What is broken rotor bar fault?
Broken rotor bar is one of the commonly encountered induction motor faults that may cause serious motor damage to the motor if not detected timely. Specifically, the Hilbert transform first extracts the envelope of the motor current signal, which contains broken rotor fault-related frequency information.
How do you test an induction motor rotor?
HIGH CURRENT ROTOR TEST – This test is performed by applying high current through the shaft of the rotor (rotor out of stator) and thermally scanning (infrared or thermoscan) the rotor O.D. searching for shorted laminations. These shorted laminations cause localized hot spots which cause uneven heating of the rotor.
What is a rotor bar?
The rotor windings are made up of rotor bars passed through the rotor, from one end to the other, around the surface of the rotor. The bars protrude beyond the rotor and are connected together by a shorting ring at each end. The bars are usually made of aluminium or copper, but sometimes made of brass.
What causes 2x line frequency?
The magnetic flux produced by current-carrying conductors in AC machines alternates at line frequency (FL). Therefore all AC motors produce a 2 X line frequency vibration. In power systems that operate at 60 Hz, the vibration frequency is 120 Hz.
Why blocked rotor test is performed at rated current?
A blocked rotor test is normally performed on an induction motor to find out the leakage impedance. In slip ring motor rotor winding is short circuited through slip rings and in cage motors, rotors bars are permanently short circuited.
How is rotor resistance measured?
There exists many methods for online estimation of rotor resistance, such as signal injection-based method, MRAS [2]-[3], least squares method, model observation method and intelligent control method. The least squares method is sensitive to measuring noise and changes in speed.
How to detect broken rotor bars in the frequency spectrum?
Detection of broken rotor bars The location of the frequency components of the current due to broken rotor bars in the frequency spectrum is given by the formula: fsb= f1(1±2s) Hz where: fsb= frequency components of the current due to broken rotor bars, also known as sidebands
How do you test the rotors on a motor?
The rotor bars are magnetized and by the use of iron filings/hacksaw blade you determine a discontinuity of current flow through a rotor bar or a cracked bar. Test works best with a heated rotor. SINGLE PHASE ROTOR TEST – This test is performed while the motor is still together.
Why does a broken rotor bar not show up at no load?
This test will not show up at no load running because a broken rotor bar can not carry current. When it is in an area of high flux, the magnetic forces on the rotor are unbalanced. Since the current flow through the rotor bar is proportional to slip, at no load when rotor current is low, the bar has virtually no magnetic forces acting on it.
What is the most accurate and reliable rotor bar test?
This test is the most accurate and reliable. VIBRATION SPECTRUM ANALYSIS – This test can detect cracked or loose bars while under load. Under load, the vibration will modulate at a rate equal to the number of poles times slip frequency. With a broken rotor bar, the amplitude of the beat increases with load.