Intelligent motor control centers help drive savings
It's easy for engineers to overlook one of the keys to success: leveraging technological advances to integrate smart devices, device-level networks and software into motor control systems.
Manufacturers are continuously seeking new ways to increase productivity, streamline processes and boost their profit margins. Plant engineers can play an important role in this effort by helping to select and implement control solutions that reduce costs, save time and increase the flow of information within automation systems. But with myriad choices available, it's easy for engineers to overlook one of the keys to success: leveraging technological advances to integrate smart devices, device-level networks and software into motor control systems.
Traditionally, motor control centers (MCCs) contained only electromechanical components with hardwired connections. While these components remain the workhorses of MCCs, advances in solid-state technology have resulted in more intelligent, programmable devices that do more than just turn on and off a motor. Today's MCCs monitor motor current and thermal capacity, perform protective troubleshooting functions and provide detailed diagnostics to help avert downtime.
These intelligent MCC designs also address some of the configuration and data-management inefficiencies that device-level networks can create, which include:
• Reliability and flexibility shortcomings associated with typical daisy-chain architectures such as adding new units or accidental breaks in the chain that can affect downstream units in that connection, potentially shutting down equipment
• Potential damage to exposed trunk-line and drop-line network cables in the wireways when pulling and installing other power cables
• Integrating motor control data into the plant control system, and sorting through the enormous data available on the network to find needed information.
The intelligent MCC integrates three major system components - communications, hardware and software - to address these issues. While early versions of MCCs with communication networks contained variations of these elements, today's solutions leverage a harmonized design that deliberately integrates these elements into a unified solution.
A standard MCC installation requires extensive interwiring, documenting and testing in the field. Pretested and pre-configured, the intelligent MCC arrives ready to install. Communication cables are installed and tested at the MCC factory, while software screens come pre-configured for the specific MCC. Additionally, intelligent devices are preprogrammed with baud rate, node number, trip current and other settings.
Communication network capability lies at the heart of an intelligent MCC. The network replaces the traditional control interwiring with a single communication wire. Ideally, all the units have input points to monitor devices such as the disconnect switch, contactor, overload relay or pilot devices. In addition, a network scanner module or network linking device connects the MCC to the plant control network, and collects and distributes the device data in the MCC.
The type of MCC you select for your application can have a significant impact on overall cost, installation time and monitoring capabilities. Therefore, it's important that engineers carefully evaluate the core components of an intelligent MCC system.
Proven, open communication network - The trend toward open networks (as opposed to proprietary networks) has clear and well-documented advantages. The network should provide proven performance, offer a low cost per node and be accepted by a wide range of suppliers and users.
Optimized physical construction - The traditional approach for routing network cables in MCCs is through horizontal and vertical wireways. Although this method works, consider these more optimized approaches:
• Trunk lines and drop lines isolated behind barriers - This design helps users avoid potential damage to communication cables during installation and maintenance
• Independent, easy-connect ports on drop lines - This configuration provides independent, readily accessible ports to simplify installing, withdrawing, relocating and adding plug-in units. The configuration is preferable to a daisy-chain architecture, in which moving or adding an MCC unit requires interrupting the chain and disabling downstream units.
Pre-configured software - To integrate the intelligent MCC hardware elements and deliver useful real-time information with minimal expense and effort, intelligent MCCs should come equipped with a pre-configured monitoring software package. The software delivers a window into the MCC and related equipment. It also eliminates the need to create costly customized MCC screens within operator interface software, yielding a true plug-and-play solution.
Traditionally, MCCs were provided without inter-wiring and required extensive field wiring, documenting, testing and system integration. Because the intelligent MCC arrives ready to install, pretested and pre-configured, it significantly reduces startup time.
Another critical aspect for efficient startup and troubleshooting is detailed documentation, which all too often is incomplete or misplaced altogether. In the case of the intelligent MCC, users can access electronic documentation on the same PC running the monitoring software. This allows users to view the real-time status of the MCC, as well as view CAD drawings, user manuals and spare parts information applicable to specific MCC units.
An intelligent MCC provides users with critical information needed to help minimize or prevent downtime. Remote access to motor-control data also affords an opportunity for reduced exposure to hazardous voltages and improved personnel safety during startup and troubleshooting. This information includes warnings of abnormal operation, identification of trip causes, automated logging of events and electronic documentation.
Reaping the rewards
Intelligent MCCs can deliver considerable cost savings in the form of reduced design, installation, commissioning and documentation time. Savings occur as a result of the significant reduction in cabling requirements. Specifically, users require fewer cables and conduit, and less interface equipment such as terminal boxes, control system I/O modules and interposing relays.
Other benefits include reduced engineering, planning and commissioning times. Intelligent MCC users report installation cost reductions of up to 15%, compared to a conventional MCC installation. In addition, users can achieve operational cost savings through improved diagnostics, which result in faster troubleshooting and, therefore, less downtime.
As the capabilities of intelligent devices continue to increase, intelligent MCCs offer plant engineers an excellent opportunity to benefit from the advanced technology of these control systems. Plant engineers reap the rewards of reduced total cost of ownership through improved diagnostics, increased system reliability, design flexibility and simplified wiring.
Keith Blodorn is a product manager at Rockwell Automation.
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