1. art and entertainment
2. visual art and design
3. design

Sample Report
PowerCET Corporation
3350 Scott Blvd., Bldg. 55. Unit 1
Santa Clara, CA 95054 USA
Voice: 408/988-1346 | Fax: 408/988-4869
URL: http://www.powercet.com
E-mail: [email protected]
Voltage Distortion & Power Quality 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 Voltage Distortion & Power Quality 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 (10) Dranetz power monitors were used and set to record both periodic
(timed) readings as well as transient conditions.
Dranetz PX5 / PG4400 (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 5/13/2012
Filename: Sample_Multiple_Monitor_Harmonic_Study.doc
Page 1 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
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 200ms window in compliance with
appropriate IEC Standards.
A summary of the Dranetz power monitor’s measurement capabilities is contained in initial proposal.
Date: Revised 5/13/2012
Page 2 of 21
Table 1 (below) is a listing of the sequence of events associated with the early morning testing conducted
on October 8, 2010.
Table 1 - Sequence of events – testing activities Harm
Filter
#1
OFF
Transfer
Power Monitor & Location
Harm
Filter
#2
ON
Transfer
Gen to Util
Active
Harmonic
Filter #1
OFF
Active
Harmonic
Filter #2
On
Mntr
Mntr Start
Util to Gen
1 Generator HV
5:04:20
6:00:43
6:35:16
7:00:59
OFF
2 ATS #1
5:14:59
6:00:52
6:31:50
6:48:29
3 ATS #2
5:16:29
6:04:02
6:35:16
6:48:29
4 ATS #3 (Xfmr Pri)
5:14:59
6:01:12
6:31:29
6:49:59
5 ATS #4
5:17:29
6:05:41
6:33:33
6:48:29
6 480-208/120 Xfmr Sdry
5:19:10
6:01:12
6:31:29
6:48:10
7 Harm Filter #1
5:19:35
6:01:12
6:15:05
6:26:05
6:31:29
6:40:05
6:45:35
6:48:05
8 Harm Filter #2
5:20:09
6:01:12
6:17:09
6:26:09
6:31:29
6:40:39
6:46:09
6:48:09
9 Pnl Bd Mntr #9
5:26:28
6:01:12
6:31:29
6:53:58
10 Pnl Bd Mntr #10
5:22:59
6:01:12
6:31:29
6:51:59
Key Findings and Recommendations
The testing conducted on Wednesday, October 8, 2010 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
1 Generator HV
2 ATS #1
3 ATS #2
4 ATS #3 (Xfmr Pri)
5 ATS #4
6 Xfmr Sdry [1]
9 Pnl Bd Mntr #9
10 Pnl Bd Mntr #10
Voltage thd %fnd
Util Sply Gen Sply
n/a
4
7
10
8
10
3
10
3
10
5
12
5
13
6
12
Current thd %fnd
Util Sply Gen Sply
n/a
17
20
24
21
20
14
27
13
8
66
57
6
6
23
24
[1] The B-phase has a preponderance of single-phase switch mode power supply load with a current
thd above 100% and skews the average.
Date: Revised 5/13/2012
Page 3 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
ATS #2 (Monitor #3) – Nominal Current 1500A/phase
ATS #2 (Monitor #3) has approximately 1500A/phase of load, most of which is 6-pulse motor drives with
dominant 5th and 7th 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 5% 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
#2.
Timeplot
300
Volts
275
250
Transfer to Generator
Transfer back to Utility
225
200
A Vrms
B Vrms
C Vrms
A Irms
B Irms
C Irms
A VThd
B VThd
C VThd
A IThd
B IThd
C IThd
Amps
2500
2000
1500
1000
500
0
11.0
%
10.0
9.0
8.0
7.0
%
22.5
21.5
20.5
19.5
05:20
05:30
05:40
05:50
06:00
06:10
06:20
06:30
06:40
06:50
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 10%
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 5% 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 15th. 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 480V waveforms associated with the phase-to-neutral waveforms
shown in Figure 3. The 480V 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 5/13/2012
Page 4 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Event Details/Waveforms
400
300
200
Volts
100
0
-100
-200
-300
-400
AV
BV
CV
AI
BI
CI
2000
Amps
1000
0
-1000
-2000
05:54:59.85
09/08/2010
05:54:59.86
05:54:59.87
05:54:59.88
05:54:59.89
05:54:59.90
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 5 (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: 5th, 7th, 11th, 13th, 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 5th and 7th harmonic values are negative indicating that harmonic energy is flowing from the loads—
i.e., the loads are generating the harmonic current.
