start delta starters

[iain1m]

im running a twin shafted mixer 2 motors , 2 gear boxes thatare coupled together with a shaft, im using one star delta starter with two over loads to start the motors. motor 1 runs ok motor 2 runs ok but when i try to run together it takes out the main breaker, rechecked both are going the correct didrection, checked speed is ok any other ideas

 

[waross]

Are the motors the same speed and gear box ratios?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Around here we call S/Delta starters 'political starters'. They're lousy. They're an open transition starter.

What this means is that they disconnect the motor from the power source then reconnect it rapidly. This results in a crapshoot because the motor loses synch with the power source before being reconnected. The reconnection can then be at any place in the power cycle. That's in sync, nearly in sync, or 180 degrees out. Hence the crapshoot. If it drops in 180 out you will trip the breaker.

It's never clear what you will happen start to start. This is why you can start 20 times with no issues then trip the breaker.

It could be you're transition timer needs tweaking or perhaps your breaker is just not going to sustain a second motor starting S/D.

Suggestions:
1) Shorten the transition time.
2) Use a softstarter for the second motor.
3) Use separate breakers for the motors.
4) Use one softstarter for both motors.
5) Use DOL start for the second motor.
6) Use one DOL for both.




Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

"Political starters"! Love it...

I seriously doubt it will EVER work reliably. It's bad enough that you can get (theoretically) a 2000% transition spike with one motor, two would almost guarantee it.

You can do this with a solid state soft starter though. Just quit being cheap on components and wasting money by not having it work.

"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

 

[waross]

If the motors are direct connected and you can use one motor to bring the speed up, you may then go DOL on the second motor. But you must be able to start unloaded every time. If the mixer stops for any reason when it is loaded you will probably have to unload it before you can start again.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

You could add resistors and another contactor to make it a closed transition.