Motor control – Making a case for intelligence

08 November 2011

Conventional low-voltage Motor Control Centres (MCCs) are ubiquitous in the oil and gas sector and in general, meet industry requirements for safe, reliable and efficient operation. So, are there any real benefits to be gained by choosing the new generation of Intelligent Motor Control Systems (IMCSs) for future projects? The answer is undoubtedly yes except, perhaps, for the most undemanding of projects.

In a conventional MCC, the power switching and protection components that make up the individual starters are linked to the device that provides the control functions – most often a PLC, with conventional cabling. In addition, the functionality of the components used, such as the protection devices, is defined within those devices. If additional information is required from the starters as an aid to managing the plant or for measuring and controlling energy usage, extra components have to be added, along with even more cabling to the PLC.

In an IMCS the power switching devices are controlled by a Smart Control Unit (SCU) that also monitors the motor operating parameters, such as voltage and current. The protection functions are implemented in the SCU, which communicates with the PLC via a data connection, eliminating much of the conventional control system cabling, replacing it with just a handful of network cables.

Also, because the protection functions of the starter are now defined by software in the SCU, decisions about these functions do not need to be finalised until after the motor control system has been built. This is a useful feature in oil and gas applications, where late changes to plant configurations and specifications are common.

The functionality of the starters in the IMCS can also be changed easily and quickly even after the plant has been put into service, providing flexibility. Finally, since the SCU directly monitors the operation of the motor and the starter, it can provide almost any operational data needed for plant management, energy reduction or maintenance purposes directly, without the need to install additional equipment.

There are, however, still those who have reservations about the adoption of IMSCs There are essentially two reasons for this. The first is that some of the earliest IMCS implementations were ill-conceived and failed to deliver on their promises. These issues have now been addressed – the technology has matured.

The second is that there are some applications where conventional MCCs are still the best option, though these are reducing in numbers. Typical of these are simple installations where there is no requirement to collect data for onward transmission to a supervisory system and where the likelihood of modifications being needed during the life of the equipment is small. In such cases, a conventional MCC may well be adequate.

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