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RASGASCOMPANY
RasGas PLANTHARMONICSSTUDY
HarmonicsMeasurement
Prof.LazharBenbrahim1,Prof.MohieddineBenammar1
,Eng.JesusRomero2
1: Qatar University Professors and RasGas Chairs in Industrial
Electronics
2: Electrical Engineer at RasGas
01/8/2010[The increasing use of nonlinear loads, in modern
industry is keeping harmonic
distortion indistributionnetworkson the rise.Keeping the
levelharmonicsunder the
standard limits isverycrucial to the stabilityof
thepowernetworks.Theobjectiveof
this harmonic study of RasGas LNG plant is the measurement of
harmonics and
investigationofcompliancewithIEEE519harmonicsstandards.]
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2
Acknowledgment
We would like to acknowledge the help from RasGas Engineers and
Technicians
for their help in carrying out the measurements at RasGas
plant.
We would like also to thank all those who helped in this
project.
Prof.LazharBenBrahim
Prof.MohieddineBenammar
Eng.JesusRomero
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Abstract
The increasing use of power electronics equipment in modern
industry is
keeping harmonic distortion in distribution networks on the
rise. The most nonlinear
devices used in the gas processing industry are the VFDs. These
and other devices
generate harmonics in the network of the plant. Keeping the
level of these disturbances
under certain limits is very crucial to the stability of the
power networks. The objective of
this harmonic study of RasGas LNG plant is the measurement of
harmonics and
investigation of compliance with IEEE 519 harmonics
standards.
Measurements of harmonics at various points of the plant have
been carried out
using dedicated power quality analyzers. The results of these
measurements have been
thoroughly analyzed. The measurements and interpretation of the
results indicate overall
compliance with IEEE 519 standard. All voltage harmonics (Total
Harmonics Distortion
and individual harmonics) at the various PCC (33kV, 6.6kV and
415V) meet the
standard. Almost the same goes for the Total Demand Distortion
(TDD) for the current.
However, in some cases, some concerns are noted for the 48th
harmonic current around
the VSCF. The UPS and battery chargers exhibit high THDI but
given their low power, in
many cases this translates to acceptable TDDI and in all cases
the chargers have little
impact on the power network. It is noted also that some 415
buses are not balanced from
the point of view linear versus non-linear loads. It is
recommended that this is taken into
consideration in future expansion, as significant unbalance may
result in violations of
harmonics standards.
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TABLE OF CONTENTS
1.
INTRODUCTION..................................................................................................5
1.1. Motivation
...........................................................................................................
51.2. Measurement Preparation & Planning
................................................................
62. BACKGROUND
....................................................................................................7
2.1. Terminology
........................................................................................................
72.2. Scope of Study and Standards
.............................................................................
92.3. Plant Network
...................................................................................................
122.4. Nonlinear Loads
................................................................................................
133.
MEASUREMENT................................................................................................13
4. ANALYSIS
...........................................................................................................18
4.1. Introduction
.......................................................................................................
184.2.
Analysis.............................................................................................................
19
4.2.1. Voltage Harmonics Study
...........................................................................
194.2.2. Current Harmonics Study
...........................................................................
20
5. CONCLUSIONS & RECOMMENDATIONS
..................................................23
6. REFERENCES
.....................................................................................................24
APPENDIX.Appendix1
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1. INTRODUCTION
1.1. Motivation
Power quality is a big concern to facility designers and
operators. When the quality of
electrical power supplied to equipment is deficient, performance
degradation results. A
good power quality necessitates a thorough study of several
issues (Fig. 1) [1]. In its
quest to make sure that the power quality of its network is up
to the international
standards, RasGas has launched several studies. Among these
studies is the harmonics
study of their LNG plant. LNG plants are relying more and more
on modern electronic equipments which are
nonlinear loads that may cause harmonic distortion in
distribution networks. The most
used nonlinear device in modern industry is perhaps the static
power electronics
converter (e.g., UPS, battery chargers and drives), [1]. A
situation that has raised
waveform distortion levels in distribution networks. Keeping the
level of these
disturbances (also called harmonics) under certain limits is
very crucial to the stability of
the power networks. Harmonic studies are effective way to keep
networks and equipment
under acceptable operating conditions and to foresee potential
problems with the
installation.
