BULETINUL INSTITUTULUI POLITEHNIC IAŞI
TOMUL LII (LVI), FASC. 5, 2006
ELECTROTEHNICĂ, ENERGETICĂ, ELECTRONICĂ
THREE CHANNELS ANALYSIS SYSTEM FOR ELECTRICAL
POWER SYSTEM DISTURBANCES MEASUREMENT
BY
*CIPRIAN DUGHIR and *GABRIEL GĂŞPĂRESC
Abstract. This paper is focused on how to reduce the amplitude of the
electrical disturbances which appears in the electrical power systems to a
low voltage supported by the acquisition boards. The signal from the
electrical power system has many types of disturbances, one of them with
amplitudes above 10kV. The main idea of this material is that the signal
from the electrical power system to be split in 3 ways, each way heaving a
different division factor. The tree signals after division process is applied
each of them to an input of the data acquisition board.
Keywords: power system, electrical disturbances, preconditioning circuit, data
acquisition.
1. Introduction
The method proposed in this paper is focused on how to detect the
disturbances without the use of a nonlinear voltage divider. A nonlinear voltage
divider is very difficult to build and can introduce errors. This method consists in
the use of 3 input channels of the acquisition board, each channel heaving a
different division factor. Each channel is then limited to ±10V. The signals from
the three channels are then analyzed and if any limitation is found on one of the
three channels a decision is made. The presence of the limitation on one channel is
a sign that it is possible to heave a disturbance on that channel. Most disturbances
detection algorithms use the frequency domain analysis. This type of analysis
being a time consumption analysis and in most of the cases the analysis can not be
done in real time, for this purpose it was used the time domains analyze.
The goal proposed is to monitor and record the disturbances presents in the
electrical power system. The disturbances are recorded for further analysis.
2. Circuit description
The preconditioning circuit consists in three voltage dividers, each of them
heaving their own transfer characteristic. The first voltage divider has the
characteristic C1, the second voltage divider has the characteristic C2, and the
CIPRIAN DUGHIR and GABRIEL GĂŞPĂRESC
third voltage divider has the characteristic C3, described in the figure 2. The
signals from the voltage dividers are then applied to an acquisition board and
analyzed. For the acquisition of the signal it was used the National Instruments
acquisition board NI PCI 6254M with a sample rate of 250Ksample/sec on each
channel.
Voltage
divider
1/50
ratio
CH1
Voltage
divider
1/200
ratio
Electrical
power
system
network
CH2
Voltage
divider
1/1000
ratio
CH3
A
c
q
u
i
s
it
i
o
n
B
o
a
r
d
Fig. 1.- Preconditioning circuit diagram.
If any disturbance is found in the first channel, the signal is tested to see if
the signal was limited or not. In the signal was not limited, the disturbance has the
amplitude smaller than 500V. If a limitation is found, the second channel is tested
for a limitation, using the same procedure as for the first channel. If no limitation
has been found, the disturbances have the amplitude smaller than 2kV. The same
procedure is applied for the third channel if the signal of the second channel was
limited.
Uout
C1
C2
10V
C3
500V
2000V
10000V
Fig. 2.- Transfer function of the voltage dividers.
Uin
BUL. INST. POLIT. IAŞI, TOMUL LII (LVI), FASC. 5
In the figure 3, is presented a signal with a spike disturbance with
amplitude about 9kV, split in three channels using the method proposed and then
applied to the data acquisition board. In the first and second channel it can be
observed a limitation of the signal. In the third channel, no limitation can be
found, so the signal from the third channel can be recorded for further analysis.
UCH1
10v
t
UCH2
10v
t
UCH3
10v
t
Fig. 3.- Spike disturbance over imposed to the signal.
The algorithm of detecting the disturbances is presented in the figure 4. The
first channel is always analyzed with the methods presented in [1] and [2]. If any
disturbances are found, the samples for all three channels is analyzed and checked
for limitation. If a limitation is found on any of the three channels, is then checked
the channel with the lower amplitude and without limitation and this channel is
then recorded. The goal is to record a signal with a maximum dynamic range.
It’s not necessarily to save all three channels because if, for example, a
disturbance with the amplitude higher than 10kV is applied at the input of the
system, in all three channels can be found limitations of the signal. The signal
which is more accurate and reflects the reality is the signal on the third channel.
The most important disturbances in this case is the disturbance with higher
amplitude because their high energy. In the first and second channel may or may
not be found disturbances with smaller amplitudes. In special cases it is useful to
record the signals from all three channels; this is the case in which among the high
voltage spike can be found disturbance with small amplitude around 220V. For
high accuracy analysis is recommended to record all three channels and analyze
the signal later.
CIPRIAN DUGHIR and GABRIEL GĂŞPĂRESC
The system record the entire period of the signal in which is fond the
disturbances.
