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Challenge: Obtaining precise energy consumption readings for each individual production machine as well as additional information for predictive maintenance.
Solution: Eaton’s digital NZM circuit breaker with integrated energy measurement
Result: At Eaton’s Schrems plant, the energy consumption of each production machine and manufactured product can now be measured with a very high level of accuracy.
Background
Today, everybody is talking about how to reduce CO2 emissions. Meanwhile, governments have been concerned with efforts to increase energy efficiency for many years. Measures such as carbon taxes or energy labels (even for machines) are about to be implemented. As a result, taxes on energy consumption are now a growing cost factor for companies in a number of countries – in Germany, for example, government levies already account for more than 50 per cent of electricity costs. At the same time, however, many EU member states have created opportunities for plant operators to reduce their tax burden. In order to become eligible for any such reductions, companies must first implement a certified energy-management system according to ISO 50001 (or an alternative system), which requires, among other things, the installation of metering equipment. Ideally, energy measurement should be carried out at the level of each production machine or plant. This makes it possible to precisely track a factory's energy usage, to identify particularly energy-intensive plant components and to determine measures to increase energy-efficiency at machine level.
Capturing the energy consumption of each individual machine also enables operators to determine the energy consumption, and thus the energy costs, of each unit produced by the machine in question – and ultimately that of the entire factory. This not only facilitates more precise calculations, but also makes it possible to assign energy values to each finished product. By integrating energy measurement directly into their systems, machine builders can thus offer their customers real added value.
But retrofitting an energy-measurement system even makes sense in existing systems – especially if there is no other way to capture the consumption of water, compressed air and, above all, electricity. And even if a machine is already equipped with conventional energy meters, it may make sense to investigate alternative solutions. This is illustrated by a pilot project that the power management company Eaton has implemented at its plant in Schrems, Austria.
Pilot project at Eaton’s Schrems facility
At the Schrems plant, around 700 employees produce 360,000 individual parts every hour, which are assembled into key components for miniature circuit breakers, residual current circuit breakers and customised low-voltage distribution boards. Each year, Eaton's plant in Schrems produces around 3 billion individual assemblies and key components. In order to keep track of the 22,000 square metres of floor space with 170 separate production lines, Eaton installed a comprehensive operational data acquisition system about 10 years ago: "Since most of our machines are partly or fully automatic and there isn't always an employee on site, we rely on the operational data acquisition system to monitor and control all our processes," explains Thomas Graf, plant manager in Schrems.
Energy measurement at the level of each individual machine
The process data that each machine sends to the operational data acquisition system via the factory’s network also include information on the consumption of water, compressed air and electricity. To measure the power consumption of each machine, the Schrems plant previously relied on separate energy meters with class 3 accuracy. This allowed for power measurements with an inaccuracy of 3 per cent at nominal current – across the entire measurement range: In the case of a device with a nominal current of 100 A, these meters would thus measure even a current of 10 A with a margin of error of 3 A. Consequently, this solution not only came with a high level of measurement inaccuracy, but also required a lot of wiring. Take the example of an automatic punching and bending machine, which is used, among other things, to manufacture the arc chambers for circuit breakers: Since the main switches of the system can handle up to 160 ampere, but the energy meters only up to 80 amperes, two meters including fuses had to be connected in parallel to this machine. Via an S0 interface, the meters transmitted their data to the machine’s PLC and then via the latter to the operational data-acquisition system.
The installation of two meters not only required additional wiring, but also took up a lot of space inside the control cabinet. In addition, the meters only measured the kilowatt hours consumed. The purpose of the retrofit that has just been completed was therefore twofold: to obtain more precise readings that can be used for more accurate calculation, and to collect additional information about the health of the system, for example in the context of predictive maintenance.
NZM with integrated energy measurement
For this reason, Eaton decided to install its digital NZM circuit breakers with integrated energy measurement at the Schrems plant. While previous generations of moulded-case circuit breakers detect overloads and short-circuits by means of thermomagnetic trip units, the latest NZM circuit breakers are equipped with an electronic tripping system, which in the case of the PXR25 version also includes an integrated energy-measurement function. These devices thus enable current and voltage measurements with an accuracy of 0.5%. This makes it possible to calculate the output and energy consumption with class 1 accuracy, in accordance with the IEC 61557-12 standard, which also applies to ammeters.
By replacing the existing NZM moulded-case circuit breaker inside the punching and bending machine with the latest model, the two electricity meters and their fuses could therefore be completely eliminated. The new devices also feature an integrated Modbus interface so that the readings can be transmitted directly to the PLC.
