Two-Contactor Vs. Three-Contactor BypassABB factory designed VFDs with Bypass take advantage of a proven two-contactor bypass design rather than a less reliable three-contactor design. This two-contactor design philosophy was implement-ed because it includes several inherent advantages for the end user. When paired with the VFD service switch (drive isolation mechanical only disconnect) a two contactor bypass provides all the features of a three contactor systemand more.A two-contactor design provides a safer bypass.One of the common rationalizations used for a three-contactor bypass is drive serviceability. A common perception is that an input contactor provides a safe disconnect method for removing input power from the VFD during servicing. Our competitors may state that the three-contactor bypass allows the cus-tomer to remove and replace the VFD while the motor is run in the bypass mode. While this may have occasionally occurred in the fi eld, a customer should never attempt to swap a drive on the load side of a contactor when power exists on the line side. The fact is that several conditions can result in unexpected power being applied to the load side of a contactor.−− The contactor could be mechanically jammed or have weldedcontacts.−− Coil voltage could be inadvertently applied to the contactorwhile the VFD control wiring is being removed and re-installed.−− Accidental pressure could be placed on the plunger, engagingthe three phase contactsAny of these conditions could result in equipment damage and physical harm. Safe electrical mainte-nance practices require removal of fuses and/or the use of a disconnect switch. How many electrical equipment enclosures do you know of that utilize a contactor as the method for removing power from theequipment inside? After all, a contactor is not an NEC recognized, lockable, physical disconnect. A two-contactor, two disconnect (one drive isolation, one external main disconnect) bypass is the only type of bypass that will allow a customer to change out the drive while running the motor in bypass. Additionally, all factory designed ABB drive / bypass systems have fast acting drive input fuses that can be easily removed to isolate (disconnect) the VFD from the line with a visible air gap if no VFD service switch is optioned.A two-contactor design provides a more reliable bypass.One of the main problems experienced with a typical 115 VAC, three-contactor bypass design is input contactor coil burnout. Under abnormal operating conditions such as a “brownout” or single-phase con-dition, an unregulated 115 VAC control transformer can cause the voltage across the input contactor coil to fall below the “hold-in” level of the contactor. Under these conditions the input contactor can chatter or drop out endingin contactor coil failure, contacts welding, or contacts failing open*. So now the three contactor Bypass system, which was purchased to make the system more reliable, has failed due to input voltages that the VFD without a bypass, would likely have not failed. Additionally if the input contactor drops out dur-ing a “brownout” or power outage, the system ride-through is reduced as the VFD immediately has zero power to draw from the line. These two types of failure scenarios cannot happen to a system that does not use a third contactor, as there is no voltage sensitive device upstream of the VFD in ABB systems.

Page 2 Mulcahy Minute

2013 Xcel Energy Motor Rebates – NEMA Premium Effi ciency vs. “Enhanced” NEMA Premium Effi ciency

Below is a sample of the 2013 motor rebate application from Xcel Energy.

The question that has come up is, “What exactly is an “Enhanced” premium effi cient motor?”

The 2013 Xcel Energy Rebates are based on the NEMA Premium Effi ciency ratings. They have included an additional column for “Enhanced” NEMA premium. The description states that motors that exceed the Premium Effi ciency standard by 1% point are defi ned as “Enhanced” NEMA Pre-mium. This “Enhanced” Premium is an Xcel term, not a manufactuer term.

Consulting engineers are starting to schedule/specify motors that are listed as “Enhanced” NEMA Premium effi cient motors in order to meet the higher rebates. The ISSUE is that the motor manu-facturers do not make a motor that is listed as “Enhanced” NEMA Premium Effi cient. Based on conversations with Baldor and Marathon they are following NEMA Premium Standards and NEMA only requires manufacturers to meet the Premium Effi ciencies. The motor manufacturers make some motors that have effi ciencies higher than those listed as Premium Effi ciency, but they do not have a specifi c designation.

If you are selecting motors or writing motor specifi cations, be aware of what is available

The Xcel Energy rebate forms can be found at the link below. http://www.xcelenergy.com/Save_Money_&_Energy/For_Your_Business/Equipment_Effi ciency/Motor_and_Drive_Effi ciency_-_MN

