Benefits of intelligent motor control centers
The concept of Intelligent Motor Control Centers (i-MCC) is widely accepted in industries today due to their benefits such as better protection along with monitoring and diagnostic features from the motor management relay. Currently, the motor management relays are capable of communicating the motor operational, diagnostic and service data to PLC/DCS over serial communication protocols like Profibus, CanOpen, DeviceNet, Modbus, etc. The need of ability of data exchange from the motor management relay is gradually rising, wherein the process industries are looking for more informative data, like on energy, at a faster rate. At the same time, it is also preferred to have common communication network right from the field devices level up to the enterprise level. Keeping-up with the changing customer needs, motor management relays are now available over Ethernet communication protocol like PROFInet, which enables high speed data transfer from i-MCC to DCS/PLC.
PROFInet has become the leading industrial Ethernet protocol in the market compared to other Ethernet based industrial protocols because of features such as determinism, real-time and isochronous real-time data transfer. More than five million PROFInet based devices were installed by the end of 2012 and this number is expected to grow with a CAGR of more than 8.7 per cent in this year.
Challenges with the serial communication bus
Master - slave communication: The serial communication bus is based on the master slave type of communication system, where a single master can only collect the data from the defined slaves. Therefore, the electrical operator is dependent on PLC/DCS to acquire motor information like faults, operating hours etc.
Data exchange: Another major limitation of the serial communication bus is in terms of the number of data bytes exchanged, which directly affects the speed and performance of the network. Exchange of a high number of data bytes from the field devices over the communication bus lowers the speed of communication and affects the performance of the automation system.
Maintenance: It is quite difficult to maintain the serial bus owing to the additional network components like repeaters, line terminator and dedicated communication cable.
Scalability: In case there is a need to expand i-MCC system based on serial bus, additional intermediate gateways like Modbus to Ethernet, bus specific cables, repeaters and other additional communication masters for communication will be required. This makes the expansion costlier with increased network complexity.
Availability: All the motor feeders inside a MCC are connected as a daisy chain (loop in and loop out). Hence, in the event of breakage of communication cable bus, the entire MCC network gets disconnected from the main PLC/DCS. Relays like SIMOCODE pro, within which logics related to motor interlocks can be written, will enable the process to continue with all field interlocks working, even after communication has failed between the relay and PLC/DCS.
Advantages of PROFInet based system
A system based on PROFInet provides better bandwidth for high speed data transfer, open connectivity and helps in standardisation of the entire plant network.
OPC UA: OPC Unified Architecture (UA) is the next generation technology from the OPC foundation for safe and reliable data transfer and defines access to industrial communication networks on Ethernet. By using a common HMI as an OPC UA client inside MCC, it is possible to control and monitor a group of intelligent feeders independent of the PLC/DCS.
Web server: Integrated web server function with motor management relay over PROFInet permits access to the motor details online, as well as control of the feeder with the required levels of user authentication using just a basic internet browser.
Cyclic send-and-receive: PROFInet, having higher bandwidth, allows high number of data exchange between motor management relays and IO controller (PLC/DCS) with good performance of the network. Selectable cyclic send/receive data allows transmission of motor status and command in real time to PLC/DCS. PROFIenergy: PROFIenergy is a profile of the real-time Industrial Ethernet protocol-PROFInet. PROFIenergy enables the deployment of more effective energy management strategies over PROFInet architectures. Its function is to place energy consuming motor feeder into æsleepÆ modes during idle times (non-productive periods). This prevents the wastage of energy. PROFIenergy also provides energy data like active power, reactive power, current, voltage, power factor to the Energy Management System (EMS) over PROFInet.
Ring architecture: Motor management relay over PROFInet has an integrated dual Ethernet switch port that forms a ring network. The ring system supported by Media Redundancy Protocol(MRP) doesn't affect the functioning of the network in the event of any single point bus failure. Hence it ensures high availability of MCC for the critical processes.
PROFIsafe: PROFIsafe protocol is the special safety signal over PROFInet which allows safe disconnection of the motor feeder in case of a hazardous situation. Such a system of motor management relay with necessary safety standards can be used in system categorised for SIL1/2/3.
Other benefits of PROFInet based motor management relays is time synchronisation with the main clock over Network Time Protocol(NTP). This helps in accurate analysis of the events in case of any faulty condition.
Systems based on PROFInet are becoming very popular as they lead to increased productivity, reduced operating costs and integrate manufacturing and business networks with field devices. Intelligent motor control centers based on PROFInet are easy to maintain and do not require communication accessories like repeater, line terminator and special connectors etc. Given the rapid growth and acceptability of Ethernet devices, the cost of the Ethernet network components is slated to reduce further in coming times. To conclude, i-MCC based on PROFInet has high availability because of the ring architecture and high transparency attributed to multiple access points like web server and OPC UA. Further its determinism allows it to integrate the field devices in a process industry up to the supervisory/SCADA level.
Exchange of a high number of data bytes from the field devices over the communication bus lowers the speed of communication and affects the performance of the automation system.
1. SIMOCODE user manual: www.siemens.com/industrial-controls/catalogs
2. PROFINET Technology the easy way to PROFINET: www.profibus.com/technology/profinet/