08-10-2012, 02:02 PM
Central Processing Scheme for Power Quality Monitoring
[attachment=35660]
Abstract
Power quality monitoring system is a basis for power
quality analysis, diagnosis and improvement. Power
Quality (PQ) measurement concepts are evolving
from instantaneous metering to continuous
monitoring and recent developments in measurement
technology make PQ monitoring system more
powerful. That is, now it is possible to construct
more flexible, reliable, fast and economical PQ
monitoring system. So this paper presents an
improved PQ monitoring system with central
processing scheme. Proposed system basically
consists of one PQ analyzer and multiple PQ meters.
PQ meter only acts as raw data acquisition system
and PQ analyzer performs all calculations and
analysis algorithm. The proposed system is very
economical especially for large-scale system because
the price of PQ meter can be dramatically lowered in
this scheme. PQ monitoring algorithms to catch
steady-state trends and to detect PQ events are also
proposed. The prototype of this system is constructed
and real-time tests are performed using this system.
Introduction.
Power quality was the ability of utilities to
provide Electric power without interruption
in the past. In recent years due to increase
in critical load and electronic device,
customers require high level power quality
than ever before, so power quality has
become an important concern to
customers as well as
utilities and facilities. Power quality is
different from reliability in that it treats
very short-duration events with a few
cycles or seconds. New PQ problems such
as sag, swell, harmonic distortion,
unbalance, transient and flicker can
impact customer operations,
causing malfunctions and costs on lost
production and downtime. To avoid these
malfunctions and unnecessary costs,
many facilities and large customers have
been required to install PQ monitoring
system [1-2]. The deregulation in power
system is based on competition between the
participants, who enter into contracts
according to their own interests. In this case,
electric power traded in market is
considered as a product which has price and
quality. As a matter of course, the quality of
the electric power must be measured and
evaluated. These facts also increase the
need for PQ monitoring system [3].
Functions of PQ monitoring system
Recent PQ monitoring devices are largely divided
into two kinds. One is the device that is based on the
traditional watt-hour meter or digital protection relay
where PQ analysis algorithm is inserted. The other is
the device that mainly deals with PQ parameters and
events. The main function of the former is the
calculation of electric parameters such as V, I, P,
energy etc. Protection parameters such as
overvoltage, under voltage and interruption are also
calculated. Harmonic analysis is performed if the
user requests that function. The latter follows the
IEEE or IEC standard to classify PQ events and
displays the results with their own panels or PC
connected through serial communication. They
measure power quality, store results and analyze the
results for future use. Recently PQ monitoring
devices are developing into monitoring system that
continuously measures the power quality of a point
and analyzes the trends of power quality. These
monitoring systems will provide such functions as
high speed communication with internet network,
statistical analysis through uninterrupted
measurements and display with web-browser. In near
future, they may also include the functions of power
quality diagnosis.
Conventional system Vs
Proposed system
The structure of conventional PQ monitoring
system is
shown in Fig. 1. It consists of meter device
and PC for display. Meter performs
measuring, processing and
communication. PC displays the results
with graphic user interface (GUI). As
stated in previous section, PQ monitoring
requires large-scale system with multiple
meters in order to analyze power quality
and diagnose PQ problems. For example,
only one meter is not enough to find the
source of sag or harmonic distortion. It
requires more than one meter to diagnose
the PQ problems. So it becomes more
important to construct large-scale PQ
monitoring system. In this case, the price
for installing this system becomes critical
factor. In conventional monitoring
structure, the price of meter is relatively
high and this can be a penalty factor for
system integration [5].
PQ Event Detection
PQ events are classified into 11 events in this paper.
They are listed in Fig. 4. First, in RMS variation, the
RMS values of voltage and current are measured
every half cycle. According to the magnitude and
duration of event, the kind of event is defined. And
then the duration, magnitude, starting time, clearing
time, and the mean value of the event are calculated.
In case of unbalance, the unbalance factor is
calculated. In flicker event, flicker indices such as st
P , lt P are calculated once every 10 minute ( st P ) or
2 hour ( lt P ). In case of transient, MAVSA index
that uses the squared value of the voltage is
calculated to detect transient event. For harmonic
analysis, the magnitudes and phase angles of each
individual harmonic component are measured using
128-point radix 2 FFT. And then total harmonic
distortion (THD), total even harmonic distortion
(TEHD), total odd harmonic distortion (TOHD), and
distortion factor (DF) are calculated. Especially for
current, total demand distortion (TDD) and K-factor
are calculated. Frequency must be measured
accurately because it indicates the balance between
supply and demand in the power system. In the paper,
over-frequency and under-frequency events are
defined. Table IV summarizes the data stored when
each event happens.
Conclusions.