Fig. 1: Power quality issues
PowerQuality
POWER FREQUENCY
DISTURBANCES
ELECTRO MAGNETIC
INTERFERENCE
POWER SYSTEM
TRANSIENTS
ELECTRO STATIC
DISCHARGE
POWER SYSTEM
HARMONICS
POWER FACTOR
GROUNDING AND
BONDING
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1.2. Measurement Preparation & Planning
The RasGas chairs together with Engineer Romero have carried out
a thorough search of
suitable equipment to be used in the harmonics study. The main
features of the
recommended equipment, the manufacturer and regional supplier,
datasheets and sample
quotation from a vendor were included in the proposal. It was
decided to acquire two sets
of power quality analyzers (PQA) type HIOKI-3196 from Japan.
This equipment is a
highly advanced measuring instrument with excellent features
that enable monitoring and
recording of normal and abnormal phenomena related to power
supply quality. The
process of acquiring the equipment was lengthy, and as a result
it was received on 6th of
January 2009.
The RasGas industrial electronics chairs received one of these
two sets for testing and
calibration in the Power Electronics Lab at Qatar University.
Extensive tests have been
carried out using a test bench made of power electronics
equipment that can generate
specific and controlled harmonics spectrum. It was concluded
from these tests that the
Hioki-3196 provides highly accurate harmonics measurements and
is well suited to the
harmonics study at RasGas plant.
Following successful testing of the equipment in the lab, it was
decided to proceed with
training of RasGas engineers/technicians and with subsequent
data collection from the
plant as follows:
1. Training was offered on February 3rd 2009 at the Power
Electronics Lab of Qatar
University (Fig. 2). Five persons from RasGas: 3 engineers and 2
technicians have
attended this training on proper use and handling of the power
quality analyzer
(HIOKI-3196). After an appropriate introduction about power
harmonics (see
training slides in Appendix), various aspects have been detailed
including
techniques of connections and setting of the system for the
measurement, what to
measure, where to measure, for how long, how to record and
collect the data, etc.
RasGas engineers were then able to use the PQA in a real power
system with
proper power electronics equipment.
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2. The measurements and data collection in the plant was
planned. All critical points
where potential generation of harmonics was suspected have been
considered
(VFDs, UPSs, Battery Chargers etc.).
2. BACKGROUND
2.1. Terminology
9 Point of Common Connection (PCC): A point of metering between
the utility and consumer. Within an industrial plant, the PCC is
the point between the
nonlinear load and other loads. This implies that harmonic
limits must be met
internally, in the consumers system. Many consultants, for
example, use this
Fig. 2: Harmonics Measurement Training: RasGas engineers and
technicians in the training about the PQA at the Power Electronics
Laboratory of Qatar University on February 3rd 2009
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statement to try to force manufacturers of nonlinear loads
(drives, UPS, battery
chargers, rectifiers, etc.) to adhere to the IEEE 519 limits for
a single load [2].
Furthermore, in LNG plant, power is generated in house and
several PCC exist as
a result harmonics limit should be met at all voltage level and
all bus bars.
9 Short Circuit Ratio (ISC/IL): The ratio of the short circuit
current (ISC) available at the point of common coupling (PCC) to
the maximum fundamental load current
(IL).
9 Voltage THD (THDV): Total Harmonic Distortion of the voltage
waveform. The ratio of the rms (root-mean-square) value of the
harmonic content of the voltage
to the rms value of the fundamental voltage:
%100....
1
25
24
23
22
1
2
2
++++===
VVVVV
V
VTHD h
h
V (1)
where Vh is the rms of the hth harmonic voltage, in volt. V1
refers to the
fundamental frequency (50Hz) voltage. V2 refers to the second
harmonic, or the
voltage at twice the fundamental frequency (100 Hz, if the
fundamental is 50 Hz)
and so on.
9 Current THD (THDI): Total Harmonic Distortion of the current
waveform. The ratio of the rms value of the harmonic content of the
current to the rms value of
the fundamental current:
%100....
1
25
24
23
22
1
2
2
++++===
IIIII
I
ITHD h
h
I (2)
Where Ih is the rms of the hth harmonic current, in Amperes. I1
refers to the
fundamental frequency (50Hz) current. I2 refers to the second
harmonic, or the
current at twice the fundamental frequency (100 Hz) and so
on.
9 Current TDD (TDDI): Total Demand Distortion of the current
waveform. The
ratio of the rms value of the harmonic content of the current to
the maximum
demand load current:
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9
%100....25
24
23
222
2
++++===
LL
hh
I IIIII
I
ITDD (3)
Where IL is the maximum demand load current, in Amperes.