Date: Revised 5/13/2012
Page 5 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Waveform harmonics
%
8
7
6
5
4
3
2
1
0
THD
H03
H02
H05
H04
H07
H09
H06
H08
H11
H10
H13
H15
H12
A VHarm
H14
B VHarm
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C VHarm
Waveform harmonics
%
8
7
6
5
4
3
2
1
0
THD
H03
H02
H05
H04
H07
H09
H06
H08
H11
H10
RMS
FND
DC
THD
AV
276.37
100.00
-0.03
8.23
BV
277.86
100.00
-0.51
7.75
CV
277.95
100.00
0.41
7.62
DV
276.82
100.00
-0.01
8.01
H13
H15
H12
A VHarm
A-BV
479.20
100.00
0.28
7.85
H14
B VHarm
B-CV
480.56
100.00
-0.53
7.64
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C VHarm
C-AV
481.57
100.00
0.25
8.07
AI
1457.28
100.00
-0.23
21.49
BI
1519.67
100.00
-0.40
21.27
CI
1525.86
100.00
0.38
20.83
DI
0.48
100.00
216.90
847.56
Figure 5 – Monitor #3 (ATS #2), utility source, voltage and current DFT plot.
Waveform harmonics
%
-0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
A PHarm
H13
H12
B PHarm
H15
H14
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C PHarm
Figure 6 – Monitor #3 (ATS #2), utility source, DFT of Watts illustrating harmonic energy (negative)
flow from the load. Dominant harmonic is 5th (300Hz).
Emergency Generator Power Source Operation
The following series of Figures, 7 through 10, 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 15th.]
Figure 8 (below) shows the corresponding line-to-line voltage from Figure 7 and has the same zerocrossing problems discussed above.
Date: Revised 5/13/2012
Page 6 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Event Details/Waveforms
400
300
200
Volts
100
0
-100
Zero Crossing Errors
-200
-300
-400
AV
BV
CV
AI
BI
CI
2000
Amps
1000
0
-1000
-2000
06:33:29.85
09/08/2010
06:33:29.86
06:33:29.87
06:33:29.88
06:33:29.89
06:33:29.90
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 10 (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 5th,
7th, 11th, 13th, etc.
The Vthd increased about 2% to a 10% 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 5/13/2012
Page 7 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Waveform harmonics
%
20
15
10
5
0
THD
H03
H02
H05
H07
H04
H06
H09
H11
H08
H10
H13
H15
H12
A IHarm
H14
B IHarm
H17
H19
H16
H18
H21
H20
H23
H22
H25
H24
C IHarm
Waveform harmonics
%
10.0
7.5
5.0
2.5
0.0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
BV
256.99
100.00
-0.02
10.62
CV
279.73
100.00
0.77
10.68
DV
283.09
100.00
0.57
1.47
H13
H15
H12
A VHarm
AV
RMS 279.23
FND 100.00
DC 0.32
THD 10.77
A-BV
470.55
100.00
0.20
10.67
H14
B VHarm
B-CV
469.68
100.00
-0.47
10.54
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C VHarm
C-AV
472.01
100.00
0.27
10.57
AI
1472.91
100.00
-0.23
20.87
BI
1501.29
100.00
-0.44
21.06
CI
1475.47
100.00
0.49
21.14
DI
0.50
100.00
168.39
1367.66
Figure 9 – Monitor #3 (ATS #2), generator source, voltage and current DFT plot.
Waveform harmonics
W
0
-250
-500
-750
-1000
-1250
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
A PHarm
H13
H12
B PHarm
H15
H14
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C PHarm
Figure 10 -- Monitor #3 (ATS #2), generator source, DFT of Watts illustrating harmonic energy
(negative) flow from the load. Dominant harmonic is 5th (300Hz).
