A Review of the ALL-TEST IV PRO 2000 and SKF/Baker AWA II

Transcription

1 A Review of the ALL-TEST IV PRO 2000 and SKF/Baker AWA II Howard W Penrose, Ph.D., CMRP Vice President, Engineering and Reliability Services Dreisilker Electric Motors, Inc. Abstract: The importance of understanding the capabilities and limitations of the technologies for testing electric machines cannot be understated. Modern methods include both high and low voltage tests including insulation to ground, turn impulse testing, and motor circuit analysis. In this paper we will review several examples of the capabilities and limitations of both PD Surge, using an SKF Baker AWA II-6kV (AWA), and a Motor Circuit Analyzer, the ALL-TEST IV PRO 2000 (AT4). The comparison will include time to test, evaluation of the scope of test, and several examples of missed findings where other methods were able to detect the fault. In each case, the actual issues, if any, were unknown prior to the performance of each test. Note: We are looking to evaluate other test instruments such as the PdMA as part of this study. If you wish to lend us your PdMA tester for 3-4 weeks, please contact Dr. Penrose at hpenrose@dreisilker.com. Introduction For well over a century the primary methods for electricians to evaluate machines have been limited to insulation to ground testing, continuity and other similar tests. During the 1980s advanced test methods came onto the market that utilized both high voltage and low voltage methods to determine the condition of machines in the field. One method is based upon the surge comparison methodology which utilizes a tank circuit and a series of fast rise time pulses sent to a winding. The other utilizes very low voltage levels and higher frequencies along with bridge circuits to evaluate the condition of the windings. The high voltage test is exploring for insulation weakness while the low voltage test is exploring for insulation condition. In both cases, the technologies require a path to detect faults. During several weeks at the end of June, 2010, and the beginning of July, 2010, Dreisilker Electric Motors, Inc. was requested to review the capabilities of the AWA II-6kV system which weighs approximately 40 lbs. It was determined by Dreisilker Engineering to take the opportunity to review the AT4 and the AWA without representatives of either vendor participating. The results were interesting and provided important information on the accuracy of both technologies both in comparison and in capability. The live tests can be viewed on the MotorDoc channel of ( The tests were performed on relatively small electric motors of about ten horsepower, 480Vac, through to 19,000 horsepower, 13.2kV, including through over 1,000 feet of run. Each case was introduced into real world conditions without prior knowledge of the actual conditions of the machines. One 8000 horsepower electric motor made for an interesting case study and will be included in this paper. The results of this paper led the investigators to a greater understanding as to the need for training and experience in each of the technologies they use. Inexperienced technicians tend to rely too much on exact results which can end with unfortunate conclusions. It will also be noted that several of the case studies presented indicate the failure of the technology(s) to detect specific faults within their advertised capability. ANY technology that claims that this proves their technology superior had obviously not been subjected to the rigors of this analysis and cannot make such claims. In effect, buyer beware of such tactics (and we would be happy to put them through the same rigors and comparisons). It is noted by the investigators that each of the technologies evaluated in this paper have performed admirably in the field for over two decades.

2 Overheated Windings During the testing that was being performed, a great number of motors, with a few of them shown in the YouTube videos, were tested both assembled and disassembled. The purpose of this paper is to identify where things were missed and to evaluate the reasons why. The first evaluation that was missed was a submersible pump. Both the AT4 and AWA were used with the full range of both instruments (abbreviated for YouTube, the PI was not performed with the AWA, just the DA). The AWA was set for resistance, 500Vdc insulation resistance and DA, a high potential test of 2000 Vdc, and a surge test at 2000 Volts. The value for the high potential and surge tests should have been: Eq. 1: DC High Potential (used winding) ( 2(480V ) V ) *1.7 *.65 = 2, 166V Eq. 2: Surge Test (new winding) ( 2(480) V ) = 1, 960V The values used were the default values of the AWA. The submersible was tested with the default 480 Vac machine values built into the AWA, including the Dielectric Absorption (DA). The findings can be found as Attachment A of this white paper. The AT4 was also utilized and all of the tests performed were satisfactory. The motor was disassembled and the stator inspected. The AT4 and AWA had detected rather low insulation readings which changed as the leads were moved. The submersible had been installed and the cable fouled and damaged. It was then energized. Upon disassembly of the pump, it was determined that the winding had overheated as the ties broke on the windings. The insulation, in general, looked to be in good condition other than the overheating (Figure 1). The low insulation resistance related to the leads was due to the insulation on the leads deteriorating. The low insulation resistance detected a potential problem; the additional work identified the issue. Figure 1: Overheated Winding The conclusion was that experience is still required even while using advanced testing equipment. Without the experience to hunt down the cause for the odd insulation resistance readings, the unit might have passed and been put back into service as both technologies passed the winding based upon automated (software) analysis. Understanding the presented data allowed the technician to focus in on the fault hp 13.2 kv Machine Another project involved reviewing the condition of two large 13.2 kv machines. One at 19,000 horsepower synchronous and one 8,000 horsepower induction that had tripped off line. The unit available for initial testing was the 6kV AWA unit at close to 40 pounds and requiring a 100 foot extension cord. The other unit was the ALL-TEST IV PRO Table 1: AT4 Pro 19000hp Data T1-T2 T1-T3 T2-T3 Resistance Impedance Inductance Fi I/F The AT4 was used from the disconnect approximately 250 yards away with results

