Download How to Improve Power Factor, Voltage Regulation

How to Improve Power Factor, Voltage Regulation
and to Reduce Harmonic Distortion of an Industrial
Plant, using a Power System Simulator
Santiago Barcón, Ignacio Suárez, and Luis Flamenco
Abstract—The present work shows a real case of an industrial
plant in México and the solution of problems in the electric
system caused by the damage of a static var compensator. With
help of a power system simulation we could evaluate several
alternatives of solution and determine which is better from the
technical and economic point of view to be applied. The objective
was to improve the conditions of electric system through a low
cost solution and quick application.
When the EBT turned on, the voltage of lamination bus is
12.68 kV with a V_THD of 2.9%, while with the EBT turned
off the voltage is 13.51 kV with a V_THD of 1.5%.
Index terms-Electric variables measurement.
Harmonic distortion.
Power system simulation.
Static var compensator.
Simulation software.
I. INTRODUCTION
In Mexico there are only two utilities, both companies are
property of the government. Since November 1991 they had a
policy of penalizing to the users with a lower power factor
than 0.90 and the users with a PF upper than 0.90 they
received a rebate up to 2.5% in their monthly electrical billing.
At this time there are not a penalizing for high harmonic
distortion on the PCC, however in a few years is too possible
will exist a regulation to this respect.
With the damage of a static var compensator of a steel mill
in Mexico, several problems arise in the electric system: low
power factor less than the utility recommendations on PCC,
poor voltage regulation, damage at the electronic equipment
and the high probabilities of harmonic resonance that meant a
risk condition to the plant.
Due the time to deliver a new static var compensator, the
company decided to look for other solutions to improve the
conditions of electric system, with the purpose of not altering
the normal production. The alternative of improvement should
be of low cost and quick application.
The plant has two productive areas: lamination and steel
mill in the last there are two electric arc furnaces (the shaft
and the EBT). In the figure 1, is included an one line diagram
simplified.
The most important equipment due peak of load is the EBT
furnace, and depending of their operation the electric system
has several behaviors, so for the present analysis considers
two general situations: the EBT furnace turned on and another
with the EBT turned off.
Fig. 1. One line diagram simplified.
The most affected area for the loss of static var
compensator was the lamination, because here is located the
mayor quantity of the electronic equipments, so all the efforts
had to be focused to solve the problems in the lamination bus.
The lamination plant is constituted by two transformers of
30 MVA working with the close link in 13.2 kV, from this bus
are fed 11 circuits that supply to several loads in which are
included: DC motor drives, AC motor drives, induction
motors, illumination and two capacitors banks.
There are two conditions to operation of lamination plant:
normal load (20.13 MW with a PF of 0.904) and low load
(11.04 MW with a PP of 0.996).
II. METHODOLOGY
In order to determine the solution of electric system it was
necessary:
A. To carry out electric variables measurement for each
one of conditions of plant.
B. To confirm the name plates data of the equipments in
the electric system.
C. Modeling the electric system in the simulation
software.
D. To obtain and evaluated the solution under the
several conditions.
E. Final results.
A. Electric variables measurement.
Electric variables measurement were carry out at each one
of feeders of plant with three power quality analyzers, with the
purpose to detect the feeders with the major harmonic
distortion and mainly to determinate the behavior of load for
each one of the operation conditions.
In the next table the measurement summary are shown, and
is included a evaluation of IEEE 519-92 [1]-[2] for current:
Feeder
kW
PF
I_THD (%)
IEEE 519-92
Evaluation
GR1-2
GR1-4
GR1-5
GR1-8
GR1-9
GR1-11
GR1-12
GR1-14
GR1-15
GR1-16
GR1-17
700
480
10,799
550
250
860
1,739
2,500
1,294
641
273
0.960
0.800
0.733
0.960
0.800
0.733
0.770
0.660
0.610
0.730
0.74
15.50
4.90
4.30
31.00
4.20
2.10
3.80
22.30
3.60
0.80
0.80
Outside
Inside
Inside
Outside
Inside
Inside
Inside
Outside
Inside
Inside
Inside
This section consisted in to verify the name plates data of
equipments that were considered in the study, from
transformers until cables size and longitude of lamination
plant.
C.
Modeling the electric system in the simulation software.
With the electric measurements and the information of
system was proceeded to modeling the loads, the transformers,
the cables, etc. in the simulation software.
D. To obtain and evaluated the solution under the several
conditions.
Once modeling the electric system, it was carry out
simulations that includes from the original situation until to
obtain the alternative solution.
Next are shown some of the results obtained in the
simulation software for the original condition, with the two
capacitors banks and EBT furnace operating. This condition
was for the normal load at lamination plant.