RECOMMENDATION: The 1500A/phase load associated with the ATS #2 is causing significant
voltage distortion on the 480Vac emergency bus distribution. Best practices recommend a Vthd
level of around 3%, with an upper action limit of 5%. In the case of this facility the nominal Vthd is
running 8%. The 5th (300Hz) harmonic is the major contributor to the problems being experienced
with equipment operation on the emergency 480V 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 5% 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 5/13/2012
Page 8 of 21
2. Employ phase shifting, zigzag transformers (30° angular displacement), on some of the
drives to cancel out 5th and 7th 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 5th and 7th 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 480Vac 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, #6-10) – UPS Charging Problem On Gen Source
The load side of the ATS #3 (see Figure 1) connects to a 480-208/120Vac step-down distribution
transformer that distributes 208/120Vac power to a series of equipment rooms on each floor. Part of the
load in each of the rooms is a UPS, 4.2kW (5.2kVA). The UPS is connected as a 208Vac 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
208Vac 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 5/13/2012
Page 9 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Figure 12 -- 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 15th 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 5kVA 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 5/13/2012
Page 10 of 21
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 480Vac
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 180Hz 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
150
100
Volts
50
0
-50
-100
-150
AV
BV
CV
750
500
Amps
250
0
-250
-500
-750
AI
05:29:40.30
05:29:40.35
BI
CI
DI
05:29:40.40
05:29:40.45
Figure 14 – Monitor #6, generator source, voltage and current waveforms on secondary of ATS #3
step-down transformer.
Figure 15 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 5/13/2012
Page 11 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Waveform harmonics
%
10.0
7.5
5.0
2.5
0.0
THD
H03
H02
H05
H04
H07
H06
H09
H11
H08
H10
H13
H12
A VHarm
H15
H14
B VHarm
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C VHarm
Waveform harmonics
%
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0.0
THD
H03
H02
H05
H04
H07
H06
H09
H11
H08
H10
RMS
FND
DC
THD
AV
117.26
100.00
0.05
10.42
BV
116.26
100.00
-0.47
10.81
CV
116.91
100.00
0.55
10.65
DV
0.07
100.00
572.34
435.67
H13
H12
A IHarm
A-BV
201.87
100.00
0.30
10.69
H15
H14
B IHarm
B-CV
201.58
100.00
-0.59
10.74
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C IHarm
C-AV
203.48
100.00
0.28
10.28
AI
458.90
100.00
0.08
13.30
BI
432.08
100.00
-0.44
14.48
CI
404.58
100.00
0.35
16.64
DI
158.12
100.00
-4.43
452.46
Figure 15 – Monitor #6 (ATS #3, transformer secondary) generator source, voltage and current
DFT plots.
Waveform harmonics
%
0.25
0.20
0.15
0.10
0.05
-0.00
-0.05
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
A PHarm
H13
H12
B PHarm
H15
H14
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C PHarm
Figure 16 – Monitor #6 (ATS #3, transformer secondary), generator source, DFT of Watts
illustrating harmonic energy (positive) flow to the load. Dominant harmonics are 5th, 11th and 13th.
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 5/13/2012
Page 12 of 21
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 #5]
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 100A/phase should not be a significant distortion source, but it will depend on the
exact mix of loads.
Volts
Amps
p
300
250
200
150
100
50
0
350
300
250
200
150
100
50
0
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
9
%
7
5
3
%
1
35
30
25
20
15
10
5
05:20
05:30
05:40
05:50
06:00
06:10
06:20
06:30
06:40
06:50
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 20, indicates that the harmonic energy
is flowing to the load as opposed to being created by the load.
Figures 21-23 (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 5/13/2012
Page 13 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
400
300
200
Volts
100
0
-100
-200
-300
-400
AV
BV
CV
AI
BI
CI
100
Amps
50
0
-50
-100
05:43:59.80
05:43:59.85
05:43:59.90
05:43:59.95
05:44:00.00
Figure 18 – ATS #1 [Monitor #2] voltage and current waveforms—utility source.
%
7
6
5
4
3
2
1
0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H13
H10
H15
H12
A VHarm
H14
B VHarm
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C VHarm
Waveform harmonics
%
30
25
20
15
10
5
0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H12
A IHarm
RMS
FND
DC
THD
AV
278.72
100.00
-0.00
7.43
BV
279.82
100.00
-0.42
7.13
H13
H10
CV
279.51
100.00
0.45
6.88
DV
0.05
100.00
247.04
2455.93
A-BV
482.95
100.00
0.24
7.17
H15
H14
B IHarm
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C IHarm
B-CV
483.41
100.00
-0.51
7.02
C-AV
485.15
100.00
0.26
7.22
AI
85.18
100.00
1.28
20.44
BI
69.50
100.00
2.25
28.28
CI
77.67
100.00
-0.27
19.77
DI
17.79
100.00
-1.21
45.76
Figure 19 – ATS #1 [Monitor #2] voltage and current DFT plots—utility source.
%
0.4
0.3
0.2
0.1
-0.0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
A PHarm
H13
H12
B PHarm
H15
H14
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C PHarm
Figure 20 – ATS #1 [Monitor #2] Watts DFT plot—utility source.
