Starting Current of a Synchronous Motor ?

Hi all
Let me know the ratio/ level of Starting Current of a Synchronous Motor ?
Normally i think it will be 4.5times the Full Load Current
Please give me answer
regards
N.A.Govind
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Can you be more specific on the motor? Synchronous motors cover a wide range, from tiny clock motors to x1000's hp industrial beasts.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Syncrhonous motors have no starting torque of their own. So the common method of starting them is to add a squirrel cage winding to the rotor and start it as an induction motor.
Because the 'squirrel cage' rotor is only designed for minimal power, it typically will draw *more* than a typical induction motor when starting. And it must be started 'unloaded' as much as possible. One such motor I've worked with has starting current in the range of eight to ten times full load.
Assuming you're not talking about some sub-sub-fraction of a hp motor like a clock :-)
daestrom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
daestrom is correct, the squirrel cage winding is call the amortosuirre (sp) winding and only has enough beef to get the rotor near synchronous speed. The industry I came from used 700hp snyc. motors and the starting current pegged a 6000amp meter, although it was short duration I have no idea what the start current was, didn't have an instrument to measure it. I'd say for a large motor daestrom's estimate of 8-10x is conservative.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.