Three Phase Hermetic Protector Application Process

Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1996 Three Phase Hermetic Protector Application Process J. Petraitis Texas Instruments Follow this and additional works at: http://docs.lib.purdue.edu/icec Petraitis, J., "Three Phase Hermetic Protector Application Process" (1996). International Compressor Engineering Conference. Paper 1192. http://docs.lib.purdue.edu/icec/1192 This document has been made available through Purdue e-pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu for additional information. Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at https://engineering.purdue.edu/ Herrick/Events/orderlit.html

THREE PHASE HERMETIC PROTECTOR APPLICATION PROCESS Jeff Petraitis Texas Instruments ABS1RACT The application of three phase hermetic protectors involve several factors. Information provided by a compressor manufacturer normally involve the three phase locked rotor current, the rundown trip current, and the estimated effective protector ambient. Accurate values of these parameters can aid in finalizing a protector selection, but these parameters are not the only ones that need consideration. A key item in the selection process that is not always fully understood up front is single phasing (secondary or primary). Many times the success of meeting the application requirements hinge upon the ability of passing these tests. The purpose of this paper is to increase the awareness of this issue, and what directions can be taken to minimize the number of samples with the protector manufacturer, motor supplier, and compressor customer as well as the time needed to obtain an acceptable application. INTRODUCTION Single phasing requirements are usually the most difficult to meet in comparison to the other application parameters. The reasons for this involve lower locked rotor current in comparison to the three phase locked rotor and that all of the phases of the motor are not fully energized. This results in a slower response time in the protector and subsequently higher motor winding temperatures. High motor winding temperature can become the negating item under single phasing conditions. The difficulty becomes in what adjustments should be made in the protector selection that will be beneficial in reducing the motor winding temperature to an acceptable level. Sometimes multiple sample iterations fail to produce acceptable results and in turn delay the application approval cycle. PROTECTOR SELECTION PROCESS The performance of three phase hermetic motor protectors are dictated by the resistive elements in the assembly. These elements are the bimetal disc and heater. Current passes through both of these components and by varying the materials, different trip time responses will result from both a low current condition (rundown) and a high current condition (locked rotor). The protectors are calibrated to a specific opening temperature (typically from 100 to 170 degrees C). This allows the device to be temperature sensitive as well as current sensitive. The contribution of each characteristic is dictated upon the fault condition on the compressor. Locked rotor performance is mostly dependent upon the current carrying resistive components, while loss of charge is relevant to the opening temperature of the protector. Rundown or ultimate trip performance is due to a combination of both the opening temperature and the resistive elements. The selection of a protector for an application is dependent upon the opening temperature, disc, and heater. Graphs 1 and 2 are indicative of typical performance curves employed when making an application. The various curves are driven by the heater and disc components and are depicted by the material resistivities. The ultimate trip curves (Graph 1) are used for rundown performance. Selections are made by determining the delta temperature from the trip current and disc/beater combination. The delta temp. is added to the effective protector ambient (EPA) of the compressor to determine the opening temperature of the device. The three phase trip time curves (Graph 2) are used for approximating the first cycle trip time performance of the device under three phase locked rotor conditions. These curves are typically compiled at various opening device temperatures. The curves in Graph 2 are at 135 degrees C opening temperature. 735

APPLICATION EXAMPLE The ultimate trip and three phase trip time curves are what is usually used in making an initial sample selection for a motor application. An example of the characteristics given from a compressor manufacturer for a 230 volt application are as follows: Rundown: Must trip at 23.0 amps, 45 Degrees C ambient Three Phase Locked Rotor: 90 amps trip in less than 5 seconds The ultimate trip curves in Graph 1 indicate the top three curves intersect the 23.0 amp reading and are considered as possible selections. However, the top two selections from the ultimate trip curves have long trip times when checked at 90 amps on the three phase trip time curves in Graph 2 (11.5 and 7.5 seconds). The third selection has a trip time of 3.6 seconds at 90 amps and would meet the trip time requirement specified. Checking the ultimate trip curve of this choice (125 Ohm/CMF disc and 150 Ohm/SMF heater), indicates that a trip of 23.0 amps would occur at a delta temperature of 90 degrees C. Adding the EPA of 45 degrees C to the delta temperature of 90 degrees C will result in an opening temperature of the protector at 135 degrees C. This is the protector selection that was built and sent to the compressor manufacturer for application evaluation. The compressor manufacturer conducts various application tests upon receiving the protector samples. Application test data from the compressor is noted below to demonstrate how well the initial sample selection meets the requirements. The parameters that have been highlighted in bold type are the requirements specified by the compressor manufacturer to be met Initial Sample Selection: Test #1 Rundown: Must trip at 23.0 amps, 45 Degrees C EPA Must trip voltage of less than 187 volts 135 Degrees C Open Temp. 125 Ohm/CMF Disc 150 Ohm/SMF Heater 22.7 amps 167 volts Three Phase Locked Rotor: 90 amps trip in less than 5 seconds 85 amps 4.2 seconds 0.53 minutes 230volts peak motor temp. (350 degrees F max:.) 244 degrees F (4th cycle) Secondary Single Phase: amperage unknown peak motor temp. (350 degrees F max.) Primary Single Phase: amperage unknown peak motor temp. (350 degrees F max.) Loss of Charge: 350 Degrees F maximum motor temp. 72amps 10.5 seconds 0.75 minutes 230volts 292 degrees F (3rd cycle) 86/43 amps 11.0 seconds 1.08 minutes 200volts 395 degrees F (3rd cycle) 293 degrees F 736

