Importance of Electric Motors
Since the invention of electric motors, the processes and efficiencies in the manufacturing and industrial industries have improved exponentially over the last several decades. Motor control systems within manufacturing and industrial environments have gone from manual control to semi-automatic to fully automatic control systems. These motor control systems have improved over the years with more sophisticated controls and sensing devices. Several of these are listed below:
- Protective relays, overload and surge protection, telemetry
- Programmable logic controllers (PLCs), Variable frequency drives (VFDs)
- Supervisory control and data acquisition (SCADA), distributed control systems (DCSs)
- Contactors, solenoids, valves, timers, float sensors, pressure sensors, flow sensors
- Temperature sensors, limit switches, other detection devices
There are enormous applications where motors are used everywhere today within the industrial industry and in the home.
Types of motors can be classified as either AC or DC, brushed
or brushless, synchronous or asynchronous (induction), series wound, shunt
wound, compound wound, permanent magnet, etc.
The most widely used motors for manufacturing and industrial
applications are the: AC, 3-phase squirrel cage induction motors because of their economical,
self-starting capabilities and reliability.
Major components of an electric motor include:
- Air gap
Characteristics of a Motor Control Center (MCC)
Wikipedia describes a motor control center (MCC) as “an assembly to control some or all electric motors in a central location. It consists of multiple enclosed sections having a common power bus and with each section containing a combination starter, which in turn consists of motor starter, fuses, or circuit breaker, and power disconnect. A motor control center can also include push buttons, indicator lights, variable-frequency-drives (VFDs), programmable logic controllers (PLCs), and metering equipment.”
The MCC provides protected and isolated enclosures equipped with controls and starters located in plug-in drawers, compartments, buckets, modules, cubicles, etc. It provides a convenient and central location for controlling all motor circuits and is usually remotely away from the equipment, machinery, and motors. The MCC can be classified within two areas – (1) low voltage (LV) and (2) medium voltage (MV). The LV MCC is generally for controlling and operating motors at voltages of 1,000 volts or less, and the MV MCC is for over 1,000 volts.
MCCs are most widely used in the utilities, manufacturing, industrial, and large commercial industries that operate machinery and motors. MCCs offer enormous flexibility across differing industries and are suitable for many applications, such as: utilities, communications, oil, gas, chemical, pulp, paper, water, waste, mining, metals, industrial production, and mass-production manufacturing. MCCs are used to house various power distribution equipment and controls, such as: main distribution panels (MDPs), main circuit breakers (MCBs), protective relaying, transformers, load centers, panelboards, distribution panels, switchboards, switchgear, programmable logic controllers (PLCs), variable frequency drives (VFDs), ethernet communications, etc. MCCs come equipped with multiple enclosed sections or bays with individual compartments, buckets, or drawers for various equipment allowing them power connectivity to a common power bus. The individual and isolated compartments can be equipped with swinging doors where the compartments can slide in or out or be fixed without an access door. Prior to any MCC construction, electrical permits and electrical building permits are required along with electrical engineering drawings that are designed and sealed by professional engineers (PEs) for electrical inspections before and after construction.
These removable compartments allow easier maintenance and provide less downtime in being able to swap out damaged buckets with new ones. MCCs are generally safer, more rugged, more reliable, and provide enhanced performance as opposed to local motor starter control cabinets or compartments installed at or near the location of motor driven equipment. Although the MCC is considered a protective barrier and usually located in separate electrical, mechanical, or control rooms, it can become dangerous during high fault current conditions. This can cause extreme and explosive arcing sending hot melted equipment and debris projecting through the air like silos, thus causing damage to other equipment and systems, including causing injuries or even death to personnel. Its extremely important to have the proper flame retardant (FR), arc resistant (AR) clothing as described on arc flash warning stickers derived from an arc flash analysis study.
Advanced MCCs are now equipped with arc resistant panels,
enclosures, and structures for helping protect personnel and equipment from the
dangerous arc blast explosions. This is a major milestone within the manufacturing
and industrial industries for improving human safety of the operators and personnel.
Other advanced MCCs are also equipped with improved solid-state motor controllers coupled with Smart microprocessor-based control systems. These Smarter MCCs offer optional remote-control features for programming, performing automation, providing real-time data, metering, maintenance, diagnostics, alarm indications, graphical views, schematics & wiring documentation, event history, etc.
Although these Smart MCCs are initially more expensive, they help reduce costs in the long run by reducing the setup time, enhancing the integration with better efficiency, providing advanced warnings, allowing for faster troubleshooting, improving operator decisions, and ultimately upholding personnel safety. The added benefits with more advanced MCCs far outweigh the startup costs. The Smart MCCs can integrate with other Smart systems, such as: PLCs, SCADA, DCS, Smart manufacturing systems, asset management, etc., along with operating across multiple communications protocols, like, Ethernet/IP, DNP, Modbus, DeviceNet, ProfiNet, and others.
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