star/delta problem
star/delta problem
(OP)
I have a three phase motor that is tripping the overload soon after start-up. L1 and L3 are pulling 40 amps, whereas L2 is pulling nothing. Motor rated for 20A. There is full voltage on each phase going to the motor on one set. There are two sets of cables going to the motor windings and the second set has L2 and L3 at half voltage, while L1 has full voltage. Can anyone explain what might cause this?





RE: star/delta problem
Rafiq Bulsara
http://www.srengineersct.com
RE: star/delta problem
RE: star/delta problem
Rafiq Bulsara
http://www.srengineersct.com
RE: star/delta problem
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: star/delta problem
RE: star/delta problem
From your description I would venture to say you have an Elevator controller set up for star-delta starting. These applications are notorious because they only use 2 contactors (strictly to save money) and one side of the motor windings is energized at all times. So if you have a welded contact, which happens a lot on star-delta starters, and you are checking for a blown fuse by measuring voltage, it will falsely read as "full voltage" even though a fuse is bad because the motor windings do not present enough resistance to show a significant voltage drop on a 9VDC battery (what's in your VOM).
So even if you do have a blown fuse, check the contacts of your contactor(s) to make sure the cause wasn't a welded contact. And by the way, that most likely damaged the motor windings as well. Such is the down side of that cheap 2-contactor configuration.
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RE: star/delta problem
RE: star/delta problem
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: star/delta problem
RE: star/delta problem
Glad that you found the issue and was able to fix it. Also thank you for the update, not everyone does that.
Rafiq Bulsara
http://www.srengineersct.com