Sarawak Campus Assignment Cover Sheet (for individual and group assignments) This cover sheet is to be attached to all assignments, both hard copy and electronic format ASSIGNMENT DETAILS Unit Code MEE40002 Tutorial/Lab Group Wed 10.30 am Assignment Title Due date Unit Title Lecturer/Tutor Name MECHANICAL SYSTEM DESIGN Prof. Basil Wong MECHANICAL SYSTEM DESIGN INDIVIDUAL ASSIGNMENT Date Received 11/16/2018 11/16/2018 DECLARATION For both individual and group assignments, in the case of assignment submission on behalf of another student, it is assumed that permission has been given. The University takes no responsibility for any loss, damage, theft, or alteration of the assignment. To be completed if this is an individual assignment I declare that this assignment is my individual work. I have not worked collaboratively, nor have I copied from any other student’s work or from any other source/s, except where due acknowledgment is made explicitly in the text, nor has any part been written for me by another person. Student Details Student ID Number Student 1 100064145 Student Name Poh Tzi Wei Student Signature Poh Tzi Wei Digitally signed by Poh Tzi Wei Date: 2018.11.16 14:26:06 +08'00' To be completed if this is a group assignment We declare that this is a group assignment and that no part of this submission has been copied from any other student's work or from any other source except where due acknowledgment is made explicitly in the text, nor has any part been written for us by another person. Student Details Student ID Number(s) Student Name(s) Student Signature (s) Student 1 Student 2 Student 3 Student 4 Student 5 MARKER’S COMMENTS 20/12 x 5 = 8.33% Total Mark Marker’s Signature Date EXTENSION CERTIFICATE This assignment has been given an extension by Unit Convenor Extended due date Date Received Version 4, 2 August 2016. Owner: The Academic Board, Sarawak. This cover sheet is a live document available on the Swinburne Sarawak intranet; a print copy may not be the latest version Question 1 1. +2 The design of a three-blade horizontal axis wind turbine is shown above. When the wind is blown towards the turbine and forcing the rotor blade to turn, energy is converted from the mechanical energy and electrical energy. When the blade is forced to turn, the shaft connecting the rotor hub to the gearbox start rotating at certain lower speed. The rotating speed of the shaft is being transmitted from low speed to high speed, through a set of gears in the gearbox, to output shaft that connects the gearbox to the generator. The mechanical energy is then converted to electrical power and transfer to the grid. The blade pitch control on the rotor turns the wind blade to align the blade in its optimum angle to maximize its efficiency. The brake located between the rotor and gearbox stops the wind turbine from turning in case of natural disaster such as storm to prevent permanent damage done to the turbine. The gearbox contains a set of gears that transmit low speed rotational motion from the rotor to high speed rotational motion, which is then transmitted to the generator. The generator generates electricity based on the mechanical energy input from its shaft. Anemometer is installed to measure the wind speed while the wind vane is to determine the wind direction. The wind orientation control turns the turbine in the direction of the wind to maximize its efficiency. 2. The maximum theoretical power is defined as: 1 ππππ₯ = ππ΄π 3 2 Where, ρ = Density of the Air A = Area Swept of Turbine, π΄ = ππ· 2 4 π2 ππππ₯ = Maximum Velocity of Wind According to Betz’s law, the Maximum Coefficient of Power, πΆπππππ₯ = 59.3% Assuming π = 1.225 ππ/π3 , ππππ₯ = 15 π/π and D = 30 m; 1 3 ππππβ = 2 ππ΄ππππ₯ 1 = 2 × 1.225 × ππππ₯ π×302 4 × 153 = 1461.21 ππ = πΆπππππ₯ ππππβ = 0.593 × 1461.21ππ = 865.9ππ +2 3. The appropriate generator for this wind turbine is a 4 poles 600-3000 kW 3-phase wound rotor doubly fed induction generator (DFIG) from Leroy Somer. It is chosen due to advantage of being able to import and export reactive power from the grid or stator. Since the wind speed range in the village is 5 ~ 15 m/s, doubly fed induction generator could be connected directly to the grid, while the rotor of the generator is connected to the grid through a crowbar and power converter. The active power and reactive power fed to the grid from stator could