Q:What is a Synchronous Generator?

Answer:The synchronous generator is a synchronous machine which converts mechanical power into AC electric power through the process of electromagnetic induction.

           Synchronous generators are also referred to as alternators or AC generators. The term "alternator" is used since it produces AC power. It is called synchronous generator because it must be driven at synchronous speed to produce AC power of the desired frequency.

        A synchronous generator can be either single-phase or poly-phase generally 3phase.

qustion bank

 

Q:Explain the working of AC series motor.

answer:

The  AC  Series motor is a modified version of the DC series motor adapted to run on alternating current (AC).motor or universal motor  works by having its field and armature windings connected in series, ensuring that both currents reverse at the same time when supplied with AC. This simultaneous reversal of the magnetic flux and armature current ensures the torque remains in the same direction, producing continuous rotation despite the alternating supply. The high starting torque and ability to run on both AC and DC power make it suitable for various appliances like drills and vacuum cleaners

Q:Compare salient pole rotor and cylindrical pole rotor.   

Answer:

Salient pole rotors have projecting poles suitable for low-speed machines (100-1500 RPM) like hydro-generators, featuring a large diameter, small axial length, many poles, and a non-uniform air gap. In contrast, cylindrical rotors have a smooth, non-projecting cylindrical shape for high-speed (1500-3000 RPM) applications like turbo-generators, characterized by a smaller diameter, longer axial length, few poles (2 or 4), and a uniform air gap

Q:What is a Salient Pole Rotor Synchronous Generator?

Answer:

        When the synchronous generator uses a projected pole type rotor, it is known as salient pole rotor synchronous generator or salient pole alternator.

In a salient pole alternator, the rotor poles are made of steel laminations and are fixed to the rotor hub. This type of rotor has rotor poles that are physically separated. Each pole carries a concentrated excitation winding. The salient pole rotor is usually used in alternators having 4 poles or more.

The salient pole alternators are mainly used in the applications where the speed of the prime mover is less because at high speeds the centrifugal forces will be large and may damage the poles of the rotor.

Q:What is an Alternator?

Answer:An electromechanical energy conversion device which converts mechanical energy into AC (alternating current) electrical energy is called an alternator.

An alternator consists of two main parts namely stator and rotor. The stator carries the armature winding whereas the rotor carriers the magnetic field winding or poles. When the rotor rotates, its magnetic field cuts the armature conductors and as a result of it an emf is induced in the armature winding. Since the magnetic poles (N and S) of the rotor alternatively cutting the armature windings, hence they induce an alternating (changing direction alternatively) emf in the armature. In this way, the alternator produces an alternating electricity.

The alternators are used in power generating station and automobiles, etc.

Q:What is a Generator?

Answer:The electrical machine which converts mechanical energy into electrical energy is known as generator or electric generator. The electric generator works on the principle of electromagnetic induction, i.e. when a conductor is moved in a magnetic field, an EMF is induced in it. The electric generators produce electricity from many different sources of mechanical energy such as internal combustion engines, steam turbines, gas turbines, water turbines, etc.

The electric generator is one of the most useful electrical machine used for generating electricity during a power shutdown. However, its maintenance is a big problem because it uses coal, oils, natural gases, etc. as the source of power. But, the generator has one main advantage that it can be operated for longer period of time.

Q:What is an Inverter?

Answer:Inverter is a power electronic device which converts direct current (DC) stored in the batteries into alternating current (AC) is known inverter. The inverter have an extra electronic circuit for controlling the battery charging and load management to enable the use of standard electrical appliances.

Basically, an inverter acts like a power adaptor to power the low power domestic and commercial electrical appliances through the conventional electric wiring based on a battery powered system. The inverters are used to run most of the modern domestic and commercial electrical appliances like lamps, fans, refrigerator, water purifier and other low power devices. The inverters can be operated in stand-alone mode as well as in connected mode to the main power grid.

Q:What is a UPS?

Answer:UPS stands for Uninterrupted Power Supply. As its name suggests, it is a device used to stop the interruption in the electric power supply caused to electrical devices during the cut out of electricity.In actual practice, the UPS is mainly used with the computer and other IT systems to provide the electric power for the sufficient amount of time to save the data and safely shutdown the computer when sudden power cut occurs.The main parts of a typical UPS system are: rectifier, battery, inverter and controller. The rectifier converts the AC supply in DC supply to charge the battery. The battery is connected to the inverter which converts the DC output of battery into AC and supply to the connected device or system. The controller is provided to control the operation of the entire system.A UPS provides a backup of up to 10 to 15 minutes. Therefore, the UPS is mainly used to provide backup power to the electronic devices and IT systems that may get damaged with the sudden power failures.

Q:What is Potential Difference?

