Motor Control Centers
0
Low voltage motor control center is an important element in electrical control systems because of its important operating role they play in controlling motors and production processes. Over the years, Motor Control Centers have evolved from cabinets that housed basic electro mechanical devices such as circuit breakers, conductors and overload relays to centers of automation that may include variable frequency drives, soft starters and programmable controllers.
Because failure or malfunction of electrical systems — specifically Motor Control Center-housed equipment — can present a serious hazard to person and property, it is imperative to comprehend how Motor Control Centers would manage. By changing from reacting when equipment fails to proactively maintaining machinery through protective and predictive practices, manufacturers can help reduce such risks and prevent failures from occurring.
MCC Inspection Using Infrared Thermography
Normal maintenance of Motor Control Centers occurs in two ways, by inspecting energized or de-energized equipment. One of the most common methods of inspecting energized equipment could be infrared thermography. While infrared thermography is a part of an overall protective or predictive maintenance program, it is not the only method of checking.
Infrared thermography is a non-invasive inspection technology that uses an infrared camera to guide temperatures and thermal patterns while equipment is running at full load to detect changes in temperature. This is often a telltale sign that equipment is executing out of spec. Used on wide range of equipment including Motor Control Centers, this technology helps manufacturers predict equipment failure and plan corrective action before an expensive shutdown, equipment damage or personal injury can occur.
Infrared used to detect potential electrical fault conditions such as loose or corroded connections (hot spots), poor contacts, unbalanced loads, overloading and overheating. Electrical fault conditions can lead to electrical system failures, bridging, equipment fires and high level short-circuits.
This inspection method is difficult and equipment relatively costly. To gain the best results from an infrared program, it’s important that inspection person should properly train to execute the task.
Safety is another concern because electrical equipment should scan during operation with enclosure doors open. If equipment scanned while enclosure doors are open and the equipment running, person should wear personal protective equipment. As an increased safety measure, some users install special camera ports on Motor Control Center enclosures. Infrared ports allow scanning of devices without an open enclosure doors. These cameras can install during manufacturing or by the user in the field.
Maintaining De-energized Equipment
The second type of Motor Control Center preventive maintenance is inspecting de-energized equipment. This requires more training than visual inspections. To start, engineers would follow specific guidelines on de-energizing, isolating and grounding the equipment to be inspected.
When performing maintenance on de-energized equipment, refer to the following general guidelines: (For a complete list of specific maintenance steps, always check the manufacturer’s user or installation manual, as well as NEMA and NFPA standards)
Structure: Check for moisture or any signs of dampness or drippings inside the Motor Control Center. Condensation in conduit and moisture from an outside source is a common cause of Motor Control Center failure. Eliminate any source of moisture and seal off conduit, cracks and openings that have allowed or could allow moisture to enter the Motor Control Center. Dry, replace and/or clean wet insulation material. Replace damaged or malfunctioning parts. Ensure that you’ve identified and eliminated the source or cause of wetness or contamination.
Buses and splice connections: For horizontal and vertical bus connections, some manufacturers do not need servicing for the life of the Motor Control Center. Follow your equipment manufacturer’s specific recommendations. For Motor Control Centers that permit servicing bus connections, check the integrity of the bus splice connections. Bus splices are normally identified with labels on the Motor Control Center structure or referenced in the Motor Control Center elevation drawings or user manuals. You’ll usually find recommended torque values on the structure, in wiring diagrams or in the manufacturer’s user manual.
Wiring and branch circuit preventive devices: Make sure conductors are not damage, worn or obstructing moving mechanical parts. Check wires and cables to indicate overheating such as discolored insulation; inspect fuses for discoloration and check for loose power and control connections. If any of these conditions are present, analyze the cause and replace wiring as necessary.
Disconnect handle mechanisms: Analyze for proper function and flexibility of movement of the detach handle and door interlock mechanisms. Lubricate as directed according to the manufacturer’s instructions as replace broken, deformed, malfunctioning or badly worn parts.
Starters and conductors: Check for excessive wear and dirt accumulation on starters and conductors. Vacuum or wipe components with a soft cloth to remove dirt. Do not use compressed air to clean these components because they may become damaged in the process. Also, do not use contact spray cleaners, which may cause sticking on magnetic pole faces.
