dimensions, markings and other construction requirements
TRANSCRIPT
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The growth of non-linear loads and renewable power generation in modern electrical
distribution networks are the new normal operating conditions for electrical power
meters. The result of these loads – distorted waveforms and various power quality
phenomena – make it necessary to regularly reevaluate and revise the standards and
requirements that continue to guide new power meter designs. This is most notable
in the latest ANSI C12.20-2015 standard, particularly its new accuracy class 0.1 (and
upcoming accuracy class 0.1S, expected to be added in IEC 62053-22 edition 2).
The American National Standards Institute (ANSI) coordinates the development and
use of voluntary consensus standards in the United States and represents the needs
and views of U.S. stakeholders in standardization forums around the globe. The
Institute is the sole U.S. representative and member of the two major non-treaty
international standards organizations, the International Organization for
Standardization (ISO), and, via the U.S. National Committee (USNC), the
International Electrotechnical Commission (IEC)1.
Even though the compliance with ANSI standards is voluntary, most North American
utilities and utility commissions use the ANSI metering standards as reference and
the basis for their revenue (billing) meter testing requirements.
In recent years both ANSI C12.1 and ANSI C12.20 metering standards have been
revised with the intent to bring them up to date with the progress of technology and
the changing regulatory environment.
This white paper discusses the major changes introduced in the latest revisions of
the ANSI C12.1-2014 and ANSI C12.20-2015, and their impact on the new meter
testing, and new meter type approvals. Only requirements applicable to energy
meters are discussed.
The ANSI C12.1-2014 (American National Standard for Electric Meters — Code for
Electricity Metering) covers all types of electricity revenue meters and other
instruments such as demand meters, pulse devices, and auxiliary devices. This
standard specifies the requirements common to all ANSI meters, such as reference
conditions, design acceptance test procedures, insulation tests, electromagnetic
compatibility tests, environmental tests and mechanical tests. In particular, the
performance requirements for active a.c. energy meters of accuracy classes 1 and
0.5 are also specified.
The ANSI C12.20-2015 (American National Standard for Electric Meters for
Electricity Meters – 0.1, 0.2 and 0.5 Accuracy Classes) references a number of
common meter requirements, test and test conditions from ANSI C12.1, and
contains particular performance requirements for active a.c. energy meters of
accuracy classes 0.1, 0.2 and 0.5. It applies only to Blondel Theorem compliant
meters, i.e. meters implementing N-1 watt-meter elements for N wires of the
measured poly-phase electrical system. Where differences exist between ANSI
C12.1 and ANSI C12.20, the more demanding requirements of higher accuracy
classes in ANSI C12.20 prevail over the specifications of ANSI C12.1.
Both ANSI C12.1 and ANSI C12.20 reference common meter construction
requirements given in ANSI C12.10 2015 (American National Standard for Electric
Meters for Physical Aspects of Watthour Meters – Safety Standard). This standard
specifies the electrical connections of the meter service terminals, pertinent
1 «Introduction.» American National Standards Institute - ANSI. American National Standards Institute.
Web. 12 Apr 2018. https://www.ansi.org/about_ansi/introduction/introduction?menuid=1
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dimensions, markings and other construction requirements for both socket and
bottom connected meters.
While the ANSI meter standards contain some safety tests and requirements, such
as insulation tests, the general product safety and electrical safety requirements for
socket (type S, or S-base) and bottom-connected (type A, or A-base) meters are
covered in UL 2735 (Standard for Safety for Electric Utility Meters) and its Canadian
equivalent, UL 2735C, which, at this paper’s publication date, is under development.
Both ANSI and IEC metering standards have been used for many decades: the first
American electricity metering standard was published in 1910, while the IEC
Technical Committee 13 (TC13) is one of the first technical committees established
by IEC in the 1920s. Today the TC13 has 33 participating countries and 16 observer
countries, representing expertise of utilities, equipment manufacturers, test
laboratories, and legal metrology organizations.
The evolution of IEC and ANSI series of metering standards has been supported by
participation from experts within equipment manufacturers, regulators, testing
laboratories and electrical utilities.
