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March 27, 2012
November 3, 2010
Drive Isolation Transformers
A common concern in the current cost conscious business climate is whether or not a Drive Isolation Transformer adds value to a Variable Frequency Drive (VFD) installation. Some VFD manufacturers take the position that an Isolation Transformer is a necessity while others view it as performance enhancing option.
A Drive Isolation Transformer (DIT) differs from a standard power distribution transformer. A DIT is built to handle the extra heating caused by the dissipation of harmonics from the non-linear drive components. It also has a minimum reactance to help protect the input rectifiers on the drive. Lastly, it is built to withstand the cyclic loading usually characteristic to a machinery load. Also, the DIT will usually be connected as a Delta Primary and a WYE Secondary.
The value proposition for installing a DIT includes several advantages. The WYE connected secondary establishes a balanced reference to ground through the earthed WYE neutral. This helps the drive resist damaging voltage surges from lightening or other downstream disturbances. The earthed WYE point also creates a path to ground for the high frequency noise generated by the drive electronics and switching devices. The DIT will absorb harmonics providing a cleaner power grid and reducing the probability of damage/nuisance tripping of nearby connected equipment.
Most VFD’s will run fine without DIT’s when the power is perfect. Manufacturers who use an SCR front end to precharge the bus caps and generate bus voltage generally are more insistant on the installation of a DIT. Those with a diode front end, are less insistant. However, any way you look at it, a DIT will offer economical long term protection of your VFD investment and allow satisfactory drive performance under not so optimal power grid conditions.
A Nova Electrical Engineer can help Design, Specify and Install a Drive Isolation Transformer matched to any drive.
November 2, 2010
DeviceNet
It is no secret that equipment manufacturers are deeply concerned about reducing the cost to produce their particular product. Using a fieldbus technology, even though the initial cost of components is higher, can result in an overall cost reduction. DeviceNet, a CAN based variant, is one of the more popular choices.
In any fieldbus network, the higher component cost is quickly overtaken by a reduced wiring cost. For the equipment builder, this means the cost to produce is less. For the owner, fewer wires mean less things to fail, more up-time. The digital nature of any fieldbus, including DeviceNet, reduces the control system’s susceptibility to noise making the process run smoother. Less noise interference can also reduce nuisance trip events.
However, troubleshooting a DeviceNet network component such as a VFD, a valve pack, a sensor or an I/O island usually falls out the area of expertise of the average industrial electrician. Is the problem in the scanner (Master) or the field component or the cabling?
Nova Systems can help. We have set up a DeviceNet network at our Milwaukee facility. Rather than waiting a day (or longer) to replace a suspected failed component, Nova can power up the device, insert it into our known working DeviceNet network, and test it immediately. This can confirm the integrity of the suspected component, possibly saving the money of replacing a functioning component. Utilizing this service could also compress the troubleshooting time. Our engineers could also aid in the component selection in the case that the defective part is not readily available or an obsolete model.
Please contact Nova for more details.
October 31, 2010
Paper Machine Upgrade
Located in the North Carolina foothills of the Blue Ridge Mountains is a paper making machine which needed a new drive system. In conjunction with the installation of a new wet end to revitalize the aging paper machine, Nova teamed with Baldor Electric to design, supply and commission a new set of 6 Variable Frequency Drives.
Baldor VS1GV technology was used on all the drives. The Ethernet/IP option cards enabled communication for the overall supervisory control by a Rockwell Automation processor. Four of the drives were equipped with pulse follower option cards to allow local electronic line shafting independent of the main system processor.
The Master VFD powered the 100 HP Yankee roll. A second 100 HP VFD powered the Suction Pressure roll which was nipped to the Yankee and operated as a torque follower. A 100 HP forming roll, a 25 HP flat dryer and a 25 HP reel were electronically line-shafted to the master with the ability to set individual draws as required by the process. A 200 HP pump drive completed the project.
Please contact Nova for more details or to discuss any upcoming projects.