Generally, discoloration and slight pitting do not harm contacts. If contacts are overly worn, replace (not repair) them in pairs to avoid misalignment and uneven contact pressure. Be very careful about filing contacts; doing so can easily damage them and decrease their life expectancy.
Best Practice of Motor Control Centers Maintenance
- Usual maintenance of Motor Control Centers includes checking energized and de-energized equipment.
- Infrared thermomgraphy is one common way to inspect energized equipment.
- Inspecting de-energized equipment requires specialized training, especially in safety.
- Safety is also one of the major causes if a fault occurs. De-energize, detach and isolate all involved equipment to protect accidental contact with live parts.
Replace Old Motor Control Centers
It’s not always easy to regulate when and with what to replace an older Motor Control Centers. Some users consider Motor Control Centers be old or out of date after 10 years of service. Other users base equipment updates on application and duty cycles. Technological improvements, such as process speed control with VFDs, feedback monitoring and network interfaces can give incentives to upgrade older equipment.
Modern Motor Control Centers designed to accommodate a variety of user needs, ranging from complete replacement to integration with older existing equipment. For example, many newly designed Motor Control Centers are good for installation in older facilities because they built to the latest industry standards and technological updates. Conversely, sometimes, newer Motor Control Centers designs can retrofit into structures built 30 years ago.
Motor Control Centers s often contain intelligent power and control components that monitor load current, provide diagnostic feedback and valuable input/output functions. For example, an intelligent Motor Control Centers feature electronic maintenance support and allow users to remotely monitor and control operations via an industrial network such as device net or ethernet.
Optional software includes Motor Control Centers layout and schematic diagrams; instruction manuals, spare parts and maintenance data log information. The software permits users to conduct remote monitoring and troubleshooting, reducing their exposure to hazardous voltage and current. In this way, users can warn of impending faults and proactively manage their equipment.
While Replacing older Motor Control Centers equipment, consider:
- Solid-state components that offer I/O, protective functions and valuable system information.
- Built-in pre-tested and pre-configured networks that can help decrease startup time.
- Real-time monitoring software that eliminates costly programming time.
- Unit designs that decrease floor space.
- Application and duty cycle.
Selecting Networked Motor Control Centers
Because of the comprehensive array of control and monitoring devices they contain, some modern Motor Control Centers incorporate control schemes and present users with an opportunity to transform islands of data into useful information that minimizes downtime. With the easier maintenance, increased safety and remote diagnostic capabilities of networked Motor Control Centers, it may make sense to consider them for your next equipment upgrade.
The plug and play technology of modern networked Motor Control Centers enables you to decrease installation time and experience smoother startups. These Motor Control Centers include devices such as solid-state overloads, drives and soft starters, with built-in communication capabilities, providing valuable diagnostic and predictive failure information. A networked Motor Control Center usually consists of three main elements: Built in communication media, intelligent motor control components and Motor Control Center observing software.
Networks greatly simplify wiring, installation and startup time by replacing wire bundles with a single network cable. Users can easily remove or add networked units, significantly reducing wiring and testing time.
Programmable controllers or distributed control systems are often part of a networked Motor Control Center configuration. Observing software or HMI applications access critical information through device-level networks, such as Device Net and Foundation Fieldbus. Users can bridge these networks to higher-level networks, such as Control Net, Ethernet and Profibus by using gateways.
Networked Motor Control Centers can make installation easy by providing access to critical information and reducing safety hazards. A maintenance person can troubleshoot units without having to open enclosure doors. Users can “plug into” a Motor Control Center and analyze data, such as current, time to trip and percentage of thermal capacity used, and remotely access diagnostic information from a maintenance laptop, a control room or even an engineer’s desk.
There are many reasons why upgrading to networked Motor Control Centers makes sense. For example, a user might upgrade Motor Control Centers equipment to replace a controller, eliminate costly interconnect wiring or attain more operative information. Also, it is necessary to upgrade a controller because of a change in network architecture.
Consider how networked Motor Control Centers could ease maintenance practices. Traditional hardwired installation is difficult to manage and does not readily bring changes. But by replacing costly control wire bundles with a single network cable, users can increase system flexibility and reduce maintenance time.
Upgrading to newer programmable controllers that pass more information at faster communication rates will help increase your up time. Also, adding solid-state overload relays to give diagnostic information, as well as valuable input/output status, is another upgrade that makes good sense.
