Jim Mimlitz, NRI

In rural areas — due to a combination of long power transmission line lengths and the relative isolation of the remote pumping facilities — it is not uncommon for stations to suffer from power quality problems.  Therefore, it is always recommended that a station’s power status be monitored, trended, and alarmed for outages.

In the most basic sense, monitoring the digital (ON/OFF) power status through use of a 3-phase monitor is recommended.  However, knowing the analog status (voltage level) would deliver a more detailed picture.

Shark 100 Power Meter, by Electro Industries/GaugeTech

Shark 100 Power Meter, by Electro Industries/GaugeTech

In order to collect detailed power telemetry information, sophisticated telemetry devices are commercially available for monitoring voltage, power, current, power factor, etc.  An excellent, Modbus-capable device that NRI has used successfully in the past is the Model Shark 100 by Electro Industries/GaugeTech.

However, if you are looking for a more basic and economical method of monitoring the electric utility’s 3-phase voltage level, then an excellent alternative is to request it from a pump station’s VFD.

How is this possible?

In this past year, NRI introduced a new firmware library — “VFD & Energy Analytics for Telemetry, SCADA, and Control Systems” — which empowers an RTU with the capability to extract a variety of useful information from a VFD through a network.  In this case, we leverage the faculties of this library to request the VFD’s DC bus voltage.  We know that the DC bus voltage is derived from a full-wave-rectification of the incoming 3-phase power, and therefore…

Utility Voltage ≅ DC Bus Voltage  /  √2
                          ≅ DC Bus Voltage  /  1.4142

For example, if the DC Bus Voltage is read from the VFD as 685 VDC, then we know — based on both theory and actual measurements — that the incoming utility voltage (average 3-Phase RMS) is  approximately 484 VAC.

Recently, we had the opportunity to retrofit such voltage-monitoring capability at two rural water district pumping stations.  Both stations had been experiencing voltage-related problems; and this upgrade was designed to alert the operators whenever the incoming voltage was outside acceptable tolerances.  Each station was already equipped with a Modbus/RTU network for collecting data from various smart devices, including EtherMeters, pressure transducers, and a tank mixing system.  The station was also equipped with VFD-driven pumps.  The Modbus/RTU network was expanded to collect an approximation of the utility’s average 3-phase voltage from the VFDs: (VAB+VBC+VAC)/3

Modbus/RTU/RS485 Isolation Repeating Equipment.

Modbus/RTU/RS485 Isolation Repeating Equipment.

Modbus/RTU/RS485 Bus Terminal Block

Modbus/RTU/RS485 Bus Terminal Block


VFD Network Interface Port

VFD Network Interface Port


RJ45-Terminal Block Adapter - Top View

RJ45-Terminal Block Adapter – Top View

RJ45-Terminal Block Adapter - Bottom View

RJ45-Terminal Block Adapter – Bottom View


Pump Station Flat Panel User Interface. Note Display 3-Phase Voltage Level.

Pump Station Flat Panel User Interface. Note The Displayed 3-Phase Voltage Level.



24 Hour History Chart. Note that the Voltage Levels are erratic and reaching higher-than-acceptable levels, especially 11PM-6AM, which was the main reason that the Water District requested this capability. History trending charts such as these can be useful tools for documenting voltage problems — and for conveying the problems to the local electric utility.


Are you interested in implementing this type of basic, economical 3-Phase Voltage Monitoring capability at one or more of your stations?

This feature — and many more — are now available as part of our new VFD & Energy Analytics Package for Telemetry, SCADA, and Control Systems.

Give us a call, and we’ll be glad to discuss this with you in further detail.

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