Answer:In an electric circuit, the difference in the potential of two points is known as potential difference (P.D.). The potential difference is also known as voltage. The SI unit potential difference is Volt.

In simple terms, the potential difference can be defined as the arithmetical difference of a higher potential and a lower potential in an electric circuit. Basically, the potential difference is the amount of energy required to move a unit charge from one point to another point in an electric circuit. The potential difference between two points in an electric circuit can be established with the help of a source of EMF like cell, battery, etc. Just like the voltage drop, we can use a voltmeter to measure the potential difference in the circuit.

Mathematically, if we require W joules of energy (or work done) to move an electric charge of Q coulombs from one point to another in an electric circuit, then the potential difference between those two points is given by,

$$V= \frac{W}{Q}$$

Potential Difference is the parameter in any electric circuit which is entirely responsible for the flow of current in the circuit. Thus, if there is no potential difference, then no current flow.

Q:What is a DC Generator?

Answer:electric generator which converts input mechanical energy into DC electrical energy is called the DC generator or direct current generator. DC generator is also known as dynamo.

A DC generator consists of a rotating armature and static magnetic field. When the rotating armature moves in the stationary magnetic field, an alternating current is induced in the armature winding and it is converted into direct current by using a commutator (a mechanical rectifier) and supplied to the external circuit.

Q:What is an AC Generator?

Answer:The type of electric generator which converts mechanical energy input into AC electrical energy output is known as AC generator. It is also known as alternator, as it produces alternating current electricity. In practice, the AC generator is a type of generator designed to generate alternating current with a frequency of 50 Hz or 60 Hz.

The AC generator consists of fixed armature and a rotating magnetic field. When rotating magnetic field links with the stationary armature winding, produces alternating current in the winding by the principle of electromagnetic induction.

Q:What is AC Electricity?

Answer:The alternating current electricity is a form of electrical current flow that alternates between positive and negative at regular intervals. This indicates that the voltage and current alternate in direction on a regular basis, resulting in a sinusoidal waveform. The type of current delivered by electrical power grids and used to power most household appliances and devices is alternating current

AC electricity has a frequency of 50 or 60 hertz, which means the current changes direction 50 or 60 times per second. The voltage of alternating current (AC) energy varies based on the electrical power grid; however, it is commonly 120 or 240 volts in residential areas.

One advantage of alternating current power is that it can be easily converted to different voltage levels using transformers. This allows for efficient long-distance transmission of power with minimum power loss. AC electricity is also more efficient for powering some types of motors, such as induction motors found in appliances and industrial equipment

Q:What is DC Electricity?

Answer:The DC electricity (direct current) is a form of electrical current flow that flows in only one direction, from positive to negative. Unlike AC power, which flips direction on a regular basis, DC current flows in a continuous direction. Batteries, electronic gadgets, and some motors all use direct current.

DC energy voltage varies based on the application and the equipment being powered, but it is commonly between 1.5 and 12 volts for household batteries and up to several hundred volts for applications in industry. The current in a direct current circuit can also fluctuate based on the circuit's resistance and the load being powered.

One of the primary advantages of DC electricity is that it is more efficient for powering certain types of motors, such as brushed DC motors. DC motors are widely found in small electronic gadgets and appliances such as fans, drills, and power tools. Another advantage is that DC power transmission often results in less power loss over distance than AC power transfer.

However, DC electricity has a few disadvantages. For example, DC cannot be easily changed to multiple voltage levels using transformers, making long-distance power transmission more complex. In addition, at lower voltages, DC power can be more harmful to people, causing burns and tissue damage.

                                         

EE-100 Basics of Electrical Engineering DEC 2017

Q1: Explain the basic working principle of a transformer. Answer: A transformer is a static electrical device used to transfer electrical energy from one circuit to another at the same frequency but with different voltage and current levels. It works on the principle of mutual induction: when an alternating current flows through a primary coil wound on a magnetic core, it produces a time-varying magnetic flux. This flux links with the secondary coil, inducing an electromotive force (emf) in it. Faraday’s Law of Electromagnetic Induction: $$e= -N \frac{dϕ}{dt}$$ where 𝑁 = number of turns, Voltage ratio:$$\frac{V_{1}}{V_{2}} = \frac{N_{1}}{N_{2}} =k$$ 

where k = turns ratio.

 Step 5 (Ideal case current relation): ​​ $$\frac{I_{1}}{I_{2}} = \frac{N_{2}}{N_{1}}$$

Step 4 – Turns ratio relation:

$$\frac{E_{1}}{E_{2}} = \frac{N_{1}}{N_{2}} =k$$

 

Q: Explain the construction and working of an electrolytic capacitor with neat diagram. (5 marks)

Answer:

• Construction: Made of two aluminum foils (anode & cathode) separated by paper soaked in electrolyte. Anodized oxide layer (Al₂O₃) on anode acts as dielectric. Enclosed in can, polarity marked.

