Voltage Distortion & Power Quality Study Report for General Hospital Somewhere Valley, AK Background / Introduction

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1 PowerCET Corporation 33 Scott Blvd., Bldg.. Unit 1 Santa Clara, CA 94 USA Voice: 48/ Fax: 48/ URL: consulting@powercet.com Study Report for General Hospital Somewhere Valley, AK Background / Introduction General Hospital has experience a series of problems associated with the electrical distribution when operating on emergency generator. The most troublesome condition is associated with UPS equipment located in the equipment rooms on multiple floors of the facility. The specific condition is the apparent inability of the UPS equipment to recognize the voltage as a viable source when operating on emergency generators resulting in a gradual discharge of the battery back-up and eventual failure of the connected electronic equipment if the utility source is not restored before the depletion of the battery supply. The problems experienced during generator testing are not limited to the above mentioned UPS equipment as there are reports of motor drives tripping-out as well. In an effort to identify the route cause and develop a mitigation strategy to correct the situation PowerCET Corporation was retained to conduct a thorough monitoring of the electrical distribution during a typical periodic generator test. The electrical environment associated with General Hospital s complex consisting of a total of four (4) automatic transfer switches (ATS) serving a variety of loads as well as two (2) active harmonic mitigation devices (aka, Harm Filter). Previous testing attempts, while providing some insight to the problem, were insufficient to provide a complete picture of this dynamic environment. The objective of the Study is to document the circuit conditions (specifically voltage distortion) during both normal and emergency generator operation. The information gathered can then be used to determine the appropriate mitigation of unsatisfactory conditions to allow for reliable operation of electrical/electronic equipment under all conditions. Methodology / Technical Approach PowerCET developed a comprehensive monitoring plan to document conditions of the facilities electrical distribution before, during and after a typical generator test. Figure 1 (below) is a simplified diagram of the normal and emergency electrical distribution associated with the facility. A total of ten (1) Dranetz power monitors were used and set to record both periodic (timed) readings as well as transient conditions. Dranetz PX / PG44 (or equivalent) monitors were programmed and installed at the locations shown in Figure 1 (above). The monitors were equipped with appropriate current probes for the application. In addition to distortion, energy and power quality information, the monitors were programmed to record a 12-cycle waveform sample of the voltage and current waveforms at the end of each power value period. Date: Revised /13/212 Page 1 of 21 Filename: Sample_Multiple_Monitor_Harmonic_Study.doc

2 Figure 1 Simplified electrical distribution with monitor locations. The monitoring equipment measures and records each cycle of the voltage and current along with the phase relationships. In addition to the measured parameters, voltage and current, the following calculated parameters are recorded. The monitor records the minimum, maximum and average value for each measured/calculated parameter. Distortion is measured over a 2ms window in compliance with appropriate IEC Standards. A summary of the Dranetz power monitor s measurement capabilities is contained in initial proposal. Date: Revised /13/212 Page 2 of 21

3 Table 1 (below) is a listing of the sequence of events associated with the early morning testing conducted on October 8, 21. Table 1 - Sequence of events testing activities - Transfer Harm Filter #1 Harm Filter #2 Transfer Active Harmonic Filter #1 Active Harmonic Filter #2 Power Monitor & Location Mntr Start Util to Gen OFF ON Gen to Util OFF On OFF 1 Generator HV :4:2 6::43 6:3:16 7::9 2 ATS #1 :14:9 6::2 6:31: 6:48:29 3 ATS #2 :16:29 6:4:2 6:3:16 6:48:29 4 ATS #3 (Xfmr Pri) :14:9 6:1:12 6:31:29 6:49:9 ATS #4 :17:29 6::41 6:33:33 6:48: /12 Xfmr Sdry :19:1 6:1:12 6:31:29 6:48:1 7 Harm Filter #1 :19:3 6:1:12 6:1: 6:26: 6:31:29 6:4: 6:4:3 6:48: 8 Harm Filter #2 :2:9 6:1:12 6:17:9 6:26:9 6:31:29 6:4:39 6:46:9 6:48:9 9 Pnl Bd Mntr #9 :26:28 6:1:12 6:31:29 6:3:8 1 Pnl Bd Mntr #1 :22:9 6:1:12 6:31:29 6:1:9 Mntr Key Findings and Recommendations The testing conducted on Wednesday, October 8, 21 revealed that while the voltage distortion is elevated when operating on emergency generators the level of voltage distortion (Vthd) under normal utility operation ranges from 3 to 8 and is contributing to equipment misoperation and stability issues. Table 2 (below) summarizes the average voltage and current distortion levels for utility and generator operation. Table 2 Power Monitor & Location Voltage thd fnd Current thd fnd Util Sply Gen Sply Util Sply Gen Sply 1 Generator HV n/a 4 n/a 17 2 ATS # ATS # ATS #3 (Xfmr Pri) ATS # Xfmr Sdry [1] Pnl Bd Mntr # Pnl Bd Mntr # [1] The B-phase has a preponderance of single-phase switch mode power supply load with a current thd above 1 and skews the average. Date: Revised /13/212 Page 3 of 21

