IEEE Electrification Magazine - March 2020 - 9

meter or system sending data to everyone in an endless
variety of special interfaces created several problems
while also being inefficient, risky, and a technological
nightmare. Therefore, Eress decided that the best
approach was to put a central crossroad-Erex Exchange-
in the middle, which would connect the different metering and settlement systems. This allowed the countries to
easily and securely receive the data and use them for billing purposes.
Erex Exchange currently exists as a subservice to
handle energy meters, making it possible to integrate metering into the equation, according to national and international requirements. Onboard energy meters send their
readings to a data-collection system, which then forwards
the information to the Exchange. The Exchange acts as a
filter, controlling the data to ensure that they correspond
to the correct meter. From there, the data are securely
stored, validated, corrected, accurately allocated, and distributed to the corresponding settlement area. This results
in the infrastructure manager, or responsible party, receiving the corrected data, which can then be used to invoice
train operators (Figure 2).
To better understand how energy exchange happens
within the Erex system, take the following scenario: a
train runs from Belgium through France to Switzerland.
Throughout its journey, the train consumes energy. Therefore, the meter on board that train will measure-every
1 to 5 min-how much energy is consumed during that
time interval and then bundle that data. This bundle is
then tagged with a GPS location as well as the time and
date showing where and when that energy was used. From
there, the metering system will send the data to a ground
station. That ground station then sends the data to the
energy exchange, which will check that the data make
sense, before allocating it to the country where the energy
was consumed. Later on, when the corresponding train
operator receives its energy bill, the operator can see how
much it is paying for the volume of energy consumed during that specific time interval. It can also see where the

DCS

Control

consumption took place on the map. If that point on the
map is in France, then the French infrastructure manager
is the one responsible for the billing because it supplied
the energy to the grid. If that point on the map is in Switzerland, then the Swiss infrastructure manager is responsible for the supply and invoicing of that energy, and so on.
Compare this to filling up your car at the gas station.
You watch the gas pump as it dispenses fuel into your
car, knowing that the meter has been publicly and commercially accepted and approved. Therefore, you trust that
it will tell you exactly how much gas is going into your car
and, based on that volume, you know how much to pay in
return. There isn't an attendant that stands there and
says, "Oh, I guess that'll be €100 for 60 L." That estimation
could result in you paying more than you would if you had
access to a meter. For the railways, the situation is similar.
Trains that have energy meters installed on board are
billed for their exact energy consumption, whereas those
that do not are billed based on an estimate. Therefore,
because trains are in constant motion-crossing borders
into different grid areas-it is important to know where
the energy was consumed, at what time, and who is
responsible for the invoicing. Erex Exchange makes all of
that possible.
A primary benefit of having a common exchange like
Erex is that it allows for better control over data flow.
When countries are talking with each other and sending
data everywhere and anywhere, there are two major risks.
One is that it is extremely hard to have control in terms of
making sure that the data are going to the appropriate
parties. The second part, of course, is that it is difficult to
have transparency in the sense of knowing how the data
are being handled and that they are being handled equally
for all.
That said, Erex Exchange is not the only one in Europe.
There are a matrix of exchanges, representing one or more
parties. Both the interfacing between the parties and the
rules for how to operate the exchange service are two areas
that have yet to be agreed upon. Despite the need for a

Erex
Exchange

Storage

Settlement

Validation Correction Allocation

Distribution

Erex
Settlement

Other
Settlement
Systems

Other
DCS

Figure 2. The Erex energy exchange system. DCS: data collection system. (Source: Eress, used with permission.)

IEEE Elec trific ation Magazine / MARCH 2 0 2 0

IEEE Electrification Magazine - March 2020

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2020