PAPER
Title
1/7
A Concept of Compatibility Level for Voltage Dips and Short Interruptions in LV Power Supply Systems
Registration Nº: (Abstract)
295
Company
Department of Electrical Power Engineering, FEEC, Brno University of Technology, Czech Republic
Jaromir Bok
Authors of the paper
Country
Czech Republic
e-mail
xbokja00@stud.feec.vutbr.cz
Jiri Drapela
Czech Republic
drapela@ieee.org
Name
Key words
Voltage dip, short interruption, compatibility level, immunity curve
[Nota:
The voltage dips and short interruptions in power supply systems are disturbances affecting operation of all supplied electrical appliances. In consequence of origin, such voltage events are of
stochastic character and cannot be fully eliminated, as well as there is practically impossible to
ensure unlimited immunity of electrical devices to such disturbances. Nevertheless a complex system providing compatible environment from point of view of the voltage dips and short interruptions has not been designed yet. The current situation in this field presents a large compatibility
gap related to missing compatibility concept that should be based on clearly defined compatibility
levels for typical electromagnetic environments which still do not exist. The paper is focused on a
proposal of the compatibility level concept for voltage dips and short interruptions in low-voltage
power supply system. The proposed compatibility levels are determined by the minimum immunity
curve and allowed number of events exceeding the curve for each of three basic environments.]
PAPER-295-17032010.DOC
1/1
A Concept of Compatibility Level for Voltage Dips and Short Interruptions
in LV Power Supply Systems
Jaromir Bok1), Jiri Drapela2),
BUT, FEEC, Department of Electric Power Engineering, Technicka 8, 61600 Brno. Czech Republic
www.feec.vutbr.cz/UEEN, 1) email: xbokja00@stud.feec.vutbr.cz , 2) email: drapela@ieee.org
ABSTRACT
2 BASE EMC CONCEPT
The voltage dips and short interruptions in power
supply systems are disturbances affecting operation
of all supplied electrical appliances. In consequence
of origin, such voltage events are of stochastic character and cannot be fully eliminated, as well as
there is practically impossible to ensure unlimited
immunity of electrical devices to such disturbances.
Nevertheless a complex system providing compatible environment from point of view of the voltage dips and short interruptions has not been designed yet. The current situation in this field
presents a large compatibility gap related to missing
compatibility concept that should be based on clearly defined compatibility levels for typical electromagnetic environments which still do not exist. The
paper is focused on a proposal of the compatibility
level concept for voltage dips and short interruptions in low-voltage power supply system. The proposed compatibility levels are determined by the
minimum immunity curve and allowed number of
events exceeding the curve for each of three basic
electromagnetic environments.
Electromagnetic compatibility (EMC) deals with
problems of electric appliances cooperation in the
same environment. There are a significant amount of
problems with mutual cooperation of many types of
appliances. Generally it is possible to say that each
electric appliance conform to EMC requirements if it
does not affect other appliances operation and it can
work continuously in the environment where the
disturbance is.
In public supply networks there are grate number
of various electromagnetic disturbance types, voltage dips and short interruptions are ones of them.
The voltage dips and short interruptions may be
specified as a low frequency conducted electromagnetic disturbance. The voltage dips and interruptions
can be of electric or weather condition causes. Than
the voltage dips and short interruptions are assumed
to have a stochastic character and cannot be fully
eliminated. The appliances response on such voltage
event differs in dependence on the appliance type
and event parameters. Nevertheless the voltage dips
and short interruptions have negative effects to connected appliances operation.
There are only three possibilities to reduce negative effect of voltage dips. The first one is the reduction of voltage dips occurrence in public supply
networks (eventually reducing of disturbances level); the second one is the increasing of the appliances immunity level and the third one is combination of previous ones. Choosing of the first variant
is not a good way, because it requires huge financial
investments to improving of power supply stability
in the customers’ connection points and as it was
mentioned before voltage dips and short interruptions cannot be fully eliminated. Choosing of the
second variant is not a good way as well, because it
means improving of all appliances immunity levels
and this way requires also huge financial investments. Bigger costs to developing and producing of
more immune appliances affect their price and interest about these appliances falls down. And as it
results from EMC principles it is not possible to
manufacture absolutely immune equipment or appliance. The correct way is the third possibility – it
is coherence between the first and the second possibilities and it is shown on Figure 1.