Date: Revised 5/13/2012
Page 14 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
400
300
200
Volts
100
0
-100
-200
-300
-400
AV
BV
CV
AI
BI
CI
200
150
100
Amps
50
0
-50
-100
-150
-200
06:20:29.80
06:20:29.85
06:20:29.90
06:20:29.95
06:20:30.00
Figure 21 – ATS #1 [Monitor #2] voltage and current waveforms—generator source.
%
10.0
7.5
5.0
2.5
0.0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H13
H10
H15
H12
A VHarm
H14
B VHarm
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C VHarm
Waveform harmonics
%
30
25
20
15
10
5
0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
BV
271.09
100.00
-0.49
9.85
H13
H10
H12
A IHarm
AV
RMS 271.26
FND 100.00
DC 0.06
THD 9.81
CV
271.31
100.00
0.41
9.41
DV
0.06
100.00
235.77
2737.33
H15
H14
B IHarm
A-BV
469.13
100.00
0.32
9.86
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C IHarm
B-CV
468.71
100.00
-0.52
9.60
C-AV
471.41
100.00
0.20
9.58
AI
97.55
100.00
0.13
22.57
BI
83.53
100.00
-0.64
29.38
CI
90.46
100.00
-1.18
21.01
DI
22.03
100.00
-2.22
58.83
Figure 22 – ATS #1 [Monitor #2] voltage and current DFT plots—generator source.
%
0.4
0.3
0.2
0.1
-0.0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
A PHarm
H13
H12
B PHarm
H15
H14
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C PHarm
Figure 23 – ATS #1 [Monitor #2] Watts DFT plot—generator source.
Date: Revised 5/13/2012
Page 15 of 21
ATS #4 (Monitor #5) – Distortion and Harmonic Energy Flow
ATS #4 (Monitor #5) at this time is another of the circuits accepting harmonic energy from the facility.
The general Vthd level is in the 10% range and rises to around 25% 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.
Volts
Timeplot Elevator ATS [Monitor #5]
325
300
275
250
225
200
A Vrms
B Vrms
C Vrms
Volts
25
20
15
10
5
A VTHDRss
B VTHDRss
C VTHDRss
Amps
350
250
150
100
0
A Irms
B Irms
C Irms
Amps
150
100
50
0
A ITHDRss
05:20
05:30
05:40
05:50
06:00
B ITHDRss
C ITHDRss
06:10
06:20
06:30
06:40
06:50
Figure 24 – ATS #4 [Monitor #5] voltage, current and distortion time plots.
The waveform record from utility source, Figure 25 (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 28-30 (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 5/13/2012
Page 16 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
400
300
200
Volts
100
0
-100
-200
-300
-400
AV
BV
CV
DV
100
Amps
50
0
-50
-100
AI
05:42:29.80
05:42:29.85
BI
CI
05:42:29.90
05:42:29.95
05:42:30.00
Figure 25 – ATS #4 [Monitor #5] voltage and current waveforms—utility source.
%
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
H13
H15
H12
A VHarm
H14
B VHarm
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C VHarm
Waveform harmonics
%
6
5
4
3
2
1
0
THD
H03
H05
H02
H04
H07
H06
H09
H08
H11
H10
RMS
FND
DC
THD
H13
H12
A IHarm
H15
H14
B IHarm
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C IHarm
AV
BV
CV
DV
A-BV
B-CV
C-AV
AI
BI
CI
DI
275.37 274.06 275.46 275.38 475.16 475.22 478.37 82.93
85.30
85.65
0.03
100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00
0.01
-0.45
0.47
0.02
0.26
-0.53
0.27
-0.28
0.06
0.76
1.46
3.72
3.53
3.45
3.71
3.71
3.39
3.60
5.60
4.03
4.94
180.65
Figure 26 – ATS #4 [Monitor #5] voltage and current DFT plots—utility source.
%
0.075
0.050
0.025
0.000
-0.025
-0.050
-0.075
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
A PHarm
H13
H12
B PHarm
H15
H14
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C PHarm
Figure 27 – ATS #4 [Monitor #5] Watts DFT plot—utility source.
Date: Revised 5/13/2012
Page 17 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
400
300
200
Volts
100
0
-100
-200
-300
-400
AV
BV
CV
AI
BI
CI
100
Amps
50
0
-50
-100
06:23:59.80
09/08/2010
06:23:59.85
06:23:59.90
06:23:59.95
06:24:00.00
Figure 28 – ATS #4 [Monitor #5] voltage and current waveforms—generator source.