Revolutionary AEGIS® Nanogap Technology…Revolutionary AEGIS® Nanogap Technology…Other shaft grounding brushes (including discrete point brushes) work only when in physical contact with the motor shaft and are plagued by problems such as contamination, wear, and frequent maintenance/replacement. The AEGIS® Bearing Protection Ring’s patented Nanogap Technology, however, ensures

effective electrical contact even when physical contact is broken . Only AEGIS® Nanogap Technology provides both mainte-nance-free contact and noncontact bearing protection for the normal service life of the motor’s bearings as well as the most reli-able operation of any shaft grounding technology. Ensures Unmatched Grounding With or Without Mechanical ContactEnsures Unmatched Grounding With or Without Mechanical ContactDue to the unique design of the AEGIS® Ring, at any point in time, some of its microfi bers are in mechanical contact with the shaft, and those that are not are in nanogap proximity to it. But thanks to the ring’s patented Electron Transport Technology™, all of its fi bers remain in electrical contact with the motor shaft, providing unmatched grounding 100% of the time. This technology ensures electrical contact for the life of the motor through mechanical contact and three Nanogap noncontact current transfer pro-cesses — all working simultaneously. And these processes ensure effective grounding, even in the presence of grease, oil, dust, and other contaminants, and regardless of the motor’s speed. No other product works both with and without contacting the motor shaft to provide the long-term, maintenance-free bearing protection of the AEGIS® Ring.

Page 3Volume 14, Issue 1

We stock AL29-4C vent in 3” - 10”. We can help you lay-out your vening projects no matter who’s equipment it is connected to! Call today!

VFD – Test –Bypass functionalityThree contactor systems are often specifi ed with a three position selector switch “VFD-Test-Bypass”. ABB two contactor bypass systems can perform all three modes of operation without the three position switch, third contac-tor and associated wiring. VFD mode AND Bypass mode, as they imply, power the motor through one of the two parallel paths. These modes and the ability to manually switch to them are bare necessities in boththe three contactor and two contactor solutions. VFD mode functionality is identical in both systems. −− In Bypass mode, the only operational difference betweenthem is:−− In the three contactor solution the VFD is not poweredbecause the input contactor is disengaged;−− In the two contactor solution the VFD (and all its functionslike serial communication) remain powered up,though not providing power to the motor.−− Test Mode, is specifi c to the three contactor solution in nameonly.−− When selected, test mode applies power to the input (third) contactor, and therefore the VFD, allowing the operator to “test” the VFD functionality without the VFD providing power to the motor because of the open drive contactor. The two contactor solution inherently has this function, as the VFD remains powered in all operationmodes, unless specifi cally powered down via the service disconnect switch or removal of the VFD fuses.*The fi x for the contactor chatter issue of a typical bypass with a control transformer is to add expensive phase monitor relay and interlocks. The ABB E-Clipse Bypass eliminates this issue across the product line from 0.5 thru 400Hp. The ABB E-Clipse Bypass utilizes a regulated power supply with a voltage monitoring circuit to power the 115V coils on both contactors. The power supply operates with an input line voltage that is ±30% of the input volt-age. On a 380 – 480 VAC bypass this translates to an entire system (VFD and bypass) voltage limits of 266 – 624 VAC. Additionally The E-Clipse System recognizes welded or mechanically jammed contactors, open contactor coils, and single phase power conditions; taking appropriate actions for each scenario.

The ABB two-contactor bypass designs ultimately give the end user better and safer functionality than a three-contactor bypass. Service capability, reliability and safety are improved through the use of drive input disconnect switch, rather than a third contactor. We feel the advantages listed will lead to a win-win situation for you and your customers, and feel that a two-contactor bypass design offers more than a three-contactor design.

continued from page 1

2700 Blue Water Rd #100Eagan MN 55121(P) 651.686.8580 (F) 651.686.8588www.mulcahyco.com

After this certifi cation process, each student will be able to do the following:Plan for and evaluate a proper installation, including mounting and wiring (both power and control wiring)Plan and install the control interface wiring for a given applicationProgram the VFD for the applicationCheck for correct rotationVerify proper operation of the VFD and motorRegister the VFD with ABB for extended-warranty registration (your responsibility if you do the startup)Provide light-duty troubleshooting of VFD faults and failures

The full certifi cation process involves four parts:An online presentation and an online product overview at ABB’s website: 3-3.5 hoursTwo online presentations for ABB’s E-Clipse Bypass Product Overview and Startup Procedures—1-1.5 hoursHands-on class, lasting 1 day. Topics include: Certifi cation & Installation requirements, Programming basic drives, Programming the PID controller, Serial communications & much more Two online tests (perhaps 1-2 hours)While not mandatory, it is recommended to do the above steps in the order described, with steps one and two fi nished before the hands-on class.

Classes are free of charge & fi ll quickly. Contact Laura Citrowske at 651-686-8580 to sign up. Location: Mulcahy Company, 2700 Blue Water Rd #100 Eagan MN 55121Conducted By: Greg Olson, Mulcahy Company

STARTUP CLASS: March 12, 2013, Tuesday at 8:00