The application test data indicates that all the results are acceptable except for the motor winding temp. from primary single phase. The single phasing currents were not originally known, but could have been estimated. Secondary single phase current is approximately 86.6% of the nominal three phase current. Primary single phase current is approximately 100% of the three phase current in the unshorted phase and 50% of the three phase current in each of the shorted phases. The difficulty becomes in predicting the protector trip time response under these conditions. Graph 3 shows secondary single phase trip time responses and is an additional item that can be employed in making applications. A revised sample selection can be produced based on the original motor test data and the use of the secondary single phase trip time curves. The rundown current can be reduced by 2.0 amps since the protector trip occurred at 167 volts. Reviewing the ultimate trip curves at 21.0 amps (Graph 1), another option becomes available. The 125 Ohm/C:MF disc and 305 Ohm/S:MF heater curve is nearly 21.0 amps at a delta temperature of 90 degrees C. The delta temperature will be increased by 5 degrees C to 95 degrees C to insure there is sufficient rundown. Checking this new selection on the single phase trip time curve at 72 amps predicts a trip time of 8.6 seconds. This is an improvement over the original, which the curve predicted a trip time of 10.5 seconds. The three phase trip time (Graph 2) of the revised selection is still acceptable at 3. 7 seconds for 85 amps. The new sample is submitted and the test data is as follows: Revised Sample Selection: Test #2 140 Degrees COpen Temp. 125 Ohm/C:MF Disc 305 Ohm/S:MF Heater Delta v.s. Test#! Rundown: Must trip at 21.0 amps, 45 Degrees C EPA Must trip voltage of less than 187 volts Three Phase Locked Rotor: 85 amps trip under 5 seconds max. motor temp. (350 deg. F) Secondary Single Phase: 72 amps max. motor temp. (350 deg. F) Primary Single Phase: 86/43 amps max. motor temp. (350 deg. F) Loss of Charge: 350 degrees F maximum motor temp. 21.2amps 171 to 175 volts 85 amps 3.8 seconds 0.80 minutes 230 volts 228 deg. F (4th cycle) 72amps 8.5 seconds 1.01 minutes 230volts 263 deg. F (3rd cycle) 86/43 amps 10.0 seconds 1.46 minutes 200 volts 334 deg. F (3rd cycle) 305 degrees F -1.5 amps +4to 8 volts -0.4 seconds +0.27 minutes -16 deg. F -2.0 seconds +0.26 minutes -29 deg. F -1.0 second +0.38 minutes -61 deg. F +12deg.F The revised sample reduced the primary single phase motor temperature to an acceptable level while still meeting the other application requirements. This was achieved by increasing the device opening temp. and heater resistance to maintain an acceptable trip for rundown performance. The higher resistance heater allowed the protector to become more responsive and at the same time generate more heat in the assembly which increased the off time. The initial sample selection that did not meet single phasing could have possibly been avoided if the secondary single phase trip time curves were used to compare potential selections. These curves are a tool that can be used to predict the protector on times. 737