The term total demand distortion or TDD is very much like the
total harmonic distortion,
or THD. The two definitions are very much alike. The only
difference is the denominator.
The THD calculation compares the measured harmonics with the
measured fundamental
current. The TDD calculation compares the measured harmonics
with the maximum
demand current. Similarly, the individual harmonic current
limits are not given in terms
of percent of fundamental (as is typical of most harmonic
measurements) at a given point
of time. The current limits in the standards are given in terms
of Maximum Harmonic
Current Distortion in Percent of IL. Note that commercially
available instruments
measure THD and individual harmonics in percent of I1. So a
post-processing of
measured data may be necessary to verify whether the measurement
are complying with
the standards or not.
2.2. Scope of Study and Standards
The scope of the present study is the measurement of harmonics
for RasGas plant and the
verification of the compliance of the plant power network with
the standards. The IEEE
519, Recommended Practice and Requirements for Harmonic Control
in Electrical
Power Systems (1992) has been used in this study [2].
If harmonics increase above certain limits, some harmful effects
on electrical equipment
may occur. Some of these effects are listed below:
9 Capacitor bank failure
9 Excessive losses, heating, and harmonic torques in AC
motors
9 Over-voltages and excessive currents in the power system,
resulting from resonance.
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9 Derating of cables due to additional eddy current heating and
skin effect losses.
9 Inductive interference with telecommunication circuits.
9 Signal interference and relay malfunctions, particularly in
solid-state and digitally controlled systems.
9 Unstable operation of firing circuits relying on zero voltage
crossing detection and latching.
9 Interference with large motor controllers
Standards were developed to keep harmonics under some acceptable
limits. These
limits are described by IEEE 519 harmonics standard which
indicates the Recommended
Practice and Requirements for Harmonic Control in Electrical
Power Systems (see Table
1&2). Note that voltage harmonics and current harmonics are
assessed through the THD
and TDD respectively. The TDD is the total demand distortion and
is identical to the
THD except that the maximum load current (IL) is used instead of
the fundamental
current component (I1). The measured harmonics distortion of
voltage and current levels
are therefore compared to the allowable limits recommended by
IEEE-519 standards [2].
Table 1: IEEE 519-1992 Standard: Recommended Practices and
Requirements for Harmonic Control in Electrical Power Systems
(Voltage Distortion Limits)
Maximum harmonic voltage distortion in percentage of the
fundamental
Bus Voltage Voltage Harmonic limit as (%) of fundamental THD_V
%
= 161 KV 1.0 1.5
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Table 2: IEEE standard 519-1992 maximum current distortion
Maximum harmonic current distortion in percentage of the
fundamental
V 69 kV
ISC
/ IL h
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2.3. Plant Network
The electrical network of the RasGas LNG plant is fed from
Kahrama and local in house
generators. All sources are working in parallel. The electrical
network configuration used
for the harmonic analysis is the complete system in normal
operation with all the loads of
Train 1 to 5 connected and Train 6&7 under
commissioning.
9 Utility KAHRAMAA (QGEWC) and 91-GT 052, 91-GT 053, 91-GT 054,
91-GT 055 generators feed the SS A HV 132kV substation.
9 The LNG Trains 3 & 4 are fed by 91-GT 051 generator and by
the SS A HV 132kV substation through three step down transformers
132/34.5 kV, 60/75 MVA
(ONAN/ONAF) with automatic OLTC.
9 The LNG Train 5 is fed by the SS A HV 132kV substation through
two step down transformers 132/34.5 kV, 85/100MVA (ONAN/ONAF) with
automatic OLTC
9 The LNG Trains 1&2 are fed by four generators and export
to SS A HV 132kV substation through one step down transformer
138/33 kV, 60/75 MVA
(ONAN/ONAF) with automatic OLTC
9 The substation SS 102 is fed by the SS A HV 132 kV substation
through three step down transformers 132/34.5 kV, 75/90 MVA
(ONAN/ONAF) with
automatic OLTC.
9 The LNG Train 6 & 7 are fed by two generators per train,
EVFDs and backed up by the SS A HV 132 kV transformer 132/34.5 kV,
75/90 MVA (ONAN/ONAF)
with automatic OLTC.
9 The substation SS 103 is fed by the SS A HV 132 kV substation
through two step down transformers 132/34.5 kV, 75/90 MVA
(ONAN/ONAF) with automatic
OLTC.