LAMINATI ON PLANT
Table 1. Summary of electrical variables measurement.
229. 08 k V
V _THD 0. 4%
At 13.2 kV bus are connected a capacitor bank of 9600
kVAR to 16.64 kV, while in the circuit GR1-8 exist another
capacitor bank of 600 kVAR to 16.64 kV, so in this feeder the
I_THD is high.
Bus 230 k V
10,054 k W
4,439 k V AR
TR1
10,054 k W
4,428 k V AR
TR2
30 M VA
230/13. 2 k V
9. 38%
I_THD 5. 4%
Next are shown the signal and harmonics for current of the
GR1-14 feeder.
E vent waveform/detail
5,573 k V AR
I_THD 24. 1%
Eve nt w ave for m/detail
Amps
2 00
1 50
I_THD 5. 4%
12. 68 k V
B us 13. 2 k V
%of FND
25
CapLam
9,600 k V AR
GR1-8
Cap LA
15
2,486 k W
928 k V AR
12. 68 k V
V _THD 2. 9%
348 k V AR
I _THD 31%
20
1 00
30 M VA
230/13. 2 k V
9. 35%
12. 68 k V
V _THD 2. 9%
600 k V AR
50
10
0
5
Fig. 3. Original condition one line diagram results.
-50
-1 0 0
-1 5 0
04: 34: 11 .0 00
04: 34: 11 .0 05
04: 34: 11 .0 10
CHA Amps
04: 34: 11 .0 15
Timed event occurre d at 08/1 1/00 04:3 4:11.000
-2 0 0
04: 34: 11 .0 20
0
Thd
H05
H10
H15
CHA Am ps
H20
H25
Total RMS: 114.27 Amps
DC Level : 10.15 Amps
Fundamental(H1) RMS: 111.05 Amps
Total Harmonic Distortion ( H02-H50) :
22.37 % of FND
Even contribution ( H02-H50) :
0.27 % of FND
Odd contribution ( H03-H49) :
22.37 % of FND
The results for the original condition can be summarized
in:
Timed event occurred at 11/08/00 04:34:11.000
1.
Fig. 2. Signal and harmonics measurement example.
In these graphs can be observed how the fifth harmonic is
outside of the recommendations and also we have seventh and
eleventh with important values.
2.
3.
On the other hand, the V_THD at 13.2 kV bus is normally
inside of the recommendation the value oscillate between
1.6% to 2.9%, depending if the EBT turned on or turned off.
In general could mentioned that in the secondary of
transformers T1 y T2 of lamination plant is fulfilled the
recommendations of the IEEE 519-92.
B. To confirm the name plates data of the equipments in the
electric system.
4.
The total power factor of the plant was 0.904, this
value is on the limit of power supply
recommendations.
The voltage at 13.2 kV bus, was 96.1% to the
nominal voltage.
The V_THD at 13.2 kV bus, was 2.9% this value
meet the IEEE 519-92 recommendations. The most
important harmonics were the 7th and the 11th with
2.3% and 1.3% respectively of the fundamental
voltage.
The capacitors banks show high THD of current,
however because they are designed to 130% up to the
nominal voltage do not present problems.
In the figure 4, are shown the signal and harmonics for
voltage at 13.2 kV bus.
In so far as, the figure 5 is shown the impedance of system
vs frequency at 13.2 kV bus.
Plot1 - Distortion Waveform
Plot1 - Distortion Spectrum
400
350
10000
Case 3
Furnace EBT ON
Cap Banks OFF
Lamination (normal)
Case 4
Furnace EBT OFF
Cap Banks ON
Lamination (low)
20,142
0.785
12.455
94.35
2.50
-------
11,045
+0.996
13.826
104.74
2.10
14.00
300
5000
Table 2. Summary results for original condition.
Bus Distortion Voltage Spectrum (Volts)
Bus D is tortion Voltage WaveForm (Volts )
250
200
0
The sign (+) indicates that the power factor is capacitive.
150
-5000
100
-10000
50
0
0
50
100
150
200
250
Time (1 Cycle) or 0-360 degrees
300
0
350
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Harmonic Order
Fig. 4. Signal and harmonics for 13.2 kV bus.
Plot1 - Scan Magnitude
17.5
In the last table can be observed when the capacitors banks
are off the harmonics go down, but affect the power factor and
the voltage regulation, on the other hand when the capacitors
banks turned on the power factor is improved and also the
voltage at 13.2 kV bus is better, however the harmonics goes
up and exist a risk condition due possible harmonic resonance
near to 7th (cases 1, 2 y 4).