The most obvious difference between a typical ANSI meter and a typical IEC meter
is form factor: ANSI meters (Figure 1) are round and designed to fit into a
standardized installation sockets, whereas IEC meters (Figure 2) are rectangular
and designed according to the DIN specifications for wall-mounting or DIN-rail
mounting, with terminal blocks for stripped wires.
ANSI and IEC series of standards share many analogous tests and requirements -
they both specify performance tests such as starting current, creep, and accuracy
over a range of load currents, voltages, and power factors. Both series of standards
also specify immunity to external influences such as electromagnetic phenomena,
environmental conditions and mechanical stresses. However, many of the less
obvious differences may be identified in the performance specifications, test
conditions, construction requirements, and testing methodology.
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ANSI standards define values of maximum meter current: 2A, 10A, 20A, 200A, 320A
– values which are the designations of the meter current classes. All the other load-
based performance requirements are based upon that classification. The accuracy
of ANSI meters is evaluated with respect to ‘reference conditions’. A ‘reference
condition’ is a load current test point that may be the current value known as ‘test
amps’ (TA), or a different reference current value specified for an individual test. The
values of the reference current test points may vary depending on the meter current
class. Meter accuracy at each reference test point must be “as close as practical to
zero error”2 3, with limits set out for each accuracy class.
The IEC standards do not use a current class designation, but instead define the
meter nominal (or rated) current value In for transformer operated meters, and the
base current Ib for directly connected meters. These load current operating points
are used as reference values for other load-based performance tests. For IEC
meters the maximum current Imax is specified as “preferably an integral multiple”4 of
In (or Ib), with a minimum permissible value of 1.2 In (or Ib). The preferred values for
In are: 1, 2, 5 A. The preferred values for Ib are: 5, 10, 15, 20, 30, 40, 50, 63, 80,
100, 125 A.
The accuracy of IEC meters is evaluated with respect to a reading of a reference
meter, with a permissible displacement of the zero-error line defined for each
accuracy class, as means of correcting errors of measurement resulting from
uncertainty of equipment calibration and other parameters capable of influencing the
measurement results;
An approximate, high-level correspondence between ANSI and IEC series of
metering standards are presented in Table 1:
2 ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5 Accuracy
Classes
3 ANSI C12.20-2010 American National Standard for Electricity Meters— 0.2 and 0.5 Accuracy Classes
4 ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5 Accuracy Classes
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Notes:
A more detailed comparison of these standards in beyond the scope of this paper.
“Most of the specifications in ANSI C12.1-2014 have been retained from the
previous edition. Changes to the temperature rise test were made to make testing
consistent with the tests in the meter socket standard, ANSI C12.7. The ANSI
C12.1-2014 section 5, Standards for new and in-service performance, and Appendix
D were extensively updated to reflect current practices. For several of the tests,
specific details for successful tolerance criteria have been modified, and test
requirements for bidirectional metering have been added. Some definitions were
also added and references to external documents were updated.”5
The existing ANSI C12.20 standard – published in 2010 – was broadened by the
ANSI C12.20 -2015 edition “to allow three phase current and voltage sources as an
optional test method to the existing single phase, series, parallel method. Other
major changes include testing under harmonic conditions, addition of a 0.1%
accuracy class, clarification that non-Blondel applications are not covered by this
standard, and addition of specifications for the optical port pulse outputs. ”6
Both ANSI C12.1-2014 and ANSI C12.20-2015 specify accuracy classes 0.5. The
differences between these two specifications may not be obvious, but they are
important for the user since they may result in significant differences in meter
performance under some operating conditions.
In the most general sense, the ANSI C12.1-2014 class 0.5 may be applied to meters
which do not adhere to the Blondel theorem. On the other hand, the ANSI C12.20
class 0.5 specification applies only to meters which meet the Blondel’s theorem.
5 ANSI C12.1-2014 American National Standard for Electric Meters, Code for Electricity Metering.
6 ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5 Accuracy Classes
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ANSI C12.20-2015 explains that “non-Blondel metering installations assume
balanced line voltage magnitudes and phase angles. Unbalanced line voltages will
introduce measurement registration error independent of instrumentation accuracy. ”7
Typical Blondel and non-Blondel meter form designations are listed in ANSI C12.20-
2015 clause 4.4.
