Purpose

The installation of energy meters in railway vehicles facilitates the exact measurements of energy consumption. This serves mainly two purposes:

1. provide consumption data for an exact energy billing system
2. provide consumption data for the identification and assessment of energy saving measures

Availability of energy consumption data

In diesel traction the energy supply is on-board and therefore the energy consumed can be clearly attributed to one single vehicle (nevertheless an additional diesel flow meter can have an additional benefit). In contrast, in electric systems energy consumption is usually measured at the substations only which does not allow for an exact assignment to one single vehicle, since several vehicles may be in the same feeding section.

As a consequence, energy billing is usually based on theoretical consumption values derived from train data or simulations of train runs. The accuracy of such a system is limited by various factors:

• Simulation algorithms are based on models that make simplified assumptions on real conditions. This creates a small but non-negligible inaccuracy of the outcome.
• Simulations or calculations do not take into account the specific external factors influencing the energy consumption of one particular train run, such as wind, track conditions etc.
• The same is true for internal factors influencing the train run, mainly the driver. The driving style has a significant impact on energy consumption through such factors as use of recuperation brakes, speed pattern and coasting.

The values derived from direct measurements by means of an energy meter do not have these limitations.

Liberalisation of railway markets

As European railway markets are deregulated, the energy consumption of individual trains is no longer just an internal affair of the railway operator. In an effort to ensure the same conditions for all competitors, a clear and transparent billing mechanism has to be introduced. Naturally, an on-board measurement of energy consumption is not a prerequisite for billing but it does put it on a more accurate basis.

Technical details

There are no technical specifications for energy meters on a European or international level, although there do exist standardisation efforts. An on-board measurement of energy consumption and data recording as well as processing requires the following system components:

• The energy meter: The energy measurement requires measurement transformers (voltage and current) as well as the meter itself. The whole measurement device usually has an accuracy of at least 2%. The measurement equipment must be protected against manipulation by unauthorised persons.
• Data collection: Depending on the needs of the operator, the equipment will produce ¼ hour or 1 hour profiles, i.e. the on-board equipment calculates the energy consumed in a period of 15 or 60 minutes by integrating the power intake over this period of time. Double registering allows for a separate collection of energy intake and recovered energy returned to the grid.
• Data recording: A memory is needed to avoid data loss in case the regular read-out is not possible. Usually, 60 days of data storage will in most cases be sufficient.
• Remote reading: A remote reading by GSM or GSM-R radio link improves the efficiency of the process.
• Display: There are controversial opinions on the question whether it is desirable to display the consumed power to the driver. While some argue that this could be an additional incentive to reduce energy consumption, others fear that the additional information could distract the driver from more relevant information.

• Obtain an accurate basis for billing
• Get more transparency on energy consumption in order to identify and assess energy saving measures

Billing

The whole energy debiting process can be put on a more costs-by-cause oriented basis.

LCC guarantees

The validity of LCC guarantees given by manufacturers can be confirmed or disproven by means of energy meters.

Acceptance

If energy meters are not needed for billing purposes, operators tend to be reluctant to invest into equipment not offering any obvious added value. SNCF who operates in market not yet liberalised is sceptical about the benefits of on-board energy measurement.

Technological

Presently no standard exists.

Retrofitting

Old vehicles often require tailored solutions.

Costs

Investment and maintenance costs can be high if a combination with refurbishment measures is not possible or unrealistic.

Management & Organisation

If energy meters are introduced only as a feature in new stock and no refitting is carried out, the fleet-wide roll-out may take several decades (~ 40 years). Experience from DB shows that great parts of the stock can be equipped with energy meters within two or three years, if old stock is refurbished.

Standardisation and interoperability

The different power supply systems may require corresponding interoperability efforts in some fields. A technological standardisation on a European level could accelerate technological development, create scale effects and improve planning reliability of manufacturers. Although a UIC standard is not a crucial prerequisite for introducing energy meters, common development efforts may be beneficial especially for small operators. However, a lengthy standardisation process could considerably delay the roll-out of energy meters.

Economic

Equip all new purchased trains with energy meters and use the already equipped part of the fleet to supply databases for improved calculations.

Management & Organisation

Be able to show the benefits from using energy meters and do not mix billing and energy saving targets. Furthermore, it has to be clearly defined, which data (e.g. measurement time intervals, train position, load situation ...) are needed to generate data basis for different saving measures.

Acceptance

The challenge of data reliability and automatic processing of data has to be tackled.

The TEMA project at DB AG (TEMA=Traktions-Energie Messung und Abrechnung)

In 2000 DB Energie tested the installation of energy meters in several trains as well as data transmission and evaluation in the TEMA project. The meters measure both energy intake and recuperation energy. At DB AG, energy metering is seen as an essential prerequisite for determining the influencing factors for energy consumption and monitoring the success of energy saving measures.

Within the project different types of measuring devices tailored to individual vehicle series were installed and tested. The devices have a minimum accuracy of 2%. The system calculates and records 15 min consumption profiles. Remote reading via GSM is implemented.

Following the projects, energy meters have now been incorporated into the specifications of new stock. A roll-out into the DB fleet is currently being realised. DB AG plans to introduce exact energy billing based on energy metering in 2003. Since energy meters are not a standard feature yet and competitors may continue operating stock not equipped with meters, billing based on metering is only offered as an option besides conventional billing.

Energy meters have two positive effects on energy efficiency which presumably are both substantial but difficult to quantify:

Economic incentive

If energy billing is based on calculations, there is no economic incentive for operators to save energy by recuperation or energy efficient driving. Consumption data collected in the TEMA project at DB AG show that the energy consumption on a given line differs by up to 20% from one day to another. This underlines the role of factors such as weather, track conditions, traffic situation or driving style for energy consumption. These conditions are not taken into account by simulations presently used. Often, the calculated energy consumption is not even accurate enough to provide an incentive for using energy efficient stock. These shortcomings of theoretical consumption data obviously don’t apply to on-board energy measurements.

Monitoring of energy saving measures

Measuring or calculating energy consumption in itself does not save energy. However a better knowledge of energy consumption will provide valuable data to identify potential for optimisation as far as regenerative braking, energy efficient driving or stopping patterns are concerned. Experience at DB AG shows that energy meters facilitate the monitoring and thus tend to improve the general acceptance of energy saving measures within the company.

Retrofitting of fleet

Experience from the TEMA project at DB AG shows that retrofitting of old vehicles with energy meters causes costs of about 2.000 € per vehicle.

New vehicles

In new stock the integration of an energy meter will be substantially cheaper if the feature is contained in the specifications and can be integrated into the vehicle design at an early stage.

Energy consumption

Energy saving effects are to be expected but are rather indirect and will be difficult to attribute to the existence of energy meters.