A motor control centrer, or MCC, manages power distribution and instrument equipment, placing various motors, control units, feeder wires, connector units, power distribution transformers, lighting distribution panels, interlocking relays, and metering equipment in an integral housing. And powered by a common enclosed busbar.
DEFINITION
In various fields of the national economy, such as electric power, petroleum, chemical industry, metallurgy, mining, paper making, light industry, automobile, shipbuilding, transportation, municipal construction, food and beverage, water treatment, garbage treatment, pharmaceuticals, etc., electric motors are being used more and more widely. In order to operate and work reliably for a single motor and an entire production line, unified control and protection of the motors are needed.
Therefore, the level of motor control centers (MCCs) has also developed rapidly. MCC refers to the complete set of control and protection equipment for motors connected to low-voltage AC circuits, assembled into standardized unit components according to certain specifications. Each component controls a corresponding motor. These standard unit components are assembled into a cabinet to achieve centralized control of multiple motors.
STATUS OF DEVELOPMENT
Traditional motor control centers MCCs (motor control centers) are widely used in engineering. Conventional MCCs only include electromechanical components, and all connections are achieved through hardwiring. To this day, these electromechanical components are still the main components of MCC products. Even in developed countries, more than half of the units in MCC products are purely electromechanical equipment. In recent years, with the development of science and technology, intelligent MCCs have been developed and gradually applied. Intelligent MCCs use new intelligent components and Fieldbus technology and are gradually developing into automated, integrated ones, closely linking hardware, software, and network technology.
TRADITIONAL MOTOR CONTROL CENTER (CMCC)
The traditional motor control center (CMCC) can achieve start and stop control of the motor and simple fault detection. It is reliable and easy to maintain. It is widely used in various fields of the national economy, especially in petrochemical, metallurgy, paper making, building materials, textile, food processing, pharmaceuticals, electric power, and other fields requiring process control.
Intelligent Motor Control Center (IMCC)
The intelligent motor control center (IMCC) is powerful and can provide motor position and speed servo control functions, as well as various motor fault detection and diagnosis functions. It is widely used in complex process control.
CMCC and IMCC can be used alone to complete motor control. They can also act as field executors for distributed control systems (DCS) or programmable logic controllers (PLC) to jointly complete control tasks. They are the key equipment for factory automation.
WORKING PRINCIPLE
The working principle and problems of traditional MCC
The traditional MCC is connected to the remote DCS system in the MCC room through hardwiring control cables and signal cables. The DCS control commands and MCC feedback information are transmitted by cables, with many cables for each connection. Traditional MCC control has the following problems:
(1) The number of control and signal cables is huge;
(2) The wiring work is large, and the installation and commissioning cycle is long;
(3) There are many wiring points, so there are many fault points, and the causes of accidents are not easy to find;
(4) When adding equipment loops, control, and signal cables need to be re-laid, which is not easy to expand;
(5) There is little management and diagnostic information for production operation, and the operation and maintenance of electrical equipment are poor;
(6) There are many spare parts that take work to unify and occupy a lot of capital.
The working principle and characteristics of intelligent MCC systems
The intelligent MCC system is a new type of electrical automation control system combining information technology, sensing technology, and computer data processing technology. Its core components are motor intelligent protectors with communication functions. The control commands of the DCS and the relevant operating information of the motors are communicated through the bus. Field buses such as Lonwbrks, PROFIBUS, Etllemet, and TCP can be configured as needed. Its characteristics are as follows:
1 No DcS cabinet is required on site. Typically, up to 100 motor loops can be controlled by each communication bus;
2 Fewer line connections, strong anti-interference ability, clear fault causes, and easy to find and eliminate;
3 Using bus communication, the installation and commissioning cycle is short;
4 When adding equipment loops, if the system allows, you only need to set up in the software, which is convenient, flexible, and easy to expand;
5 Rich operating management information can provide detailed equipment maintenance information, achieve preventive maintenance of equipment, and minimize accidental downtime;
6 It has spare parts management functions, fewer spare parts, and less capital occupation.
COMPARATIVE ANALYSIS
1) From a hardware perspective, intelligent MCCs have simple and quick connections.
There are two main ways for traditional MCCs to connect with basic automation. One is to set up a remote I/O cabinet next to the MCC cabinet, and the monitoring and control signals of the MCC are connected to it through control cables. The remote I/O station then communicates with the PLC via the field bus. The other is to directly connect the monitoring and control signals of the MCC to the local I/O cabinet of the PLC through control cables. The point-to-point control signal connection determines that there are many cables and a large amount of construction.
