soft starter still tripping main breaker

[krbernier]

i have 2 smc-flex soft starters running 350 hp motors at a water lift station. the main 1600a incoming breaker is tripping when one of the motors is shut off. sometimes it trips sometimes it doesn't. i finally got the use of a fluke 435 power quality meter and was able to record the main when it tripped.

i have a recording of a normal shutdown and a shut down with a trip.

when this happened both motors were running and only one was shut down. stop time is 15 seconds. im going to attach both recordings hoping someone with more knowledge can help!

 

[krbernier]

now the recording of the trip

 

[itsmoked]

I can't view those strange file types. And I sort of doubt a lot of others will be able to see them either.

Can you post them in another format? pdf, jpg, gif?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

CAREFUL!
In doing a search for that file type it appears to be an extension used by FoxPro, a MS dBase program, but I also got hits on a number of worms and trojans!



"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[krbernier]

they are fluke power logger files

 

[krbernier]

fluke power log 2.9

 

[krbernier]

i will try to figure out how to post screens off of power logger

 

[Zogzog]

What type of trip are you getting?

 

[jraef]

Do you have software on your PC that is allowing you to view them on your screen? If so, hit "Print Screen" (usually with the Ctrl key) and you will get a screen capture copied to your Scratchpad, then you can paste it into MS Paint which will allow you to save it as a jpeg file type (using the Save As function and changing the file type).

Comes out like this:


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[krbernier]

i am pretty sure it is a harmonics issue.

here is a screen shot of the harmonics when it trips.

 

[jraef]

Harmonics generally don't cause a main breaker to trip. What are we looking at there, is this the minute before the trip even or after?

Are your SMC-Flex starters set up for Decel of the pumps to reduce water hammer? If so, what is the size of your main breaker? It's entirely possible that when one is running full load and the other goes into Decel, the current is exceeding the capacity of the main breaker. Just a SWAG though at this point.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[krbernier]

this is the harmonics when the breaker trips. on a shutdown without a trip the thd is less than 1%.

max current is well below the trip setting of the breaker.

the smc does decel the motor. main breaker is 1600a instantaneous trip setting is set at 4600a. the trip occurs after the current has dropped.

i will post screens of the voltage and current when it trips.

this is the power harmonics of a normal shutdown

 

[krbernier]

here is a screen of the voltage and current when it trips

 

[krbernier]

now voltage and current of a normal shutdown

 

[LionelHutz]

I can't make out anything useful from your attachments. Did you open and look at the final file yourself before you attached them?

 

[krbernier]

yes i can see them fine....are they blurry?

 

[krbernier]

since it appears no one can see the info i have from the fluke 435 lets try it this way.....

when the breaker trips the power harmonics screen is showing THD of 60%.

when the motor stops and the breaker doesn't trip THD is .4%.

why am i getting so much distortion intermittently and what can i do to stop it?

this is a 480v wye system with no neutral load. ab smc-flex soft starters.

 

[electricpete]

There motors "share" a load.... like parallel pumps, right?

Is it possible that when you switched off one motor, the other motor becomes overloaded beyond breakdown torque?


=====================================
(2B)+(2B)' ?

 

[electricpete]

Looking at the other (non-trip) curve, there is also a large current increase (800 to 1500A), followed by a current decrease (down to 400A).

I would propose this scenario: when you shut off one pump, discharge pressure initially goes down and the remaining pump is initially overloaded. Then maybe there is some automatic water pressure control mechanism which acts to limit the demand and bring the discharge pressure back up..... so remaining motor sees a 5-10 second overload which may or may not be enough to trip it. Can you tell us a little about the water system?

=====================================
(2B)+(2B)' ?

 

[krbernier]

there are 2 pumps both feeding into a single discharge line.
i dont see any additional loading of the pump that is still running. flow is halved and pressure drops slightly.

i see the current climb to about 1500 amps while the motor stops. motor stop time is 15 seconds.

after the current has peaked and the motor is almost stopped the main breaker trips. this is when i see the harmonic distortion. im pretty sure the gfi is tripping because of the thd on the neutral.