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Which of the following statements are true for synchronous motor losses? A)Friction and windage losses increase with the cube of speed. B)The Eddy current loss is reduced by laminating the core. C)Copper losses are independent of load. D)Core losses increase with the square of the load.
A and D
A and B
B and C
C and D
A and B
Statement A is correct because friction and windage losses in rotating electrical machines are proportional to the cube of the speed, represented by PfwтАЛтИЭN3. Statement B is correct because laminating the magnetic core increases the resistance path for eddy currents, thereby reducing the induced I2R losses within the core.
IS 4889:1968
Statement A is correct because friction and windage losses in rotating electrical machines are proportional to the cube of the speed, represented by PfwтАЛтИЭN3. Statement B is correct because laminating the magnetic core increases the resistance path for eddy currents, thereby reducing the induced I2R losses within the core.
PfwтАЛ=kтЛЕN3 тАФ where k is a constant and N is the rotational speed
PeтАЛ=KeтАЛтЛЕBm2тАЛтЛЕf2тЛЕt2 тАФ Eddy current loss formula where t is the lamination thickness
Friction and windage losses arise from mechanical drag and bearing friction, which typically scale with N3 in fluid media. Eddy current losses occur due to the circulation of induced currents in the conductive core material when subjected to a time-varying magnetic field; laminations restrict these paths, limiting the magnitude of these current loops.
Friction and windage losses are independent of load and depend primarily on machine speed.
Copper losses (I┬▓R) vary with the square of the armature current, meaning they are load-dependent.
Core losses (hysteresis and eddy current) are generally considered constant in a synchronous machine under constant voltage and frequency operation.
Laminations are thin sheets of silicon steel coated with insulating varnish to increase resistivity.
Lamination significantly improves the efficiency of machines by minimizing core heat.
Synchronous machines can operate at unity or leading power factors for voltage regulation.
High-speed operation significantly increases cooling requirements due to non-linear windage loss growth.
Increased manufacturing complexity and cost due to core stacking and insulation.
Industrial power factor correction using synchronous condensers.
Large-scale power generation in hydroelectric and thermal power plants.
Option C is incorrect because copper losses are dependent on the square of the armature current (load).
Option D is incorrect because core losses are predominantly dependent on the flux density and frequency, not the load level.
B is correct тАФ Statements A and B accurately describe the physical behavior of mechanical and eddy current losses in synchronous machines.
Always remember that in electrical machines, 'constant losses' (core + mechanical) are often separated from 'variable losses' (copper losses) for efficiency calculations using the OC/SC test method.
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