4 ATS #2 (Monitor #3) Nominal Current 1A/phase ATS #2 (Monitor #3) has approximately 1A/phase of load, most of which is 6-pulse motor drives with dominant th and 7 th harmonic distortion. These drives are associated with the larger environmental loads in the building. A survey of the equipment by facilities staff indicates that all drives are equipped with 3 or impedance line reactors (inductors). Normal Utility Power Source Discussion Figure 2 (below) shows the voltage, current and distortion plots for monitoring Monitor Location #3, ATS # Timeplot 2 22 Transfer to Generator Transfer back to Utility 2 A Vrms B Vrms C Vrms A Irms B Irms C Irms A VThd B VThd C VThd A IThd B IThd C IThd :2 :3 :4 : 6: 6:1 6:2 6:3 6:4 6: Figure 2 Vthd and Ithd time plots of ATS #2 (Monitor #3). Under normal, utility operation the Vthd is in the 7 to 8 range and increase to between 9 and 1 when operating on the generator supply. This increase in Vthd is the result of the higher (about 3) source impedance presented by the generators to the distribution system. Industry practices attempt to operate facilities in the 3 to Vthd range for Utility operation and expect an increase when switching to the emergency generator supply. Figure 3 (below) shows the voltage and current waveforms during normal utility source operation just prior to the generator test conducted on October 1th. The current waveforms are typical of 6-pulse rectified loads with line-reactors installed. Comparing the current waveform with the associated voltage waveform it is obvious that the distortion of the voltage is the result of the load current interacting with the source impedances. Figure 4 (below) is the phase-to-phase 48V waveforms associated with the phase-to-neutral waveforms shown in Figure 3. The 48V waveform is actually what the load is seeing and has distortion near the zero-crossing point on the sine wave which, if severe enough, can cause timing errors of the drives and drop-out. The amount of distortion present in this environment is dependent on the power source and the characteristics of the loads operation at any given time. Date: Revised /13/212 Page 4 of 21

5 Event Details/Waveforms A V B V C V -1-2 A I B I C I :4:9.8 9/8/21 :4:9.86 :4:9.87 :4:9.88 :4:9.89 :4:9.9 Figure 3 Monitor #3 (ATS #2), utility source, voltage (phase-to-neutral) and current waveforms showing typical 6-pulse current waveforms. Figure 4 Monitor #3 (ATS #2), utility source, voltage (phase-to-phase) waveform showing distortion near zero crossing which can result in motor drive drop-out. Figure (below) shows the Discrete Fourier Transform (DFT) plot for the voltage and current waveforms from Figure 3 (above). The vertical bars represent the level of the various frequency content of the waveform. The dominant harmonic frequencies for 6-pulse loads is represented by the formula 6n 1 and results in the series: th, 7 th, 11 th, 13 th, etc. The purpose of the DFT plot is to provide information relative to the frequency and magnitude of the distorting signal that requires mitigation. Further analysis of the waveform data is contained in Figure 6 (below) which is the DFT plot of the power (Watts) associated with the signals in Figure 3 (above). In this case the DFT graph shows a positive and negative plot area. The positive/negative plots indicate the direction of harmonic energy flow. In Figure 6 the th and 7 th harmonic values are negative indicating that harmonic energy is flowing from the loads i.e., the loads are generating the harmonic current. Date: Revised /13/212 Page of 21

