New Trends in Intelligent Motor Management
Intelligent Motor Control Centers (i-MCC) provide more information, early warnings and enhanced data transparency from individual motor feeders to the plant operator. This helps prevent tripping, failure and sudden shut-down of motor, says
Mayank Nigam, Industry Sector, Control Products - Business Development, Siemens India.
Process industries are increasingly getting more complex where various small processes are closely linked with each other. Some of these process industries are power, cement, steel, oil & gas etc. In process industry, each motor is a critical part in the production chain and its tripping, failure or sudden shut-down can lead to a huge monetary loss. In conventional MCC, these failures are caused due to limited motor protections like overload and short-circuit, massive control wiring from MCC to control room, no alarm or diagnostics and so on. In order to prevent these failures, we need to have more sophisticated control & protection system. At the same time, plant operator should have more information, early warnings and enhanced data transparency from the individual motor feeders.
Above requirements are nowadays achieved by Intelligent Motor Control Centers (i-MCC). i-MCC has become very popular in last few years and is now a standard of process industry. In i-MCC, intelligent motor management relays are used on which a communication port is available. This communication port is directly connected to a Distributed Control System (DCS) by a single communication cable. This communication cable replaces numerous control and signaling cables of a conventional MCC. Features such as multiple protection, monitoring and logical functions is integrated into a compact communication capable intelligent relays.
The motor management relay is the main component in an Intelligent Motor Control Center and it comprises of various essential functionalities in a single device like:
- stand-alone motor protection
- motor control logic (DOL, R-DOL, Star-Delta etc.)
- monitoring of motor feeder data
- data measurement, evaluation and storage
- communication with a DCS system
Since the volume of data from MCC to DCS and back from DCS to MCC is quiet high & the response required is very fast, the most preferred communication protocol followed in process industry is Profibus. i-MCC offers multiple protections like overload, over & under current, over & under voltage, stalled rotor... almost all protection needed for a LT motor. In addition it provides data transparency, low maintenance cost, profibus communication, low downtime etc.
The known benefits of an i-MCC are numerous but at the same time one should ensure that basic requirements that were considered in conventional MCC are also met in i-MCC. One of these key requirements is Type-2 co-ordinated feeder.
Type 2 co-ordination in i-MCC
Two protections are necessary in all conventional MCC. One is overload protection by overload relay and another is short circuit protection by a circuit breaker. Overload relay (OLR) is used to save motor from burning due to overload and short circuit protection device (SCPD) from short-circuit. Since, both the faults are a form of over-current it is very important to ensure OLR operates in overload zone and SCPD operates in short circuit zone.
In an i-MCC, intelligent relay replaces OLR which provide overload protection whereas SCPD remains the same. Like conventional MCC it is also recommended to use tested Type-2 co-ordinated feeder in i-MCCs. Recommended and tested Type-2 charts are published by the manufacturers of intelligent motor management relay which provides tested combination of SCPD, intelligent relay and contactor. These charts should be adhered to for complete motor protection and safety of plant & personnel.
Safety integrated in i-MCC
Safety of working personnel is paramount importance for any manufacturer. Generally, automation systems and components are responsible for safety-related tasks in many applications (process industry, machines, conveyor systems etc.). This means that the health and safety of persons as well as protecting equipment and the environment depends on the correct functioning of the relevant systems and components.
Today, the proper functioning of systems and components is covered by the term "Functional Safety". This is especially documented in Standard IEC 61508 "Functional safety of electrical, electronic and programmable electronic safety-related systems" and IEC 62061 "Safety of machinery - Functional safety of safety-related electrical, electronic and programmable electronic control systems". Functional safety relates to the principles of machine or plant safety that depends on the control and protective equipment functioning properly.
The focus is on protecting personnel and equipment itself which should not suffer damage in the event of malfunctions. Every person who comes into contact with the system must be protected against the hazards emanating from the machine. But the machine and system itself must be protected against hazards to avoid damage to the investment and production losses.
The system implies use of safety relays or safety automation systems which monitor critical components of a machine or plant. Some of these critical devices are E-stop, pull-cord switch, limit switch, contactors main contacts etc. which if malfunction then it may lead to an accident. Monitoring of these devices will help in safe disconnection of feeder during accidents.
Depending on the application, the component of safety system can vary widely. Safety system always comprises of a chain of sensors, evaluation devices and actuators. In safety technology, the requirements regarding cost-saving potential can be especially fulfilled by selecting the appropriate installation system. In standard technology, the move to distributed concepts and the use of modern fieldbuses have already resulted in significant cost savings. Further cost savings in the future will be achieved by transferring additional safety-related signals along existing standard fieldbuses, e.g Profi-safe.
Flexibility of integrating safety system in i-MCC is now possible and the same can be followed to ensure personnel and plant safety. In i-MCC, intelligent device, e.g. SIMOCODE, is integrated with safety circuit by using Digital Expansion Failsafe Module (DMF) of an intelligent relay (see picture below).
The critical inputs of field are taken to DMF inputs and the failsafe DMF outputs are used to disconnect control supply of the switching device (contactors). The safety signals are taken from i-MCC to PLC or DCS through Profibus or if required Profisafe. These failsafe signals sent from DMF through intelligent device are then processed at automation level. It goes without saying that i-MCC,that are already influencing today's automation environment; new trends in it will soon be found with Type-2 co-ordinated feeders and safety integrated.