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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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What is the role of Compensating winding in the universal motor?
To reduced the sparking at the brushes
to improve power factor
to improve efficiency
All of these
All of these
Quick Summary: Compensating windings in a universal motor are auxiliary windings connected in series with the armature to neutralize the armature reaction. By nullifying the cross-magnetizing effect of the armature MMF, they reduce sparking, improve commutation, and enhance the overall efficiency and power factor of the machine.
Compensating windings in a universal motor are auxiliary windings connected in series with the armature to neutralize the armature reaction. By nullifying the cross-magnetizing effect of the armature MMF, they reduce sparking, improve commutation, and enhance the overall efficiency and power factor of the machine.
Mc=−Ma — The compensating MMF (Mc) is equal and opposite to the armature MMF (Ma)
Φnet=Φmain+(Φa−Φc) — Net flux is stabilized as Φa≈Φc
In a universal motor, the armature current creates a flux that opposes or distorts the main field flux (armature reaction). By placing a compensating winding in the stator slots such that it carries a current equal and opposite to the armature current, the induced armature MMF is effectively cancelled. This reduction in armature flux linkage decreases the leakage reactance, which directly improves the power factor and prevents excessive voltage drops, leading to higher efficiency and reduced brush sparking.
Compensating windings are connected in series with the armature circuit.
They neutralize the cross-magnetizing flux produced by the armature.
They are primarily used in high-power universal motors to ensure commutation stability.
They effectively reduce the reactance voltage in the coils undergoing commutation.
Reduced sparking at the brushes
Improved commutation
Higher power factor
Increased machine efficiency
Increased manufacturing cost
Increased complexity in stator design
Requires more space in the stator slots
High-power universal motors
Portable power tools
Large domestic appliances
Sparking occurs due to the reactance voltage in the armature coils; compensating windings mitigate this by reducing the flux per ampere.
Option B and C are correct because improving the flux profile and reducing armature leakage reactance directly contributes to better power factor and efficiency.
D is correct — The compensating winding neutralizes armature reaction, which simultaneously reduces sparking, improves the power factor, and increases the efficiency of the motor.
Always remember that in AC machines, neutralising armature reaction is synonymous with improving both commutation quality and overall efficiency due to reduced copper and stray losses.