AMIE Study Circle Blog

Design the 5 sections of a 6-stud starter for a 3-phase slip-ring induction motor The full-load slip is 2% and the maximum starting current is limited to twice the full-load current. Rotor resistance per phase is 0.03 Ω. (AMIE Winter 2023)

Answer all the questions (2 x 10) Explain what happens when a d.c. motor is connected across an a.c. supply? If a DC series motor is connected to a ac supply same current will flow through the series field and armature field after being rectified by the commutator. So, the machine will run but with high sparking at brush, poor pf, low speed and low efficiency. What is Scott connection in a transformer? In this connection, single-phase transformers having 50 percent and 86.6 percent taps on the three-phase side are required. One transformer, called the MAIN transformer is connected between two of the three-phase wires; the other, called the TEASER is connected between the third phase wire and its 86.6 percent tap is connected to the 50 percent tap of the MAIN transformer. What are the advantages of having rotating field system? It is always better to protect high voltage winding from centrifugal forces caused due to the rotation. So high voltage armature is generally keep stationary. It...

 Answer the following, in brief: (2 x 10) The lap winding is used for low-voltage and high current, whereas the wave winding is employed to satisfy the requirements of high voltage and low current in de machine, justify. Lap winding is suitable for low voltage high current machines because of more number of parallel paths. Comment on the shunt field winding has many turns of fine wires, while a series field winding has comparatively fewer turns of heavy wire. Series Field winding carries high current  so conductor size increases(thick  wire) whereas  shunt field winding carries  less current hence  (thin wire). The circular section of armature of a dc machine is made of thin, highly permeable, and electrically insulated steel laminations (stacked), why? The process of lamination involves dividing the core into thin layers held together by insulating materials. Due to lamination effective cross-section area of each layer reduces and hence the effective resis...

    Answer the following in brief (2 marks each) List industrial applications of servomotors. Servo motor is a rotary actuator or linear actuator . It allows for precise control of angular or linear position, velocity and acceleration.  these are used in the machine tools, packaging, factory automation, material handling, printing converting, assembly lines. In many other demanding applications robotics, CNC machinery or automated manufacturing. Discuss repulsion motor. A repulsion motor is a type of single-phase electric motor that operates by the principle of repulsion between two magnetic fields. It was formerly used as a traction motor for electric trains but has been superseded by other types of motors due to its limitations. The working principle of a repulsion motor is based on the repulsion between two magnetic fields. When an alternating current is supplied to the stator winding, it creates a rotating magnetic field. This rotating magnetic field induces an electr...

 Answer the following in brief: Find the angle by which no-load current in a transformer lags the applied voltage. No-load current is nothing but the vector summation of these two currents. Hence, the no-load current will not lag behind applied voltage by exactly 90° but it lags somewhat less than 90°. It is in practice generally about 75° At what power factor, transformer maximum efficiency occurs for a constant load current. Unity power factor. What are the aims and objectives of parallel operations of DC generators. Increased Power Capacity Improved Reliability and Flexibility Enhanced Efficiency Ease of Maintenance Future Expansion Explain vector grouping of transformers. Vector grouping is a method for classifying three-phase transformers based on their winding connections and phase shifts. It is a crucial aspect of transformer design and is particularly important when connecting multiple transformers in parallel. The vector group designation consists of two or three letters, ...