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2.4. Nonlinear Loads
Nonlinear loads are loads in which the current waveform does not
resemble the applied
voltage waveform due to a number of reasons [3]. Among the most
common nonlinear
loads in power systems are:
9 Power converters 9 Variable Frequency Drives (VFDs) 9 DC
Drives 9 Cycloconverters 9 Cranes 9 Elevators 9 Power supplies 9
Uninterruptible Power Supplies (UPSs) 9 Battery chargers (BCs) 9
Inverters 9 Fluorescent lighting 9 ARC furnaces 9 Welding
machines
In an LNG plant many nonlinear loads exist especially the VFDs,
UPSs and BCs which
are the main sources for voltage and current harmonics in the
power plant networks.
3. MEASUREMENT
Following the acquisition of the two sets of PQA and the
adequate training carried out
for RasGas engineers, the first measurement was conducted on
March 2nd 2009, we have
recorded some data around a well know harmonics-generating
equipment (SS-
53:TR5342,TR5343, TR5344 which includes VFDs installations and
we also verified the
UPS units UPS5731A and UPS5731B) and the data confirmed the
existence of harmonics
as expected. This initial test gave us trust on the technician
measurement capability and a
confidence in the reliability of the PQA, and decided to proceed
with a wide range of
measurements at various locations in the plant. Instructions
were given by the chairs to
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the measurement team composed of RasGas engineers and
technicians (to check the
direction of connections of the current sensors and to increase
the sampling frequency of
measurement as the data taken is two little).
Extensive measurement has started on April 7th 2009, and due to
periodic maintenance
at the RasGas plant several delays in the measurement occur. It
is worth noting that we
were suspecting harmonics from nonlinear loads such as VFDs,
UPSs, BCs and in a
lesser gravity from transformers that may operate in saturation
or resonant conditions. As
data was received, the chairs and engineer Romero were checking
for data that may
represent a threat to the grid. Depending on measurement
results, in some cases further
measurements were carried out to verify the causes for some of
the measured harmonics,
this is the case of the Variable Speed Constant Frequency (VSCF)
generators. Therefore,
harmonics spectrum especially at the 6.6kV may change depending
on the operating
conditions of the plant where VSCF is in service. This has
caused some delays in order to
investigate more the causes of these harmonics. The last data
collected were carried out
by mid-December 2009. The period of measurement lasted 8 months
which were enough
to carry out measurement at various operating conditions.
Sample of measurement data are shown in the Appendix. For each
measurement point the
followings are given:
1. A general information about the measurement point (Hioki DMM
tables)
2. Voltages and currents waveforms as well as harmonics
spectrum
3. Lists of harmonics and THDs for the voltages and currents
Note that all measured data are stored into a CD included with
this report.
The plant is composed of several trains and several substations
which are more or less
similar. Measurements shown in this report were selected and
represent all types of
loads within the plant. Focus is on the SubStation SS02 which
contains the most critical
nonlinear loads of the plant. Measurements at other substations
(SS01 & SS03) were
carried out for the validation of the results obtained in
SS02.
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A summary of the results obtained from measurements carried out
in SS01, SS03 and
mainly in SS02 is given in Table 3 below. A detailed analysis of
these results is given in
the section below.
Table 3 : Summary of voltage/current harmonics measurement (the
noted problems are highlighted).