be controlled by adjusting the rotor current with converter, while disregarding the generator turning speed. DFIG operates at the slip frequency, which is dependant on the rotor speed of the generator. When the generator is operating above its synchronous speed, the power of the wind turbine delivered from the rotor would pass through the power converter to the grid. When the generator is operating below its synchronous speed, the power is then deliver to the rotor through the power converter. Therefore, the induction generator is always synchronizing with the grid even when the wind speed is unstable. Torque calculation? safety factor for your design? 4. In terms of safety, induction generator has a self-protection feature where the machine would shut down itself when there is a short circuit, fault occurs in terminals and excitation fails to prevent mechanical and electrical failure. Brake could be used to stop the turbine manually if necessary to prevent permanent damage done to the generator. A crowbar is connected from the generator to the power converter to prevent any short circuit. The cost of DFIG is relatively low as compare to other variable speed induction generator because only 25 ~ 30% of the mechanical power is fed to the grid through power converter. The efficiency of DFIG is also higher compare to fixed speed wind turbine. The noise of the wind turbine can be reduced significantly by improving its design and minimizing the noise of mechanical components. The generator selected has water-cooled or air-cooled system that cools down the active parts in the generator to ensure it does not get over heat, which then improves the generator life and allow it to sustain for longer period of time. Wind energy is clean and sustainable a renewable energy source. Wind turbine can generate electricity based on wind speed while not generating any carbon footprint or greenhouse gases. Therefore, the source of energy is sustainable. A detailed manual on how to operate and maintain the turbine’s useful lifespan should be provided. +1.5 5. The voltage of the wind turbine is typically around 400V when the generated power is 600kW. ππππ‘ππ = 1450~1500 πππ ππ€πππ = 5~15 π/π 1450~1500 π = 5~15 = 96.67~300 πΊπππ πππ‘ππ The tip speed ratio can be optimized since the wind turbine has rotor blade control that adjust the blade in the direction of optimum angle. The optimum TSR of wind turbine is 7. ππ πππ π ππππ πππ‘ππ = =7 π 7 × (5~15) 60 π= = 44.56~133.69 πππ 15 π The rotational speed of the input shaft of the induction motor will only be able to run at speed slightly (30%) above or below synchronous speed, the slip of the induction generator is given as 0.3. Therefore; ππ − π π 0.3 = =1− ππ ππ 44.56~133.69 0.7 = +1 ππ ππ = 63.66~190.99πππ Assuming that the generator has 4-pole lap-winding generator that has 90 coils, with 4 turns in each coil and produces a flux of 0.05Wb per pole. The induced voltage is calculated as; ππ∅ (60 × 4 × 2) × (63.66~190.99) × (0.05) ππππ = = = 25.46~76.40 π 60 60 The power of the wind turbine can be calculated using the formula below, but the coefficient of power of practical turbine can only reach to 75% of Betz’s coefficient: π= 1 ππ΄π 3 × πΆππ 2 Where, πΆππ = 0.25~0.4 π = 1.225 ππ/π3 π΄ = π ππ‘ππ π π€πππ‘ ππππ = ππ· 2 4 π = 5~15 π/π Therefore, 1 ππΆππ=0.25 = 2 ππ΄π 3 × πΆππ0.25 1 = 2 × 1.225 × ππΆππ=0.4 π×302 4 +2 × (5~15)3 × 0.25 = 13,529.71~365,302.18 π 1 = 2 ππ΄π 3 × πΆππ0.4 1 = 2 × 1.225 × π×302 4 × (5~15)3 × 0.4 = 21,647.54~584,483.50 π The current produced by the turbine can be calculated as; π = πΌπ ππΆππ,0.25~0.4 = πΌππππ 13529.71 584483.50 πΌ= ~ = 531.41~7,650.31 π΄ 25.46 76.40 6. Since the efficiency of the wind turbine calculation above does not include any other factors such as friction and energy losses, the calculated power output is still very much optimistic. Practically, only 75% of the calculated power output can be produced; 1 πππ£π = ππ΄πππ£π 3 × πΆππππ£π = 142.87 ππ 2 π = πππ£π × 0.75 = 107.16 ππ The power output of the wind turbine is very dependent on many factors such as wind speed, the angle of rotor blade against wind and wind direction. Furthermore, wind turbine also suffers against mechanical and electrical losses and overheating. Every machine suffers energy losses during operation, which the energy losses will be transacted into heat energy, thus heating up the