Keywords: voltage dip, short interruptions, compatibility level, immunity curve
1 INTRODUCTION
Electric appliances have declared a specific voltage
conditions for their usage in which the manufacturers guarantee their correct function. Especially sinewave supply voltage of rated frequency and RMS
value should be ensured. More precisely there is a
set of others voltage parameters that should be held
on permitted tolerances as well. For example that set
of voltage parameters and their allowed deviation
limits is given in the standard EN 61000-2-2 [2] for
public distribution LV systems
If the voltage parameters exceed their permitted
tolerances, correct operation of any electric appliances connected to supply network may be endangered. In many cases it results in failure of a
production process and resulting economic loss. The
structure of the power supply system is very complicated (it contains lots of interconnected elements)
and that is why it is not possible to ensure all voltage
parameters to be in tolerable limits for all the time.
For example, each appliance switching causes the
change of network current which creates variable
value of voltage drop on the network impedance.
1
than the compatibility level for public supply networks in Class 2.
Class 2 – is typical for Points of Common Coupling
(PCC) and some factories supply points. In this class
there are the most of domestic and office electric
appliances. These appliances have no special supply
protections.
Class 3 – is typical only for Internal Points of
Coupling (IPC) in industries. The electromagnetic
disturbance level is taken to be much greater than in
public supply networks and that is why the immunity level of connected appliances has to be higher
than appliances immunity level in Class 2. Compatibility level should be higher in comparison with
Class 2.
Figure 1 Optimal appliances immunity level in context with dimension of electromagnetic disturbance
occurrence [2]
3.1.2 Voltage level
The compatibility level should appear from voltage
level of power supply. In the supply system there are
following voltage levels: low voltage (LV), medium
voltage (MV), high voltage (HV) and extra-high
voltage (EHV). Of course the compatibility level
should be different in various voltage levels of
supply systems.
As Figure 1 shows the disturbance emissivity
level in the supply system and the appliances immunity level can be depicted in principle by two
curves, whereas point of curves crossing represents
in this case the compatibility level for given disturbance phenomenon and electromagnetic environment. The third possibility ensuring EMC consists in
finding of optimal position of both curves (emissivity level curve and immunity level curve) – it means
adequate financial investments given onto improving
of appliances immunity level as well as onto reducing of disturbance level in supply networks. The
compatibility level means the disturbance emissivity
level, which would not be exceeded in more than 5%
of events for public power supply systems. Appliances immunity level should be equal or better
than declared compatibility level [3].
3.1.3 Immunity curves of electric appliances
Compatibility levels should be assessed in terms of
electric appliances immunity to voltage dips and
short interruptions. In the case of voltage dips and
short interruptions the appliances immunity use to be
expressed by immunity curves. In the supply system
there are many types of electric appliances which
more or less depend on the quality of power supply.
Especially devices with modern power electronics
are the most threatened appliances. The appliances
immunity testing is not a simply process; it requires
a perfect knowledge of function principles of tested
appliance. Therefore its immunity depends on many
factors which can be divided to the voltage phenomena, the appliances phenomena and others nonelectric phenomena [6].
The voltage phenomena category contains all
voltage parameters before, during and after voltage
dip or short interruption, such as RMS voltage value,
voltage wave distortion by harmonics, initial voltage
phase angle at the dip or interruption beginning,
shape of voltage event different from rectangular,
etc. The appliances phenomena category contains
especially method of appliance connection to supply
system, actual appliance process conditions, such as
load of tested appliance. The non-electric phenomena category contains all non-electric parameters
which can influence some of appliance electric parameters. In this category there is temperature, humidity, air pressure, altitude, vibration presence etc.
More information about influence of each voltage, appliances and non-electric parameters to appliances immunity is written in [6][7][8][9].
3 COMPATIBILITY LEVEL
ASSESSMENT
3.1 Conditions for compatibility level assessment
For correct assessment of compatibility level some
important conditions must be had in mind. Omission
of the under-mentioned conditions negatively affects
the application of them with electromagnetic compatibility problems.
3.1.1 Electromagnetic environment
The compatibility level nearly relates to type of the
electromagnetic environment in which the electric
appliances are declared to use. In accordance with
[4] there are following three common classes of
electromagnetic environments:
Class 1 – is typical for appliances which need continual supply. Very sensitive devices, laboratory or
emergency equipment, etc. fall into this class.
