What is a measurement concept?
The measurement concept is the foundation of effective operational energy management. With the help of the measurement concept, you can obtain a structured and comprehensive picture of the structure of the energy infrastructure in the company by breaking down the existing measuring points. It includes both the metadata of the measuring points, such as the designation, as well as the assigned physical measurement by a measuring device. The creation of a measurement concept often begins with an inventory of the existing infrastructure. However, it is also used to plan new measuring points and design the measurement technology required for them.
Why do I need a measurement concept?
Energy management is becoming increasingly important in companies in all sectors due to legal requirements and internal cost pressure. A holistic measurement concept serves to fulfill legal requirements and regulations in the context of certifications and audits. However, the use of funding opportunities, such as BAFA funding, also places demands on industrial companies in terms of energy management and, in particular, the development of a measurement concept.
In addition, there are further regulations and obligations to provide evidence if, for example, you have your own generation systems and would like to benefit from possible concessions in this regard. The metering concept also includes an inventory of the current situation. It is also used for structured planning of the expansion of the metering system. In addition to a simple list of systems and other logical measuring points, the measuring concept can also be used to map the topology, i.e. the relationships between the various measuring points in your company. As a result, the energy distribution of different media such as electricity or gas in your company can be displayed, e.g. in the form of the familiar Sankey diagram. The measurement concept is also an elementary part of energy monitoring and management software, which, thanks to the transparency it creates, makes it possible to identify and then realize optimization potential in your company.
What needs to be considered when creating a measurement concept?
When creating a comprehensive measurement concept, the need for measurement in compliance with calibration law must be taken into account. This means that the measurement technology used for these measuring points must meet the requirements of a measurement that complies with calibration law.
The creation of a measurement concept generally comprises three major steps, which in turn consist of subtasks. In order to arrive at the target image of a holistic measurement concept, we have to enter the existing measuring points and plan further ones. In addition, we have to design and procure the appropriate measurement technology for those measuring points where measurement is planned. And, of course, this measurement technology also needs to be installed and configured.
Where do I start measuring?
Unnecessary or incorrect meters can quickly drive up the cost of the energy management system by €5,000 or more for no reason. We therefore recommend starting measurement at the transfer meter and the main distribution boards. Only after an initial data-based analysis should the system be extended to specific installations.
Three meter levels: Transfer meter, main distribution board and sub-distribution board
The electrotechnical topology is the same in almost every industrial company: the energy is supplied from the electricity grid at the transfer point and recorded there by the transfer meter. This meter is the meter relevant to the energy industry for billing purposes. Industrial companies receive the 15-minute load profile from their supplier as basic information. In fact, the meter contains significantly more parameters and fundamental errors can already be detected with regard to load peaks, standby consumption, voltage fluctuations or power asymmetries. We recommend starting with such an analysis in order to decide whether there is any potential for savings.
The transfer meter is often the only meter at 20 kV level and is therefore necessary for determining transformer or distribution losses. From an energy management perspective, "submetering" begins after the transfer meter.
The 20 kV distribution with the transformers is located directly behind the transfer meter. The transformers feed the busbars of the low-voltage main distribution board (LVMD). Some kind of measurement is usually located at this point on the "transformer underside".
Depending on the year of construction and equipment, power quality measuring devices, multifunction devices or analog current and voltage measuring devices can be found at the bottom of the transformer. In most companies, we recommend normal universal measuring devices. These have the best price-performance ratio and can be read out via Modbus TCP, for example, with very high data quality using any evaluation software. High-quality power quality measuring devices should be used if there are frequent faults in the power quality (e.g. screen flickering, UPS).
In older systems, there are usually four analog display devices. One is for the voltages and the other three for the phase currents. Although the devices cannot be read out, they considerably reduce the work for the electrician: both the current transformers and the voltage tap can simply be reconnected to a modern universal measuring device (caution when converting: current transformers should always be short-circuited). The holes in the switch cabinet door can also continue to be used, as the installation dimensions are identical. The new universal measuring device replaces all four displays. The three holes in the switch cabinet door that become free provide space for additional sub-meters.
The low-voltage main distribution board (LVMD) has the task of distributing the current coming from the transformer via the busbar. The main distribution boards are usually ideal for measuring devices: the cables are easily accessible. There is also less cabling required for communication lines, as several meters can be installed in one place. This is a major advantage over metering in the sub-distribution board or directly at the installation.
The costs of the metering system can be optimized if not all systems are equipped with meters straight away. The best result is achieved by proceeding step by step along the energy distribution system. First, only the transfer meter is recorded in order to determine from the load profile whether energy management is worthwhile at all. Then the bottom of the transformer is connected to the system at the feed-in of the low-voltage main distribution board.
Practical tip:
1. meter selection: Universal meters have the best price-performance ratio. A variant with Modbus TCP should be used. These are compatible with all evaluation systems. Manufacturer-specific protocols or pulses should always be avoided!
2. Meter location: The low-voltage main distribution board is the ideal location for meters. Several meters can be installed here at the inlets and outlets, thus reducing the amount of cabling required for the communication lines. Only if the individual system cannot be tapped at the low-voltage main distribution board does it make sense to install a meter at the system.
The unmeasured remainder is always decisive for the expansion of data acquisition. If this can be fully explained both in the Sankey diagram and in the stacked chart over time, no additional meter is necessary. If it is not clear which system is responsible for the consumption characteristic, additional meters should be installed.
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