Page 87 - From Smart Grid to Internet of Energy

Smart metering and smart monitoring systems Chapter 2 73

shortly. There are many commercial smart meters can be given as examples to
measurement periods based on hourly, half an hour, and even 15-min intervals.
In addition to central smart meters, some featured smart meters provide multiple
measurement channels for dedicated uses of main asset, DERs such as solar or
wind turbines, and individual load types. This is called multi-channel metering
and it prevents requirement for spare smart meter utilization for DG and loads.
In addition to measurement frequency, data recording and warning is another
important feature of smart meters. It provides information for both of utility
operators and customers to know about consumption rates and usage limits.
Some countries prefer prepaid metering systems to provide this function where
customers charge a limited credit for their smart meter and they become able
to consume electricity until the credit discharged. Another solution in contrast
to prepaid usage is alarm-based warning function of smart meters those can be
programmed to an exact usage limit and smart meter warns consumer when the
limit is reached [1, 10].
In addition to RTP information, smart meters can store measurement data
for usage history and cumulation of periodic usage including consumption, tar-
iff programs, overall costs and so on. The stored data can be monitored over
HEMS by reaching user interface of smart meter or provided interface software
of smart meter vendor. Most of the service suppliers also provide web-based
monitoring interface for their customers. It is obvious that smart meter deploy-
ments are leading the way in smart grid applications all around the world. The
United States is also leading among countries with around 50% replacement of
millions of electricity meters with smart meters [10, 11].
The advanced smart meters should meet smart grid requirements according
to regional arrangements. In the United States, the most appropriate communi-
cation system for smart meters is low power radio frequency (LPRF) mesh
network operating at Sub-1 GHz frequency band. On the other hand, it will
be better solution to use wireline communications instead of wireless in some
European countries such as Spain or France. The narrowband PLC technologies
are widely preferred in these countries due to technical infrastructures. Since
there is not any solution fitting to each situation, a smart meter requires com-
bination of many alternatives in metering and communication interfaces. In
addition to analog front end (AFE) and communication requirements, smart
meters should comply with residential ICT and gateways. It is noted that ZigBee
technology based on IEEE 802.15.4 standard is widely used in smart meter and
HEMS integration at 2.4 GHz frequency in the United States while Sub-1 GHz
RF and PLC combination is mostly preferred in smart metering applications in
United Kingdom and Japan [11].
The block diagram of a three-phase four-wire smart meter has been pre-
sented in Fig. 2.5 as a very detailed example of commercial smart metering
devices. Although current transformers (CTs) and voltage transformers (VTs)
comprise the AFE, low cost implementations are also possible to comprise
AFE by using current and voltage sensing resistors. An internal rectifier mostly