What do rotor bars do?

What do rotor bars do?

The axial currents in the rotor bars will interact with the radial flux wave to produce the driving torque of the motor, which will act in the same direction as the rotating field, the rotor being dragged along by the field.

What causes rotor bar failure?

The thermal stress during motor starts and at running overload conditions is a major cause of broken rotor bar/end- ring faults in medium-voltage induction motors [12]. The excessive overheating of the rotor cage causes thermal expansion and thus mechanical stresses on the rotor cage structure.

What is rotor bar current?

Bar current in the rotor of a squirrel cage induction motor may be determined by comparing the mmf developed in rotor and stator.

What is rotor bar frequency?

As a loose rotor bar passes a winding slot, the magnetic force causes it to momentarily lift and then drop. The frequency, then, is the number of windings slots x RPM (Winding Slot Pass Frequency or WSPF). The number of winding slots will be between about 25 and 100.

Why are squirrel cage rotor skewed?

The conductors are often skewed slightly along the length of the rotor to reduce noise and smooth out torque fluctuations that might result at some speeds due to interactions with the pole pieces of the stator, by ensuring that at any time the same fraction of a rotor bar is under each stator slot.

Why rotors are skewed?

If the rotor and the stator conductors are parallel to each other, there is a strong possibility of the magnetic locking between the rotor and the stator. Therefore, the rotor slots are skewed.

How do you know if a rotor bar is broken?

5 Common Ways To Detect A Broken Rotor Bar

1. Single Phase Rotor. The single phase rotor test is looking to see if there is any alternation in AMP draw.
2. Vibration Spectrum. This is a good test to conduct if the motor is running under load.
3. High Current Rotor.
4. Current Spectrum.
5. Growler.

What is broken rotor bar?

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. Past efforts on broken rotor bar diagnosis have been focused on current signature analysis using spectral analysis and wavelet transform.

How is rotor bar frequency calculated?

Loose or open rotor bars in AC induction motors are indicated by a 2 X line frequency (2 FL) sidebands surrounding rotor bar pass frequency and/or its harmonics (rotor bar pass frequency = number of bars X rpm).

How are motor rotor bars calculated?

One other method to determine the number of rotor bars it to examine the the RBPF +/- K*2LF pattern in vibration: take vibration using high Fmax (above RBPF) and high # lines (to get good frequency resolution) – something like Fmax=300,000, lines =6400. Look for the set of peaks separated by by 2*LF.

Why are squirrel cage motors so reliable?

They are low cost. Require less maintenance (as there are no slip rings or brushes) Good speed regulation (they are able to maintain a constant speed) High efficiency in converting electrical energy to mechanical energy (while running, not during startup)

Which motor has no rotor winding?

Hysteresis Motor
Detailed Solution. Hysteresis Motor: Hysteresis motor is a single-phase synchronous motor with a cylindrical rotor made up of ferromagnetic material and does not require any DC excitation to the rotor. Construction of Hysteresis motor: Hysteresis motor consists of a stator and rotor.