Abstract - Single-phase induction motor (SPIM) has been widely used in home appliances due to its simplicity, low cost, low noise and ruggedness. However, to produce a cost effective high efficiency SPIM is necessary to have a good knowledge and good control of process parameters. Dynamometer’s results of motors made with different process parameters show that rotor cages are more sensitive to process variations than stators and that they can to worsen the motor efficiency and torque characteristics. The aim of this work is to evaluate some steps of rotor cage process, namely rotor laminates coating, aluminum die-cast methods and rotor annealing and to analyze the effect of such parameters on motor performance. Results obtained from tests with a 2-pole, 100 W, high-efficiency SPIM are presented.
I. INTRODUCTION
The popularity of cage induction motor is due to the simplicity of its rotor, which is made of laminated steel and cast aluminum. The basic steps for rotor cage production are laminates punching, bluing of laminates in furnace, stack assembling, casting, machining finish and finally the rotor annealing. However, despite of its simplicity, the rotor plays an important role in motor performance. Primary performance variations in motors usually come from the rotor and this is more visible in small motors. From the literature, we know that to assure the good resistance between rotor cage and steel is very important to avoid parasitic torques, which can considerably reduce the breakdown torques (BDT) and causes the presence of saddles and inflexion points on motor torque-speed characteristic. The main process variable that plays role in boundary resistance is the internal coating of rotor slots, which must show good resistivity and sufficient mechanical strength to withstand the aluminum cast process. Another important variable that affects the boundary resistance of rotor cage is the rotor heat treatment (annealing process) used to “detach” the rotor bars from steel and relief mechanical stress in cast aluminum. The rotor cage of small induction motors is traditionally made by high-pressure, where molten aluminum is pressed extremely fast by a piston inside a mould which enclosures the rotor stack and end-rings cavities. Although this casting process is widely used, it shows some intrinsic problems like adhesion of aluminum in laminate steel, which reduces the inter-bar resistance. Another problem is the dispersion of gases and aluminum oxide in the cast aluminum due its fast solidification, which reduces its conductivity. Lower inter-bar resistance and lower aluminum conductivity leads to reduction in maximum torque and reduces the motor efficiency.
บทคัดย่อ - มอเตอร์เหนี่ยวนำ 1 เฟส (SPIM) มีการใช้ในบ้านเรียบง่าย เสียงรบกวนต่ำ ต้นทุนต่ำ และ ruggedness อย่างกว้างขวาง อย่างไรก็ตาม ในการผลิตที่มีประสิทธิภาพสูงมีประสิทธิภาพต้นทุน SPIM ได้จำเป็นต้องมีความรู้ดีและควบคุมดูแลของพารามิเตอร์กระบวนการ ผลของ dynamometer มอเตอร์ทำ ด้วยกระบวนการที่แตกต่างกันพารามิเตอร์แสดงว่า กรงใบพัดจะอ่อนไหวมากกับการเปลี่ยนแปลงมากกว่า stators และพวกเขาจะ worsen ลักษณะประสิทธิภาพและแรงบิดที่มอเตอร์ จุดมุ่งหมายของงานนี้คือการ ประเมินบางขั้นตอนของกระบวนการกรงใบพัด ใบพัดคือ ประกบเคลือบ วิธีอลูมิเนียมเหล็ก และการอบเหนียวใบพัดและ การวิเคราะห์ผลของพารามิเตอร์ดังกล่าวประสิทธิภาพมอเตอร์ ผลลัพธ์ที่ได้จากการทดสอบด้วย 2- 100 W, SPIM ประสิทธิภาพสูงมีแสดง I. บทนำ The popularity of cage induction motor is due to the simplicity of its rotor, which is made of laminated steel and cast aluminum. The basic steps for rotor cage production are laminates punching, bluing of laminates in furnace, stack assembling, casting, machining finish and finally the rotor annealing. However, despite of its simplicity, the rotor plays an important role in motor performance. Primary performance variations in motors usually come from the rotor and this is more visible in small motors. From the literature, we know that to assure the good resistance between rotor cage and steel is very important to avoid parasitic torques, which can considerably reduce the breakdown torques (BDT) and causes the presence of saddles and inflexion points on motor torque-speed characteristic. The main process variable that plays role in boundary resistance is the internal coating of rotor slots, which must show good resistivity and sufficient mechanical strength to withstand the aluminum cast process. Another important variable that affects the boundary resistance of rotor cage is the rotor heat treatment (annealing process) used to “detach” the rotor bars from steel and relief mechanical stress in cast aluminum. The rotor cage of small induction motors is traditionally made by high-pressure, where molten aluminum is pressed extremely fast by a piston inside a mould which enclosures the rotor stack and end-rings cavities. Although this casting process is widely used, it shows some intrinsic problems like adhesion of aluminum in laminate steel, which reduces the inter-bar resistance. Another problem is the dispersion of gases and aluminum oxide in the cast aluminum due its fast solidification, which reduces its conductivity. Lower inter-bar resistance and lower aluminum conductivity leads to reduction in maximum torque and reduces the motor efficiency.
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