WYE ûDELTA MOTOR STARTERS OPEN TRANSITION FOR 170 HP MOTORS WHAT KIND 1

[fwivey]

The motor starts in Wye runs for ten minutes with the delta windings shunted. The motor starter for the Wye has no thermal overload protections. The delta starter has thermal protection. The question; what can I do to protect the motor during the 10 minute start-up

 

[jtkirb]

add overload protection to the wye contactor....

JTK

 

[jraef]

Any standard OL relay is going to trip in 10 minutes of starting current, even in Y. Most likely you have a custom motor, probably a centrifuge. Most of them are custom designed specifically for this kind of application and are expected to start without any overload protection. To do it properly, you should have a motor protection relay connected on the line side of the starter that has separate starting and running protection curves. You then need the protection information from the motor mfgr to design a custom curve for starting, i.e locked rotor current, thermal time constant, stall time and current etc. etc. A Multilin 469 is a good one for this, or possibly a Schweitzer SEL-701, although I'm not sure about separate curves on that one. I'm sure there are others. The problem is, the relay will likely cost more than the motor! That's why most people choose to go 'naked' on Y-D centrifuge start up, with just the short circuit protective device.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[rbulsara]

Explore installing a VFD on delta winding and do away with wye.

 

[waross]

if it is a centrifuge, then be guided by the posts of those with direct experience.
The ten minute starting time is new to me.
However, the Star/Delta motors and motor starters that I am familiar with in industrial settings do not have two seperate windings, one Wye and one Delta.
They have three windings. The windings are connected in Wye for starting and reconnected in Delta for running.
To connect in Wye, three leads have to be connected together.
Heating in a winding is dependant on the current in the winding. On the wye connection, the motor current will equal the winding current. On Delta the motor current will be 1.73 times the winding current. In a Star Delta motor both ends of all three windings are brought back to the starter. The
winding current is monitored by an overload device that may be physically located next to the contactor which completes the Star connection.
The question is:
Is the Delta winging shunted, or is the protection shunted while on the Wye connection.
If you have mistaken the contactor that completes the Wye connection for a "Delta Shunting" contactor, then most likely everything is as it should be and the windings are properly protected by the existing overload device.
I'm worried about the 10 minutes starting time. If it is the actual starting protection that is "Shunted" during starting, then disregard this and reread raef's post.
Remember, there is NOT a Wye and a Delta winding. There are three windings that are reconnected in Wye or Delta.

 

[aolalde]

Fwivey.

Provide the complete nameplate data and load type. We could be guessing for ever. Is this a two speed single-winding motor?

 

[Fintan]

I have had this problem many years ago on induction generators (before inverters & soft starters were available)
There is a possibility that the star contactor will burn out if it is not properly rated. It should be the same size as the line contactor & both should be rated for Locked Rotor Star current for 10 minutes.
I assume that the motor is water cooled.
In future use an inverter or a liquid resistance with a wound rotor motor.

Regards

Fintan