Incorporating motor management as part of a total control system upgrade allowed Lafarge's Alpena, Mich. plant to obtain greater diagnostic and preventative maintenance capabilities and improve kiln operations.

The Alpena plant is the company's largest cement-producing facility in the United States, generating approximately 2.5 million tpy. Five large rotary kilns operate 24 hours a day and, except for an annual maintenance shut down, run every day of the year. Approximately 500 motors, varying in size from 0.3 to 336 kW (0.5 to 450 hp), power various kiln functions. The loss of a critical motor could shut a kiln down and have a dramatic impact on the plant's productivity and subsequently its profitability, especially since the five kilns average more than 9,500 tons of clinker each week.

The five kilns each yield around 1,250 tpd. Plant control is distributed over 40 PLCs, with more than 18,000 I/O points having been installed over the last 10 years.

To maintain the operational integrity of these motors, Lafarge installed Allen-Bradley SMP-3 Smart Motor Protectors (overload relays) as a solution that would deliver the required information (beyond run, start-up, and stop commands) to actually manage each motor.

According to Jim Grochowski, systems engineer at the Alpena plant, the previous motor control centers were vintage 1960 units becoming prone to mechanical failures. "Since they were in need of upgrading anyway, the SMP-overload relays integrated with DeviceNet network communications seemed like the best solution," he said.

Designing a solution The first phase of the upgrade involved three of the five kilns and consisted of roughly 250 motors. One of the primary concerns was the need to install the new control system within the annual 21-day scheduled maintenance period. This meant rewiring existing motor control centers was not a feasible option.

Considering the short time window available for installation and the need for diagnostic communications, Lafarge decided on a packaged solution consisting of prewired Allen-Bradley 2100 Motor Control Centers (MCCs), which included the DeviceNet network. "This decision ultimately proved to be the right one," Grochowski said. "The time saved by not wiring the MCCs was significant, not to mention the cost savings involved with replacing hardwired I/O."

The SMP-3 solid-state overload relay allows the desired trip class to be programmed, guards against phase loss and ground fault, and protects motors from jam conditions. Jam protection takes the motor off-line within two seconds of when a jam occurs. It protects against overheating of motor windings and damage to drive gears, belts, chains, and other components. These fully digital devices also simplify data acquisition by monitoring motor current remaining thermal capacity. This defines how close motor conditions are to tripping the overload.

With this information, Lafarge might find that a filter needs cleaning, a conveyor is nearing its capacity, or be able to identify motor bearings that need attention-actions that are more predictable in nature.

By linking the SMP-3 overload relays to programmable controllers via DeviceNet, Lafarge obtained more detailed motor management data at rates faster than those transmitted by traditional control wiring. It also was able to reduce both the wiring and component content of the system, such as transducers and analogue input modules.

The new motor management solution actually provides Lafarge's technicians with more information than they were used to. "With DeviceNet, we can interrogate motor starters through communications, rather than hardwiring," Grochowski said. "The goal is to avoid motor conditions that result in unscheduled trips. The faster we can diagnose the problem and resolve it, the sooner we can get a kiln back on line, resulting in saved revenue."

The DeviceNet architecture incorporates a trunk line across the horizontal wireway; a drop line is brought into each vertical wireway. Devices like the SMP-3 overload relays are then daisy-chained within each section. Control is distributed throughout the kiln system to the motor level by an integrated network of Allen-Bradley PLC-5 units. Using this architecture, Lafarge simplified its initial design while reducing on-site engineering and wire-up for the kiln upgrade.

Information on line With this information, operators have a better understanding of motor loads. According to Scott Simonye, automation programmer at the Alpena plant, the company is able to respond to mechanical and electrical problems with greater precision. "Before we would have to physically send a process assistant out to a motor control center to see what went wrong. Now we can just call the data up on screen."

Lafarge is planning to program the system to respond to thermal capacity data generated by the SMP-3 overload relays. With the amount and type of real-time and historical process information available from the SMP-3s, the plant personnel can monitor day-to-day trends and develop more sophisticated, predictive maintenance procedures.

In addition, Lafarge not only saved in wiring costs and installation but also achieved greater plantwide integration and reliability.