Supply use to be backed up by UPS. Immunity of
appliances connected to this class has lower level
than immunity of standard used appliances is and
that is why the compatibility level should be better
2
3.1.4 Voltage dips and short interruptions occurrence in real supply systems
Of course the compatibility level should appear from
voltage dips and short interruptions which are assessed in real power supply system. As it was mentioned before, the voltage dips and short interruptions are unpredictable phenomena which are associated with faults, switching operations in supply
networks, etc. To reliable assessment of voltage dips
and short interruptions occurrence in the real supply
system it is possible to use the statistical results from
short voltage events monitoring systems installed in
recent years. Regarding short voltage events initiation reasons very similar dips and interruptions occurrence is expected in the following years and this
process does not cause marked deficiencies.
In agreement with [1][2][4][10] and [11] the
short voltage events as voltage dips and short interruptions are described by two fundamental parameters – minimal value of residual voltage during
dip/interruption 1 and dip duration. Description of
voltage dips/interruptions by only these two parameters supposes that all voltage events have a rectangular shape. Many occurred voltage dips in the electric
supply system have not strictly rectangular shape,
they have other shapes, which are not possible to
describe by only these two parameters. In the case of
big induction motors starting the originated voltage
dips have approximately saw shape. Because voltage
event recorders are set to record only residual voltages and event durations (in according with EN
standards) this fact brings a lot of inaccuracies into
the voltage events classification. To improve voltage
events classification, assessment of some coefficients to conversion of real voltage events into basic
two-parameter events is necessary to introduce,
whereas the converted voltage events should be of
the same effect on electric appliances as the original
real voltage event.
3.2 Proposed compatibility levels
In agreement with above mentioned conditions the
following compatibility level for the low-voltage
electric power supply system and for single phase
voltage events was proposed. Figure 2 shows proposed compatibility level for all three classes of
electromagnetic environment together with the immunity curves of many types of electric appliances.
Compatibility levels indicate the boundary between
acceptable and unacceptable appliances function
change whereas the unacceptable function change
during immunity tests is mostly defined by function
criterion C 2 [10]. The boundary means that appliance work properly or with acceptable function
change yet.
compatibility level - class 1
compatibility level - class 2
compatibility level - class 3
Voltage V/Vn (%)
100
80
60
40
20
0
1
10
100
1000
10000
Dip duration ∆t (ms)
Figure 2 Immunity curves of many types of electric
appliances (black lines) measured and declared by
many authors [6][7][8] and the proposed compatibility levels for known classes of electromagnetic
environment
The proposed compatibility levels showed on
Figure 2 are expressed by coloured lines which divide the whole area into the particular zones I, II, III,
IV (shown on Figure 3). Zone signed I belongs to
class 3; zone II belongs to class 2 and zone III belongs to class 1 of electromagnetic environment.
Zone IV is unspecified.
The immunity levels have been proposed considering the voltage event zones of origin established
in section 3.3. In other words the compatibility level
for each electromagnetic environment type was
created using a starting method where the devices
falling into a class are expected to be immune to
voltage events of specific parameters range accordant with kind of faults.
Each electric appliance should be used in the relevant class of electromagnetic environment which
is determined by producers. For example, if the
immunity curves of some electric appliance belong
into zone III – it should be used only in the class 1 of
electromagnetic environment. However the appliance which immunity curves belong into zone II
can be used in class 2 or class 1 of el. environment.
1
Residual voltage during the short voltage interruption should be zero. In many occasions the voltage
limit for short interruption recording use to be upper
than zero, it use to be 1% (5%, 10%) of reference
voltage Vn [11]. It is caused by two different definitions of voltage interruption. From point of view of
electromagnetic compatibility standards
series
[1][2][4][10] the short interruption is the short duration voltage dip to zero value. Because it is very
difficult to measure values about zero the analyzers
are mostly set to limit 1% (5%, 10%) of Vn. From
physical point of view the interruption is disconnection of electric circuit so there is no voltage on the
load. The conflict between these two definitions of
short voltage interruptions causes a different interpretation of the same phenomenon by many authors
and affects the reproducibility of their results.
2
The function criterion C is defined as a momentary
loss or change of function or technical parameters
where human operator intervention is required for
nominal state recovery.