3 showing in Table 1 for the 19,000 horsepower motor. The AWA was used with the resistance, insulation resistance, and polarization index being used from the disconnect. It required disconnection at the motor (the lightning arrestors and surge arrestors were disconnected for all testing) to perform the high potential test and surge test. Figure 2: Surge Test hp The motor was pulled from service and disassembled for evaluation. It was immediately apparent that one winding had blown and had impacted the coil immediately across. It was also apparent that the sole reason why the fault was detected with insulation resistance and capacitance testing was carbon dust and conductive contaminants on the surface of the conductors. If there had been any break, the fault would not have been detected even with four wire Kelvin technology. Figure 3: Actual Fault Image A phase to phase insulation resistance test was also performed with the neutral open and a phase to phase capacitance test was performed with the ATIV. Based upon the success of all of the testing, it was determined that this motor could be started, and was, successfully. The 8000hp machine was evaluated at the motor. The surge test passed at 6,000 Volts, the insulation resistance and PI tests passed, the step voltage high potential test passed, and the ATIV test passed (Table 2). Table 2: ATIV Test 8000 hp T1-T2 T1-T3 T2-T3 Resistance Impedance Inductance Fi I/F Figure 4: Image Inside Faulted Coil The capacitance readings using the ATIV identified an issue and the insulation resistance test between A phase and B phase tripped on overcurrent at 3250 Vdc. As only these tests identified a fault, a second high voltage insulation resistance test was performed with a different meter. It also failed at over 3200 Vdc.

4 During the investigation, it was noted that the machine and coil passed a surge test at 22,700 V. The fault was in the first two turns of the first coil of Phase A. What surprised the investigators was that resistance, AWA, surge, and AT4 should have identified this fault even at the test voltages used. It was also noted that when the carbon and contaminants were brushed away from the coils that the insulation resistance and capacitance between phases was excellent. Single Phased Motor During a field analysis of an electronic soft start, an electric motor was found to have a good insulation to ground, good ohm readings and continuity, and passed a surge comparison test. The AT4 was used and the results showed as in Table 3, which shows a turn to turn short and overheated windings. Table 3: AT4 Blower Motor Evaluation T1-T2 T1-T3 T2-T3 Resistance Impedance Inductance Fi I/F Figure 5: Stator Condition As shown in Figure 5, one coil group was burned in the motor. Conclusion As noted in Electrical Motor Diagnostics: 2 nd Edition, no one test method can be relied upon to detect all faults. There is also a high risk of missing faults if the operator does not have a full understanding of the technologies used and equipment that is being tested. It is equally important to note when a single component of a suite of tests performed identifies a potential fault that additional investigation is necessary. The experienced technician needs to use his senses and knowledge as a tool as much as the test equipment available. This is particularly important as 20% or more of electric machines are pulled for repair or replacement that have no problems to begin with. Even worse is when parts are swapped in an effort to plug and play a solution to a problem when equipment is down. These issues occur a majority of the time, especially when the technician does not trust himself or his technology. Bibliography Penrose, Howard W, Ph.D., CMRP, Electrical Motor Diagnostics: 2 nd Edition, SUCCESS by DESIGN, Connecticut, About the Author Howard W Penrose, Ph.D., CMRP is the Vice President of Engineering and Reliability Services for Dreisilker, the Web Editor-in-Chief of the IEEE Dielectrics and Electrical Insulation Society, the Director of Membership for the Society for Maintenance and Reliability Professionals (SMRP) and serves on the Board of Directors for the Autism Society of Illinois. He has won five consecutive UAW and General Motors People Make Quality Happen Awards ( ) for energy, conservation, production, and motor management programs developed for GM facilities globally and is an SMRP Certified Maintenance and Reliability Professional (CMRP). Dr. Penrose is the author of the Axiom Business Book Award (2008 Bronze and 2009 Bronze) winning Physical Asset Management for the Executive (Caution: Do Not Read This If You Are on an Airplane), and the 2008 Foreword Book of the Year Finalist textbook, Electrical Motor Diagnostics: 2 nd Edition. Dr. Penrose may be contacted by at hpenrose@dreisilker.com.

