How to 'size' contactors for star delta circuit ?

[electek]

Hi All , How do i size the main , star and delta contactors for a motor control circuit using a 50Kw motor ? Do i just rate all contactors at 50 kW ?

Any help appreciated.

Thanks

 

[davelerave]

at a guess size the main for the the FLA ac3 rating

the star and delta contactor maybe 60% FLA ac3 or more

the overload can go in any of 3 places for star/delta in theory

 

[benji]

Why not just buy a 50 kw s/d starter

yours benji

 

[benji]

CLE Electrical Wholesales 50kw open frame starter £299.00

yours benji

 

[davelerave]

that should be 35,60,100% for star delta and main

the main contactor makes in star but breaks FLA

can't recall if they're sized that way in practice-i assume so

the overload in series with the motor windings gives the closest protection folowed by supply lines and delta

 

[ericks]

Hi All , How do i size the main , star and delta contactors for a motor control circuit using a 50Kw motor ? Do i just rate all contactors at 50 kW ?

Any help appreciated.

Thanks

Hi there,
Main = IFL x 0.58 - if your main contactor is in phase, else IFL.
Delta = IFL x 0.58
Star = IFL x 0.33
Note your overload size/setting:
If your overload in in line the = IFL
If your overload is in phase then = IFL x 0.58

Just remember you are starting a motor so choose contactors at ac3 rating.

Greetings

 

[davelerave]

ya the main is in phase on my drawing as well ( i misread it) so thats 35,60 and 60 appprox for star delta and main


i i supppose the 'main' may go on the lines as well if the overload is placed there so that would be 35,60 and 100 in that case

 

[thepurple1]

Star Delta is an old way of doing thing now, on something this size we would use an inverter. most companies have now changed over to soft starts but the do get hot so you panel will need some ventilation/fan