Efficiency Of A DC Machine And Condition For Maximum Efficiency
- 1. Efficiency of a dc machine and condition for maximum efficiency By: Muhammad Fazil Memon ID: 2852-2016 Electrical Machines
- 2. Table Of Contents Introduction DC Machines Fundamentals Basic Structure of DC Machines Efficiency of a Dc Machine Condition for Maximum Efficiency in DC Machine Power Flow and Losses in DC Machines References
- 3. Direct Current (DC) Machines Fundamentals Generator action: An emf (voltage) is induced in a conductor if it moves through a magnetic field. Motor action: A force is induced in a conductor that has a current going through it and placed in a magnetic field. Any DC machine can act either as a generator or as a motor.
- 4. Basic Structure of DC Machines The rotating electrical or DC machine has mainly two parts; one is Stator, and another one is Rotar. The stator and rotor are separated from each other by an air gap. The stator is the outer frame of the machine and is immovable. The rotor is free to move and is the inner part of the machine
- 5. Efficiency of a Dc Machine Electric motor efficiency is the ratio between power output (mechanical) and power input (electrical). Mechanical power output is calculated based on the torque and speed required (i.e. power required to move the object attached to the motor), and electrical power input is calculated based on voltage and current supplied to the motor. Mechanical power output is always lower than the electrical power input, as energy is lost during conversion (electrical to mechanical) in various forms, such as heat and friction. Design of an electric motor aims to minimize these losses to improve efficiency. For a d.c. machine, its overall efficiency is given by,
- 6. Continue Efficiency: Efficiency = (output / input )*100 Input to the Motor (Total power) = VI Motor efficiency Ƞm = 1 – losses / input
- 7. Condition for Maximum Efficiency in DC Machine It varies from motor to motor, but typically the maximum efficiency is when running at about 80 percent of maximum speed, driving a load that is about 20 percent of the maximum stall torque. Exact details should be available from the manufacturer.
- 8. Power Flow and Losses in DC Machines Electrical or copper losses (I2 R losses) Brush losses Core losses Mechanical losses Stray load losses Armature loss: Field loss: Copper losses Brush losses Core losses the hysteresis losses and eddy current losses occurring in the metal of the motor. These losses vary as B2 and, for the rotor, as the (n1.5)
- 9. References: 1. Dr. Bhag S.Guru, “Electric Machinery and transformers”, oxford university press, 3rd edition. 2. D.R. Kohli-S.K Jain, “A laboratory course in ELECTRICAL MACHINES” Nem Chand & Bros., 2000