3
Likewise appliance with immunity curves falling
into zone I can be used in all of three classes of el.
environment. The immunity curves of no appliance
should belong into zone IV.
100
Zone of acceptable voltage tolerances
90
IV
80
Voltage V/Vn (%)
have the information about their origin saved in their
parameters and it is possible to subsequently specify
voltage dip origin with relatively great accuracy. Of
course that voltage dips and short interruptions (generally voltage events) are described only by value of
residual voltage and dip duration but both parameters change along the voltage dip/short interruption
origin.
In accordance with the previous text it is possible
to determine several zones which characterize various origins of voltage dips and short interruptions.
Dip origins separation is depicted on Figure 5 and
individual zones are described in Table 1.
70
60
50
40
III
30
20
II
I
10
0
0,01
0,1
1
10
Dip duration ∆t (s)
100
1000
Figure 3 Compatibility levels proposed for all three
types of electromagnetic environments
100
90
Voltage V/Vn (%)
80
As it is obvious the proposed compatibility levels on
Figure 3 for all three classes of electromagnetic
environment hardly increase to 90 percents of nominal voltage in the time of 60 seconds of dipduration. There is a simple explanation for it. In the
point of electric appliances view the voltage dip with
60 seconds duration is considered as a permanent
voltage decrease in which the all electric appliances
should be work continually. The value of 90 percent
of nominal voltage is the minimal allowed permanent voltage value in the electric power supply system. In other words the voltage value 90% of V n
should guarantee the failure-free work of all connected electric appliances.
In case of need to imply heat or other effects of
voltage dips with longer durations into compatibility
levels it was proposed the second variant of compatibility levels – it is shown on Figure 4. In the 10
second point of dip duration the compatibility levels
for all three classes of electromagnetic environments
hardly increase – to 70% of V n for class 3, to 80% of
V n for class 2 and class 1 of elmag. environment.
100
Voltage V/Vn (%)
50
40
III
I
II
10
0
0,01
0,1
1
10
Dip duration ∆t (s)
100
M
R
60
40
P
L
S
30
20
0,1
1
10
100
1000
Table 1 Description of voltage dips and short interruptions zones of origins
Zone Dip / interruption cause
Zone of voltage dips caused by start of
Z
large loads
Long-duration voltage dips usually caused
N
by unbalanced loads (single phase loads
in three-phase supply system)
Voltage dips usually caused by insuffiR
cient dimensioning of grid elements or by
improper setting of voltage regulators
Voltage dips in the point of supply netP
work between generator and point of short
circuit occurrence
Voltage dips between fault and power
O
generation relate to fault tripping with
short time delay of auto-reclosing
The same as zone O with middle time
M
delay of auto-reclosing
The same as zone O with long time delay
L
of (auto) reclosing
S
Non-specific dip reasons
Short-duration voltage interruptions behind a fault in direction from power genT
eration related to short circuits tripping
with short time delay of auto-reclosing
The same as zone T with middle time
U
delay of auto-reclosing
The same as zone T with long time delay
V
of (auto) reclosing
Long duration voltage interruptions in the
W
point of supply network behind short
60
20
O
NL NR
T U Dip duration ∆t (s) V
W
Figure 5 Areas of voltage dip and short interruption
origins along with voltage events recorded in real
supply network during one year period
70
30
ZM
50
0
0,01
IV
80
ZO
10
Zone of acceptable voltage tolerances
90
ZP
70
1000
Figure 4 Other variant of proposed compatibility
levels
3.3 Zones of voltage dips and short interruptions origins
As it was mentioned in Chapter 2, voltage dips and
short interruptions can be initiated by lots of different reasons which occur in public supply networks.
During a lot of studies about short voltage events in
the public supply systems and their origins it was
detected that all voltage dips and short interruptions
4
nally adopted for events occurrences restrictions, if
ever, in the following there is a proposal for the
events limitation sorting.
The project of restriction of voltage events frequency occurrences and its implementation into
EMC standards results from the proposed zones of
voltage dips and short interruptions origins. Each
zone is divided into several other subzones which
also correspond with proposed compatibility levels
(shown on Figure 7).
The each subzone is signed by a unique code
whose explanation is showed in detail on Figure 8.