• Working: Positive voltage → oxide layer blocks DC → capacitor stores charge. Very thin dielectric ⇒ large capacitance. Reversing polarity destroys oxide.

• -------Equation:$$C = \dfrac{\varepsilon A}{d}$$

(Draw cross-sectional diagram of foil, oxide, electrolyte, can.)

Q:Explain Faraday's laws of electromagnetic induction

Answer: 

Michael Faraday discovered the principle of electromagnetic induction in 1831. It explains how an emf (electromotive force) is induced in a coil when magnetic flux linked with it changes.

Faraday’s First Law

• Whenever the magnetic flux ($\phi$) linking a closed circuit changes, an emf is induced in the circuit.

• The induced emf lasts only as long as the flux is changing.

• If the circuit is closed, this emf causes an induced current to flow

Faraday’s Second Law

• The magnitude of the induced emf is directly proportional to the rate of change of magnetic flux linkage.

Mathematically,$$e= -N \frac{dϕ}{dt}$$ where,  e = induced emf (volts)  N = number of turns in coil 𝜙  = magnetic flux (Wb) minus sign (–) shows Lenz’s Law (induced emf opposes the cause producing it).

Faraday’s laws form the basis of transformers, electric generators, and inductors, where emf is produced due to changing magnetic flux

Q:What is Lenz’s Law?

Answer

Statement
Lenz’s law states that the direction of the induced emf (and hence induced current) is always such that it opposes the change in magnetic flux that produced it.

Explanation:

When magnetic flux linked with a coil changes, an emf is induced (Faraday’s law). According to Lenz’s law, this induced emf produces a current whose own magnetic field opposes the original change in flux.

If flux increases → induced current produces flux in opposite direction.

If flux decreases → induced current produces flux in same direction to oppose reduction.

Mathematical form:

The negative sign in Faraday’s law shows Lenz’s law:$$e= -N \frac{dϕ}{dt}$$

Q:Deduce the relationship between line and phase voltage in a star connected system

Step 1 – Star connection basics

• In star connection, one end of each phase winding is joined to form the neutral (N) point.

• The other ends are connected to the line conductors (R, Y, B).

• Phase voltage ( Vph​ ) = Voltage between a line and neutral (e.g., VRN​).

• Line voltage ( VL​ ) = Voltage between any two lines (e.g., VRY​).

Express line voltage

              $$VR​=Vph​∠0∘$$ 

            $$VY​=Vph​∠−120∘$$

            $$VB​=Vph​∠−240∘$$

Now,

$${}_{}$$

$$VRY​=VR​−VY$$

Phasor subtraction 

$$V_R = V_{ph} \angle 0^\circ$$

$$V_Y​=V_{ph}\angle -120^\circ$$

$$VRY​=V_{ph} \angle 0^\circ−V_{ph}\angle -120^\circ$$ 

----------------------------------------------------------------------------------------------------------------

Vph​(1+j0)−Vph(−21​−j23

exam

Q:what is electric motor.

Answer:An electric motor is a machine that converts electrical energy into mechanical energy, typically by using the interaction between magnetic fields and electric currents to create force. This force is often applied to a motor's shaft, causing it to rotate and produce torque. Common examples of electric motors are found in fans, washing machines, and electric vehicles

Q:what is the working  principle of an DC motor

Answer:A DC motor works on the principle of electromagnetism, specifically the Lorentz force: when a current-carrying conductor is placed in a magnetic field, it experiences a force. This force, called torque, causes the motor's armature to rotate. The direction of this force and torque is determined by Fleming's left-hand rule, while the magnitude is given by the formula F = BIl.

Q:what is fleming's left hand rule

Answer

Fleming's Left-Hand Rule determines the direction of the force on a current-carrying conductor in a magnetic field by using the left hand: if the forefinger points in the direction of the magnetic field (North to South) and the middle finger points in the direction of the current (positive to negative), then the thumb will point in the direction of the force or motion. This principle is crucial for understanding how electric motors work;

Q:Explain different types of dc motors

Answer:

DC motors are categorized as Permanent Magnet (PMDC), Separately Excited, and Self-Excited motors, with self-excited motors further divided into Series wound, Shunt wound, and Compound wound types. Another fundamental classification is between Brushed and Brushless DC motors, the latter requiring an electronic drive.

Q:What is Permanent Magnet DC Motor (PMDC Motor)

Answer:DC MotorUses permanent magnets to create the magnetic field, making them simple and efficient for many applications.

Q:what is dc motor?

