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Activity Task Part 1 Contract load demand of a new facility in your workplace is 62 kVA and the load diversity may be taken to be 80%

Mechanical Engineering

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Activity

Task Part 1

Contract load demand of a new facility in your workplace is 62 kVA and the load diversity may be taken to be 80%. A 65 kVA, 11000 V/415 V, 50 Hz, 3-phase transformer has been proposed for this facility. This transformer from ABC Ltd. guarantees a voltage regulation of 4.4% and 97% full load power efficiency at 0.8 lagging power factor. A continuous full load operation for a considerable period of time is expected every day. Full load power factor is 0.82 lagging. Utility side voltage can be considered to be well regulated at 11000 V. You have been tasked with finding out whether this transformer will be overloaded during this full load period and justify your conclusions with clear calculations and discussion to the senior engineering management. You have been tasked with comparing the transformer from ABC Ltd. with a 65 kVA, 11000 V/415 V, 50 Hz, 3 - phase transformer from a different manufacturer, BCC Ltd. in terms of percentage voltage regulation and power efficiency at the rated load. Load power factor may be assumed to be 0.8 lagging. Single phase equivalent circuit parameters of this 3-phase transformer are given below.

Parameters(Per phase circuit parameter)	Symbol	Value
Primary resistance	R1	10.0 ?
Secondary resistance	R2	0.05 ?
Primary leakage reactance	X1= wL1	20.0 ?
Secondary leakage reactance	X2= wl2	0.12 ?
Magnetizing reactance	Xm=wLm	20k ?
Core-loss resistance	Rc	200k ?

 

 The nameplate of the 65 kVA, 11000 V/415 V, 50 Hz, 3-phase transformer states vector: Dyn. Further, the winding connection is depicted in the handbook as shown in Fig. T1.1. you are supposed to discuss the methods of connections in the primary and secondary sides of this 3 phase transformer with the electrical safety expert of your workplace.

The CNC machine in the machining facility is generally in a poor electrical network environment. The transformer in Fig. T1.2 is proposed to provide additional safety to the users of the CNC machine that will be used in the newly built facility. You are required to identify the type of this transformer and explain the nameplate data. Further you are asked to explain the electrical safety team, using suitable clearly labelled diagrams, on how the user electrical protection is different when the device is used with and without the transformer in Fig. T1.2. Since many of the technical staff is not familiar with the type of transformer in Fig. T1.2, you are also required to briefly explain the other typical applications of the type in Fig, 1.2.

Electricity supply to new facility is metered at the 11 kV side. It is observed that 3 of the devices shown in Fig. T1.3 are inserted through the three 11 kV lines and the outputs are sent to the metering panels. Discuss the applications and the working principles of the device in Fig. T1.3.

Task Part 2 In a belt conveyor system used to transport bulk solids, the belt speed is required to be maintained constant at the set speed all the time irrespective of the bulk solids content on the belt. Hence, the electric motor used in this system should be able to operate more or less at a constant speed in a wide range of different torque values.

a. Selection of the motor type is part of the conveyor system design task. You are supposed to analyse the types of electric motors available in terms of basic construction, power range, maintenance cost, and applications. You are also expected to select a motor type for this conveyor system application and justify the selection. Special discussion is required on the speed control aspects with regard to the underlining application.

b. One of your colleagues argues that induction and synchronous motors should not be selected because they often require special starting methods. You may want to analyze at least 3 commonly used ac motor starting methods using suitable diagrams and torque-speed curves. Giving reasons, recommend a method that can be used both as the starter as well as an adjustable speed drive (ASD) of the induction and synchronous motors

c. A 5 hp, 1800 rpm, 440 V, 60 Hz, 3-phase, squirrel cage, induction motor from AAC Ltd. draws a 6.7 A full load current. Under no-load conditions, the speed is 1786 rpm. It has 85% and 46% lagging power factor under full and no-load conditions, respectively. A second induction motor from supplier XXZ Ltd. has the same nameplate data but draws a line current 7.2 A at 84% lagging power factor at full load. The full load speed is 1750 rpm. Under no load conditions, the speed is 1790 rpm. You have been tasked with comparing the two motors in terms of full-load efficiency, speed regulation, and input power at no-load.

d. One of the colleagues argues that a permanent magnet synchronous motor (also called brushless dc motor BLDCM) is the ideal option for constant speed applications under varying loads. Compare the better induction motor selected in part (c) above with a BLDC motor with closely similar specifications in the market. Also compare the two motor types in terms of cost.