Figure 8 shows that each subzone has assigned a
maximal limit of occurred voltage events in two
time frames – in time one year and in time a week
(optionally a day), whereas both limits have to be
observed together. One-day time limit was chosen to
restrict the voltage dips and short interruptions
which originate in sequence with short time intervals. In most cases these sequences of voltage dips
do not evoke the appliances failures due to appliances inability to properly work during longtime
or deep voltage dips. The sequences of voltage dips
affect all connected appliances especially by extreme heat stress.
circuit in the generator point of view.
Network services operating start by handle switching.
Causes Z and P combination
Causes Z and O combination
Causes Z and M combination
Causes N and L combination
Causes N and R combination
ZP
ZO
ZM
NL
NR
Dip origin zones correspond with proposed compatibility levels as it is shown on Figure 6.
100
90
Voltage V/Vn (%)
80
ZP
ZO
ZM
NL
P
O
M
L
R
NR
70
60
50
40
S
30
20
10
0
0,01
0,1
1
10
100
1000
T U Dip duration ∆t (s) V
W
Figure 6 Zones of voltage dips and short interruptions origins and theirs relationship to proposed
compatibility levels
3.4 Restrictions of voltage events frequency
occurrences
In accordance with European EMC standards
[1][2][4][10][11] the voltage dips and short interruptions have two basic parameters for their description
– residual voltage during dip and dip duration. In
addition to both parameters voltage dips and interruptions may have many other parameters, which
improve voltage events description; the frequency of
their occurrence is one of the most important. The
frequency of voltage dip (interruption) occurrence
indicates the number of voltage dips and interruptions which occur in specified time period. The standard time period for classification of dips frequency
occurrence is one year. Currently this parameter has
only information character and it is used only to
statistical purposes.
In the general point of view, the compatibility
level represents for given type of disturbance and
compatibility environment the minimum immunity
level of appliances and maximal disturbance level in
the environment. Generally accepted allowed interference is in 5% of cases or for %5 of time for public distribution power systems. On the basis of this
prime rule ensuring EMC with respect to economical
optimization, there is permissible that just 5% of all
recorded voltage dips and short interruptions can
exceed relevant compatibility level, can be under
the compatibility level curve, respectively. Nevertheless such voltage events are extraordinary type of
disturbance phenomenon and the described method
for voltage dips/interruptions restrictions can not be
obviously used because of consequent immoderate
massive investments. Whatever method will be fi-
100
90
Voltage V/Vn (%)
80
70
60
X_ZM_1
(r,d)
X_ZP_2(r,d) X_ZO_2(r,d) X_ZM_2
(r,d)
X_ZP_1(r,d) X_ZO_1(r,d)
X_ZM_3(r,d)
X_ZM_4(r,d)
X_P_1(r,d)
X_O_1(r,d) X_M_1
(r,d)
X_M_4(r,d)
X_P_2(r,d)
X_O_2(r,d) X_M_2
(r,d)
X_M_5(r,d)
X_P_3(r,d)
X_O_3(r,d) X_M_3
(r,d)
X_M_6(r,d)
X_NL_1(r,d) X_NR_1
(r,d)
X_S_1
X_L_1(r,d)
(r,d)
X_R_1(r,d)
X_S_5(r,d)
X_R_2
(r,d)
X_S_9
(r,d)
X_S_2
(r,d)
X_S_6(r,d)
X_S_10
(r,d)
X_L_3(r,d)
X_S_3
(r,d)
X_S_7(r,d)
X_S_11
(r,d)
X_L_4(r,d)
X_S_4
(r,d)
X_S_8(r,d)
X_S_12
(r,d)
X_L_2(r,d)
50
40
30
20
10
X_T_1(r,d)
0 X_P_4(r,d)
0,05
0,01
0,1
0,3
X_U_1
(r,d)
X_U_2(r,d)
1
X_V_1(r,d)
10
60
Dip duration ∆t (s)
X_W_1
(r,d)
100
180
X_W_2(r,d)
1000
X_W_3
(r,d)
3600
10000
Figure 7 The general concept of compatibility levels
for all three electromagnetic environments types
together with frequency of voltage dips and short
interruptions occurrences restrictions
Figure 8 Detail of unique code for each subzone
Figure 7 and Figure 8 also show that restriction
limits of voltage events occurrences will not be
identical in the all three classes of electromagnetic
environments. For each class of electromagnetic
environment (and corresponding compatibility level)
there are relevant only restrictions in subzones under
the compatibility level curve. Nevertheless measuring and recording of voltage events in subzones
above the compatibility level curve is recommended.