This paper has presented the new
structure of PQ
monitoring system with central processing
scheme. In this system, PQ meter only
performs raw data acquisition and PQ
analyzer performs all PQ monitoring
algorithm. This structure is especially
suitable and competitive for large-scale
monitoring system. In addition, this
system has more flexibility and modularity
than the conventional system. PQ
monitoring algorithm that detects 11
events and captures steady-state trends
also has been implemented. Finally the
prototype of this structure has been
constructed and real-time tests have been
performed using this proposed system
[attachment=35660]
Abstract
Power quality monitoring system is a basis for power
quality analysis, diagnosis and improvement. Power
Quality (PQ) measurement concepts are evolving
from instantaneous metering to continuous
monitoring and recent developments in measurement
technology make PQ monitoring system more
powerful. That is, now it is possible to construct
more flexible, reliable, fast and economical PQ
monitoring system. So this paper presents an
improved PQ monitoring system with central
processing scheme. Proposed system basically
consists of one PQ analyzer and multiple PQ meters.
PQ meter only acts as raw data acquisition system
and PQ analyzer performs all calculations and
analysis algorithm. The proposed system is very
economical especially for large-scale system because
the price of PQ meter can be dramatically lowered in
this scheme. PQ monitoring algorithms to catch
steady-state trends and to detect PQ events are also
proposed. The prototype of this system is constructed
and real-time tests are performed using this system.
Introduction.
Power quality was the ability of utilities to
provide Electric power without interruption
in the past. In recent years due to increase
in critical load and electronic device,
customers require high level power quality
than ever before, so power quality has
become an important concern to
customers as well as
utilities and facilities. Power quality is
different from reliability in that it treats
very short-duration events with a few
cycles or seconds. New PQ problems such
as sag, swell, harmonic distortion,
unbalance, transient and flicker can
impact customer operations,
causing malfunctions and costs on lost
production and downtime. To avoid these
malfunctions and unnecessary costs,
many facilities and large customers have
been required to install PQ monitoring
system [1-2]. The deregulation in power
system is based on competition between the
participants, who enter into contracts
according to their own interests. In this case,
electric power traded in market is
considered as a product which has price and
quality. As a matter of course, the quality of
the electric power must be measured and
evaluated. These facts also increase the
need for PQ monitoring system [3].
Functions of PQ monitoring system
Recent PQ monitoring devices are largely divided
into two kinds. One is the device that is based on the
traditional watt-hour meter or digital protection relay
where PQ analysis algorithm is inserted. The other is
the device that mainly deals with PQ parameters and
events. The main function of the former is the
calculation of electric parameters such as V, I, P,
energy etc. Protection parameters such as
overvoltage, under voltage and interruption are also
calculated. Harmonic analysis is performed if the
user requests that function. The latter follows the
IEEE or IEC standard to classify PQ events and
displays the results with their own panels or PC
connected through serial communication. They
measure power quality, store results and analyze the
results for future use. Recently PQ monitoring
devices are developing into monitoring system that
continuously measures the power quality of a point
and analyzes the trends of power quality. These
monitoring systems will provide such functions as
high speed communication with internet network,
statistical analysis through uninterrupted
measurements and display with web-browser. In near
future, they may also include the functions of power
quality diagnosis.
Conventional system Vs
Proposed system
The structure of conventional PQ monitoring
system is
shown in Fig. 1. It consists of meter device
and PC for display. Meter performs
measuring, processing and
communication. PC displays the results
with graphic user interface (GUI). As
stated in previous section, PQ monitoring
requires large-scale system with multiple
meters in order to analyze power quality
and diagnose PQ problems. For example,
only one meter is not enough to find the
source of sag or harmonic distortion. It
requires more than one meter to diagnose
the PQ problems. So it becomes more
important to construct large-scale PQ
monitoring system. In this case, the price
for installing this system becomes critical
factor. In conventional monitoring
structure, the price of meter is relatively
high and this can be a penalty factor for
system integration [5].
PQ Event Detection
PQ events are classified into 11 events in this paper.
They are listed in Fig. 4. First, in RMS variation, the
RMS values of voltage and current are measured
every half cycle. According to the magnitude and
duration of event, the kind of event is defined. And
then the duration, magnitude, starting time, clearing
time, and the mean value of the event are calculated.
In case of unbalance, the unbalance factor is
calculated. In flicker event, flicker indices such as st
P , lt P are calculated once every 10 minute ( st P ) or
2 hour ( lt P ). In case of transient, MAVSA index
that uses the squared value of the voltage is
calculated to detect transient event. For harmonic
analysis, the magnitudes and phase angles of each
individual harmonic component are measured using
128-point radix 2 FFT. And then total harmonic
distortion (THD), total even harmonic distortion
(TEHD), total odd harmonic distortion (TOHD), and
distortion factor (DF) are calculated. Especially for
current, total demand distortion (TDD) and K-factor
are calculated. Frequency must be measured
accurately because it indicates the balance between
supply and demand in the power system. In the paper,
over-frequency and under-frequency events are
defined. Table IV summarizes the data stored when
each event happens.
Conclusions.
This paper has presented the new
structure of PQ
monitoring system with central processing
scheme. In this system, PQ meter only
performs raw data acquisition and PQ
analyzer performs all PQ monitoring
algorithm. This structure is especially
suitable and competitive for large-scale
monitoring system. In addition, this
system has more flexibility and modularity
than the conventional system. PQ
monitoring algorithm that detects 11
events and captures steady-state trends
also has been implemented. Finally the
prototype of this structure has been
constructed and real-time tests have been
performed using this proposed system