Motor Relay Evolution
Motor protective relaying has evolved in utility power and industrial systems since protection was introduced more than 100 years ago.
Many large industrial plants today still rely on thermal motor protection commonly based on bimetallic relays. While these relays work to shut down motors in dire situations, they aren’t effective at diagnosing and predicting future motor failures.
Smart motor management with new intelligent relays provide real-time, remote condition monitoring and fault diagnostics that alert plant operators and maintenance personnel of potential failures before they happen, ultimately boosting OEE.
Conventional overload relays are cumbersome when it comes to control functionality:
Motor control parameters are managed through the control system (PLC), which involves complex manual programming and hardwiring of I/O.
More advanced monitoring requires additional devices and more wiring.
Smarter relays natively measure, filter and report critical data from the motor to be used for diagnostics and protection. The data is easily accessed from its user-interface, requiring little to no network knowledge or even a PC. In addition to local availability, the data can be passed upstream to a central PLC or DCS system, or even a laptop. Eaton’s Xpert C445 Motor Management Relay is a good example of a smart relay. On-board connectivity options include EtherNet/IP, ModbusTCP, Profibus, Modbus serial, USB and embedded webpages.
The C445 is the third in Eaton’s C400 series of advanced motor protection. It’s ideal for heavy industrial and continuous process plants (paper and pulp, oil and gas) because of its ability to withstand harsher environments.
Three main concepts differentiate this model from legacy versions:
1. It’s a motor management relay
Control signals can be sent directly to the device from a network, the user interface or even by wiring pushbuttons directly to the on-board inputs. This differs from traditional overload relays where the contactor output is protection only and all starter logic must be hardwired outside the relay. Ultimately it saves on materials, space and complexity. This also allows for advanced features such as voltage loss restart, where the relay can auto-stagger motor restarting after a voltage dip event.
2. It was designed for full connectivity
The communications offered do not require a separate control power source or increase the footprint of the device. Multiple networks can be used at the same time.
3. User interface similar to smart phones
An LCD screen provides local access to all data and makes it easy to view or set any parameters locally within the device. In new electronic relays, this is invaluable to maintenance staff who may lack specialty training or the proper tools.
Data and diagnostics
When it comes to available data, the options are limitless. As we stress in our guide to smart manufacturing, it really depends on the application as to what data is most valuable to plant operators. The single greatest impediment to the adoption of smart manufacturing may be the absence of information goals. At some point, it’s imperative to start turning data into valuable information.
Most operators would agree that access to current data for each motor, including average current, current imbalance and what %FLA they are running, provides a basis of what is happening with motors throughout the facility. Clearly identified fault reasons are also critical. For instance, an undervoltage event may indicate utility issues while a ground fault would have a totally different troubleshooting process. Knowing why a fault occurred helps maintenance fix the root cause faster.
Other unique data captured by the C445:
Motor start time/count
Motor efficiency
Motor torque
Energy (kWh)
Apparent power (kVA)
Trip snapshot
How the C445 helped catch a dead headed pump condition
A Southeastern based industrial maintenance team decided to improve protection after suffering repeated pump failures due to dead head conditions. A pump dead head is when a centrifugal pump operates with no flow through the pump due to a closed discharge valve or line blockage. The pump recirculates the same water, causing water temperature to continually rise and eventually damage expensive seals and reduce the life of the pump.
This condition is difficult to detect with traditional methods – a float switch won’t catch it because water level does not decrease. Using undercurrent protection (available in many motor protection devices) to detect the issue is ineffective because current is close to constant up to 50 percent of the motor load.
In contrast, input power varies linearly across the load range, making low power detection a reliable method for catching even small decreases in motor load.
The team decided to test a variety of different detection methods. When they tried low power protection offered by the C445 they were amazed at how reliably it could detect the issue. While there are dedicated pump protection relays on the market using this same method, having it embedded in C445 along with traditional overload and other required protections saves wiring, space and of course, money.
