By Mike Bacidore, managing editor
For the past eight months, visitors to www.ControlDesign.com/multimedia have watched our market intelligence report videos. In addition to discovering industry trends about I/O systems, power supplies and simulation software, viewers also learned about the information-gathering organization behind the data. In fact, the Control Intelligence Agency became such an integral part of our reports that we expanded recruitment and created a virtual brigade of agents to help us keep our finger on the pulse. These members of the CIA Virtual Brigade will be participating in print, audio and video reconnaissance missions the results of which we will share with you. To introduce you to these efforts two agents volunteered to offer some insights in a Q&A on motor starters.
Both of them are from Ohio. Bob Wagner is a system integrator in Cleveland, and Don Lanhart is manager of production systems at Specialty Minerals in Jackson.
Control Design: What non-product performance criteria, like technical support, documentation, brand name or recommendations from colleagues, affect your decisions about what to buy or whom to buy from?
BW: Plant or company standards and commonality of plant spares or local availability often limit selection to specific name brands.
DL: You’re always trying to build a facility as economically as possible, so price is the biggest criterion. Local codes are the second biggest, depending on where it is. In addition to the U.S., we have a pretty good presence in both Europe and Asia.
CD: Does your company specify NEMA-rated starters or IEC?
BW: My preference is NEMA-rated starters, although IEC starters provide a more compact installation. NEMA starters allow for easier troubleshooting and in my experience, typically provide better reliability.
DL: That depends on the location. In the U.S., we spec NEMA. Outside the U.S. it’s IEC. A lot of the regulations outside the U.S. are tighter, so IEC fits into that niche better. We use NEMA in the U.S. because process and design engineers like to change a motor size at the last minute. NEMA is more forgiving on changing out heaters or fuse boxes. We’ve got facilities in the U.S. that are more than 20 years old, and they’re still humming right along.
CD: Enclosures can protect against contamination from airborne particles, such as steel dust, as well as exposure to moisture, vibration and electromagnetic interference. What are the best ways to ventilate and cool enclosures for the lowest cost vs. ease of maintenance in areas that are difficult to access?
BW: Sealed enclosures provide the best protection against damage from contaminants. It is also a good idea to maintain desiccants in enclosures to avoid the accumulation of moisture. In many situations, careful component spacing and placement can minimize the need for additional cooling. Where components, space or location dictate the need for additional cooling, in areas with a high concentration of contaminants, vortex coolers are a good choice. Care must be taken to assure that the air source is clean, dry and non-oily. Normal plant air supply is often not suitable. A heat exchanger can be used to provide cooling without requiring additional openings in the enclosure. Most heat exchangers though will require additional maintenance. Air conditioners and forced ventilation are typically only suitable for relatively clean environments. All of these solutions tend to require some additional maintenance to maintain performance.
CD: Can you discuss a particular problem or opportunity involving motor starters that has arisen in your job recently?
DL: A couple years ago, some very old motors that had been at a production facility for more than 20 years had lost a coil. It should have been a 10-minute job, but there wasn’t a direct spare out there on the market. That antique coil had been made obsolete by the vendor. Our team found a third-party vendor that would supply the coils. It wound up being a lengthy ordeal, but you can’t just throw in another bucket.
BW: The availability of motor starters as part of a local rack assembly or individually with a network connection or an add-on network interface provides a wealth of status information and operation flexibility to the system. Additionally installation costs are reduced due to decreased wiring and space requirements.
CD: What about issues with noise in the communication network on which the motor starters are located. This noise can cause the loss of feedback from the motor starter for short periods of time, which in turn can cause the motor to stop. What is a good method for cleaning up the noise, when the source seems to be the starters?
DL: I’ve got one production facility where we’ve had problems for multiple years. The vendor has been in and looked at it and made recommendations. It’s gotten better, but there are still motors that will drop information and will start to go into the shutdown routine. Vendor suggestions included pulling out the network cables and rerouting them because they were running too close to the frequency drives in the MCC center and cable shielding.
BW: Heavily shielded cables properly terminated to a high-integrity, separate ground bus and careful routing of communication cables separated from and, where possible, perpendicular to current carrying conductors will help minimize noise problems. In extreme cases, fiberoptic cables can completely eliminate electrical noise problems.
CD: What are the advantages of a soft starter vs. a standard on/off starter in your machine applications?
DL: For us, it’s ease on the equipment. We use soft starts on big motors—250 hp and up. If you’re in a location with a huge demand charge, it can help with the inrush.
BW: A soft starter reduces the inrush current associated with standard on/off starting and thereby limits peak currents, which can reduce utility costs. Soft starters also provide considerable flexibility in optimally tailoring the motor starting and operation to specific process requirements.
CD: Can a VFD serve the same purpose?
DL: In some of the new ones we’re building, we’re going to VFDs on the same ones we used to do a soft start. And you can bring it up to speed over several seconds.
BW: A VFD can typically provide the same functionality plus additional continuously variable parameters to make the installation even more flexible and economical where required. The VFD though comes typically at a higher initial cost.
CD: What about under extreme loads?
DL: Over the years, we’ve used VFDs because you have pretty good control of the torque.
BW: The best way typically varies with the application. Autotransformer starters provide reduced inrush current while maintaining starting torque. Wye-delta starters are typically used for high inertia loads.
CD: How do you balance effective overload protection with not having too many dropouts and the need to have fast restart capability?
DL: The way we split up our plants, we put a little balance of the loads across the MCCs so it’s not an issue. In our facilities, it’s not really an issue. Maybe we should be pushing our motors harder.
BW: Solid-state programmable overload protection reduces a lot of the nuisance trips associated with the old thermal overloads. The old thermal devices would typically degrade over time and become problematic. Programmable features of SSOLRs provide the ability to not only more closely match the overload device to the actual operating requirements, but also adjust those parameters with experience over time while maintaining increased protection against failures.