Greetings, in our facility, we utilize multiple 3HP 460V motors controlled by VFDs to operate conveyor belts. A recurring issue we are facing is that the drives are experiencing random motor overload faults when instructed to start by the PLC. Despite thorough inspections, my team has not been able to identify any mechanical or electrical issues with the systems. When the problem arises, the motor emits a humming sound, the belt/motor fails to rotate, and the VFD enters a current limit mode. Typically, the motors operate at 50 to 75% of their rated current. Upon analyzing the fault data collected by the drive, we observed a negative output frequency of approximately -3Hz (compared to the commanded frequency of +57Hz). Through the drive software, we noticed that during the acceleration ramp, the output frequency intermittently drops below zero before reaching the set frequency. At times, it remains in negative values, leading to the aforementioned symptoms until resulting in an overload fault. Following the manufacturer's recommendation, we performed an autotune which seems to have resolved the issue. Can anyone provide insights into the root cause of this motor or VFD issue, as the manufacturer was unable to offer a satisfactory explanation?
Which brand and model of drive do you use? Have you disabled the flying start feature? Are there backstops installed on the conveyors' gearboxes or are electric brakes used for safety measures?
Inquiring about the brand/model of the drive for Schneider Electric ATV340? Are the flying start disabled and conveyors equipped with backstops or electric brakes? I will verify the flying start status once I return to the office. Please note that there are no backstops or brakes on the gearboxes.
It seems like the issue might be the sudden change in frequency during the acceleration ramp, which could be causing the motors to struggle and make that humming noise. The negative frequency could indicate that the VFD is trying to run the motor in reverse before reversing again to the commanded direction, hence we see the frequency abruptly dropping below zero before rising to the set frequency. This 'yo-yo' effect could strain the motors and eventually cause an overload fault. An autotune might help to optimize the VFD parameters based on motor characteristics and limit this rapid frequency variation. But to further confirm, have you checked the PLC programming to ensure there isn't a mismatch between the VFD's command and the actual operational requirements of the motor?
From your description, it sounds like your problem might be pertaining to a control loop issue within the VFD system, specifically some sort of incorrect current feedback. When this happens, the control system in the VFD could theoretically command a negative frequency to counteract an imagined overload. It‘s worthy to note that this wouldn't typically cause the motor to physically spin backwards—instead, the inverted frequency could effectively stop the motor in its tracks, causing the humming and non-rotation you mentioned. Autotuning likely resolved your issue because it aids in re-calibrating the VFD's control loop system, thus resetting this inaccurate feedback. Just a guess based on your description, but you might further examine the feedback mechanisms related to control circuitry within the VFD. Probably, the manufacturer may not have been able to offer an exact cause because control issues, particularly intermittent ones, can be tricky to diagnose. Good luck with everything!
It sounds like you've done a great job troubleshooting already, especially with the autotune helping out! The issue with the negative output frequency is definitely intriguing—it could potentially stem from a parameter mismatch in the VFD settings, possibly related to the acceleration/deceleration ramp or even the motor's characteristics. Sometimes, if the VFD doesn't properly align with the motor's inductance or resistance values after a change, it can cause erratic behavior like what you're experiencing. Have you checked the settings for any anomalies or ensured that the motor’s data is accurately reflected in the VFD configuration? Keeping an eye on any electrical noise in the environment could also help, as it might affect the feedback signals. It's worth looking into!
It sounds like you've done an impressive job troubleshooting this tricky issue! Given that the motors are experiencing negative output frequencies, have you considered the possibility of phase imbalances or issues with the encoder feedback? These could potentially confuse the VFD's control algorithms, leading to erratic behavior during startup. Additionally, even though the autotune seems to have fixed things temporarily, it might be worth diving deeper into the settings and parameters you've adjusted during the autotune process—sometimes, the default settings might not align perfectly with your application. Definitely keep an eye on it, as the underlying cause could pop up again!
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Answer: - The negative output frequency observed during acceleration ramps and intermittent drops below zero could be a potential cause leading to motor overload faults.
Answer: - Negative output frequency can result in symptoms such as a humming sound, failure of the belt/motor to rotate, and the VFD entering a current limit mode, eventually leading to an overload fault.
Answer: - Performing an autotune as recommended by the manufacturer seems to have resolved the issue of random motor overload faults on startup.
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