In addition, a meter of ANSI C12.20-2015 accuracy class 0.5 will have to pass the
tests of harmonic influences, whereas such influence tests are not required in ANSI
C12.1-2014.
Meter accuracy classes are defined in IEC standards and in ANSI standards, and
marked by an accuracy class index, which is a number representing the maximum
meter percent error at reference test conditions. Other metering standards such as
CENELEC EN 50470-x or OIML R46 recommendations also define meter accuracy
classes, but use capital letters as accuracy class indices. For example, the
“accuracy class C” defined in EN 50470-3-1 standard or OIML R46 recommendation
roughly corresponds to “accuracy class 0.5” defined in the IEC 62053-22 standard,
or in the ANSI C12.20 standard. A detailed analysis of differences between these
accuracy classes is outside of the scope of this paper.
The ANSI C12.20-2010 specified accuracy classes 0.5 and 0.2. A notable
development in the ANSI C12.20-2015 standard is the introduction of a new
accuracy class 0.1. Using an example of three-element current class 20 meter,
Figures 3 and 4 summarize the performance differences between accuracy classes
specified in the ANSI C12.20-2015.
7 ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5 Accuracy
Classes.
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Permissible errors at each test point given in ANSI C12.20 are specified with respect
to the reference condition - the error at this reference condition is measured when
the meter is stabilized at room ambient temperature, rated voltage, rated frequency,
“test amperes” (TA) current, unity power factor, and sinusoidal waveforms (ANSI
C12.20-2015 section 5.5.1 specified tolerances for all these reference test
conditions). “The meter performance under the test conditions [..] shall be as close
as practical to zero error and in no case shall exceed 0.2% error for accuracy class
0.5, 0.1% error for accuracy class 0.2, or 0.05% error for accuracy class 0.1.”8 9
For a discussion of the benefits of high accuracy metering, please refer to the
Schneider Electric white paper “A high accuracy standard for electricity meters” by
Lance A. Irwin (2011).
Previous editions of ANSI C12.1 and NASI C12.20 did not clearly state a
requirement for testing of bidirectional meters with energy flowing in the “delivered”
and “received” directions.
The latest edition of ANSI C12.1-2014 clarifies that if the meter is designed for
measurement of energy in both directions, then the test conditions shall be applied
twice, once with energy flowing only in the forward or “delivered” direction, and once
with energy flowing only in the reverse or “received” direction.10
The requirement for testing in both directions applies to the starting load tests, the
load performance tests and the test of variation of power factor.
The same clarification is not included in the ANSI C12.20, but presumably it also
applies.
8 ANSI C12.1-2014 American National Standard for Electric Meters, Code for Electricity Metering
9 ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5 Accuracy Classes
10 ANSI C12.1-2014 American National Standard for Electric Meters, Code for Electricity Metering.
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Due to the proliferation of non-linear loads and renewable power generation in
modern electrical distribution networks, distorted waveforms and various power
quality phenomena are a common occurrence and should be considered as normal
operating conditions for electricity meters. The industry experience and numerous
academic studies demonstrate that some static electricity meters cannot correctly
measure electrical energy in distorted waveforms. Modern static electricity meters
seem to be more sensitive to distorted waveforms than the induction (Ferraris)
electromechanical meters. The sensitivity of static meter to the waveform distortions
depends on many factors, including the implemented measurement algorithms,
signal conditioning and filtering, or even the type of current or voltage sensors11 12 13
[6, 7, 9]. Many publications reported accuracy-related problems with meters exposed
to highly distorted waveforms14 15 16 17, albeit without precisely identifying the root
causes.
Metering errors induced by highly distorted waveforms may have significant impact
in revenue billing applications, but their causes and nature are not well understood;
consequently, comprehensive tests for influence of distorted waveforms are often
not included in meter type approval programs.
Some basic tests with distorted waveforms are prescribed in the IEC metering
standards and in the OIML R46 recommendations, however the ANSI C12.20-2015
specifies probably the most comprehensive harmonic influence testing to date.
