms or buoys that rise and fall with the swells.

 wave power can be generated by exploiting the changes in air pressure occurring in wave capture chambers that face the sea or changes in wave pressure on the ocean floor.

 wave power can be generated by exploiting the changes in air pressure occurring in wave capture chambers that face the sea or changes in wave pressure on the ocean floor.

The electric power generated by an ocean wave is sinusoidal wave in nature