6 H2 H3 H4 H H6 H7 H8 H9 H1 A VHarm B VHarm C VHarm H2 H2 H3 H4 H H6 H7 H8 H9 H1 H2 A VHarm B VHarm C VHarm AV BV CV DV A-BV B-CV C-AV AI BI CI DI RMS FND DC Figure Monitor #3 (ATS #2), utility source, voltage and current DFT plot H2 H3 H4 H H6 H7 H8 H9 H1 H2 A PHarm B PHarm C PHarm Figure 6 Monitor #3 (ATS #2), utility source, DFT of Watts illustrating harmonic energy (negative) flow from the load. Dominant harmonic is th (3Hz). Emergency Generator Power Source Operation The following series of Figures, 7 through 1, are basically the same as previously discussed except the power source has been transferred to the emergency generators. Figure 7 (below) shows the voltage (line-to-neutral) and current waveforms for the ATS #2 (Monitor #3) operating on the generator supply. Note the increase in voltage distortion and the prominent multiple zero-crossings which typically cause drives to trip-off as they can not synchronize properly. [Note: It was reported that a number of drives had trip-off during the early morning testing on October 1th.] Figure 8 (below) shows the corresponding line-to-line voltage from Figure 7 and has the same zerocrossing problems discussed above. Date: Revised /13/212 Page 6 of 21

7 Event Details/Waveforms Zero Crossing Errors A V B V C V -1-2 A I B I C I 6:33:29.8 9/8/21 6:33: :33: :33: :33: :33:29.9 Figure 7 Monitor #3 (ATS #2), generator source, voltage (phase-to-neutral) and current waveforms showing distortion and multiple zero-crossing errors. Figure 8 Monitor #3 (ATS #2), generator source, voltage (line-to-line) showing distortion and multiple zero-crossings. Figures 9 and 1 (below) are DFT plots of the voltage and current waveform while operating on the emergency generator supply. As was the case when operating on the utility supply the dominant frequencies are, as expected, the th, 7 th, 11 th, 13 th, etc. The Vthd increased about 2 to a 1 level and the current, Ithd, actually decreased slightly. This is a typical situation in that the load interacting with higher source impedance of the generator can result in lower Ithd and higher Vthd. Date: Revised /13/212 Page 7 of 21

8 H2 H3 H4 H H6 H7 H8 H9 H1 A IHarm B IHarm C IHarm H2 2.. H2 H3 H4 H H6 H7 H8 H9 H1 H2 A VHarm B VHarm C VHarm AV BV CV DV A-BV B-CV C-AV AI BI CI DI RMS FND DC Figure 9 Monitor #3 (ATS #2), generator source, voltage and current DFT plot. W H2 H3 H4 H H6 H7 H8 H9 H1 H2 A PHarm B PHarm C PHarm Figure 1 -- Monitor #3 (ATS #2), generator source, DFT of Watts illustrating harmonic energy (negative) flow from the load. Dominant harmonic is th (3Hz). RECOMMENDATION: The 1A/phase load associated with the ATS #2 is causing significant voltage distortion on the 48Vac emergency bus distribution. Best practices recommend a Vthd level of around 3, with an upper action limit of. In the case of this facility the nominal Vthd is running 8. The th (3Hz) harmonic is the major contributor to the problems being experienced with equipment operation on the emergency 48V bus for the facility. The following are some possible mitigation activities that have a good possibility of improving equipment operation and overall system reliability. 1. Change out the existing 3 impedance line reactors for impedance reactors provided the drives can tolerate the higher circuit losses. The increased impedance will results in higher circuit losses and will attenuate the associated harmonics. There is an energy penalty in that the circuit IR losses will increase slightly. [TCI, Trans-Coil International, would be a good supplier for these types of products.] Date: Revised /13/212 Page 8 of 21

