Prior joint research by Advanced Energy and Duke Energy recently helped solve a 10-year-old mystery at a sewer pump lift station.
The lift station has two pumps it can use to move waste and water runoff to a nearby treatment facility. Starting in 2008, however, the pumps would not function as intended: When both attempted to run simultaneously, they would cycle on and off every few seconds and then shut down due to excessive starting.
An investigation by Duke Energy at the time revealed no noticeable utility-related issues, and without a solution, the lift station got by operating just a single pump. With the recent hurricanes, heavy rainfall and flooding, however, additional help was needed. The lift station attempted to run both pumps again, but the problem remained. The customer believed the issue stemmed from electricity delivery because both pumps worked fine when drawing power from backup generators, so Duke Energy returned to the site.
Matt Davey, a power quality engineer at Duke Energy, was part of the team that conducted this new investigation. Matt is a former employee of Advanced Energy, and although he is new to the power quality role, his participation in the earlier research proved essential to solving the puzzle.
This prior work examined the effect of power quality on end-use equipment, such as pumps, fitted with motor protective devices. These devices, known as voltage monitors or thermal overload relays, are supposed to protect motors from voltage unbalances and increasing motor currents (that can lead to overheating) by shutting them down until appropriate voltage levels return. Voltage disturbances and overheating can damage motors and equipment, so it is important that these products function properly.
Testing in Advanced Energy’s lab revealed, however, that the monitors and relays often tripped erroneously and could likely be the source of nuisance tripping problems in customer equipment. They either shut down motors when no problems existed or failed to trigger when an issue arose. These findings were troublesome given that the products are widely used. Furthermore, utilities like Duke Energy cannot guarantee flawless voltage delivery and advise their customers to use motor protective devices. It was clear from the research, though, that these tools may not perform as expected.
This is precisely what happened in the case of the lift station: The voltage monitor, designed to protect from under-voltage conditions, was not working as intended and was tripping unnecessarily. One pump alone was not enough to trigger the monitor, but the two pumps operating together were. With Matt’s knowledge and additional troubleshooting efforts, Duke Energy was able to home in on the issue. After adjusting the voltage monitor to reduce its sensitivity, the problem was solved, and both pumps could run unimpeded. Furthermore, the team found that the backup generators helped to regulate voltage levels above the sensitivity of the monitor and therefore avoided triggering the shutdown of the pumps.
Matt’s experience demonstrates how lab testing at Advanced Energy and joint research between Advanced Energy and Duke Energy can have a positive real-world impact on Duke Energy and its customers. And with this particular technology, Duke Energy and Advanced Energy have conducted demonstrations and trainings to educate customers on its potential issues. In the future, hopefully more facilities will be aware of the possible pitfalls of these protective devices.
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