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soft starter still tripping main breaker

soft starter still tripping main breaker

soft starter still tripping main breaker

(OP)
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!  

RE: soft starter still tripping main breaker

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

RE: soft starter still tripping main breaker

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  
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RE: soft starter still tripping main breaker

(OP)
they are fluke power logger files

RE: soft starter still tripping main breaker

(OP)
fluke power log 2.9
 

RE: soft starter still tripping main breaker

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

RE: soft starter still tripping main breaker

What type of trip are you getting?

RE: soft starter still tripping main breaker

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  
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RE: soft starter still tripping main breaker

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  
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RE: soft starter still tripping main breaker

(OP)
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

RE: soft starter still tripping main breaker

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

 

RE: soft starter still tripping main breaker

(OP)
yes i can see them fine....are they blurry?

RE: soft starter still tripping main breaker

(OP)
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.

RE: soft starter still tripping main breaker

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)'  ?

RE: soft starter still tripping main breaker

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)'  ?

RE: soft starter still tripping main breaker

(OP)
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.

RE: soft starter still tripping main breaker

Quote:

which may or may not be enough to trip it
actually for some reason if there is individual pump protection, it seems that it is not coordinated with the main breaker.

Attached I have put 2 of the pictures into powerpoint and resized...may be easier to read

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

RE: soft starter still tripping main breaker

(OP)
the current increase is the motor stopping. each motor pulls 400A running normally.  the softstarts do not fault. the fuses in the soft starts dont blow and the 600a breakers feeding the softstarts dont trip. the 1600A main trips.  the instantaneous trip setting is set to 4600A. so the breaker is not tripping on overcurrent.

im thinking of changing the trip unit in the main breaker to one that has an adjustable gfi.

i am also thinking about line reactors on the drive outputs but i am still unsure what is the best option.

RE: soft starter still tripping main breaker

I see a dramatic increase in current when the motor is shut off.

It suggests either:
1 - the remaining pump is overloaded... either due to system requirements or maybe backflow through the secured pump (discharge check valve malfucntion?)
or else
2 - the pump being secured is ramped down in voltage slowly and so draws increasing current during shutdown?

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

RE: soft starter still tripping main breaker

(OP)
i have alot more readings from these motors...would you like to see the 2 sets of power harmonics recordings?


i also have the complete recordings in fluke power log if you have that installed..actually i have a copy of power log you can have if it will help

RE: soft starter still tripping main breaker

(OP)
number two would be correct...the softstart reduces voltage to slow the pump before dropping it out completely...this is set at 15 seconds stop time to avoid water hammer

RE: soft starter still tripping main breaker

So, an increase in current is expected during shutdown.  Do you have a long-time overcurrent trip on your main breaker that is tripping?  How close does it come to the current excursion seen during normal shutdown?

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

RE: soft starter still tripping main breaker

What I meant is: if you plotted time vs current during shutdown, how close does it come to the time/current curve of the main breaker time overcurrent trip?

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

RE: soft starter still tripping main breaker

(OP)
i am way below all trip settings on the breaker...

RE: soft starter still tripping main breaker

then... the breaker is malfunctioning due to trip with current far below all settings?

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

RE: soft starter still tripping main breaker

(OP)
i believe the breaker is tripping because of the gfi. the harmonics are "fooling the gfi trip unit because they are in the neutral.

RE: soft starter still tripping main breaker

When you soft stop using a solid state starter, you are doing phase-angle voltage reduction and that is inherently harmonic rich, especially as the phase angle is at the lowest levels. So in this case that would be right when the soft stop function is almost complete. You can technically mitigate it somewhat with load reactors, but that will also cost you in added permanent losses in the motor circuit. Most likely though, you are probably right that the GFP on the breaker is picking up some of the harmonics as a current imbalance and falsely tripping. Can you increase the delay time on the GFP? It might be one of those issues that can be easily solved by understanding and adjusting to the reality rather than chasing a cure.

If I remember correctly, the older A-B SMC soft starters had an issue with how they did the Decel function and as a result, they had to disable the OL protection in the starter while soft stopping. Their original Pump Stop system was closed loop with a PF feedback but if the pump response took too long, it stayed in the voltage control mode and caused an OL trip before it detected that the valve had closed. This came to my attention because of a spectacular (and very expensive) series of large pump failures I heard about at the Las Vegas Valley Water District during an IEEE meeting I presented at down there. But to be fair, I was told they fixed that when they released the SMC Flex a few years ago.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
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RE: soft starter still tripping main breaker

(OP)
unfortunately the gfp is non adjustable on this trip unit.

i am leaning towards replacing the trip unit with one that has an adjustable gfp.

RE: soft starter still tripping main breaker

Might be the least expensive solution. Or disable it in the breaker (i.e. un-wire the shunt trip from the sensor) and use an external GF relay wired to the shunt trip. What breaker is it?


"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: Eng-Tips.com Forum Policies  

RE: soft starter still tripping main breaker

(OP)
seimens type vl   breaker

pg frame 1600 amp

right now it has a 545 lig trip unit with fixed gpf sensing and delay.

im going to replace it with a 576 lsig trip unit that is fully adjustable

RE: soft starter still tripping main breaker

Oh yeah, that would be easier. The 545 trip unit is referred to as "out of the box GF coordination" but in reality it's just the least expensive way out of the requirement, so nothing is adjustable.  


"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: Eng-Tips.com Forum Policies  

RE: soft starter still tripping main breaker

(OP)
after further scrutiny of the logs. there is a huge amperage imbalance happening during motor stop. at the point of trip the amps are  L1- 4000 A  L2 4500A  L3 1500 A.

the 4500a is causing the breaker to trip on the instantaneous setting.

RE: soft starter still tripping main breaker

4500A instantaneous trip setting on a 1600A breaker is pretty low in my opinion, that's only 281%. For example on the 525 trip unit on a 1600A VL breaker you can't set the IT below 7000A. The 545 trip unit allows you to set it as low as 1.5X In, but that doesn't mean that's a good idea. Has anyone ever done a Fault Coordination Study at your facility? Sounds as though you need one. At the very least your IT setting of the main should be higher than any down stream device, unless you like having a complete shutdown.

 


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
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RE: soft starter still tripping main breaker

(OP)
this facility was engineered and installed by the electrical contractor. the soft starts have 800 amp time delay fuses in them. they are fed by 600 amp circuit breakers. other that a lighting transformer these are the only loads on the switchgear.  i will try adjusting the IT setting to 5600a (350%) hopefully this will allow it to ride through the shutdown. per nec code i cant adjust any higher correct?

RE: soft starter still tripping main breaker

You need to find someone locally who understands these types of systems.  The problem can't be solved over the internet.  Everybody that has answered here has woefully incomplete information about the problem and are offering ideas based on that incomplete information and you want to take stabs in the dark based on those suggestions.

Hire somebody that can find the problem rather than simply trying to find a way to mask the symptoms.

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