September 2020

Vibration measurement flexibility provides cost-effective and enhanced protection Maintenance Matters Problem Solver 18 | Plant & Works Engineering www.pwemag.co.uk September 2020 A s the use of premium efficiency (IE3 ) motors has increased, due in part to strengthened regulation, the question of maintaining motor efficiency after a rewind process has reappeared. The most recent study, conducted in 2019, by AEMT and EASA has again used independent testing facilities and revealed that even these higher efficiency units are unaffected by a repair using good practice procedures. The original study in 1998 by the AEMT and UK Government established the first Good Practice Guide, under the DETR Best Practice Programme, using 40 smaller motors of around 5.5kw supplied by manufacturers. In 2003 a very comprehensive joint study using 23 large motors was completed by AEMT and EASA in America. Considerable time was spent determining the parameters of the investigation as well as the procedures and testing facilities that would be used. As part of this process, options such as multiple rewinds and round robin testing were included in that study. As these had no effect on those results, they were not included in the latest 2019 tests. The results of that study were published as The Effect of Repair/Rewinding on Motor Efficiency. It established that efficiency was maintained on repairs to current machines up to IE3 efficiency. To enable comparisons, the ten premium efficiency or IE3 motors under evaluation had similar characteristics to those in the 2003 tests. The power ratings ranged from 30 kW to 75 kW (40 hp to 100 hp) with half being IEC and half NEMA designs. They had totally enclosed fan-cooled enclosures, covered both 50 Hz and 60 Hz supplies with 2-pole and 4-pole models. The repair procedures that were published in the Good Practice Guide to Maintain Motor Efficiency in 2003 were followed for each motor. This Good Practice Guide has now been incorporated into the latest international repair standard IEC 60034:23:2019, and the latest American Ansi/EASA standard AR100. As per the previous 2003 study the IEEE 112B test standard was used. The international IEC 60034-2-1 test standard is now harmonised with the IEEE 112B standard, so that the results of the latest study comply with both standards. All the efficiency testing was performed at North Carolina Advanced Energy Corporation (Advanced Energy) located in Raleigh, North Carolina, using the eddy current dynamometer test stand. Currently, Advanced Energy remains the only independent motor lab in North America to hold the National Voluntary Laboratory Accreditation Program (NVLAP) accreditation for motor efficiency testing. The test results from the ten motors showed no significant change in efficiency compared to figures taken before the rewind, which mirror the results from 2003. On average there was a decrease in efficiency of just 0.1 of a percent, as this is well within the range of the standard calibration test accuracy of +/- 0.2 of a percent, it effectively means that there was no efficiency change beyond that which would normally be expected during testing. The main conclusion that can be drawn from these results is that by using the latest international repair standards, to repair a motor, the efficiency of the machine will be maintained within the tolerances that it was originally manufactured to. The effect of repairs on motor efficiency T he advantages of applying vibration condition monitoring to rotating equipment is well established but this technique can only provide the maximum benefit when applying the correct measurement technique. So what is the correct measurement and how do I implement this? What if I need to make a change to the measurement to optimise early fault detection? Whilst industrial vibration sensors offer a broadband performance suitable for most machines it’s the signal processing that makes the difference. Furthermore, the right hardware that provides a range of measurement algorithm options will maximise the return on investment and future proof the installation. Typically the higher cost of more sophisticated vibration monitoring systems offering this type of flexibility can be difficult to justify for smaller machinery. This is why condition monitoring specialist Sensonics developed the DN26 G3 protection monitor to provide a more suitable stand-alone monitor to complement their successful range of rack-mounted products. The dual channel din rail mountable unit provides monitoring of bearing vibration, shaft vibration, or shaft position with fully programmable signal conditioning and with a range of measurement algorithms and sensor options. The unit is designed for optimum flexibility; as a universal module (single hardware platform) it is field upgradable and fully programmable. Special protection options include slow rotation vibration monitoring down to 0.2Hz and narrow band filter measurements for specific vibration signatures. In addition the DN26 G3 offers a dedicated speed monitor channel which can also be utilised as a phase reference for further harmonic analysis of the vibration signals. The sensor interface is programmable to accept IEPE type accelerometers/ velomiters, proximity probes (API 670 standard), and active / passive speed probes. All sensor signals are available via a buffered interface which provides the option of further detailed analysis if required. Three alarm relays are available as standard (expandable to up to seven relays via a digital interface), one dedicated to indicate module and sensor integrity. The other two relays are fully programmable across the alarm criteria selected and all three input channels measured values are available via a 4-20mA interface. The unit is available with Ethernet communications as standard, permitting configuration either locally or remotely through the in-built webserver and offering Modbus over TCPIP for connecting measured data to other plant wide systems. The DN26-G3 features a built-in intuitive colour LCD display and menu drive facility providing various display modes and an alarm historian with real time logging capability.