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Photovoltaic cells

• A photovoltaic (PV) cell is an energy-harvesting technology, that converts solar energy into useful electricity through a process called the photovoltaic effect.
• The photovoltaic effect is a process that generates a voltage or electric current in a photovoltaic cell when it is exposed to sunlight.
• These solar cells are composed of two different types of semiconductors: a p-type and an n-type which are joined together to create a p-n junction.
• By joining these two types of semiconductors, an electric field is formed in the region of the junction as electrons move to the positive p-side and holes move to the negative n-side.
• This field causes negatively charged particles to move in one direction and positively charged particles in the other direction.
• When the light of a suitable wavelength is incident on these cells, energy from the photon is transferred to an electron of the semiconducting material, causing it to jump to a higher energy state known as the conduction band.
• In their excited state in the conduction band, these electrons are free to move through the material, and it is this motion of the electron that creates an electric current in the cell.

The correct answer is option 1

The function of the tap changer in a transformer is to increase and decrease the Voltage

Concept:

Tap changing transformer:

• A tap is a connection point along a transformer winding that allows a certain number of turns to be selected. The tap selection is made with a tap changer mechanism.
• A tap changer is a mechanism in transformers that allows for variable turn ratios to be selected in discrete steps. These are often placed on the high voltage (low current) transformer winding for easy access and to minimize the current load during operation.
• This means a transformer with a variable turns ratio is produced, enabling voltage regulation of the output. So Secondary side voltage changes.

Soft magnetic material

• Soft magnetic materials are magnetic materials with low coercivity and high permeability.
• Due to the low coercivity of the soft magnetic material, it is easy to demagnetize after the technical magnetization reaches saturation and the external magnetic field is removed.
• The most widely used soft magnetic materials are iron-silicon alloys (silicon steel sheets) and various soft ferrites.
• These materials have a small hysteresis loop.

Hard magnetic material

• Hard magnetic materials have a high anisotropy field, high coercivity, and a large hysteresis loop area.
• Due to the high coercivity, after the technical magnetization to saturation and the magnetic field, is removed, it will remain in very strong magnetism.
• Alloys composed of iron, cobalt and aluminum are generally acted as hard magnetic materials.

Rewirable fuse is a low-cost protection for an electrical system.

Fuse wire

• In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit.
• Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current.
• ​It is a one-time-use device; once a fuse has operated in an open circuit, it is of no use and must be replaced or rewired.

Additional Information

• A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk of fire.
• An isolator is a type of disconnecting switch which is used in an electrical circuit to ensure that the circuit is totally isolated from the supply mains

The correct answer is option 1): ( 318.4 )

Concept:

The capacitive reactance is

Xc = \(\frac{1}{ω× C}\)

ω = 2 × π × f × C

ω = frequency in radians/sec

C is the capacitance value of the capacitor in  farad

f  is supply frequency

Calculation:

Given

C = 10 μF = 10 ×  10-6 F

V = 220 V

f = 50 hz

Xc = \(\frac{1}{ω× C}\)

=  \(\frac{1}{ω× C}\)

= \(\frac{1}{2 × \pi × C \times f}\)

= \(\frac{1}{2 × \pi × 10 ×10^-6 × 50}\)

= 318.4 Ω

Additional Information 

Inductive reactance:

Inductive reactance (XL) is given by

XL = ω × L 

ω = frequency in radians/sec

which can be written as

ω = 2 ×π × f

XL = ω × L

XL= 2 × π × f × L

f = frequency in Hz

L = value of inductor in Henry

Solar PV System

• The electric circuit used to convert unregulated electrical energy to regulated energy in solar PV applications is known as a power electronics converter.
• A photovoltaic (PV) system is a power electronics converter that generates electricity when it is exposed to light.
• Direct Current (DC) needs to be converted into alternating current (AC) so it can be used in a domestic building; this is performed by an inverter.
• The AC electricity then passes via the generation meter, which measures how much electricity has been created, and on to the consumer unit where it can be fed into the property for use or exported back to the national grid via the electricity meter.

Gallium arsenide (GaAs) is a type of semiconductor.

Classification of substance

1.) Conductor

The substances that allow the flow of current through it are known as conductors.

Materials made of metal are common electrical conductors.

2.) Insulator

The substances that do not allow the flow of current through them are known as insulators.

The atoms of the insulator have tightly bound electrons which cannot readily move. 

Some common insulator materials are glass, plastic, rubber, air, and wood.

3.) Semiconductor

A semiconductor is a material, which has an electrical conductivity value falling between that of a conductor and an insulator.

Its resistivity falls as its temperature rises; metals behave in the opposite way.

Examples of Semiconductors: Gallium arsenide, germanium, and silicon are some of the most commonly used semiconductors. 

4.) Superconductor

A superconductor is a material that achieves superconductivity, which is a state of matter that has no electrical resistance and does not allow magnetic fields to penetrate.

Correct option 3

Concept:

HVDC: High voltage direct current transmission. The massive transmission of electricity in the form of DC over long distances by a submarine cable or overhead transmission lines is High voltage direct current transmission.

The AC power is generated in the generating station. This should first be converted into DC. This takes place with the help of a rectifier.

The DC power will flow through an overhead transmission line. At the receiving end, this DC power converted into an AC with the help of an inverter 

Advantages of HVDC

1. corona lossless
2. no skin effect
3. no  reactive power compensation is required

The component used in HVDC

Rectifier: The function of the rectifier is to convert the AC component into a DC component.

Types of Rectifier

1. 1- phase Rectifier
2. 3- phase Rectifier

Inverter: The inverter's function is to convert the system's DC component into an AC component.

Type of Inverter

1. Voltage source inverter
2. Current source inverter

Transformer: A transformer is a static device used to step up or down the voltage or current without changing frequency. 

Types of transformer

1. 1- phase transformer
2. 3- phase transformer

Symmetrical diagram of HVDC

Correct option 2

Concept:

Overload relay: an overload Relay is a protective device used to protect an electrical motor from overheating .

it's mainly three types**:**

1. Thermal relay: Thermal overload relay is a protective device, that is mainly designed to cut the power whenever the motor uses too much current for an extended time period.
2. Magnetic relay or Induction Relay: Magnetic overload relay is operated by detecting by measuring magnetic field strength, which is generated by the flow of current toward the motor. this relay can be built with a variable magnetic core within a coil.
3. Electromagnetic or solid-state relay: Solid-state relays are semiconductor or equivalent to electromagnetic relays and can be used to control the electrical loads without the use of moving parts

Interpoles in DC machine

 Interpoles are similar to the main field poles and are located on the yoke between the main field poles.

They have windings in series with the armature winding.

Interpoles in DC machine basically serves two purposes:

• Automatic neutralization of cross magnetization due to armature reaction.
• To counter and cancel reactance voltage in the coil undergoing commutation.

Additional Information

Compensating winding

• Compensating winding in an AC series motor is used to reduce the sparking of brushes.
• A compensation winding in a DC shunt motor is a winding in the field pole face plate that carries armature current to reduce stator field distortion.