Multiple benefits
Using the NZM for current measurement offers a range of advantages: On the one hand, this significantly reduces the number of components required for the system. Furthermore, as the Schrems pilot project demonstrated, the new solution also requires considerably less wiring: Whereas previously, two cables had to be connected to the S0 interface, plus the wires of the electricity meters themselves and the associated fuses, only one cable is now required – between the Modbus terminal and the NZM.
Using the NZM with integrated energy measurement also has positive effects inside the control cabinet, as there is no longer any need for separate meters. And since the latest generation of the NZM has exactly the same dimensions as the previous versions, replacing the devices couldn’t be easier. The reduced wiring requirements and the space savings inside the control cabinet make the NZM particularly interesting for use in new machines. In the case of new machinery, installing the NZM with integrated energy measurement translates into direct cost benefits: At the Schrems plant, Eaton was able to reduce the costs – for both equipment and labour – by around 27 per cent.
Advantages also during retrofits
Beyond the cost factor, installing the NZM in the machine provided real added value, which makes this solution interesting also for retrofit projects. In this case, the most important aspect is the significantly greater accuracy of the energy measurement: This makes it possible to determine the energy required for the production of each unit and thus to precisely calculate the final costs per item – which may even lead to a price advantage in the market.
At the same time, the NZM delivers far more information than a conventional energy meter. This includes practically all the electrical data of the circuit it protects: In addition to reactive current, active current and voltage, this now also includes power and energy values as well as other data; similarly, the power factor no longer needs to be calculated separately, but can be called up instantly. This information can be used to verify the proper functioning of downstream equipment and sub-distribution boards for the purpose of predictive maintenance. All that is required is an electrical "fingerprint" of the machine, which can be created by recording the electrical values during normal operation.
During operation, this fingerprint will be regularly compared with the real-time data supplied by the NZM. As soon as any anomalies, i.e. deviations from the electrical fingerprint, are detected, it becomes possible to deduce information about the actual ageing process of the system.
Should a failure nevertheless occur, the NZM offers a range of analytics options to keep downtime to a minimum. Digital circuit breakers thus enable operators to keep track of their applications: Did the device trip due to a short-circuit, or due to an overload? What was the maximum current flow? The data recorded in the run up to the trip event are stored in the switch and can be retrieved remotely. The NZM's integrated analytics functions can also be used to identify issues that affect the machine’s supply network. This makes it possible to detect faults that affect the entire plant, such as harmonic oscillations.
Improved system availability
Apart from the benefits of real-time data, the circuit breaker also offers additional advantages that contribute to improving system availability. For example, the circuit breaker is able to determine its remaining service life at any time. This means that after each trip, regardless of whether due to overload or short-circuit, operators can quickly decide whether the circuit breaker needs to be replaced or not. Whereas in the past, circuit breakers were often replaced immediately as a precautionary measure, they can now remain in operation much longer.
Safe and simple maintenance
The electronic trip mechanism of the latest generation of the NZM also improves the safety of maintenance staff at the Eaton plant in Schrems. For many tasks, they no longer need to open the distribution board: "Via the USB interface in the distribution board enclosure, we can communicate directly with the electronic release without having to open the door," says Wolfgang Strondl, division manager for metal parts production at the Eaton plant in Schrems. By means of a laptop and the Power Xpert Protection Manager software, the technicians can thus easily access the switchgear information and adjust the settings accordingly. Eaton is continuing to improve the NZM circuit breaker so that in future it will also be possible to test the protection functions via the USB interface. Even without the use of any costly external testing equipment, it will thus be possible to check the protection parameters selected by the user, the functioning of the internal converters, or if the device is properly connected to the trip unit. In addition, the software allows operators to simulate any current and to compare tripping times automatically, in accordance with the selected tripping curve.
Added value for new machines and retrofits
"Our pilot project has shown that installing the NZM with integrated energy measurement pays off in more ways than one," concludes Wolfgang Strondl. Even in the case of a retrofit project, the NZM not only provides very accurate data, but its additional features also improve machine operation in terms of maintenance and availability. In new machines, the NZM with integrated energy measurement demonstrates its advantages over a conventional solution with energy meters: in addition to the significantly lower overall costs for procurement and installation, it also facilitates significantly more compact machine and control panel designs. Thomas Graf: "This project has confirmed our decision to use the NZM with integrated energy measurement in all future machines at the Schrems plant.”