RECOMMENDATIONS There are several factors in the protector selection process that can help reduce the single phase motor winding temps. before an application is even evaluated. Incorporating these factors in the selection will increase the probability of success with an initial sample. The considerations are as follows: - Employ a low closing device temp. (61 or 57 degrees C nominal). This will increase the off times when the protector is cycling and will help reduce the peak motor winding temperature. - Use the option of a higher resistance heater with a higher opening temperature instead of a lower resistance heater with a lower opening temperature. This is demonstrated in the application example where the revised sample reduced the on time and increased the off time which both have an effect of decreasing the peak motor winding temperature. Maximum opening temperature will be limited by the loss of charge condition. - Refer to the secondary single phase trip time curves if available to compare potential selections at 86.6% of the three phase current. If secondary single phase curves do not exist, then single phase trip times can be approximated by using the three phase trip time curves at 70.7% of the three phase current The goal is to have secondary single phase trip times less than 10 seconds. These guidelines should be applied where it is deemed as necessary. Compressor applications vary and some may not need to be screened to this extent. Past experiences within a compressor model line can add insight as to what extent these guidelines need to be followed. CONCLUSIONS There are areas where all of the parties involved can help meet the requirements for single phasing. This includes the protector supplier, motor manufacturer, and compressor manufacturer. - The protector supplier publishes secondary single phase trip time curves (See Graph 3) in addition to the standard three phase trip time curves on the newer three phase protectors. These curves are intended to be used in the application process. They provide frrst cycle on times for a given amperage and can be used in comparing potential protector selections. - The motor manufacturer should provide motor temperature rate of rise data when submitting a motor to a compressor manufacturer for application work. This would help provide information on how quickly the protector would need to trip under single phasing conditions. - Past application test data from the compressor manufacturer should be reviewed of similar models to provide insight on how difficult it may be meeting the single phasing requirements. The type of protector chosen on previous models would also give guidance as to if something similar may be needed for a new application. Three phase hermetic protector applications involve passing various tests prior to being released for production. The ability to complete this cycle on a timely basis can hinge upon minimizing the amount protector sample iterations needed to complete the application. The level of success can be enhanced by following the actions outlined in this discussion that will result in the single phasing motor peak temperatures being at an acceptable level 738

ULTIMATE TRIP ULTIMATE TRIP CURRENT VS. DELTA TEMPERATURE BETWEEN PROTECTOR OPENING TEMPERATURE AND PROTECTOR AMBIENT TEMPERATURE APPROXIMATE, TO BE USED ONLY FOR SELECTING SAMPLE FOR MOTOR VERIFICATION TEST DISC HEATER TYPE 150 nt CMF GAGE OHMS/ SMF I 100 90 80 70 60 so 35 70 125 70 125 250 250.010 55.010 150 _._Q_l_Q 15_Q.. olo :los -.010 305 v.010 305 v.010 Hl 40 472 010 1)4_Q., 10 m 9 8 7 6 5 4 JJP 04/19/96 90 so 70 60 50 40 30 20 10 3 6, TIN DEGREES CENTIGRATE Graph 1 739

THREE PHASE TRIP OPEN TEMP. l35 C AVERAGE FIRST CYCLE TRIPPING TIME VS, CURRENT IN 25 C. AMBIENT APPROXIMATE, TO BE USED ONLY FOR SELECTING SAMPLES FOR MOTOR VERIFICATION TEST 30 25 20 15 10 9 8 7 6 5 4 3 2.5 DISC HEATER TYPE nt I GAGE o:::' CMF II 400 300 200 150 I 35 010 55 _l_q 010 150 II 70 010 305 11? <; n 1 n 1<;{) v 112S nln 3Cl5 v 250 010 305 1250 010 491 1m _{) 1 {) 64_0_ [I - m 100 90~ a:: w so~ <l 70 ~ 1-60~ a:: a:: so a w :;; j:: 401-30 20 a::., 0 ::1: 15 JJP 04/19/96 30 25 20 15 10 9 8 7 6 TRIPPING TIME IN SECONDS 10 5 4 3 2. 5 Graph2 740

SINGLE PHASE TRIP OPEN TEMP. - 135 C AVERAGE FIRST CYCLE TRIPPING TIME VS. CURRENT IN 25 C. AMBIENT APPROXIMATE. TO BE USED ONLY FOR SELECTING SAMPLES FOR MOTOR VERIFICATION TEST 30 25 20 15 10 9 8 7-6 5 4 3 2.5 DISC HEATER TYPE n; GAGE CMF ~~::' - 400 300 200 150 35. 01( 55 70 011 150 70 011 305.?<; n 1 1 1 sn ~""'--,?<; (11 <nc; v I:> 5o 0 1( 305 ~50 OlC 491 «72 0 lc 640 [',_ - - o; 100 90~ c: w 80 a. :;! < 70 z 1- m sob Ill 30 60~ a: a: w :;! i= 20 40tc: 0 ::t: "" 15 JJP 04/19/96 30 25 20 15 10 9 8 7 6 5 4 Graph3 TRIPPING TIME IN SECONDS 3 10 2.5 741