machine and reducing its efficiency. In wind turbine, energy is loss at the rotating parts such as rotor, shaft, gearbox and generator. Additionally, movable parts in wind turbine suffers from friction and windage. The electrical circuit in wind turbine experienced electrical losses, such as conductor losses, stator and rotor copper loss in generator and brush losses. Both mechanical and electrical losses in the form of heat would then increase the temperature of the turbine, mainly at the rotor and generator. A continuously overheating turbine would further damage the insulation in turbine, thus reducing its useful service life. The wind turbine should be operated under its temperature-limited power. These losses act as an additional loading on the turbine, which reduces its efficiency and power output. +2 Question 2 1. Based on the given measurements of the conveyor belt system, the required rated speed 60π 60×1 of the motor must be at least ππΊ = ππ· = π×0.1 = 190.99 πππ for the conveyor belt to function properly. The selected motor is an Oriental BLM5120HP-15S, 120W Brushless DC Motor Speed Control System with Parallel Shaft Gearhead. The motor frame size is 90 mm with 120W output power and a variable speed range of 5.3 to 267 rpm. The gear ratio of the motor is 15:1 with a rated torque of 6.1Nm as provided in the catalogue. The permissible load inertia is 420 × 10−4 πππ2. The selected DC motor has a driver unit which can convert the 115 VAC power supply to DC power supply. It also allows speed control of the conveyor belt with the speed-torque curve is approximately linear. A Parallel Shaft Gearhead is integrated to the motor, which improves the speed range and torque of the motor. 2. To determine whether a motor is suitable for the given task is by making sure the rated speed of the conveyer is within the range of the motor, the load inertia is lower than the permissible load inertia of the motor and the rated torque of the motor must be at least 1.5 times the calculated required torque. In other words, the safety factor of the motor needs to be at least 1.5. 60π The required speed at the gearhead output shaft is given as ππΊ = ππ· πππ 60π 60 × 1 +2 ππΊ = = = 190.99 πππ ππ· π × 0.1 The calculated speed is within speed range of the chosen DC motor (5.3 ~ 267 rpm). Next, the moment of load inertia is the summation of both inertia of belt and load and the roller. π½ = π½π1 + 2π½π2 π· 2 1 = π1 ( 2 ) + 2 (8 π2 π·2 ) 0.1 2 1 = [7 × ( 2 ) ] + 2 [8 × 1 × 0.12 ] +3 = 0.0175 + 2(1.25 × 10−3 ) = 200 × 10−4 πππ2 (< 420 × 10−4 πππ2 ) The load inertia is lower than the permissible load inertia of the motor. Lastly, the required torque with load is calculated as shown below; πΉ = ππΉπ + 2πΉπππ§π§ππ cos 30π = (0.4 × 8 × 9.81) + (2 × 10 cos 30π ) = 48.7125π ππΏ = = +1.5 πΉπ· 2π 48.7125 × 0.1 +1 2 × 0.9 = 2.706ππ From the catalogue, the permissible torque of the Oriental Motor is 5.4 Nm. The safety factor is calculated to be; ππ 6.1 = = 2.254 π. πΉ. ππΏ 2.706 3. The theoretical calculation of the rated speed of the conveyor belt is roughly around 191 rpm. However, the belt and roller only have an efficiency of 0.9, which means only 90% of the calculated speed is being transmitted due to minor friction in the system. Therefore, the actual belt speed should be: belt speed, not the 60π 60 × 1 ππΊ,πππ‘π’ππ = ×π = × 0.9 = 171.89 πππ rotational speed of ππ· π × 0.1 shaft. 4. Safety factor is defined as the ratio of the permissible motor torque compare to the load torque. From the catalogue, the permissible torque of the Oriental Motor is 6.1 Nm. The safety factor is calculated to be the permissible motor torque by the load torque. ππ 6.1 = = 2.254 π. πΉ. +2 ππΏ 2.706 In this case, the safety factor implies that the motor is capable of handling 2.254 times the load torque applied. The safety factor has to be more than one to ensure the safety of the appliance and to prevent any minor errors made in calculation or assumptions. Reference https://catalog.orientalmotor.com/item/bmu-series-brushless-dc-motor-speed-control/120wbmu-series-brushless-dc-motors/blm5120hp-15s-bmud120-a2 http://acim.nidec.com/generators/leroy-somer/products/power-alternators/alternators-forwindturbines https://www.researchgate.net/publication/286372317_A_RealTime_Sliding_Mode_Control_for_a_Wind_Energy_System_Based_on_a_Doubly_Fed_Indu ction_Generator/download