The ANSI C12.20 introduces six tests of meter accuracy under the influence of
distorted waveforms (tests #39 – #44).” The purpose of these tests is to verify that
the meter maintains accuracy under a variety of non-sinusoidal voltage and current
conditions.”18
11 F. Leferink, C. Keyer, and A. Melentjev, .Static energy meter errors caused by conducted
electromagnetic interference,. IEEE Electromagnetic Compatibility Magazine, vol. 5, no. 4. pp. 49.55, 2016.
12 A. Ferrero, M. Faifer, and S. Salicone, .On Testing the Electronic Revenue Energy Meters,. IEEE Transactions on Instrumentation and Measurement, vol. 58, no. 9. pp. 3042.3049, 2009.
13 Quijano Cetina, R. and Roscoe, Andrew J. and Wright, P.S. (2017) A review of electrical metering accuracy standards in the context of dynamic power quality conditions of the grid. In: 52nd International Universities Power Engineering Conference (UPEC), 2017. IEEE, Piscataway, N.J.. ISBN 978-1-5386-2345-9 , http://dx.doi.org/10.1109/UPEC.2017.8231871
14 F. Leferink, C. Keyer, and A. Melentjev, .Static energy meter errors caused by conducted electromagnetic interference,. IEEE Electromagnetic Compatibility Magazine, vol. 5, no. 4. pp. 49.55, 2016.
15 A. Ferrero, M. Faifer, and S. Salicone, .On Testing the Electronic Revenue Energy Meters,. IEEE Transactions on Instrumentation and Measurement, vol. 58, no. 9. pp. 3042.3049, 2009.
16 A. Domijan Jr., E.Embriz-Santander, A. Gilani, Watthour meter accuracy under controlled unbalanced harmonic voltage and current conditions, IEEE Transactions on Power Delivery, Vol. 11, No. 1, Jan 1996.
17 Quijano Cetina, R. and Roscoe, Andrew J. and Wright, P.S. (2017) A review of electrical metering accuracy standards in the context of dynamic power quality conditions of the grid. In: 52nd International Universities Power Engineering Conference (UPEC), 2017. IEEE, Piscataway, N.J.. ISBN 978-1-5386-2345-9 , http://dx.doi.org/10.1109/UPEC.2017.8231871
18 ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5 Accuracy Classes
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Table 2 below shows the adoption of the harmonic influence test in various metering
standards. The only tests listed are those representing long-term or continuous
waveform distortions capable of influencing the accuracy of energy measurements.
For each of these influence conditions the metering standards specify some level of
allowable degradation of measurement accuracy.
● ● ● ●
●
● ●
●
● ●
●
●
●
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●
● ● ●
● ● ●
U5 = 10 % of Un (IEC, EN)
U5 = 5 % of Un (OIML)
I5 = 40 % of I fundamental
● ● ●
Superimposed current
harmonics sweep:
2 -150 kHz
○ ●3)
Superimposed harmonics
sweep: 15 fn - 40 fn
Superimposed harmonics
sweep: 15 fn - 40 fn
●
Notes:
Table 2 does not list short-term, transient phenomena (disturbances) since the
metering standards do not specify any allowable accuracy degradation for such
conditions.
Both the influences and disturbances are also considered as a part of meter
electromagnetic compatibility testing.
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The test output facilitates the most commonly used meter accuracy test methods
which are based on counting the energy test impulses. All metering standards, ANSI
and IEC alike, specify that a meter shall be equipped with a test output proportional
to the measured energy and compatible with external devices typically used to
check the registration of the meter both during type approval testing and during
verification testing in field installations. The optical test output is the preferred
implementation of a test output and the latest edition of ANSI C12.20-2015 provides
clarified requirements for its acceptable implementations.
As per ANSI C12.20-2015, the optical test output may be implemented as ANSI
Type 2 optical port according to the ANSI C12.18, with its function switched between
normal communications and the energy pulsing (called “optical port Type A”), or as
a separate port constructed according to the characteristics given in the Annex C of
the ANSI C12.20-2015 (called “optical port Type B”). In either case, the test output
must be accessible in normal use, without removing the meter cover.
