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!
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
RE: soft starter still tripping main breaker
Can you post them in another format? pdf, jpg, gif?
Keith Cress
kcress - http://www.flaminsystems.com
RE: soft starter still tripping main breaker
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!
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RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
Comes out like this:
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RE: soft starter still tripping main breaker
here is a screen shot of the harmonics when it trips.
RE: soft starter still tripping main breaker
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.
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RE: soft starter still tripping main breaker
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
RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
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
Is it possible that when you switched off one motor, the other motor becomes overloaded beyond breakdown torque?
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(2B)+(2B)' ?
RE: soft starter still tripping main breaker
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?
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(2B)+(2B)' ?
RE: soft starter still tripping main breaker
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
Attached I have put 2 of the pictures into powerpoint and resized...may be easier to read
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(2B)+(2B)' ?
RE: soft starter still tripping main breaker
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
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?
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(2B)+(2B)' ?
RE: soft starter still tripping main breaker
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
RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
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(2B)+(2B)' ?
RE: soft starter still tripping main breaker
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(2B)+(2B)' ?
RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
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(2B)+(2B)' ?
RE: soft starter still tripping main breaker
attached is both recordings in power log format incase you decide to install it.
RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
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.
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RE: soft starter still tripping main breaker
i am leaning towards replacing the trip unit with one that has an adjustable gfp.
RE: soft starter still tripping main breaker
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RE: soft starter still tripping main 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
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RE: soft starter still tripping main breaker
the 4500a is causing the breaker to trip on the instantaneous setting.
RE: soft starter still tripping main breaker
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RE: soft starter still tripping main breaker
RE: soft starter still tripping main breaker
Hire somebody that can find the problem rather than simply trying to find a way to mask the symptoms.