Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
Which loss is negligible for induction motor ?
Stator copper loss
Rotor iron loss
Friction loss
Windage loss
Rotor iron loss
In an induction motor, the rotor iron loss is negligible because the frequency of the magnetic flux reversals in the rotor core is extremely low under normal operating conditions. The frequency of rotor flux is defined by the slip frequency, which is frтАЛ=sтЛЕfsтАЛ, and since the slip s is very small (typically 2-5%) at rated loads, the hysteresis and eddy current losses in the rotor core are minimal.
In an induction motor, the rotor iron loss is negligible because the frequency of the magnetic flux reversals in the rotor core is extremely low under normal operating conditions. The frequency of rotor flux is defined by the slip frequency, which is frтАЛ=sтЛЕfsтАЛ, and since the slip s is very small (typically 2-5%) at rated loads, the hysteresis and eddy current losses in the rotor core are minimal.
frтАЛ=sтЛЕfsтАЛ тАФ Relationship between slip frequency, slip, and stator frequency
PironтАЛтИЭfn тАФ Proportionality of iron loss to supply frequency
The iron loss (core loss) in any ferromagnetic material is directly proportional to the square of the frequency of flux reversals (PhтАЛтИЭf and PeтАЛтИЭf2). In the rotor of an induction motor, the magnetic field rotates at synchronous speed (NsтАЛ), and the rotor rotates at speed (NrтАЛ). The flux cut by the rotor conductors and core changes at the slip frequency frтАЛ=sfsтАЛ. Under normal full-load conditions, s is very small, making the frequency of rotor core flux cycles nearly zero, thus rendering iron loss negligible.
Stator iron loss is significant because it operates at the full supply frequency (fsтАЛ).
Rotor iron loss is only significant at starting or during stalled conditions when s=1.
Under normal running conditions, sтЙИ0.02тИТ0.05.
Friction and windage losses depend on mechanical speed and are non-negligible.
High efficiency at rated load
Low maintenance due to absence of rotor iron loss heating
High starting current
Variable torque performance with frequency
Industrial pumps
Fans and blowers
Conveyor systems
Rotor copper loss (I2R) is the primary loss in the rotor circuit and is NOT negligible.
Option A (Stator copper loss) is significant as it carries full stator load current.
Options C and D (Friction and Windage) are mechanical losses which are significant at high speeds.
B is correct тАФ Rotor iron loss is negligible at normal operating speeds because the slip frequency is very low.
Always remember that while rotor copper loss is a function of slip (PrcuтАЛ=sтЛЕPagтАЛ), rotor iron loss is essentially zero during running conditions; this is a common point of confusion in power system analysis.