15.0
After studying several solutions alternatives, was concluded
that the present the more advantages due low cost and quick
application consisted:
Bus ScanMagnitude (pu)
12.5
10.0
7.5
5.0
1.
2.5
0.0
0
5
10
15
20
25
30
Harmonic Order
35
40
45
50
2.
Fig. 5. Impedance vs frequency at 13.2 kV bus.
3.
In the last curve can be observed the parallel resonance at
8th harmonic and is important to mention that this represent a
risk condition for the plant, because is near to the 7th
harmonic.
The signal and harmonics for current of capacitor bank
9600 kVAR are shown in the next graph.
Plot1 - Distortion Waveform
55
50
200
45
40
Branch Distortion Current Spectrum (Amps)
100
Branch Distortion Current Waveform (Am ps)
The detuned filter was used in the past, to improved the total
power factor of plant before the construction of EBT furnace
and their harmonic filters, after when this area was turned on
the detuned filter was disconnect and some of their
components were used in other sections.
The results obtained in the simulation software after the
application of the recommendations are show in the next one
line diagram.
Plot1 - Distortion Spectrum
60
300
Rehabilitate and install the detuned filter of 12 MVAR
to 16.64 kV at 13.2 kV bus, this filter was off operation.
To disconnect both capacitors banks of 9600 kVAR and
the 600 kVAR.
Change the actual tap position of transformers T1 and
T2, to increase the voltage at secondary in 2.5%.
0
-100
-200
-300
35
LAMINATI ON PLANT
30
25
50
100
150
200
250
Time (1 Cycle) or 0-360 degrees
300
15
10
10,053 k W
3,527 k V AR
5
0
350
1
2
3
4
5
6
7
8
9
TR1
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Harmonic Order
Fig. 6. Signal and harmonics for 9600 kVAR
Applying the same procedure of analysis, several
conditions of electric system where studied, in the next table
are show the summary of results.
Case 1
Furnace EBT ON
Cap Banks ON
Lamination (normal)
Case 2
Furnace EBT OFF
Cap Banks ON
Lamination (normal)
kW
PF
kV
(%Vnom)
20129
0.904
12.679
20,122
0.921
13.513
10,053 k W
3,517 k V AR
TR2
30 M VA
230/13. 2 k V
9. 38%
I_THD 2. 0%
In these graph could be observed that the most important
harmonics are the 7th, 11th and the 13th with 16.2%, 14.6%
and 8.9% respectively of the fundamental current.
Original Situation
Bus 230 k V
20
0
0
228. 26 k V
V _THD 0. 2%
96.05
V_THD
(%)
2.90
I_THD(%)
Cap. Bank
24.0
102.37
2.50
21.0
B us 13. 2 k V
I_THD 2. 0%
12. 95 k V
2,486 k W
36.29 k V AR
12. 95 k V
7,705 k V AR
I_THD 3. 22%
V _THD 0. 5%
FLTR-1
30 M VA
230/13. 2 k V
9. 35%
12 M V AR
Fig. 7. Future condition one line diagram results.
V _THD 1. 6%
Plot1 - Distortion Waveform
The results of future condition can be summarized in:
9
2.
3.
4.
In the next figure, are shown the signal and harmonics for
voltage at 13.2 kV bus.
8
200
7
100
6
Branch Distortion Current Spectrum (Amps)
The power factor of the plant was 0.935, this value
fulfill with the power supply recommendations.
The voltage at 13.2 kV bus, was 98.13% at nominal
voltage.
The V_THD at 13.2 kV bus, was 1.6% this value
fulfill the IEEE 519-92 recommendations. The most
important harmonics were the 11th and the 13th
with 1.02% and 0.09% respectively of the
fundamental voltage.
The detuned filter show a low THD of current 3.2%.
Branch Dis tortion Current Waveform (Am ps )
1.
0
-100
-200
-300
175
150
10000
125
5000
100
Bus Distortion Voltage Spectrum (Volts)
Bus D is tortion Voltage WaveForm (Volts )
Plot1 - Distortion Spectrum
0
-5000
-10000
75
50
25
0
0
50
100
150
200
250
Time (1 Cycle) or 0-360 degrees
300
0
350
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Harmonic Order
Fig. 8. Signal and harmonics for 13.2 kV bus (future).
In the figure 9, are shown the impedance of system vs
frequency at 13.2 kV bus.
5
4
3
2
1
0
0
50
100
150
200
250
Time (1 Cycle) or 0-360 degrees
300
350
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Harmonic Order
Fig. 10. Signal and harmonics for detuned filter.