9 2. Employ phase shifting, zigzag transformers (3 angular displacement), on some of the drives to cancel out th and 7 th harmonic currents. The advantage of the phase shifting is that it is a passive harmonic filter and does not present the problem of cross-talk or interaction between other system distribution components that conventional harmonic filter might. [There are a number of suppliers of this equipment: Hammond Power Solutions, Inc.; Mirus International Inc.; SquareD (Schneider Electric).] 3. Employ a single point harmonic filter on the load side of the ATS #2 (Monitor #3) to mitigate the th and 7 th harmonics. This solution would require some engineering and the equipment can be rather large depending on the level of harmonic current. If space in the electrical equipment room is not available it may be possible to roof mount such a unit. The major advantage of this is a single point solution. It may be possible to re-configure the existing active harmonic filters to work on the 48Vac bus this possibility might be worth checking out. [There are a number of harmonic filter suppliers and generally they have a good engineering/application support.] ATS #3 (Monitors #4, #6-1) UPS Charging Problem On Gen Source The load side of the ATS #3 (see Figure 1) connects to a 48-28/12Vac step-down distribution transformer that distributes 28/12Vac power to a series of equipment rooms on each floor. Part of the load in each of the rooms is a UPS, 4.2kW (.2kVA). The UPS is connected as a 28Vac single-phase device and has input power factor correction. Several of the USP installations have experienced problems during the periodic generator testing in that the rectifier (input power supply) will not recognize the emergency generator as a valid power source. In an apparent effort to mitigate the USP situation two active harmonic filters were installed on the 28Vac distribution bus associated with the secondary of the step-down transformer discussed above. Figures 11 and 12 (below) show the current and voltage waveforms for the UPS equipment when powered from the utility source and generator source respectively. The UPS s power supply is power factor corrected which means it tries to follow the voltage waveform. If the voltage is distorted then the corresponding current waveform will be distorted. Figure 11 UPS input voltage and current waveforms utility source Date: Revised /13/212 Page 9 of 21

10 Figure UPS input voltage and current waveforms generator source The active harmonic filter is also a voltage following device which means there are we have the two devices trying to compensate for the distortion. The result is generally an unsatisfactory condition. During the testing activities on October 1th several of the UPS s failed to come on-line when transferred to generator. As an experiment the active harmonic filters were turned off, Figure 13 (below), and the current hunting from the UPS equipment stopped and the UPS equipment came on-line and started charging the batteries. It appears from this experiment that the increase in voltage distortion when operating with the generators as the power source results in an unstable condition in which, at least some of the UPS s, can not accept the voltage signal. Disabling the active harmonic filter equipment allows the UPS equipment to return to normal operation. Observations of the active harmonic filter equipment under normal operating conditions does not reveal any significant benefit from operation of the equipment (harmonic filters) in this application. Figure 13 Harmonic Filter current time plots versus UPS current plot documenting UPS power supply stability when Harmonic Filters are OFF. RECOMMENDATION: Install kva transformers on the input power to the UPS equipment. This will buffer the power factor corrected supply from the source and result in improved performance. Do NOT install any type of active regulating device in series with this type of application. Date: Revised /13/212 Page 1 of 21

11 RECOMMENDATION: From the testing results the active harmonic filter equipment is not improving the operating environment for the UPS equipment and should be removed from this application. During emergency generator operation the equipment actually interferes with the reliable operation of the UPS equipment. RECOMMENDATION: If the active harmonic filter equipment can be reconfigured for a 48Vac application then there may be a good application associated with the ATS #2 harmonic mitigation. This possibility certainly should be investigated as the equipment is in close proximity to the load side of the ATS #2. Figure 14 (below) is a record of the voltage and current waveforms on the secondary of the ATS #3 stepdown transformer secondary. There is a significant level of 18Hz neutral return current from the singlephase rectified (computer) loads served by this transformer. There does not appear to be significant distortion associated with the loading of the transformer. The B-phase loading appears to have a high level of non-power factor corrected loads, but the load imbalance calculations are within acceptable limits maximum unbalance is 14 with an average of 7 during the monitoring period. Event Details/Waveforms A V B V C V A I B I C I D I :29:4.3 :29:4.3 :29:4.4 :29:4.4 Figure 14 Monitor #6, generator source, voltage and current waveforms on secondary of ATS #3 step-down transformer. Figure 1 and 16 (below) summarize the distortion associated with the secondary of the step-down transformer. The voltage distortion appears to be associated with the general distortion caused by the large harmonic ATS #2 load and Figure 16 showing the harmonic energy flow indicates that this circuit is an acceptor of harmonics. Date: Revised /13/212 Page 11 of 21