LoadTypes POWER(MW)
(measured)Short Circuit
Current Isc (kA)
VOLTAGE(kV)(atMeasurement
point)TotalHarmonicDistortionTHDV
CURRENT(A)(atMeasurementpoint)
TotalHarmonicDistortionTHDITotalDemandDistortionTDDI
TR 0221 (GT 051)
12.00 33 222.7 THDV=3.15% THDI=3.28%
TR 5143 11.96 33 228 THDV=2.67% THDI=1.8%
TR 5142 12.38 33 239 THDV=2.74% THDI=0.43%
TR 5154-2 1950 KVA
1.13 6.6 99.7
Isc= 0.2 THDV=3.03% THDI=4.46% I48/I1=3.7%
Isc /IL=1.2 TDDI=2.61% (0.3%)
TR 5141B 4/5 MVA
0.67 6.6 69.7
Isc= 5.6 THDV=2.72% THDI=6.8% I48/I1 =4.3%
Isc /IL=16 TDDI=1.35% (0.3%)
TR 5155-2 1550 KVA
0.884 6.6 77.88
Isc= 0.2 THDV=2.65% THDI=6.65% I48/I1=3.9%
Isc /IL=1.5 TDDI=3.82% (0.3%)
TR 5151A 1600 KVA
0.330 0.415 540.8
Isc= 26 THDV=2.26% THDI=1.52% I48=0.9%
Isc /IL=11 TDDI=0.36% (
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TR 5152E 400 KVA
0.047 0.415 90.23
Isc= 24.6 THDV=1.53% THDI=30.73% I5/I1=28.52%
Isc /IL=44 TDDI=5.0% (
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1950 KVA Isc= 0.2 THDV=2.94%
THDI=4.26% I48/I1=3.64%
Isc /IL=1.2 TDDI=1.84% (0.30%)
TR 5355-2 1550 KVA
0.733 6.6 76.38
Isc= 0.2 THDV=2.79% THDI=4.24% I48/IL=3.56%
Isc /IL=1.5 TDDI=2.38% (0.30%)
TR 5351A 1600 KVA
0.366 0.415 563
Isc= 26 THDV=2.02%
THDI=2.17% I48/I1=1.19%
Isc /IL=11 TDDI=0.55% (0.30%)
TR 5351B 1600 KVA
0.065 0.415 140
Isc= 24.4 THDV=3.0% THDI=4.32% I48/I1=0.45%
Isc /IL=11 TDDI=0.27% (
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11.5/2-5.75 MVA Isc= 31.4 THDV=2.66%
THDI=8.87% I11/I1=7.03%
Isc /IL=156 TDDI=2.75% (
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a. 33kV bus level
b. 6.6kV bus level
c. 415V bus level
2. Current harmonics measurement data measured at nonlinear and
linear loads which are connected to PCCs with various voltage
levels.
4.2. Analysis
4.2.1. Voltage Harmonics Study
This is the most critical information in the analysis of
harmonics. The acceptance criteria
for the harmonic study according with the IEEE 519 standard
(Table 1) are:
1. Maximum total voltage distortion THDV : 5%;
2. Maximum voltage distortion for each harmonic Vh : 3%;
Summary of all harmonics measurement data are given in Table 3.
The study showed that
all the measured voltage harmonics at the plant comply with the
IEEE 519 standard; the
highest THDV was only 3.03% and it is well below the 5% limit of
the standard; this
maximum THD was recorded at the PCC SB5141A (TR5154-2, in
train#4 Substation
SS51 at the 6.6kV level). It is worth to note that this
distortion is at the point of coupling
with the Variable Speed Constant Frequency (VSCF) and was
recorded on November
25th 2009. This VSCF indicated some concerns in the current
harmonics compliance, and
is further discussed below.
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Figure 3: Voltage & current waveforms at 6.6kV PCC :
TR5154-2 with THDV= 3.03%
(while the VSCF is connected to the PCC and generating power to
the network).
4.2.2. Current Harmonics Study
Methodology:
Unlike the voltage harmonic limits of the IEEE 519 standard, the
current harmonic limits
depend on the short circuit level of the system they are being
injected into. The limit for
the current harmonics according with the IEEE 519 (Table2)
depends on (Isc/IL): ratio of
the short circuit current (Isc) available at the PCC to the
maximum load current (IL).
In the current harmonics study, we should be selective as it is
impractical to measure at
all loads. Sometimes current harmonic distortion can be assessed
through simple
inspection of the types of loads. All this requires is
familiarity with the characteristic
harmonic spectrum of each type of common nonlinear load.
However, harmonics
measurement is essential to verify their compliance with the
IEEE519 standards. These
current harmonic measurement data are useful for some of these
nonlinear loads that may
need designing suitable harmonic filters. This involves direct
measurements at selected
locations for example, the point of common coupling (PCC) and
the node where
nonlinear loads are connected.
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We started the measurements by emphasis on the nonlinear high
power loads which
consist of the Mega- drives called VDFs, AFDs or simply drives.
Given that the power
quality analyzer (PQA) instruments provide measurement of the
THD for both current
and voltage quantities, and in order to compare results against
the IEEE standard, it was
necessary to compute the TDDI from the THDI, IL, I1, and Isc.
Since the TDDI is always
less or equal than THDI, the followings procedure for current
harmonics analysis is
adopted and applied in Table 3:
Case 1. THDI and all individual harmonics are less than the
minimum of the
standard limits (for the strictest limit applicable to
ISC/IL1000), then there is violation of the IEEE 519 standards and
no
further calculation is needed.