5
In some countries the voltage interruptions with
duration time more than 180s are assessed by a special legislation (National directives, laws, etc.). In
such case the corresponding limit should not be
applied. Nevertheless the recording of these interruptions is recommended again (especially for statistical purposes).
[4] EN 61000-2-4 Electromagnetic compatibility
(EMC). Environment. Compatibility levels in
industrial plants for low-frequency conducted
disturbance.
[5] Djokic, S., Milanovic, J.V.: Sensitivity of Electrical Equipment to Voltage Sags and Short Interruptions. Recommendation for Testing.
Electrical Power Quality and Utilization Journal, Vol. XI, No. 1, 2005, p.17-32.
[6] Bok, J., Drápela, J., Šlezingr, J., Pithart, J.:
Light Sources Immunity to Short Voltage Dips
and Interruptions. In Proceedings of 20th International Conference on Electricity Distribution.
Prague,
Czech
Republic,
2009.
ISBN: 978-1-84919-126-5.
[7] Drápela, J., Bok, J., Toman, P.: Personal Computers Immunity to Short Voltage Dips and Interruptions. In Proceedings of 13th International
Conference on Harmonics and Quality of Power. University of Wollongong, Australia, 2008.
ISBN: 978-1-4244-1770-41-6.
[8] Stephens, M., McGranaghan, M., Bollen, M.:
Evaluating voltage dip imunity of industrial
equipment. Semi F47 – Voltage Sag Immunity
Testing, EPRI PEAC, Power Quality Solutions.
[9] EN 61000-4-11 ed.2 Electromagnetic compatibility (EMC). Testing and measurement techniques – Voltage dips, short interruptions, and
voltage variations immunity tests.
[10] EN 61000-2-8:2000 Electromagnetic compatibility (EMC). Section 8: Voltage dips and short
interruptions on public electric power supply
systems with statistical measurement result.
4 CONCLUSION
The voltage dips and short interruptions can not be
totally eliminated in power systems as well as it is
not possible to ensure unlimited appliances immunity to such disturbance phenomenon. Moreover the
disturbance level is generally higher than a possible
immunity of appliances. In spite of evident incompatibility a simple method for preliminary estimation
of the compatibility level for voltage dips and interruptions in low-voltage public distribution systems
was proposed. Thus a needful interconnection of the
electrical appliances immunity testing and the voltage events measurement was realized and related
deficiencies were discussed. Then a compatibility
levels were introduced on the basis of chosen appliances immunity curves and of voltage dips and
interruptions origins analysis. The fundamental
premises about the electromagnetic compatibility
coordination are presented simultaneously.
The paper just gives a proposal of a possible approach to solve one of many electromagnetic compatibility problems in electric supply systems. Proposed compatibility levels and related requirements
on appliances immunity and voltage dips and interruptions occurrence restrictions should not be strictly observed. One of the aims of this paper is to refer
necessity of well-judged determination of the compatibility levels.
BIOGRAPHIES
Jiri Drapela received his M.Sc. and Ph.D. in Electrical Power Engineering from Brno University of
Technology in 1999 and 2006, respectively. He is
currently an associate professor at the same university. His main research interests are power quality and
low-frequency conducted disturbances, especially
immunity, emission of electrical appliances and
power quality measurement techniques.
ACKNOWLEDGEMENT
This paper contains the results of research funded by
the Ministry of Education, Youth and Sports of the
Czech
Republic
under
project
No.
MSM0021630516.
Jaromír Bok received the M.Sc. in 2007 at Brno
University of Technology at the Department of Electrical Power Engineering of the Faculty of Electrical
Engineering and Communication and currently is the
PhD student at the same university. He deals with
power quality and low-frequency disturbances in
public supply networks and with appliances immunity to short voltage events.
REFERENCES
[1] EN 50160 Voltage characteristics of public
distribution systems.
[2] EN 61000-2-2 Electromagnetic compatibility
(EMC). Part2-2: Environment. Compatibility
levels for low-frequency conducted disturbances and signalling in public low-voltage
power supply systems.
[3] IEC 1000-2-1 Electromagnetic compatibility
(EMC). Part 2: Environment. Section 1: Description of the environment – Electromagnetic
environment for low frequency conducted disturbances and signalling in public power
supply systems.
6