This method of signal preconditioning and analysis can be used alone for
detecting the singular and symmetrical disturbances in the electrical power system
with the amplitude over 500V. The method is simple: the signal from the first
channel is analyzed, and if any disturbances with the amplitude over 500V are
over imposed to the signal, then a limitation appears on the first channel signal.
Electrical
power network
Acquisition
board
Analyze one
sample for each
channel
Channel 1
voltage limit?
3
Signal analysis
algorithm
3
no
yes
Decision block
Channel 2
voltage limit?
no
yes
Channel 3
voltage limit?
no
Record signal
yes
Fig. 4.- Diagram of the algorithm for detecting and monitoring the disturbances.
The presence of this limitation is an indication that a disturbance is present
in this point. The algorithm is identical for the second and third channel. The
presence of the limitation in the signal shape is always an indication of the
presence of a disturbance. In this way all disturbances with amplitude higher than
500V can be easily detected. The decision block presented in figure 4 can classify
the disturbance depending on their amplitude.
BUL. INST. POLIT. IAŞI, TOMUL LII (LVI), FASC. 5
3. Software application
The software application is written using Microsoft Visual C++ 6. The
main window of the application contains three plots (in the left of the window)
which display on-line the three channels of signal. The signal captured presents a
disturbance with amplitude of 2.5kV. The first and the second channel present a
limitation in their maximum amplitude. In the upper right corner of the window is
displayed a period of the signal with the last disturbance found in the first channel
to be easily visualized. This image is displayed until a new disturbance is found,
and replaced with a new image.
Fig. 5.- Main window of the software application for detection and monitoring the disturbances
in the electrical power systems
The second plot in the right part of the window is the regularity index. This
index is a number representing the presence of a disturbance if his value is
nonzero as is explained in [1], [2] and [3]. This plot is scrolling from right to left,
this means that the last disturbance is displayed in the right of the plot, being a
history of the apparition of disturbances.
The circular plot in the bottom right corner of the window displays the
status of the operations in the circular buffer [1]. The samples from the
acquisition board are stored in the circular memory and then are analyzed.
CIPRIAN DUGHIR and GABRIEL GĂŞPĂRESC
5. Conclusions
The preconditioning circuit presented in this paper is very simple and low
cost. The analysis method proposed in this paper can be used alone, or together
with other methods of analyze, improving their performance. Using this method
together with the method presented in [1], increase the accuracy of detecting the
disturbances with amplitudes higher than 500V at 100%. In this case, the
computing time increase with 10%, due to the supplementary calculations which
are made.
Appendix
*“Politehnica” University, Department of Measurement and Optical Electronics,
Electronics and Telecomunications, Timişoara, Romania;
REFERENCES
1. Ciprian Dughir, Detecting symmetrical disturbances in electrical power systems, lucrările
sesiunii ştiinţifice “Doctor Etc 2005”, Timişoara, September 22, 2005.
2. Traian Jurca, Ciprian Dughir, Monitorizarea perturbaţiilor din reţeaua de joasă tensiune,
lucrările sesiunii ştiinţifice “Electroenergetica”, Sibiu, November 2004.
3. Marcello Artioli, Gaetano Pasini, Lorenzo Peretto, Renato Sasdelli, Fiorenzo Fillippetti,
Low-Cost DSP-Based Equipment for the Real-Time Detection of Transients in Power
Systems, IEEE Transactions on Instrumentation and Measurement vol. 53, no. 4, August 2004
4. Tarlochan S. Sidhu, Accurate Measurement of Power System Frequency Using a Digital
Signal Processing Tehnique, IEEE Transactions on Instrumentation and Measurement vol.
48, no. 1, February 1999
5. Giovanni Bucci, Edoardo Fiorucci, Carmine Landi, Digital Measurement Station for Power
Quality Analisys in Distributed Environments, IEEE Transactions on Instrumentation and
Measurement vol. 52, no. 1, February 2003
6. A.Y. Zayezdny, I. Druckman, Short time measurement of frequency and amplitude in the
presence of noise, IEEE Comput. Applicat Power, vol. 10, Apr. 1997
SISTEM DE ANALIZĂ PE TREI CANALE PENTRU MĂSURAREA PERTURBAŢIILOR DIN
SISTEMELE DE DISTRIBUŢIE A ENERGIEI ELECTRICE
(Rezumat)
Se prezintă un sistem de detectare şi măsurare a perturbaţiilor din sistemele de
distribuţie a energiei electrice ce utilizează un sistem de achiziţie de date pe trei canale şi un
sistem de precondiţionare a semnalelor construit cu ajutorul a trei divizoare de tensiune cu
diferite rapoarte de divizare. Sistemul propus poate fi utilizat şi pentru detectarea perturbaţiilor
simetrice şi nesimetrice cu amplitudini mai mari de 500V ce apar în sistemele de distribuţie a
energiei electrice.