Troubleshooting series: Current unbalance

Just before 5:30 am on a weekday morning, you receive an urgent notification on your cellphone from your EAM application: “Motors@Work detects a 100% current unbalance on Pump #1.”

So begins two recent stories told by two Motors@Work clients affecting two different pump assets. Here’s how Motors@Work helped both of them identify, troubleshoot, and resolve two very different situations that otherwise would have gone undetected without Motors@Work’s timely condition-monitoring alerts.

Since a current unbalance of 100% means at least one phase is not drawing current, the maintenance supervisors who received these alerts immediately dispatched technicians to the sites.

The message from Motors@Work contains help content as well as that asset’s most recent measurements to help the technician troubleshoot the issue. Motors@Work’s suggested actions include

  1. Verify the measurement and data transmitted to Motors@Work
  2. Check whether the motor’s leads are loose
  3. Check for blown fuses in any power-factor-correction device, motor starter, or VFD
  4. Troubleshoot whether the current unbalance originates from the motor or your power supply

So, when the technicians arrive at their respective sites 30 minutes later, they proceed to verify the measurements. And this is where our two stories diverge:

CLIENT ONE

Using a clamp-on ammeter, one technician immediately finds that the motor is not experiencing the purported current unbalance — i.e., the current on all phases coming into the motor are balanced. Following our advice to check the data transmitted to Motors@Work, the technician begins troubleshooting upstream, checking the current coming into the VFD, the VFD’s reporting of those current measurements, and finally, how the PLC reports the measurements to SCADA. The technician finds that the PLC has one phase of current mapped to a different variable; so, he corrects the assignment, makes his notes, and closes out the work order.

During our after-action review, we learned that another technician replaced that PLC the day before and improperly commissioned it, which would have continued undetected without Motors@Work’s alert.

CLIENT TWO

This client’s technician finds the reported current unbalance to be accurate — one phase is drawing zero current. He calls Operations and asks the operator-on-duty to shed load, then begins working through Motors@Work’s troubleshooting steps.

Quickly working from the motor back, he first checks the motor’s leads; next, he checks at the VFD. The VFD is receiving three balanced phases of current and voltage, but only outputting two. A visual inspection confirms that one of the relays in the inverter circuit burned out. The technician radios the operator to remove the motor from service before the dropped phase can do any more damage.

The technician orders the component; later, once the motor has cooled, he runs a Megger test to check the motor’s windings. Since we caught this early, the motor is still healthy. When the part arrives the next day, the component gets replaced and the pump returned to service.

In both of these cases, Motors@Work’s continuous, near-real-time condition monitoring alerts caught potentially motor-damaging conditions that would’ve gone unnoticed otherwise. Additionally, our help content and content-rich alerts reduced the time required to troubleshoot the issue. Most importantly, Motors@Work enabled our client to intervene before conditions could damage their motor-driven asset.

How will condition monitoring benefit your organization? Email Nicole at info@motorsatwork.com to learn more.

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