Download monitoring of energy quality for residential consumers

ISSN 1843-6188
Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17)
MONITORING OF ENERGY QUALITY FOR RESIDENTIAL CONSUMERS
Oana Florentina MARIN, Marius Robert GHITA, Traian IVANOVICI, Horia ANDREI
Department of Electrical Engineering, University Valahia Targoviste, Romania
E-mail: [email protected], [email protected], [email protected], [email protected]
Abstract. This paper proposes a real measurement analysis
of non-sinusoidal regime of the residential consumers in
order to identify the equipmenst that pollute and affect the
power quality. Power quality issues important to the
functioning of energy systems as a whole, have become
topical in recent years and of particular importance especially
due to explosive development of equipment and power
electronics technologies and consumers due to the emergence
of increasingly more sensitive to disturbance.
sector and residential electrical network causes important
disturbances that lead to lower levels of power quality
(harmonics, unbalance, flicker, etc.).
The presence of harmonics indicates a distorted current
or voltage wave. The distortion of the current or voltage
wave means that the distribution of electrical energy is
disturbed and power quality is not optimum.
Harmonic currents are caused by non-linear loads
connected to the distribution network. The flow of
harmonic currents causes harmonic voltages via
distribution network impedances and consequently
distortion of the supply voltage.
Devices and systems that cause harmonics are present in
all sectors, i.e. industrial, commercial and residential.
Harmonics are caused by non-linear loads (i.e. loads that
draw current with a waveform that is not the same as that
of the supply voltage). For example, non-linear loads
are:
Industrial equipment (welding machines, arc
furnaces, induction furnaces, rectifiers)
Variable-speed drives for asynchronous or DC
motors
UPSs
Office equipment (computers, photocopy machines,
fax machines, etc.)
Home appliances (television sets, micro-wave
ovens, fluorescent lighting)
Certain devices involving magnetic saturation
(transformers)
The disturbances caused by non-linear loads are
harmonic current and voltage. Non-linear loads draw
harmonic currents that flow in the distribution network.
Harmonic voltages are caused by the flow of harmonic
currents through the impedances of the supply circuits
Keywords: quality of electric energy, real measurements,
LabVIEW application, non-sinusoidal regime.
1. INTRODUCTION
In 1985, the Commission determined that electricity is a
(EC Directive 85/374), and clearly defining the essential
characteristics and test methods to ensure proper
functioning electricity consumers. Produced electricity is
used by different consumers, from the industrial to
household [1]-[4].
Power quality is a concern for energetics, becoming the
subject of numerous studies, both internationally and
nationally, that led to the introduction of rules, standards
and regulations on the parameters of delivery/supply of
electricity. Thus, deviations beyond predetermined limits
void all receivers to normal operation, damage and / or
damage.
Thus, based on studies conducted by specialists in
accordance with international norms, ANRE introduced
performance and quality requirements for both electricity
suppliers and industrial consumers and the like
connected to public networks.
Energy Strategy [4]-[7] is "a complex activity involving
initiation, development and correlation of political
action, economic, technical and ecological to national
energy security, diversification of supply sources both
internal and external, to improve and diversify the forms
of energy production, increase production efficiency and
energy consumption, improving the impact of polluting
energy production and consumption ".
If so not much attention to ensure proper quality of
power given to large industrial consumers are connected
to high voltage networks, the impact it has customers
connected to the low voltage begins to be questioned.
Development of modern industrial technologies,
increasing the share of consumption in the services
2.
NON-SINUSOIDAL REGIME AND QUALITY
OF ELECTRICAL NETWORKS
Troubleshooting power quality is a complex process
which requires energy supplied quality assessment,
monitoring voltages and currents in power points, and by
monitoring disturbances introduced by the consumer to
determine the source that generates symptoms.