 

breakdown torque = 22.3Nm

r phase

24 a (per phase)

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= 20 1800 rimin 60 Hz | a Va

a 7 yO

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= 16 | A

a | CHARACTERISTIC

 

Fig. T1.3: The torque-speed curve: 5 hp, 1800 rpm, 440 V, 60 Hz, 3-phase, induction motor from AAC Ltd.

Task Part 3 Conventional diesel engine-generator sets are used as backup electricity generators at your workplace. A new 100kVA generator is required to supply the load created by a proposed expansion plan of the factory. An inverter type diesel generator is proposed instead of conventional type. Comparison between two types is given in the following table.

	Conventional	Inveter type
Power rating	100kVa	100 KVA
Fuel consumption	3.5 KWh/liter	4.4 kWh/liter
THD	15%	1%
Voltage regulation	5%	1%
Frequency regulation under inrush loads	3-5%	0%

 

Rated load of the extended facility is supposed to be 100 kVA with 0.8 power factor. This load is supposed to operate 5 days per week and 8 hours a day. You are requested to make a report (maximum of 2 pages) identifying the construction and technologies used in the conventional type and inverter type diesel generators. It is important to relate the identified technologies to the performance characteristics outlined in the above table.

Inverter type is generally more expensive. You are expected to estimate the price difference between the two types required to ensure that the payback period of the extra investment is no more than 3 years. Assume 20 working days per month on average. Low workplace noise and power quality are of serious concern at the extended facility. You are expected to select the type of the generator also explaining the comparison based on the characteristics and the technologies involved in the two types.

A printing machine is supplied by a conventional diesel generator. However, during the operation, the engine-generator set vibrates rapidly. The recorded output frequency is found to be chattering fast around the rated value. It is also noted that the printing machine consists of certain electric heating loads that turn on and off quite rapidly.

a. Theoretically explain this scenario giving the reasons why the encountered problems happen

b. It is recommended that the conventional generator be replaced by an inverter type diesel generator of the same capacity to rectify the two problems; namely, mechanical vibrations of the engine-gen set and frequency chattering of the output. Your opinion is sought with clear discussion of the problem in the light of the technologies used in the inverter type generator.

Frequency regulation curves from a proposed supplier are given in Fig. T3.1. Both types have

a speed governor and AVR.

Task Part 4

A magflow meter has been recommended to measure the liquid flowrate in your workplace application that requires high precision measurements. Two options have been put forward. The cheaper option does not have a battery level indicator. Other option has but it is found to be expensive. One of your colleagues argues that magflow maters are active transducers and hence the dc supply to the mater has to be regulated at a constant value or the flowrate measurements will be erroneous. Further, it is also emphasized that a battery charge level indicator is a must in this device. Do you agree? Explain giving reasons. You are encouraged to use a clearly labelled schematic diagram to explain the principle of operation of the magflow meter to support your reasoning.

At the workplace liquid flow system application, malfunctioning of a solenoid valve is believed to be due to weaker solenoid force. To encounter higher line pressure and larger orifice, it is recommended to replace the existing direct acting solenoid with an internally piloted solenoid valve. You are asked by senior management to analyze the operation of the two types and review the above recommendation. It is always advisable to use a clearly labelled schematic diagrams to explain the principles of operation in support of your review. The vibration sensor in the vibration monitoring system of the engine-gen set is found to be an electromagnetic type. It is stated that EMI may be significant in the environment and hence a sensor type with better EMI resistance should replace the electromagnetic type sensor. You are asked to compare the electromagnetic vibration sensor and piezoelectric vibration sensor types in terms of EMI resistance, off-axis sensitivity, mounting orientation and mechanical durability, and hence make recommendations to improve the operating efficiency of the vibration monitoring unit. You are encouraged to use a clearly labelled schematic diagrams to explain the principles of operation of the sensors in support of your arguments.