12 H2 H3 H4 H H6 H7 H8 H9 H1 A VHarm B VHarm C VHarm H H2 H3 H4 H H6 H7 H8 H9 H1 AV BV CV DV A-BV B-CV C-AV AI BI CI DI RMS FND DC A IHarm B IHarm C IHarm H2 Figure 1 Monitor #6 (ATS #3, transformer secondary) generator source, voltage and current DFT plots H2 H3 H4 H H6 H7 H8 H9 H1 A PHarm B PHarm C PHarm H2 Figure 16 Monitor #6 (ATS #3, transformer secondary), generator source, DFT of Watts illustrating harmonic energy (positive) flow to the load. Dominant harmonics are th, 11 th and 13 th. RECOMMENDATION: Once harmonic mitigation has been implemented on the ATS #2 loads the ATS #3 loads should be reevaluated with respect to distortion and loading. Date: Revised /13/212 Page 12 of 21

13 Harmonic Acceptors The following circuits all appear to accepting harmonic energy from the facility at this time. The voltage distortion and to a certain extent the current distortion for these circuits are, in large part, triggered by the general voltage distortion from the ATS #2 (Monitor #3) location. The following circuits (monitor locations) are documented in this section: ATS #1 [Monitor #2] ATS #4 [Monitor #] 12.47kV [Monitor #1] ATS #1 (Monitor #2) Distortion and Harmonic Energy Flow The ATS #1 (Monitor #2) at this time appears to be one of the circuits accepting harmonic energy from the facility. The general Vthd level is in the 7 range and rises to around 9 during generator operation Figure 17. The nominal loading of 1A/phase should not be a significant distortion source, but it will depend on the exact mix of loads. p y[ ] A Vrms B Vrms C Vrms A Irms B Irms C Irms A VThd B VThd C VThd A IThd B IThd C IThd :2 :3 :4 : 6: 6:1 6:2 6:3 6:4 6: Figure 17 ATS #1 [Monitor #2] voltage, current and distortion time plots. The waveform record from utility source, Figure 18 (below), show the moderate distortion level for the voltage and a more significant distortion characteristic for the current waveform. The current waveform may have more to do with the individual loads reaction to the existing voltage distortion. The harmonic analysis contained in the DFT plots, Figures 19 and 2, indicates that the harmonic energy is flowing to the load as opposed to being created by the load. Figures (below) document the ATS #1 circuit performance with the generators as the power source. As expected the distortion increases and harmonic energy is still flowing toward the loads. RECOMMENDATION: Loading associated with the ATS #1 should be inventoried and evaluated with respect to harmonic contribution. Date: Revised /13/212 Page 13 of 21

14 A V B V C V -1 A I B I C I :43:9.8 :43:9.8 :43:9.9 :43:9.9 :44:. Figure 18 ATS #1 [Monitor #2] voltage and current waveforms utility source H2 H3 H4 H H6 H7 H8 H9 H1 H2 A VHarm B VHarm C VHarm H2 H3 H4 H H6 H7 H8 H9 H1 H2 A IHarm B IHarm C IHarm AV BV CV DV A-BV B-CV C-AV AI BI CI DI RMS FND DC Figure 19 ATS #1 [Monitor #2] voltage and current DFT plots utility source H2 H3 H4 H H6 H7 H8 H9 H1 H2 A PHarm B PHarm C PHarm Figure 2 ATS #1 [Monitor #2] Watts DFT plot utility source. Date: Revised /13/212 Page 14 of 21

15 A V B V C V A I B I C I 6:2:29.8 6:2:29.8 6:2:29.9 6:2:29.9 6:2:3. Figure 21 ATS #1 [Monitor #2] voltage and current waveforms generator source H2 H3 H4 H H6 H7 H8 H9 H1 H2 A VHarm B VHarm C VHarm H2 H3 H4 H H6 H7 H8 H9 H1 H2 A IHarm B IHarm C IHarm AV BV CV DV A-BV B-CV C-AV AI BI CI DI RMS FND DC Figure 22 ATS #1 [Monitor #2] voltage and current DFT plots generator source H2 H3 H4 H H6 H7 H8 H9 H1 H2 A PHarm B PHarm C PHarm Figure 23 ATS #1 [Monitor #2] Watts DFT plot generator source. Date: Revised /13/212 Page 1 of 21