Answer:The DC motor is an electrical machine that converts direct current (DC) electrical energy into mechanical energy, or motion. It operates on the principle of Lorentz force, where a current-carrying conductor within a magnetic field experiences a force, creating a torque that rotates the armature (a rotating component). These motors are known for their precise speed control and high starting torque, making them suitable for applications requiring fine adjustments and powerful initial force

equation

Q:Formula for Self Inductance is: 

Answer:$$ L = \frac{N \phi}{I} = \frac{\Phi}{I} $$

Q:Formula fo induced emf is:

Answer:$$ e = -L \frac{dI}{dt}$$ 

mangneticinduction

 Q:S.I. Unit of Mutual Induction

Answer:The SI unit of mutual inductance is the Henry (H). One Henry is defined as the amount of mutual inductance that will induce an EMF of one volt when the current changing at the rate of one ampere per second.

 Q:What is Induced EMF?

Answer: Induced EMF (Electromotive Force) is the voltage generated in a conductor or coil due to a changing magnetic field. This phenomenon is a fundamental principle of electromagnetism and is described by Faraday's Law of Induction. The magnitude of the induced EMF is directly proportional to the rate of change of the magnetic flux. It's used in generators and transformers.

Q: Derive the expression for Self Inductance. Answer: Flux linkage is proportional to current. $$ \phi = L \cdot I $$ For N turns: $$ \Phi = N \phi = N L I $$ Induced emf is: $$ e = -\frac{d\Phi}{dt} = -L \frac{dI}{dt} $$ Thus, $$ L = \frac{N \phi}{I} = \frac{\Phi}{I} $$

Q: What is the coefficient of mutual induction equation? Answer: The induced emf in the secondary coil is: $$ e_2 = -M \frac{dI_1}{dt} $$ where $$ M = \frac{N_2 \phi_{12}}{I_1} = k \sqrt{L_1 L_2} $$

Q: Derive the expression for energy stored in an inductor. Answer: The power is: $$ P = V I = L \frac{dI}{dt} I $$ Energy stored is: $$ W = \int_0^I L I \, dI = \tfrac{1}{2} L I^2 $$

basic electrical

 Q:what is voltage

Answer:Voltage is the measure of electric potential difference between two points in an electrical circuit. It represents the "push" or pressure that drives electric current through a circuit. Think of it like water pressure in a pipe; the higher the pressure, the more water can flow. 

Q:what is current

Answer:A current is the flow of electric charge, typically electrons, through a conductor.This flow is caused by a potential difference,or voltage, and is measured in amperes (A), with a higher current meaning more electricity is flowing. Think of it like water flowing in a river: the voltage is the force pushing the water, and the resistance of the riverbed affects the flow.

Q:what is emf

Answer:EMF, or Electromotive Force, is the electrical energy supplied by a source (like a battery or generator) per unit charge to push charges through a circuit, measured in volts (V). It represents the potential for a source to move charge, fundamentally understanding how devices convert one form of energy into another to create electrical energy. 

Q:what is electrical power

Answer:Electrical power is the rate at which electrical energy is transferred or work is done within a circuit. Its standard unit is the watt (W), which is equivalent to one joule per second. Power is calculated by multiplying voltage (V) by current (I) (P = V x I), and it indicates how fast an electrical device uses or supplies energy. Key aspects of electrical power:

Definition:

Power is the speed at which energy is transferred or transformed. 

Unit:

The SI unit for power is the watt (W), where 1 watt equals 1 joule per second. 

Formula:

The basic formula for electrical power is P = V × I.

P is power in watts.

V is voltage in volts.

I is current in amperes. 

Q:what is Mutual induction 

Answer:Mutual induction is an electromagnetic phenomenon where a changing electric current in one coil induces an electromotive force (voltage) in a nearby coil, or vice versa, due to the changing magnetic field created by the first coil. This principle is fundamental to the operation of transformers and other electronic devices, relying on the magnetic flux linking the two coils. The extent of this induced voltage is quantified by the coefficient of mutual induction, also known as mutual inductance (M), with the SI unit being the Henry (H).

Q:Coefficient of Mutual Induction equation

Answer:The coefficient of mutual induction (M) quantifies the extent to which a change in current in one coil induces an EMF in the other coil.It is defined mathematically as

M=$$\frac{N_{2}\Phi_{12}}{I_{1}}$$

- $$M$$ is the mutual inductance,
- $$N_2$$ is the number of turns in the second coil,
- $${\Phi }_{12}$$ is the magnetic flux through the second coil due to the current $$I_1$$ in the first coil.

Q:What is resistance?

Answer:Resistance is the opposition of a material to the flow of electric current, caused by collisions between moving electrons and the atoms or molecules of the material, which convert electrical energy into heat. It is measured in ohms (Ω) and is a fundamental property of materials that influences how much current flows for a given voltage, as defined by Ohm's Law (V=IR).