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In case of DC machines, mechanical losses are primary function of
Current
Voltage
Speed
None of the above
Speed
Mechanical losses in a DC machine, which consist of friction and windage losses, are primarily dependent on the rotation speed of the machine. Since these losses are caused by the motion of the rotor, they are considered constant if the speed remains constant, regardless of the load current.
Mechanical losses in a DC machine, which consist of friction and windage losses, are primarily dependent on the rotation speed of the machine. Since these losses are caused by the motion of the rotor, they are considered constant if the speed remains constant, regardless of the load current.
PmechтАЛ=PfrictionтАЛ+PwindageтАЛ тАФ definition of total mechanical loss
PmechтАЛтИЭN1.5┬аto┬аN2 тАФ dependence of mechanical losses on rotational speed N
Friction loss occurs at the bearings and between the brushes and the commutator, while windage loss occurs due to air resistance against the rotating armature. Both frictional force and air turbulence energy dissipation scale with the angular velocity of the shaft. Consequently, as the rotor speed increases, the energy required to overcome these mechanical resistances increases proportionally.
Mechanical losses are also known as constant losses in a machine operating at a fixed speed.
These losses are independent of the load current (Armature current IaтАЛ).
Friction loss is primarily linear with speed, while windage loss varies as the square or cube of the speed.
Total rotational losses are measured during the No-Load test.
Easy to estimate during no-load testing
Predictable based on rotational velocity
Increases significantly at high speeds, reducing machine efficiency
Requires proper lubrication to minimize friction component
Efficiency calculations in DC Motors
Performance analysis of rotating machinery
Option A (Current) relates to Copper losses (I2R).
Option B (Voltage) influences Core/Iron losses (Hysteresis and Eddy Current losses).
Mechanical losses are distinct from Magnetic/Iron losses which depend on Flux density and frequency.
C is correct тАФ Mechanical losses (friction and windage) depend directly on the rotational speed of the DC machine armature.
Always remember that in electrical machines, 'constant losses' (Mechanical + Iron) are independent of load, whereas 'variable losses' (Copper losses) are proportional to the square of the current.