In this respect, intelligent MCCs show excellent performance. After connecting with the on-site equipment, only one DEVICENET field bus is needed to achieve information exchange between the MCC and the basic automation. By eliminating the control cables and I/O cabinets, the connection becomes simple and communication faster.
2) Due to the introduction of the DEVICENET fieldbus, control cables and a large number of I/O are saved, and the number of PLC chassis is also reduced, reducing the cost of integrating the control system. Offset the slight disadvantage of the higher cost of intelligent MCC than traditional MCC.
3) When debugging the system on-site, dotting the system greatly reduces the debugging time; and there is no need for PLC I/O terminal cabinets and intermediate relay cabinets, which greatly reduces the number of fault points in the system.
4) From a maintenance point of view, the reduction of intermediate links makes maintenance simpler. Judging the operating status and fault conditions of on-site equipment can be based solely on the status monitoring information of the PLC.
5) The intelligent MCC control system has openness and scalability, which is incomparable to traditional MCC. Fieldbus and configuration software technology are applied in sewage treatment projects.
MANAGEMENT PROGRAM
MCC (Motor Control Center) is a set of professional, intelligent management solutions specially designed for low-voltage motor groups (mainly constant-speed motors). It is an important part of the automated control system in large-scale industrial production. By using this solution and adopting motor intelligent control protection devices (hereinafter referred to as intelligent protectors) to replace the current control and transmission technologies (such as 4-20mA, AC/DC signal transmission), more information can be transmitted bidirectionally between the intelligent protection device and the higher-level host computer. Realize functions such as centralized protection, control, monitoring, and measurement of on-site motors.
MCC transmits motor overloads, phase loss, ground faults, loss of speed, blocking, underload current, motor overtemperature, current imbalance, and other faults through the built-in PROFIBUS network to the control center (PLC) and monitoring center (PC) to obtain a simplified fault elimination method. Intelligent MCCs have been widely used in metallurgy, textile, light industry, petrochemical, electric power and other industrial, and mining enterprises, as well as transportation, construction, and other industries.
For the MCC (Motor Control Center) motor control center intelligent management solution, many world-renowned companies have launched their own intelligent protector products, such as ABB’s M101/102 series, Siemens’ SIMOCODE pro series, Acrel’s ARD series, etc. Here, Acrel’s ARD series intelligent motor protector product is taken as an example to introduce its main functions and characteristics:
The ARD series intelligent motor protector has overload, phase loss, imbalance, underload, ground/leakage, and blocking protection functions. The products are divided into two categories: ARD2 simplified series and ARD3 advanced series. The ARD protector can form a motor control and protection unit with contactors, motor starters, and other electrical components. It has functions such as automatic remote control, on-site direct control, panel indication, signal alarm, and field bus communication. It can be widely used in power distribution in industries such as coal mines, petrochemicals, metallurgy, electric power, and construction.
EXQUISITE STRUCTURE AND EASY INSTALLATION
The intelligent motor protector has a small size, compact structure, and convenient installation. It can be directly installed, and used in low-voltage control terminal cabinets, 1/4 modulus and above various drawer cabinets to improve the reliability and automation level of the control circuit.
Intuitive display and easy to learn and use
The high-definition LCD display interface intuitively reflects the measurement parameters and operating status of the motor. All measurement data can be easily viewed by keys, and parameters can be set through the meter panel or input through the communication port. The LCD display interface has backlight support for convenient use in environments with low light.
ADVANTAGE
The adoption of MCC (Motor Control Center) professional, intelligent management solutions has all the advantages of remote monitoring and can also reduce a large number of isolation devices, terminal rows (boxes), I/O cards, analog transmitters, etc. And intelligent devices are installed on-site and connected to the host computer through communication lines, which can save a lot of control cables, save a lot of investment, and installation and maintenance work, thereby reducing costs. In addition, the functions of each device are relatively independent, and the devices are only connected through the network. The network configuration is flexible, which greatly improves the reliability of the entire system. If any device fails, it will only affect the corresponding components and will not cause system paralysis. This distributed control system, combined with centralized management mode, has stronger functions and higher safety. It is the main trend of electrical automation control in the current metallurgical and steel industry.