Non-sinusoidal regime is only bad consequences on the
functioning of the consumer and overall power system,
the main effects [8]-[10]:
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Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17)
a) affecting the operation of electronic equipment
connected to mains voltage, including the rectifier
control equipment;
b) Introduction of additional errors of measurement
devices, protective relays and distorting ripple control
receivers; measurement errors of their wattmeters (up to
3%) and induction meters (up to 14%) are due to
decrease power factor deforming under k = P / S < cos ϕ ;
c) request beyond established facilities for reactive
power compensation capacitors;
d) Additional loss of power and active power in
electricity networks, because the term apparent power
S = P2 + Q2 + D2
corresponding
increase
PF =
ISSN 1843-6188
P
S
(1)
• Crest factor
The crest factor is the ratio between the value of the peak
current or voltage (Im or Um) and its rms value
CF =
Um
U
(2)
For a sinusoidal signal, the crest factor is therefore equal
to 2 , and for a non-sinusoidal signal, the crest factor
can be either greater than or less than 2 .
In the latter case, the crest factor signals divergent peak
values with respect to the rms value.
• Distortion power
When harmonics are present, the distortion power D is
defined as
(3)
D2 = S 2 − P 2 − Q 2
where S, P, and Q are respectively the apparent, active
and reactive power[11].
- Harmonic spectrum and harmonic distortion
Each type of device causing harmonics draws a
particular form of harmonic current (amplitude and
phase displacement).
These values, notably the amplitude for each harmonic
order, are essential for analysis.
- Individual harmonic distortion
The individual harmonic distortion is defined as the
percentage of harmonics for order h with respect to the
fundamental.
power
deforming D;
e) lower yields due to additional losses of electric motors
and couples pests;
f) additional loading of power system elements (lines,
transformers);
g) the emergence of dangerous overvoltage conditions
for certain harmonic resonance.
Deforming element is a device that produces or increases
the harmonic tension. In Budeanu’s acceptance
deforming elements separate into two categories [11]:
a) distorting elements of class I - powered strictly
sinusoidal voltages or currents produce deformed
phenomena (eg. arc furnaces, rectifiers, electric charge
any pronounced nonlinear character); In other words,
supply with sinusoidal voltage currents produce
deformed (generate harmonic currents);
b) distorting elements of class II - powered by currents
deform the deformation increases (such power lines whose
own up circuit inductance and capacitance-frequency
oscillating harmonic currents close to the network)
capacitors of reactive power compensation installation.
The quality indicators of electricity should allow
measurement / estimate the level of quality at some point
in the network and at a time and comparing information
obtained with the considered optimal or at least tolerated
by most consumers connected to the electrical network.
The number of consumers computerized greatly
increased, with adverse consequences for installation
that are connected.
These include consumer electronic circuit components
and features that have strong nonlinear effects of
deviation in particular, the power curves from the ideal
form, that the sinusoid.
A number of indicators are used to quantify and evaluate
the harmonic distortion in current and voltage
waveforms [12]-[19], namely:
Power factor
Crest factor
Distortion power
Harmonic spectrum
Harmonic-distortion values.
These indicators are indispensable in determining any
necessary corrective action.
• Power factor
The power factor PF is the ratio between the active
power P and the apparent power S.
(
)
I
Uh
100 , I h (% ) = h 100
I1
U1
U h (%) =
(4)
By representing the amplitude of each h-harmonic order
with respect to its frequency, it is possible to obtain a
graph called the harmonic spectrum.
- rms value
The rms value of the voltage and current can be
calculated as a function of the rms value of the various
harmonic orders
n
I =
∑ I h2
(5)
h =1
U =
n
∑U h2
(6)
h =1
where n is the total number of harmonics. Generally
speaking, for a non-linear circuit element the total
number of harmonics n can be different for voltage and
current.
• Total harmonic distortion (THD)
The term THD means Total Harmonic Distortion and is
a widely used notion in defining the level of harmonic
content in alternating signals.
For a signal y, the THD is defined a as:
n
∑ yh2
THD =
h=2
(7)
y1
wher y1 is the first (fundamental) harmonic.
This complies with the definition given in standard IEC
61000-2-2. Note that the value can exceed 1.
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Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17)
According to the standard, the variable h can be limited
to 50. The THD is the means to express as a single
number the distortion affecting a current or voltage
flowing at a given point in the installation. The THD is
generally expressed as a percentage.
- Current or voltage THD
For current harmonics the relation for THD is:
and analysis. The measurement data are transferred into
computer through a high speed PCI highway.
