The traditional MCC control is through hard wiring, the control and signal cables are placed in the MCC control room and connected to the remote I/O of the DCS. DCS's control commands and MCC's feedback information are transmitted by cables. Each motor control loop requires plenty of cables.The traditional MCC control has the following shortcomings:
· A great amount of control and signal cables
· Remote I/O cabinets are required at work site
· Need multiple intermediate components, such as intermediate relays, transmitters, isolators etc.
· Heavy wiring work, long installation and commissioning cycle
· There are many wiring points, so there are many fault points, and the cause of the accident is hard to quickly locate
· When increase equipment loops, control and signal cables have to be laid again, with poor extension possibility
· Less management and diagnostic information for production operations, poorer operation and maintenance of motor equipment
· The number of spare parts is large, which is hard to unify and occupies a large amount of capital
The introduction of intelligent motor protection devices has rapidly transformed traditional MCC cabinets into intelligent MCC cabinets. As the core component of MCC control segment, the advantages of modern motor protection devices are extremely obvious:
·It integrates measurement, control, protection, management,communication and other functions as one compact unit
·Decrease the use of intermediate components and reduce the failure rate in the MCC cabinet
·The extract cost of the MCC is limit comparing to the benefit which the intelligent motor protector bring with
The advantages of high integration greatly simplify the design of the MCC cabinet,so that the space layout is clear and reasonable, the high voltage and low voltage areas are separated，improve the safety level and have good heat dissipation; meanwhile, the number of contacts are less, the fault is easy to troubleshoot, simplified the maintenance labor cost.
Focus on equipment management:
The intelligent motor protection device contribute to the recording of the daily information of the motor equipment, such as: start and stop records, fault records, harmonic excess records, contactors, circuit breaker action times, loop power data, etc.At the same time, the insulation resistance of the motor can also be automatically monitored in the shutdown state. These seemingly simple and cumbersome works, under the traditional MCC (hard-wired) control mode, require professionals to manually complete records, and now, the intelligent motor protection device can be easily competent.
The core of the intelligent MCC cabinet is to use an advanced field-bus to replace a large number of original signal cables.The control instructions of the DCS system and the operation management information of the motor are transmitted and interacted through the bus communication mode. Modern motor protection devices are equipped with the most commonly used field-bus communication interfaces, such as Modbus, Lonworks, Profibus, Ethernet/IP and so on. Its characteristics are as follows:
·Remote I/O cabinet is not required, each bus can control up to 128 motor circuits, and the required cables are much less than traditional MCC
·The line has few contacts, anti-interference ability is strong, and the cause of the fault is clear
·Short installation and commissioning cycle, and low cost
·When adding equipment loops, the expansion is extremely convenient and flexible as long as the bus capacity allows
·Provide detailed equipment maintenance information to minimize downtime caused by unexpected equipment failure
Generally, the cost of a particular project by using the intelligent motor protector could be reduced 20% comparing to the the traditional MCC, and it’s about 50% less time consuming. Due to the perfect control function, maintenance and strong extensional possibility, so that the long-term operating costs are also greatly reduced as well.
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