Problems with softstarter
Problems with softstarter
(OP)
Dear All
Attached you will find a sketch with the problem description.
This is happening in many 50 kW, low voltage motors. In all windings we can see on terminal blocks, a phase over-heating.
What could be the cause?
Thanks for the inputs
Carlos
Attached you will find a sketch with the problem description.
This is happening in many 50 kW, low voltage motors. In all windings we can see on terminal blocks, a phase over-heating.
What could be the cause?
Thanks for the inputs
Carlos





RE: Problems with softstarter
Always W winding? I think so.
Balanced currents? Also during start? Any DC component? Anywhere?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Problems with softstarter
The softstarter isn't likely causing this by itself. For example, it could be a combination of a heavy load for the motor and poor soft-starter setup. Too often, people just point fingers before fully understanding the problem.
RE: Problems with softstarter
RE: Problems with softstarter
Yes, it was happened in all motors, not in the same phase but always in one of them.
The starting current is umbalanced in 30% in one phase.
Regards
Carlos
RE: Problems with softstarter
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Problems with softstarter
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Problems with softstarter
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Problems with softstarter
If you can't accept the high current imbalance during starting because it persists long enough to damage the motor then you will have to switch soft-starters for one that controls all 3 phases.
Personally, I would never use one of the POS cheap 2-phase soft-starters on a 50kW motor.
RE: Problems with softstarter
Another inherent danger on that design is a shorted SCR. If you have a 6-SCR design soft starter and one SCR shorts, it's not immediately dangerous to the motor because there is no complete circuit path. But in this design, 1/2 of the circuit path is ALWAYS present, so a single shorted SCR immediately results in unrestricted current flow into one winding.
In addition, SCRs can "self commutate" (turn themselves on) if there is a high dv/dt situation, such as high noise spikes on the line. Normally because you would need to have at least TWO of the SCRs self commutate for that to be a complete circuit, it's not much of a problem. But again, because 1/2 of the complete circuit is ALWAYS present here, it can be.
At the very least, I would put isolation contactors ahead of these soft starters so they are truly off-line when not being used. Ideally, junk them and start over with a 6 SCR designed soft starter.
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Problems with softstarter
Tell us what make and type of motors and SS.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.