16 ATS #4 (Monitor #) Distortion and Harmonic Energy Flow ATS #4 (Monitor #) at this time is another of the circuits accepting harmonic energy from the facility. The general Vthd level is in the 1 range and rises to around 2 during generator operation Figure 24. The nature of the load, ATS #4, makes it difficult to assign a nominal load value as the cycling of the equipment results in substantial variations in current levels. There were no reported problems during the test period, but the significant increase in voltage distortion makes this circuit a candidate for additional monitoring/study under both nominal and generator operation. Timeplot Elevator ATS [Monitor #] A Vrms B Vrms C Vrms A VRss B VRss C VRss A Irms B Irms C Irms 1 1 A IRss B IRss C IRss :2 :3 :4 : 6: 6:1 6:2 6:3 6:4 6: Figure 24 ATS #4 [Monitor #] voltage, current and distortion time plots. The waveform record from utility source, Figure 2 (below), show the moderate distortion level for the voltage and current waveforms. The harmonic analysis contained in the DFT plots, Figures 26 and 27, indicates that the harmonic energy is flowing to the load as opposed to being created by the load. This could be misleading as the start/stop operation of the elevators is difficult to characterize. Figures 28-3 (below) document the ATS #4 circuit performance with the generators as the power source. As expected the distortion increases and harmonic energy is still flowing toward the loads. RECOMMENDATION: Loading associated with the ATS #4 should be studied in more detail to document inrush (start-up) conditions under both normal and emergency operations. Now that there is some baseline information it will be much easier to set meaningful thresholds to capture the necessary information. Date: Revised /13/212 Page 16 of 21

17 A V B V C V D V -1 A I B I C I :42:29.8 :42:29.8 :42:29.9 :42:29.9 :42:3. Figure 2 ATS #4 [Monitor #] voltage and current waveforms utility source H2 H3 H4 H H6 H7 H8 H9 H1 H2 A VHarm B VHarm C VHarm H2 H3 H4 H H6 H7 H8 H9 H1 H2 A IHarm B IHarm C IHarm AV BV CV DV A-BV B-CV C-AV AI BI CI DI RMS FND DC Figure 26 ATS #4 [Monitor #] voltage and current DFT plots utility source H2 H3 H4 H H6 H7 H8 H9 H1 H2 A PHarm B PHarm C PHarm Figure 27 ATS #4 [Monitor #] Watts DFT plot utility source. Date: Revised /13/212 Page 17 of 21

18 A V B V C V -1 A I B I C I 6:23:9.8 9/8/21 6:23:9.8 6:23:9.9 6:23:9.9 6:24:. Figure 28 ATS #4 [Monitor #] voltage and current waveforms generator source H2 H3 H4 H H6 H7 H8 H9 H1 H2 A VHarm B VHarm C VHarm H2 H3 H4 H H6 H7 H8 H9 H1 H2 A IHarm B IHarm C IHarm AV BV CV DV A-BV B-CV C-AV AI BI CI DI RMS FND DC Figure 29 ATS #4 [Monitor #] voltage and current DFT plots generator source H2 H3 H4 H H6 H7 H8 H9 H1 H2 A PHarm B PHarm C PHarm Figure 3 ATS #4 [Monitor #] Watts DFT plot generator source. Date: Revised /13/212 Page 18 of 21

19 Generator 12.47kV (Monitor #1) Distortion and Harmonic Energy Flow The Generator 12.47kV (Monitor #1) accepts th and 7 th harmonic energy from the loads. The general Vthd level is slightly under 4. Figure 31. It will be interesting to reevaluate the current distortion after mitigation of the ATS #2 1A of harmonic load A-B Vrms B-C Vrms C-A Vrms A Irms B Irms C Irms A-B VThd B-C VThd C-A VThd A IThd B IThd C IThd 6:2 6:1 6:1 6:2 6:3 6:3 Figure kV Generator Supply [Monitor #1] voltage, current and distortion time plots. The waveform record from utility source, Figure 32 (below), shows moderate distortion levels for the voltage and current waveforms. The harmonic analysis contained in the DFT plots, Figures 33 and 34, indicates that the harmonic energy is flowing to the load as opposed to being created by the load A-B V B-C V C-A V - -1 A I B I C I 6::29.8 6::29.8 6::29.9 6::29.9 6::3. Figure kV Generator Supply [Monitor #1] voltage and current waveforms generator source. Date: Revised /13/212 Page 19 of 21