%
10.0
7.5
5.0
2.5
0.0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
H13
H15
H12
A VHarm
H14
B VHarm
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C VHarm
Waveform harmonics
%
9
8
7
6
5
4
3
2
1
0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
BV
271.84
100.00
-0.46
9.71
CV
271.56
100.00
0.42
9.25
DV
274.78
100.00
0.44
3.19
H13
H15
H12
A IHarm
AV
RMS 271.64
FND 100.00
DC 0.06
THD 9.77
A-BV
469.91
100.00
0.30
9.72
H14
B IHarm
B-CV
469.50
100.00
-0.51
9.49
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C IHarm
C-AV
472.20
100.00
0.21
9.43
AI
71.92
100.00
-0.39
8.37
BI
75.77
100.00
-0.20
8.06
CI
74.67
100.00
0.53
6.73
DI
0.03
100.00
0.49
618.87
Figure 29 – ATS #4 [Monitor #5] voltage and current DFT plots—generator source.
%
0.15
0.10
0.05
0.00
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
A PHarm
H13
H12
B PHarm
H15
H14
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C PHarm
Figure 30 – ATS #4 [Monitor #5] Watts DFT plot—generator source.
Date: Revised 5/13/2012
Page 18 of 21
Generator 12.47kV (Monitor #1) Distortion and Harmonic Energy Flow
The Generator 12.47kV (Monitor #1) accepts 5th and 7th harmonic energy from the loads.
The general Vthd level is slightly under 4.5%—Figure 31. It will be interesting to reevaluate the current
distortion after mitigation of the ATS #2 1500A of harmonic load.
13500
Volts
13000
12500
12000
11500
A-B Vrms
B-C Vrms
C-A Vrms
Amps
100
75
50
25
%
A Irms
B Irms
C Irms
4.5
4.0
3.5
3.0
2.5
2.0
A-B VThd
B-C VThd
C-A VThd
20.0
%
17.5
15.0
12.5
10.0
A IThd
06:10
06:15
B IThd
C IThd
06:20
06:25
06:30
06:35
Figure 31 – 12.47kV 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.
15000
10000
Volts
5000
0
-5000
-10000
-15000
A-B V
B-C V
C-A V
100
Amps
50
0
-50
-100
AI
06:05:29.80
06:05:29.85
BI
06:05:29.90
CI
06:05:29.95
06:05:30.00
Figure 32 -- 12.47kV Generator Supply [Monitor #1] voltage and current waveforms—generator
source.
Date: Revised 5/13/2012
Page 19 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report
%
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0.0
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H13
H10
H15
H12
A IHarm
H14
B IHarm
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C IHarm
Waveform harmonics
%
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
THD
H03
H02
H05
H04
H07
H06
H09
H11
H08
AV
7210.21
N/A
-0.27
3.93
BV
7212.09
N/A
-0.29
3.87
CV
7147.61
N/A
0.54
3.78
DV
0.04
100.00
-157.96
1937.29
H15
H12
A VHarm
RMS
FND
DC
THD
H13
H10
H14
B VHarm
A-BV
12473.29
100.00
0.01
4.00
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C VHarm
B-CV
12446.20
100.00
-0.48
3.76
C-AV
12440.77
100.00
0.47
3.82
AI
60.17
100.00
-0.28
17.38
BI
59.74
100.00
-0.11
17.76
CI
59.81
100.00
0.58
17.49
DI
0.03
100.00
-12.02
224.92
Figure 33 -- 12.47kV Generator Supply [Monitor #1] voltage and current DFT plots—generator
source.
%
0.000
-0.025
-0.050
-0.075
-0.100
-0.125
-0.150
THD
H03
H02
H05
H04
H07
H06
H09
H08
H11
H10
A PHarm
H13
H12
B PHarm
H15
H14
H17
H16
H19
H18
H21
H20
H23
H22
H25
H24
C PHarm
Figure 34 -- 12.47kV Generator Supply [Monitor #1] Watts DFT plot—generator source.
Summary
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 5% 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 480V 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
1500A/phase at 480Vac. All drives were verified to have either 3% or 5% line reactors installed with,
obviously, is insufficient to control the 5th and 7th 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 5/13/2012
Page 20 of 21
The mitigation of the harmonics, especially the 5th (300Hz) 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 5% (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 5/13/2012
Page 21 of 21
Sample Report
Site: General Hospital
Voltage Distortion & Power Quality
Study Report