Instrumentation & Measurement Magazine 26-4 - 45

Energy Meters
An EM is a key device for SOs and final users. EMs allow for
measurement and registration of the consumption or generation
of electricity inside residential or business buildings. In
addition, EMs may be equipped with anti-fraud or anti-tampering
functionalities to avoid illegal operations.
Hand in hand with the development of smart grids,
EMs have changed from being electromechanical devices to
smart energy meters (SEMs). SEMs have acquired several
fundamental features over previous models such as: their
operation does not include moving parts-unlike electromechanical
Ems-so they are not slightly affected by wear; with
bidirectional communication SEMs can either send the measurement
results or receive instruction from other devices;
and SEMs allow consumers to supervise their energy consumption
in real-time and even to have a remote control on
their appliances [10].
Fig. 2. Main LPITs technologies and the relevant influence quantities.
IT Standards
LPITs exploit technologies available since the 19th
century.
However, the development of efficient devices is only two-decades
old. In addition, LPITs are well covered by international
standards thanks to the technical committee (TC) on ITs. The
TC compiled all of the documents to help final users and manufacturers
with the use of both ITs and LPITs.
The standard series dedicated to ITs is the IEC 61869. It
consists of fifteen documents, each of which covers a specific
kind of IT or interface. The two most important documents of
the series are the IEC 61869-1 [9] and IEC 61869-6, which provide
the general requirements that apply for all kinds of ITs
and LPITs, respectively. Such requirements span from testing
guidelines to rated values and accuracy requirements. The additional
documents of the series go into much more detail for
each kind of device. For example, IEC 61869-10 and IEC 6186911
are dedicated to LPCTs and LPVTs, respectively. In those
documents, tests developed for a specific device are described
(like the immunity test for LPVTs, or the positioning test for
Rogowski coils).
Of course, standards are always evolving to be aligned with
the current research findings. However, one may find several
limited areas if specific aspects are considered. An example of
a topic that is not treated in the standard yet is the use of LPITs
with other devices. There is no mention of the possibility that
the LPIT might be part of a more complex measurement chain
and how this affects the results. The only reference to devices
different from the LPITs is the so-called merging unit (MU) or
stand-alone merging unit (SAMU), described in IEC 61869-13.
They are two versions of a device that aims to collect and synchronize
the output of several LPITs, before sending them to a
data concentrator or a generic receiver. Such a device is typically
implemented within distributed measurement systems
consisting of a significant number of LPITs.
June 2023
Thanks to these new characteristics and functions, SEMs
will play a crucial role in electrical power systems, resulting
in more honest behaviors by the consumers more efficient
energy dispatching because the real-time measurements
enable SOs to improve both load and generation control.
However, there is a relevant obstacle: the installation of
SEMs, for all domestic and industrial users, requires a huge
investment by the SOs. Therefore, basic electromechanical
and electronic meters are still widely used in many developing
countries.
Due to the increasing penetration of renewable energy
sources, non-linear power converters, and loads into electrical
power systems, the distortion of currents and voltages is no
longer negligible. Consequently, lower levels of power quality
are being experienced, challenging the measurement performance
of the instrumentation, including the EMs. Therefore,
in the literature several studies on EMs accuracy can be found.
For example, [11] and [12] suggest some test waveforms to assess
the EM behavior, while in [13] one of the starting points
is the THD level of the input signal. These studies and others
have been conducted to find the best test signal that may represent
actual operating conditions of an electrical power system.
Another reason is that the testing waveforms defined in the
relevant standard are far from being representative of a typical
signal.
In addition to the test signals, the literature focuses also
on the influence quantities affecting the EM performance. For
example, amplitude, frequency, harmonic content, power factor,
harmonic power factor, crest factor, and the symmetry and
balance for three-phase systems are some quantities that have
been investigated. In conclusion, EM literature provides a lot
of material to be used by TCs for preparing new standards.
Such a process is significant and highly necessary if one considers
the EM usage for billing purposes.
EM Standards
The regulatory context dedicated to EMs is quite wide and
complex. Three main standards apply to EMs, namely the European
Directive 2014/32/EU [14], the EN 50470 series, and
IEEE Instrumentation & Measurement Magazine
45
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