20 H2 H3 H4 H H6 H7 H8 H9 H1 A IHarm B IHarm C IHarm H2 H2 H3 H4 H H6 H7 H8 H9 H1 H2 A VHarm B VHarm C VHarm AV BV CV DV A-BV B-CV C-AV AI BI CI DI RMS FND N/A N/A N/A DC Figure kV Generator Supply [Monitor #1] voltage and current DFT plots generator source H2 H3 H4 H H6 H7 H8 H9 H1 H2 A PHarm B PHarm C PHarm Summary Figure kV Generator Supply [Monitor #1] Watts DFT plot generator source. It is surprising how well thing operate in view of the level of distortion under normal operating conditions. As a general rule of thumb we try to maintain Vthd to less than and expect some increase when switching to generator operations with the corresponding higher source impedance. In the case of General Hospital the nominal Vthd on the 48V bus is about 8 and increases, as expected during operation on the emergency supply. The major contributor to the distortion levels is the ATS #2 loads that typically appear to run about 1A/phase at 48Vac. All drives were verified to have either 3 or line reactors installed with, obviously, is insufficient to control the th and 7 th harmonics associated with 6-pulse loads. There may be additional load issues, but they will be difficult to identify as they would be masked by the size of the ATS #2 load and associated harmonics. Date: Revised /13/212 Page 2 of 21

21 The mitigation of the harmonics, especially the th (3Hz) harmonic, associated with the ATS #2 loads should be the first priority. A number of possible solutions are available to address these issues which are discussed in more detail in the earlier sections of this report. Specifically Replace 3 line reactors with (assuming the drives can tolerate the higher losses) Install phase-shifting transformers on selected drives to cancel harmonic currents. Replace (or supplement) existing line-reactors with harmonic filters NOT RECOMMENDED. This solution would require very careful management of the installation and probably constant tweaking to prevent interaction between filters. Install a single point solution, active filter, on the load side of the ATS #2. Size/space can be an issue with this equipment; it all depends on the amount of harmonic current being mitigated. Please understand that reducing the Vthd from 8 to 4 would probably resolve most, if not all, of this type of problem and improve performance and reliability. The other issue investigated in the activity is the performance of the UPS equipment. The problem has been the unreliable operation of the equipment when on the emergency generator power source. Specifically the UPS input power module does not always recognize the generator as a viable power source and under extended runtime the back-up battery supply is depleted. In a previous effort to resolve the UPS performance problem a set of active harmonic filters were installed. Unfortunately, these are not an appropriate solution for this type of problem. The UPS equipment has a power factor corrected input power supply which is a voltage following device the current tracks the input voltage signal. The active harmonic filter is also a voltage following device two similar devices in series seldom works. During the testing, while operating on the generator supply, the active harmonic filter equipment was turned-off the UPS equipment returned to normal operation with the active harmonic filters off. Recommend discontinuing use of the active harmonic filter equipment for this application. General Hospital is a large complex facility and some type of on-going monitoring capability should be implemented on the key distribution locations. This will allow for tracking of conditions over time and with the proper analysis can result in identifying unsatisfactory conditions before they become catastrophic. In addition with permanent monitoring should a problem occur much better information is available to facilities personnel to help them determine the appropriate course of action. Prepared by: Bruce Lonie President, PowerCET Corporation Disclaimer The information contained in this document is provided for educational purposes only as an example on how to incorporate power monitoring data and other observations into a report format. It is not intended to provide consulting advice for any specific problem or situation. This is a copyrighted document and intended for individual use and should not be reproduced or distributed in any form without specific written permission from PowerCET Corporation. Date: Revised /13/212 Page 21 of 21