Meters that measure delivered and received energy, or can measure other time
integrated quantities, such as VARh, VAh, V2h etc., are expected be able to use the
test pulse output for these measured quantities. In such meters, a single physical
test output may be used for these measured quantities only when a method is
available to select which quantity is being output on the test port, and when a visible
indication is present as to which quantity is currently active.19
19 ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5 Accuracy
Classes
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While the largest markets for ANSI standard electricity meters are in the United
States, Canada and Mexico, ANSI C12 electricity metering standards are also used
in many countries around the world, especially by utilities in parts of Asia, Central
America and South America. In many cases, notwithstanding the non-ANSI form
factors, the accuracy specifications of ANSI standards are applied to evaluate or
describe performance of industrial panel meters, power monitors (PMDs), branch
circuit power meters (BCPMs) or even power quality instruments (PQIs).
The latest revisions of C12.1 and C12.20 introduce many new requirements, and
provide several important clarifications which influence new meter designs and type
testing. At the cost of modest increase in the number of tests and consequently a
higher cost of meter type approvals, these new revisions provide the benefits of
higher accuracy class 0.1 metering, increased meter robustness, and increased
metrological performance with highly distorted signals. These new requirements
make ANSI revenue meters more suitable for use on modern electricity distribution
networks and result in meter designs updated to match the technical progress in
metrology, and the increased customer expectations of more robust and more
accurate measurements in billing applications.
Piotr Przydatek
Sandra Pedro
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«Introduction.» American National Standards Institute - ANSI. American National Standards
Institute. Web. 12 Apr 2018.
https://www.ansi.org/about_ansi/introduction/introduction?menuid=1
ANSI C12.1-2014 American National Standard for Electric Meters, Code for Electricity
Metering
ANSI C12.1-2008 American National Standard for Electric Meters, Code for Electricity
Metering
ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5
Accuracy Classes
ANSI C12.20-2010 American National Standard for Electricity Meters— 0.2 and 0.5 Accuracy
Classes
IEC62052-11 Electricity metering equipment (AC) – General requirements, tests and test
conditions – Part 11: Metering equipment, First edition, 2003.
F. Leferink, C. Keyer, and A. Melentjev, .Static energy meter errors caused by conducted
electromagnetic interference,. IEEE Electromagnetic Compatibility Magazine, vol. 5, no. 4.
pp. 49.55, 2016.
A. Ferrero, M. Faifer, and S. Salicone, .On Testing the Electronic Revenue Energy Meters,.
IEEE Transactions on Instrumentation and Measurement, vol. 58, no. 9. pp. 3042.3049,
2009.
A. Domijan Jr., E.Embriz-Santander, A. Gilani, Watthour meter accuracy under controlled
unbalanced harmonic voltage and current conditions, IEEE Transactions on Power Delivery,
Vol. 11, No. 1, Jan 1996.
Quijano Cetina, R. and Roscoe, Andrew J. and Wright, P.S. (2017) A review of electrical
metering accuracy standards in the context of dynamic power quality conditions of the grid.
In: 52nd International Universities Power Engineering Conference (UPEC), 2017. IEEE,
Piscataway, N.J.. ISBN 978-1-5386-2345-9 , http://dx.doi.org/10.1109/UPEC.2017.8231871
Daniele Gallo, Carmine Landi, Nicola Pasquino, Nello Polese, A New Methodological
Approach to Quality Assurance of Energy Meters Under Nonsinusoidal Conditions, IEEE
TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 56, NO. 5,
OCTOBER 2007
Lance A. Irwin, “A high accuracy standard for electricity meters” , April 2011,
http://www2.schneider-electric.com/documents/support/white-papers/998-4531_electric-
utilities_High-accuracy_EN.pdf
EPRI, .Accuracy of Digital Electricity Meters.. Electric Power Research Institute, Palo Alto,
California, USA, 2010.
P. S. Filipski and P.W. Labaj, Evaluation of reactive power meters in the presence of high
harmonic distortion, IEEE Trabsactions on Power Delivery, Vol. 7, No. 4, Oct 1992.
P. S. Filipski and R. Arseneau, .The Effects of Nonsinusoidal Waveforms on the Performance
of Revenue Meters,. National Research Council Canada,1990