High-performance measurement devices determine very
quickly, almost instantly, deformed shapes of the curves
of current and voltage harmonics and the number and
rank a series of indicators that characterize the intensity
of deforming regime.
In this paper for waveform analysis, harmonics,
diagrams, graphs, we used a three-phase electrical
network port analyzer model CA 8352 – CHAUVIN
ARNOUX (figure 2), measurements were made in the
project PREDEX - POSDRU/CPP107/DMI1.5/S/77497.
n
∑ I h2
THDi =
h=2
(8)
I1
The equation below is equivalent to the above, but easier
and more direct when the total rms value is available
2
 I 
THDi =   − 1
 I1 
(9)
An analogue relation exists for voltage THD
n
∑U h2
THDu =
3.
h =2
U1
 U
= 
Um
2

 −1


(10)
LabVIEW APPLICATION FOR
MONITORING THE ENERGY QUALITY
FOR RESIDENTIAL CONSUMERS
Power quality monitoring involves collecting and
processing the voltage and current signals in different
points of power system.
Power quality monitoring using data acquisition systems
impose certain requirements on the system and tehnical
process used. These include hardware and software
structures, the project dedicated to certain types of
applications, in accordance with industry standards. Current
development of hardware and software technology has
made possible the deployment of real-time data acquisition,
flexible, with multiple channels [20]-[23].
A monitoring system can generally include three
components (Figure 1):
1. Subsystem input signal conditioning and acquisition;
2. Digital processing and storage subsystem;
3. System user interface.
Figure 2. Three-phase electrical analyzer
model CA 8352 - Chauvin ARNOUX
The following are the harmonic spectrum of some
equipment used for residential consumers: television,
washing machine, refrigerator, lamps with minimum
power consumption (economics), computer, air
conditioning, microwave oven.
All these receivers with less distortion effect or intense,
especially the current curves are sources of harmonic
currents which pollute and affect power quality, reason
why the measurements presented in this article were
made to the public network.
Among the indicators that characterize the intensity of
deforming regime, according to the purpose of this
communication, the actual values of the curve is kept
current and voltage distorted and harmonic spectrum,
which can reach up to rank 50, i.e. 2500 Hz.
An indicator that expresses very well the intensity of
regime is the distortion factor THD deforming.
In figure 3 are shown for a few standard consumers the
deformed current curves, the spectrum of current
harmonics and distortion factors.
According to standard EN 50160 harmonics are allowed
to rank 25 and distortion factor ≤ 8%, 95% of the week.
It is found that the refrigerator is less distorted (THD =
7.24%), air conditioning (THD = 17.74%), microwave (THD
= 36.19%), washing (THD = 53.45 %) TV (THD = 94.42%),
computer (THD = 109.69%), maximum deformation effect,
is that given the economic lamp operation (THD = 111.07%)
Figure 1. The main components of a monitoring system
The measurement of the current and voltage harmonics for
the non-sinusoidal generator and for each element of the
circuit are made it using LabVIEW application [24], [25].
LabView is a software packet for analysis and virtual
instrumentation meant to make easier the data acquisition
31
Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17)
Non-linear
consumer
Computer
Current waveform
Spectrum
ISSN 1843-6188
THD
109,69%
Fluorescent
lamps
111,07%
Television
94,42%
Microwave
ovens
36,19%
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ISSN 1843-6188
Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17)
Air
conditioning
17,74%
Refrigerator
7,24%
Washing
machine
53,45%
Figure 3. Harmonics characteristics of residential consumers
4.
For each problem as there are many and varied ways to
solve their specific limits required for each consumer.
Obviously, their introduction requires an analysis of a
cost - benefit, the investment required to reveal their
effects on growth and economic efficiency for
consumers.
CONCLUSIONS
Most modern electronic equipment used in switching
power supplies (SMPS).
Advantage - for equipment manufacturer - is that the
size, cost and weight are significantly reduced and the
power unit can be made in almost any required form
factor.
Disadvantage - in addition to other types - is that instead
of DC source, absorbs a current of mains power pulses
as containing a large amount of harmonics of rank 3 and
higher and higher frequency components harmonic.
So consumers in the home computer network low
voltage injected harmonic currents, ideal curves greatly
distortig the fundamental (50 Hz).
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