[TCML] Salient Pole Query Fresh Post

["Phil Tuck" <follies@xxxxxxxxxxxx>]

Hello. I have reposted this thread as the order of the replies had become
jumbled in the web page version. (Possibly by me replying out of order? I'm
not sure)

 

[MODERATOR:-] What is the best way to reply to avoid this problem? The
posting rules make no mention.

 

 

JOHN:

I think you have solved things. Prior to modification the speed was 1440
[just under] on a decent hand held tacho. Now it is 1498 - 1501 rpm
variable. I checked it this time using an electronic rev counter [Microset
Clock Timer, that uses a photo electric] The mechanical one also gave 1500
in this instance.

 

I no longer have a Variac [don't ask] so could not observe the hunting
period that you and the archives often refer to.

 

I am presuming you can't convert an induction into a Hysteresis by accident
using the pole shaving method, if so mine would appear to be correctly done
at 1500 rpm.

 

Regards

Phil

 

Futuret wrote:-----

 

 

Phil,

 

No. Only a sync motor will run at 1500 rpm. An async induction motor will 

run at around 1425 rpm.  BUT there is another type of sync motor

(not salient pole) This other type is called "hysteresis" sync motor. This
type will run at 1500 rpm, but will always start in a different position. 

Oviously you want the salient type.  When you modify a 1425 induction

motor to make it salient, it will always give 1500 rpm, and will always

sync-lock to the same phase.

 

If you have an old fastioned flourescent fixture (not electronic) it's

pretty easy to verify sync lock.  Just slow the motor with a variac

and vary the speed and observe carefully, and you'll see the very

blurry rotating pattern.  then as you raise variac voltage, pattern

will stop rotating at some point.  Also you will hear the sound change.

When you're near (but below) sync lock voltage, you'll hear the motor

hunting (uneven pulsing sound), then as you raise voltage.  The sound

will become very steady roaring sound. Some folks take awhile to "learn" how
to see this pattern. But after you learn, it's very easy to see. Also make
sure there isn't daylight or other indescent lights on in the room. These
motors often sync lock at about 50 to 60% line voltage or so. (without a
electrode 

rotor attached).

 

Some people prefer to build a circuit like a strobe to check sync-lock.

 

John

 

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