Case 3. Above cases are not applicable. In this case, we proceed
as follows:
i. The ratio ISC/IL is determined to identify the appropriate
row in
Table 2.
ii. TDDI is determined: TDDI= THDI(I1/IL).
iii. Determine harmonic current distortion in percent of IL from
(Ih/I1)
which is PQA-measured value: Ih/IL= (Ih/I1)(I1/IL).
iv. Use the computed values in (ii) and (iii) to compare
distortion to
the IEEE limits (Table 2). The example shown below illustrates
the
applied method.
Analysis:
As illustrated in Table 3 the measurements show that the mega
drives, whether VSI type
(without filters) or LCI type (with filters) used for the helper
motors of the compressors,
are complying with the IEEE519 standards. This is a reassuring
result as these drives are,
currently, the largest non-linear loads. From the table, we note
for example that the THDI
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values for VFDs connected to TR5342, TR5343 and TR5344 are
3.07%, 1.75% and
2.89% respectively. These values are complying even with the
strictest limits of the TDDI
(
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carrying more measurements where VSCF are not connected to the
bus. This has pointed
out to the fact that the 48th harmonic was not load-injected
distortion but rather VSCF-
generated. This voltage harmonic component induced a current
with the similar
harmonics content where the dominant harmonic was the 48th (see
Figure 3). The IEEE
standard stipulates that the first row of Table 2 must be
applied for all generators
regardless of the actual value of Isc/IL. As shown in Table 3
and after processing all the
data, the results indicate no violation at the TDDI level.
However, the 48th harmonic
component of the current is beyond the limits for TR5154-2
(I48/IL=2.16%>0.3%) and
TR5155-2 (I48/IL=2.24%>0.3%), both of which are connected to
the VSCF generators.
This harmonic component is most likely caused by the VSCF; this
may be substantiated
by the following reasons: (a) the non-linear loads at the plant
are not expected to inject
this 2.4 kHz component (48th harmonic); (b) measurements at
substations where no
VSCF are connected show no presence of such harmonic (see data
for TR5241A,
TR5241B, TR5441A and TR5441B in Table 3). This could be further
confirmed by
measurement using the PQA, as this is capable distinguishing the
outflow and inflow
harmonics. Unfortunately, many of the measurements taken
including these taken around
the VSCF have been carried out by technicians without proper
training. Thus the
collected data is adequate for evaluating harmonics but could
not be used to precisely
determine source of injected harmonics.
We note that, although not violating the TDDI limits of the IEEE
standard in all cases
except for one (UPS0171A in SS01), the UPS and battery chargers
used in the plant are
exhibiting very high THDI (in some cases around 50%). The reason
the TDDI limits are
not generally violated is because these units are operating well
below their rated power.
Care must be taken in future in case the load of these units is
increased, as this would
raise the TDDI to levels that may violate IEEE limits.
5. CONCLUSIONS & RECOMMENDATIONS
From the present harmonics study, the measurements and
interpretation of the results
indicate overall compliance with IEEE 519 standard. All voltage
harmonics (Total
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24
Harmonics Distortion and individual harmonics) at the various
PCC (33kV, 6.6kV and
415V) meet the standard. Almost the same goes for the Total
Demand Distortion (TDD)
for the current. However we note that, in some cases, the
individual harmonic current
violates the IEEE limit especially around the VSCF. From
harmonics point of view, this
VSCF generator is the weakest unit in the studied network; it is
recommended that
solutions to mitigate harmonics generated by these units be
considered. Although so far
this did not cause any problem to the LNG plant as the generated
harmonics are
intermittent and therefore the better way to deal with it is to
report findings to the
manufacturer in order to fix this within the equipment itself.
The UPS and battery
chargers exhibit high THDI (in some cases around 50%). The
reason the TDDI limits are
not generally violated is because these units are operating well
below their rated power.
Care must be taken in future in case the load of these units is
increased, as this would
raise the TDDI to levels that may violate IEEE limits.
It is noted that some 415 buses are not balanced from the point
of view linear versus non-
linear loads. It is recommended that this is taken into
consideration in future expansion,
as significant unbalance may result in violations harmonics
standards.
6. REFERENCES
[1] Francisco C. De La Rosa, Harmonics and Power Systems Taylor
& Francis
Group, LLC CRC Press, 2006.
[2] IEEE 519 Standard : Reference Standard
[3] Mohan, Undeland and Robbins Power Electronics: Converters,
Application and
Design,. Published by John Wiley & Sons, 1989, 667
pages.
[4] RGX-S-91-2181-020Rev2- Electrical Network Studies-Short
Circuit
