How many rotor bars does my motor have?
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.
What is a motor 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.
How many Poles has the rotor of the motor?
As shown in Figure 9, the stator has six magnetic poles and the rotor has two poles.
What are rotor bars used for?
The interaction of the magnetic fields of currents in the stator and rotor produce a torque on the rotor. By adjusting the shape of the bars in the rotor, the speed-torque characteristics of the motor can be changed, to minimize starting current or to maximize low-speed torque, for example.
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 do you measure a rotor bar?
The rotor induces currents back in the stator windings. These currents appear as side bands around the supply line frequency (60 HZ) peak, and are a function of the motors number of poles and slip frequency. By comparing the sideband amplitudes, you can estimate the number of broken rotor bars.
What is rotor consist of?
The rotor is a cylindrical core made of steel lamination with slots to hold the wires for its 3-phase windings which are evenly spaced at 120 electrical degrees apart and connected in a ‘Y’ configuration.
What is rotor bar pass 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.
What is broken rotor bar?
If a rotor bar is broken, the amplitude of the beat increases with load. In addition, a cracked rotor will lead to a localized increase in temperature, which in turn causes bowing and uneven expansion. This results in imbalance, additional vibration, and side bands that are related to slip frequency.
What is a 2 pole 3 phase motor?
On a three-phase motor the pole pattern has to be repeated for each phase. Therefore a 2=pole, 3-phase motor will have six poles.
How many types of rotors are there?
Induction motor rotor is of two types: Squirrel Cage Rotor. Wound Type Rotor or Slip Ring Type Rotor.
Which is better 2 pole or 4 pole motor?
The speed of the motor depends on the number of poles and frequency. The speed of the 2 poles and 4 poles machine is 3000 RPM and 1500 RPM respectively. As the other Answer which is correct. Speed is double that of a 4 pole Motor.
Which motor has no rotor winding?
An induction motor can therefore be made without electrical connections to the rotor. An induction motor’s rotor can be either wound type or squirrel-cage type. Three-phase squirrel-cage induction motors are widely used as industrial drives because they are self-starting, reliable and economical.
Why are the rotor bars of a motor skewed?
The rotor or stator slot of the induction motor skewed through some angle so that the bars lie under alternate harmonic poles of the same polarity or other words, bars must be skewed through two pitches. The main purpose of skewing is to reduce the magnetic logging between the starter and the rotor.
Is squirrel cage motor synchronous?
Synchronous motor: Stator has axial slots which consist stator winding wound for a specific number of poles. … It is wound for a specific number of poles. A squirrel cage rotor or a wound rotor can be used. In squirrel cage rotor, the rotor bars are permanently short-circuited with end rings.