Activity

Task Part 1

You are required to design a binary clock using a binary counting system to display time by addressing each segment (hours, minutes, and seconds) with its own byte. Each byte is broken into two parts, the first half representing the tens place and the second showing the ones place of a particular number. For example, if the byte representing hours shows 010010 that equates out to 12 hours. You have been asked to make a binary clock using a matrix of LEDs and a control system that can continue to monitor time while continuing to update its outputs. By creating a matrix of LEDs, you will be able to control a higher number of LEDs with the same number of digital output lines. In this two-part module you may build an 8 bit binary clock that displays individual characters at a time. You may then design and build an LED matrix that will be driven by NPN transistors. That is capable of displaying multiple characters. Memory addresses are required to be displayed as two hex numbers. An example is C800:5. The part to the left of the colon (C800) is called the segment address, and the part to the right of the colon (5) is called the offset. The offset value can have as many as four hex digits. The actual memory address is calculated by adding a zero to the right of the segment address and adding the offset value, like this:

C800:5 = C8000 +5 = C8005.

C8005 is called as the absolute or linear address of the memory. Similarly F000:FFFD can be computed to get the memory address. You are also required to find the memory address in F000:FFFD in Binary and Decimal.

Task Part 2

A linear shock absorber model was used to study the peak amplitude of vibration of the sprung mass of the car as a result of two components of displacements as follows:

( ) = 6 sin(1200 + 65°) - 4 sin(1200 + 46°)

Here, the phase angles are given in degrees. You are supposed to obtain the peak amplitude of ( ) as well as its phase angle exclusively using complex number theories. You may also plot ( ) as the sum of its 2 components and its 2 components on the same graph to verify the answer. Shock absorber non-linear model produced a displacement profile which has a fundamental component of the frequency of 0.4 rad/s superimposed with a 5th order harmonic component of the frequency of 2.0

rad/s as follows:

( ) = 2 sin 0.4 + 1.4 sin 2 cm

where is in seconds. You are faced with a situation where there is no access to advanced analytical software but only a scientific calculator. To that end, you are compelled to use De Moivre’s theorem to

express ( ) as a function of sin 0.4

( ) = 2 sin 0.4 + 1.4 sin 2 = (sin 0.4 )

and hence use root finding techniques of polynomial functions to find the time instances where ( ) = 0. In order to accomplish this, you may first check the correctness of the trigonometric identity sin 5 = 16 sin5 - 20 sin3 + 5 sin . Later on, you are also asked to use commercially available software to plot

( ) versus to verify the answers of ( ) = 0 as well as the peak amplitude of ( ).

Task Part 3

In order to perform computer simulation studies, you are expected to derive mathematical models of the system in the form of differential equation and transfer function. Model parameters of the model in vertical direction represented by a spring, mass, damper systems are; = 1, = 3, = 4 where , , are mass of the sprung mass, damping coefficient, and spring constant in appropriate units, respectively. The external horizontal force input, ( ), is in newton and ( ) is displacement output in meters. Sudden, large, and short duration force due to an earthquake is an impulse input to the spring, mass, damper system. In order to study the effect of the damper, you are supposed to obtain the impulse response of the system for an impulse input of magnitude of unity for = 1, 3, 5. You are also supposed to study the impulse response for impulse inputs of different magnitudes, show them on the same plot for comparison and discussion.

You are also expected to study the impulse response in terms of velocity of the mass. For this you may obtain a transfer function between velocity as the output and external force as the input. Using this transfer function, in order to study the order of the system and its behaviors, you may consider special cases of the spring, mass, damper system, to obtain a 1st order system.