The solution was studied under the several conditions of
operations and the results were summarized:
Future Situation
Plot1 - Distortion Waveform
Plot1 - Distortion Spectrum
10
300
Case 5
EBT Furnace on
Detuned Filter on
Lamination (normal)
Case 6
EBT Furnace off
Detuned Filter on
Lamination (normal)
Case 7
EBT Furnace off
Detuned Filter on
Lamination (low)
Case 8 (worst)
EBT Furnace on
Detuned Filter on
Lamination (normal)
Worst
harmonic
condition.
kW
FP
kV
(%Vnom)
V_THD(%)
20126
0.935
12.953
98.13
1.60
I_THD(%)
Filter
3.20
20120
0.953
13.818
104.68
1.4
2.80
11045
+0.961
14.19
107.50
0.80
-------
20126
0.934
12.916
97.85
1.60
3.90
Table 3. Summary results for future condition.
The sign (+) indicates that the power factor is capacitive.
Plot1 - Scan Magnitude
10
The Case 8 considers the worst harmonic condition,
because here includes another source injecting harmonics from
the PCC that correspond to electric arc furnace in the melting
stage.
9
8
7
Bus Scan Magnitude (pu)
6
5
4
E.
3
2
Final results.
1
0
0
5
10
15
20
25
30
Harmonic Order
35
40
45
50
Comparing the results obtained in the cases 1 and 5 we
have:
Fig. 9. Impedance vs frequency at 13.2 kV bus (future).
In the last curve can be observed like near of 4th harmonic
the impedance of system was reduce due the operation of
detuned filter and later the trend is directly proportional to the
frequency.
The signal and harmonics for current of detuned filter are
shown in the figure 10.
In these graph can be observed that the most important
harmonics are the 5th, 11th and 13th with 1.93%, 1.81% and
1.35% respectively of the fundamental current
Power Factor
V_THD
Voltage at 13.2 kV Bus
I_THD at Capacitor Bank
or Detuned Filter
Case 1
0.904
2.90
12.679 kV
(96.05 % Vnom)
24%
Case 5
0.935
1.60
12.953 kV
(98.13% Vnom)
3.2%
Table 4. Results comparison.
Whit the application of this recommendation a better power
factor was obtained, decreased the V_THD almost in half,
improvement of the voltage regulation at 13.2 kV bus in 300
volts and mainly the possibility of a harmonic resonance
disappear.
III.
CONCLUSIONS.
The present work illustrate one of the multiples applications
of power system simulator to solve real problems at industrial
plants.
Is important to remember that the possible solutions of
power system was selected the alternative of low cost and the
quick application, just a temporal solution.
Finally, in this specific case was analyzed like an
application of detuned filter could be a very good solution to
power quality problems, such voltage regulation and harmonic
reduction.
IV. REFERENCES.
[1] IEEE Standard 519-92, “Recommended Practices and
Requirements for Harmonic Control in Electrical Power
Systems”, 1992.
[2] IEEE Harmonics Working Group, “Guide for Applying
Harmonics Limits on Power Systems”, May 1996.
Santiago Barcón was born in Mexico City in
1957. He is electrical engineer from the
Universidad Iberoamericana, he received the
master degree in BA from Instituto
Tecnológico de Estudios Superiores de
Monterrey.
He has worked in several companies attending from
electrical maintenance areas up to sales and production
management, among them Vitro and ABB. Presently, he is
partner and president of Inelap,* S.A. de C.V. manufacturer
low and high voltage capacitor for power factor correction,
harmonic filters and protection panels. Inelap is an ISO 9001
facility. His research interests include capacitor banks,
harmonics and power quality. He participated in the Power
Quality 93, 95 and 97 and many conferences in Mexico and
Central and South America. He is member of IEEE.
Ignacio Suárez was born in México City. He
is electrical engineer from Universidad
Nacional Autonoma de Mexico, his
experience is more than 15 year in the
electric area, he has worked in many different
companies where he has participated in design engineering,
equipment installation, training, planning, commercial and
administrative functions. At the moment he is engineering
manager in Inelap,* S.A. de C.V., where his participation it
obtained the ISO-9001 certification.
He has participated in many conferences in Mexico, in 2000
he was speaker in the Power System World in USA.
Luis M. Flamenco was born in Mexico City,
in 1967. He is electrical engineer from the
Universidad Nacional Autónoma de Mexico.
Since 1991 he has worked for different
companies carry out studies including: short
circuits and protection and coordination, low flow and
harmonics analysis.
Actually, he is manager of power quality department at Inelap,*
S.A. de C.V. He has participated two times in the Power
System World in USA in 1998 and 2001.
*Arteche acquired Inelap in 2005