- Be sure your DCS control network supports all devices implemented in your Smart MCC configuration. Some of the attractiveness of implementing a Smart MCC solution is in the cost savings achieved by networking the devices together and bringing the data back to the DCS. All smart devices in the MCC area motor overloads, variable frequency drives, power meters, protective relays, etc. should be capable of communicating data back to the DCS on the same network.
- Choose smart devices that will cover all of your motor needs. For example, when using intelligent motor overloads your device should support direct starting, reverse starting, star-delta starting, soft-starters, and valve/positioner motor control profiles. This way all motors used in the plant are serviced by the same type of device.
- Avoid monitoring only important motors! By choosing a system that is both flexible and modular, it will be cost effective to monitor all motors in the plant. It would be reasonable to monitor basic functions overload, phase failure, phase unbalance, earth fault, diagnostic data - on non-critical motors; and monitor additional functions temperature, voltage, power, cosine-phi, phase sequence on motors deemed more critical due either to function or repair cost. A flexible system allows you to monitor both scenarios using the same device but perhaps with add-on modules to perform the extra functions. This allows a consistency of control across all motors that is very beneficial to both the maintenance personnel and from a spare parts perspective.
- Parameterize the smart devices before installation in the field! Devices implemented in Smart MCCs require configuration parameters for proper operation. Thats why theyre Smart! Whether it is a variable speed drive, intelligent overload device, or power meter, basic configuration data such as network address, motor full load amps, and operating profile are required. Avoid configuration in the field as much as possible by doing this work in the factory or during a factory acceptance test. This will generally assure a smoother start-up of the smart MCC in the field. And while were speaking of parameters, now would be a good time to mention that you should advise your installers in the field that this is a smart MCC system being installed. There will no dials to tweak or knobs to turn during startup the parameters are digital and if changes are necessary they will likely be via a PC and software.
- Strictly adhere to network wiring guidelines! Assure cable shielding, network terminations, data cable routing, bending, and separation from power leads, and other pertinent network rules are followed. A Smart MCC is a unique mix of high power bus bars, high voltage motor leads, variable frequency drive harmonics, and a digital data bus communicating to the DCS. The person terminating the motor leads in the MCC may not have experience wiring to digital-based systems or be aware of the close proximity of the data bus. Make them aware!
- Make use of the data available! Now that youve invested in a smart MCC be certain to set up a monitoring program to utilize all of the newly available data. During conception of the project there are often grand plans for use of the smart MCC data, but once installation begins the focus reverts to lets just get this running. Dont fall into this trap. Be sure to use the running hours and number of starts of your motor in a preventive maintenance program. Track the number of overload trips and use this information to catch a problem before a major failure occurs. Save trend data of the normal running current of your motors and watch for a rise from typical it is probably an early warning of an imminent mechanical problem. Configure reports to capture the data. Your DCS is now collecting data that previously was not available use it!
Don Kazak is a sr. application engineer at Siemens in Spring House, Pa.. He can be reached by e-mail at email@example.com.