5 Nameplate Information Location DEM Winding Building Incoming Model Manufacturer FAIRBANKS MORSE Serial Number HP/KW 25 Volts-Rating 460 Volts-Operating 460 Amps-Rating 32 Amps-Operating 32 Insulation F Enclosure SUB RPM 1760 Service Factor 1.15 Frame Freq-Hz 60 LR Code LR Amps 0 NEMA Design b Max Amb C 40 NEMA nom eff 0 Duty Cycle cont Manuf's Type Manuf Dt Cd Description Place holder MotorID. After adding valid motors, delete this one

6 Nameplate Information Location DEM Winding Building Incoming Model Manufacturer FAIRBANKS MORSE Serial Number HP/KW 25 Volts-Rating 460 Volts-Operating 460 Amps-Rating 32 Amps-Operating 32 Insulation F Enclosure SUB RPM 1760 Service Factor 1.15 Frame Freq-Hz 60 LR Code LR Amps 0 NEMA Design b Max Amb C 40 NEMA nom eff 0 Duty Cycle cont Manuf's Type Manuf Dt Cd Description Place holder MotorID. After adding valid motors, delete this one Application Information Test Date/Time 6/29/ :13:14 PM Test ID 480V w/rotor<100hp Repair/Job # StepV Tested By Tested For Room # MCC Location DEM Winding Building Incoming Use % Load Vert/Horiz Starter Starts/24Hrs Rewind Dt Install Dt Basic Dt Volts Amps Volts Amps Volts Amps Tester Type AWA4_6kV_4Wire Tester SN Tester ID PP30 SN 0 Cal Date 09/01/2009 Next Cal Date 09/01/2010

7 Results Summary Test ID: Nameplate Information Location DEM Winding Building Incoming Model Manufacturer FAIRBANKS MORSE Serial Number HP/KW 25 Volts-Rating 460 Volts-Operating 460 Amps-Rating 32 Amps-Operating 32 Insulation F Enclosure SUB RPM 1760 Service Factor 1.15 Frame Freq-Hz 60 LR Code LR Amps 0 NEMA Design b Max Amb C 40 NEMA nom eff 0 Duty Cycle cont Manuf's Type Manuf Dt Cd Description Place holder MotorID. After adding valid motors, delete this one 480V w/rotor<100hp StepV Test Date/Time 6/29/ :13:14 PM Repair/Job # Tested By Tested For Room # MCC Location DEM Winding Building Incoming Temp Status Tested PI Status PASS Temp 26.7 C 80.0 F Volts (V) 500 Resist Status PASS DA Ratio 1.0 L1-L2 (Ohms) Corr: PI Ratio DA Only L2-L3 (Ohms) Corr: HiPot PASS L3-L1 (Ohms) Corr: Volts (V) 2000 Max Delta R % 0.083% Current(µA) Coil 1 (Ohms) Corr: Resist (Mohm) 167 At 40 C 66 Coil 2 (Ohms) Corr: Surge Status PASS Coil 3 (Ohms) Corr: Peak Volt(V) L Megohm Status PASS Peak Volt(V) L Volts (V) 500 Peak Volt(V) L Current(µA) 2.50 Max P-P EAR% 3.2%,3.3%,3.1% Resist (Mohm) 200 At 40 C 79 EAR 1-2,2-3,3-1 No Test

8 DA/PI Test Date/Time 6/29/ :13:14 PM Voltage (V) 500 DA Ratio 1.0 PI Ratio DA Only PI Status PASS Time (Min) Current(µA) Megohms 0: : : : : : : :

9 Surge: Nested Waveforms Test Date/Time 6/29/ :13:14 PM Surge Status PASS Lead Peak Voltage (V) PP EAR Status Max P-P EAR% PASS 3.2% PASS 3.3% PASS 3.1%

10 Pulse-to-Pulse EAR Test Date/Time 6/29/ :13:14 PM Surge Status PASS Lead Peak Voltage (V) PP EAR Status Max P-P EAR% PASS 3.2% PASS 3.3% PASS 3.1%

11 Surge Phase-to-Phase Comparison Test Date/Time 6/29/ :13:14 PM Surge Status PASS Compare Peak Voltage (V) LL EAR Status L-L EAR% No Test 15% No Test 11% No Test 24%