Electrical Engineering assignments | first year engineering assignment | problems |

 QUESTIONS:

PART A                                                                                                                                                    (10 Marks)

 

Preamble

Electrical engineering is a professional engineering discipline that deals with the study and application of electricity, electronics and electromagnetism. Electrical engineering deals with power and energy systems. Energy is transmitted from one place to another, and power is converted from one form to another in these systems. The two types of supply available is AC and DC supplies. AC supply is more widely used rather than DC supply due to its advantages. In this context, debate on the topic:

 

“AC supply system is more superior to DC supply system for domestic wiring.’’ 

 

Your debate should address the following:

A1.1 Differentiate between AC supply and DC supply system. 

A1.2 Discuss the preferred type of supply system for domestic wiring.

A1.3 Discuss the types of AC supply system available. 

A1.4 Justification of your stance with conclusion.

 

 

PART B                                                                                                                                                    (15 Marks)

 

B1

In the circuit shown in Figure 1, determine the current through the 2 kΩ resistor using the following methods:

B1.1 Mesh analysis

B1.2 Superposition theorem

 

Figure 1

Note: For values of ‘x’ contact course leader

 

B2

A building has

·          12 light points of 60 watts each used 5 hours a day.

·          4 fan points of 75 watts each running 10 hours a day.

·          Plug point for a 750 watts heater used one hour a day.

·          One radio 80 watts used 6 hours a day and

·          A ½ H.P pump of 80% efficiency running 2 hours a day.

Compute:

a.        the total connected load in kilowatts

b.       maximum possible current

c.        the daily consumption of energy

d.       monthly bill

The supply is at ‘Y’ volts and energy cost is according to Karnataka electricity board. The rent for a meter is Rs. 20 per month. Assume the month of 30 days.

Note: For values of ‘Y’ please contact course leader.

MARKING SCHEME

ANSWERS:

PART A                                                                                                                                                                   (10 Marks)

“AC supply system is more superior to DC supply system for domestic wiring.’’

 

AC:- In alternating current, the electric charges flow changes its direction periodically. AC is the most commonly used and most preferred electric power for household equipment, office, and buildings, etc. It was first tested, based on the principles of Michael Faraday in 1832 using a Dynamo Electric Generator.Alternating current can be identified in waveform called a sine wave, in other words, it can be said as the curved line. These curved lines represent electric cycles and are measured per second. The measurement is read as Hertz or Hz. AC is used to powerhouses and buildings etc because generating and transporting AC across long distances is relatively easy. AC is capable of powering electric motors which are used on refrigerators, washing machine, etc

DC:-Unlike alternating current, the flow of direct current does not change periodically. The current electricity flows in a single direction in a steady voltage. The major use of DC is to supply

power for electrical devices and also to charge batteries. Example: mobile phone batteries, flashlights, flat-screen television, and electric vehicles. DC has the combination of plus  and minus sign, a dotted line or a straight line.Everything that runs on a battery and uses an AC adapter while plugging into a wall or uses a USB cable for power relies on DC. Examples would be cellphones, electric vehicles, flashlights, flat-screen TVs.

Differentiate between AC and DC:-

1.   Ac current changes its direction during flow while the DC current does not changes its direction during flow and remains constant.

 

2.   The AC current has a frequency that shows how many times the direction of current flow changes during flow while the frequency of the direct current is zero as it do not change the direction of flow.

 

3.  The power factor of AC is 0 to 1 While DC is Constant Zero.

 

4.   The AC current is generated by the alternator while DC current is generated by Photovoltaic cells, generators and batteries.

 

5.  The AC load can be capacitive, inductive or resistive but the load on DC is always resistive.

6.   The DC current graph has a constant line showing magnitude and direction is constant while the AC current can be a sinusoidal wave, square wave or triangular wave.

 

7.   The AC converted into DC using a device named rectifier while the DC converted into AC named inverter.

 

Preferred type of supply system for domestic wiring:- With increase in voltage,line current is reduced for transmitting same power to long distance. Hence changing the voltage level is required for lossless transmission.AC transmission system has the property of transforming the level of voltage and current without change in frequency with the help of transformer.Plant cost for AC transmission is much lower than the equivalent DC transmission. DC machine has brush, commutator arrangement which require more maintenance due to its armature reaction effects.While interrupting any large fault in the system, the arc quenching medium in the circuit breaker puffs the arc while the sine wave current is naturally comes to zero. This makes the interruption process easier. In DC circuit breaker this facility is not available. External circuit is required to do the same.If we use dc transmission, rectification and inversion is required at source and sink respectively which is a costly affair.Hence, AC is preferred over DC for intermidoiate length transmission

 

Ac power supplies:-

AC adapter:-

An AC adapter is a power supply built into an AC mains power plug. AC adapters are also known by various other names such as "plug pack" or "plug-in adapter", or by slang terms such as "wall wart". AC adapters typically have a single AC or DC output that is conveyed over a hardwired cable to a connector, but some adapters have multiple outputs that may be conveyed over one or more cables. "Universal" AC adapters have interchangeable input connectors to accommodate different AC mains voltages.

 

Programmable power supply:-

A programmable power supply (PPS) is one that allows remote control of its operation through an analog input or digital interface such as RS232 or GPIB. Controlled properties may include voltage, current, and in the case of AC output power supplies, frequency. They are used in a wide variety of applications, including automated equipment testing, crystal growth monitoring, semiconductor fabrication, and x-ray generators.

 

Bipolar power supply:-

A bipolar power supply operates in all four quadrants of the voltage/current Cartesian plane, meaning that it will generate positive and negative voltages and currents as required to maintain regulation.When its output is controlled by a low-level analog signal, it is effectively a

low-bandwidth operational amplifier with high output power and seamless zero-crossings. This type of power supply is commonly used to power magnetic devices in scientific applications

 

High-voltage power supply:-

A high-voltage power supply is one that outputs hundreds or thousands of volts. A special output connector is used that prevents arcing, insulation breakdown and accidental human contact. Federal Standard connectors are typically used for applications above 20 kV, though other types of connectors (e.g., SHV connector) may be used at lower voltages. Some

high-voltage power supplies provide an analog input or digital communication interface that can be used to control the output voltage. High-voltage power supplies are commonly used to accelerate and manipulate electron and ion beams in equipment such as x-ray generators, electron microscopes, and focused ion beam columns, and in a variety of other applications, including electrophoresis and electrostatics.

 

Conclusion:-

AC motors are generally considered to be more powerful than DC motors because they can generate higher torque by using a more powerful current.

PART B:

B1.1 Mesh analysis

Solution:-

    

            

   At mesh--- 1

24-4000I₁-4000(I₁-I₂)=0

24-4000I₁-4000I₁+4000I₂=0

24-8000I₁+4000I₂=0

8000I₁-4000I₂=24------------------------------------- 1

 

At mesh -- 2

-4000(I₂-I₁)-2000I₂-4000(I₂-I₃)=0

-4000I₂+4000I₁-2000I₂-4000I₂+4000I₃=0

-8000I₂+4000I₁-2000I₂+4000I₃=0

10000I₂-4000I₁-4000I₃=0------------------------------ 2

At mesh--- 3

-4000(I₃-I₂)-4000I₃-24=0

-4000I₃+4000I₂-4000I₃-24=0

8000I₃-4000I₂=-24                                               3

From equation 1,2 and 3

8000I₁-4000I₂+0I₃=24

4000I₁-10000I₂+4000I₃=0

0I₁+4000I₂-8000I₃=24

    

I₁=3mA

I₂=0mA

 I₃= -3mA

Current through 2KΩ = 0mA

B1.2 Superposition theorem: