A motor control centre (MCC) sits at the heart of an industrial plant. If well maintained, an MCC can last for decades, but despite their sturdiness, even the most reliable MCCs have to be retired at some point. Here, Pat McLaughlin, operations director of Boulting Group, explains the early warning signs that an MCC needs replacing.
There are several reasons for replacing an MCC, but the most common ones include obsolescence, incompatibility with new legislation or the condition of the MCC deteriorating. Technological advancements that allow the design of intelligent, more efficient MCCs are another reason why companies sometimes opt for an upgrade.
Many engineers will wait until an MCC breaks down completely before commissioning a replacement, but best practice dictates that through proactive maintenance and regular checks, plant managers and maintenance engineers can identify the early warning signs of a failure and better plan for the upgrade.
The potential defects discussed below are what maintenance engineers should look for when performing regular MCC checks. These audits should take place at least twice a year and log faults so that the information can be used retrospectively to better understand the condition of an MCC and predict potential risks.
A motor control centre has several electro mechanical components that are particularly susceptible to failure. These include the filters and fans, which need to be cleaned and checked regularly because they provide adequate air ventilation within the MCC. Poor ventilation can easily lead to overheating and the failure of critical components.
Visual checks should also cover whether the relevant warning labels are in place before performing maintenance on an MCC, so that maintenance engineers are not put in any danger during these audits.
Maintenance engineers can employ several methods to check electrical equipment. These vary from simple visual checks that identify discoloured or burned out components, to more complex investigations using an infrared camera to analyse electrical equipment or bus bars and to highlight hot spots.
Engineers should also pay particular attention to the cables and connectors of the MCC, as these tend to degrade relatively quickly. Checks should also cover the running currents and shielding of the MCC, to ensure employees cannot access live components.
Health and safety
MCCs, particularly ones that have been in operation for a long time, can become health and safety hazards. Engineers were not as safety conscious back in the 80s or 90s as they are today, so there is a good chance that any MCC that is a couple of decades old could be revisited to ensure it doesn’t pose any health and safety risks.
For example, Boulting Group engineers recently helped a utilities company replace an MCC that had been in operation for 43 years. Because of its age, the condition of the MCC had deteriorated resulting in some component failure and potentially live and, possibly dangerous to maintenance staff.
The well-known BS EN 61439-2 standard, which came into play on November 1, 2014, states that the enclosure of an MCC should fit the “type and degree of protection suitable for the intended application.” Best practice dictates that the enclosure should provide protection for equipment against external influences from any accessible direction and against direct contact, meaning that an ingress protection of at least IP2X is required. Older MCCs may not have been built to this standard, so it’s important to check that your equipment is compatible with the latest regulations.
Another critical design verification introduced by BS EN 61439-2 refers to the temperature rise limits of motor control centres. Temperature rise is essential to the reliability and long service capability of an MCC, because excessive temperatures result in the premature ageing and failure of components and insulation. The introduction of the new standard means that manufacturers must verify that each circuit within the assembly can individually carry its rated current.
If you are considering purchasing a new MCC, it’s important to make sure that it complies with BS EN 61439. This is the responsibility of the MCC manufacturer, but the client should also be aware of the requirements and the benefits of the new standard.
Because MCCs often operate in demanding environments, there are certain environmental factors that can affect the equipment and shorten its operational life. Such factors include dust, moisture and steam, all of which can be very corrosive and damage bus bars or electrical equipment. Similarly, because MCCs are often tucked away in the depths of a building, there is the danger of vermin damaging cables.
Maintenance engineers need to be aware of these potentially harmful environmental forces and perform the relevant checks periodically. Although some of these variables — such as moisture or dust — can’t be eliminated, they can be mitigated and engineers can monitor sensitive components more closely.
More often than ever, companies are deciding to change or upgrade their MCCs to take advantage of the benefits that new technologies offer. One common upgrade involves replacing conventional starters with variable speed drives (VSDs) and adapting the MCC to accommodate this change. Since a VSD can reduce the energy consumption of a motor by as much as 60 per cent, this type of upgrade helps companies make significant energy and cost savings in the long term.
Intelligent MCCs also feature remote controls and better data collection capabilities, which can be used for condition monitoring and preventative maintenance. In turn, this reduces maintenance and breakdown costs in the long run and helps companies minimise overall operational costs and enhance productivity.
Regardless of the age of your motor control centre, preventative maintenance is the key to making sure it performs well for longer. After all, you wouldn’t skip an MOT on your car, so why would you pay any less attention to the motor control centre that lies at the heart of your industrial plant?