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WHAT IS A SALENT POLE
5

WHAT IS A SALENT POLE

WHAT IS A SALENT POLE

(OP)
I AM JUST STARTING OUT IN ELECTRIC MOTORS LOOKING FOR INFO. IF ANYONE CAN HELP ALL INFO IS WELCOME

RE: WHAT IS A SALENT POLE

Salient means "sticking out".

Some lower speed syncronous machines use salient pole rotors. That means the rotor windings are wound on a pole piece which sticks out from the center of the rotor. The other type of rotor used on higher speed machines is a smooth rotor which has grooves for the winding so nothing sticks out.

RE: WHAT IS A SALENT POLE

There are some good pictures of the type of machine mentioned by electricpete on this link:
http://gess.ge.com/pdf/acdc_mo_4_large_ac.pdf
e.g. top of page 5 and bottom of page 8.

Another example is a switched reluctance motor, they have laminated poles on the rotor that stick out, though no windings.  For example see:
www.fleadh.co.uk/srm.htm

Note that although stators (the stationary outer structure in a motor on which the windings are mounted) normally have teeth and slots, they are not described as salient - maybe because the teeth are relatively small.

RE: WHAT IS A SALENT POLE

Suggestion: Visit
http://www.tech.purdue.edu/eet/Courses/eet331/331lc04.pdf
etc. for more info.
Reference:
1. IEEE Std 100-2000 "Dictionary" defines the salient-pole machine as an alternating-current machine in which the field poles project from the yoke toward the armature and /or the armature winding self-inductance undergoes a significant single cyclic variation for a rotor displacement through one pole pitch.

RE: WHAT IS A SALENT POLE

Synchronous motors is usually of a salient pole type construction with the higher number of poles corresponding to the low speed of a 2-speed motor. The high speed is obtained by regrouping the poles so as to obtain two adjacent poles of the same polarity followed by two poles opposite polarity. This gives the effect of reducing the number of poles on the rotor by one half for high speed operations.

Synchronous motors require an unfailing external source of direct current for field excitation. Excitation voltages are norminally 125 volts for small motors and 250 volts for large motors.

Kind Regards,
motorhead

RE: WHAT IS A SALENT POLE

First of all, the spelling is "salient".
The answers provided thus far are correct.

However if your new to the electric motor repair industry, a basic understanding of what a salient pole motor (or generator) does.

In a 3 phase AC induction motor, when voltage is applied to the stator windings, a rotating magnetic field is generated.
Current is then induced into the rotor cage and the magnetic fields in the rotor are both attracted and repelled by the rotating field of the stator, resulting in shaft rotation.  The higher the current, the stronger the magnetic field.  However, in an induction motor, there is a certain amount of slip as more load is applied, that's why a induction motor's full load rpm rating may be 1785, for example, rather than 1800 rpms.  At no load, the motor should run pretty close to synchronous, that is the rotor is turning as fast as the rotating magnetic field, but as load is applied, more slip comes into play. (can be 5% or more)

In a synchronous motor, the salient poles described by the others are energized with a DC current.  This DC current in the salient pole creates a stronger magnetic field than can be induced in an induction motor's rotor.  This DC magnetic field then "locks on" to the rotating magnetic field of the stator.  As load is applied, the strength of this field is such that there should theoretically be "NO SLIP", as long as the load is not greater than the hp design for the motor. That's why the motor is called "synchronous", because the rotor is synchronized with the stator field.

Further, salient poles are used in portable power generators for the reverse process.  DC current once again flows in the salient fields, but this time it is used to excite current in the stator winding by the passing of magnetic fields through a coil (as you should have learned in the very earliest "how a motor works theory").

The DC for the main rotor salient poles is usually generated by an exciter, which again uses the passing of a coil through a fixed magnetic field of some kind.  That however, we can save for another discussion.  Feel free to come to my office anytime.

KR

RE: WHAT IS A SALENT POLE

Small encore. The salient generators are usually applied to hydroprojects because of the low speed of hydro turbines.
Another interesting phenomenon is the somewhat different two-reaction theory. The synchronous reactances are:
Xsd=X+Xad
Xsq=X+Xaq
for the direct and quadrature axes respectively.
The q-axis reactance is smaller than the direct-axis reactance because a given m.m.f. gives the rise to a smaller gap flux.                          

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