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Yes, certainly. The modernisation was carried out at the Holcim Concrete Plant located at 2 Fredry Street, 30-605 Kraków, Poland.

The idea emerged during my visit to the site, at a time when yet another electric motor failure had occurred. One day, the facility manager, Mr. Krzysztof Rejdych, contacted me with an urgent request to repair a damaged motor. As it happened, I personally delivered the repaired unit. During our meeting, Mr. Krzysztof gave me a tour of the plant and showed me the application in which the motor we had repaired was operating.

To begin, I will briefly outline the situation as I found it. Let us consider a section of the process line driven by a two-speed electric motor rated at 18,5/23 kW, coupled with a mechanical gearbox. This drive system moves a set of cables to which a trolley is attached. The mechanical structure itself includes a series of limit switches that indicate the trolley’s current position and signal when a gear change or a stop is required. All motor starts and speed changes (firsth or second gear) were performed directly from the mains using line contactors. Each start-up resulted in significant electrical and mechanical overloads. The entire structure was therefore subjected to substantial stress.

While touring the facility, we discussed the causes of the failures. At one point, Mr. Krzysztof asked whether it would be possible to eliminate them, or at least reduce them, since downtime generates considerable costs. In response, I suggested installing a variable frequency drive (VFD), which would address the existing issues by providing full control of motor operation, limiting overloads, and changing the braking behavior, as the frequency converter would assume the primary braking duty. I explained the difference between the previous operation - where the brake stopped the trolley at full speed, causing significant overloads - and a scenario in which the brake engages when the trolley is virtually at rest, which substantially extends service life by greatly increasing the operating time of the brake discs. With a VFD, the brake operates sequentially and protects the entire drive system in the event of a power loss; it is, in practice, not part of the motor’s braking process. After the upgrade, the brake effectively serves as a holding device. During the visit, I also noted the trolley’s mass and the potential energy accumulated each time it was positioned at the top. Until then, I had not given this much consideration, and like many engineers and automation specialists I know-when faced with excess regenerative energy returning from the motor, especially during rapid deceleration, I would routinely recommend a braking resistor. In this case, however, being on site prompted me to reconsider and ask myself: why waste what appears to be a substantial amount of energy when it could be utilised? I knew that Mitsubishi Electric offers energy regeneration modules, yet I had never heard of anyone applying such a solution at a concrete batching plant, where a gearbox with a significant reduction ratio is typically used. Nevertheless, I concluded that the amount of energy involved was sufficient to justify the approach. Therefore, instead of a braking resistor - which dissipates energy as heat, I proposed using a regenerative module to recover energy and apply it within the production process. Mr. Krzysztof responded very positively to my proposal and immediately requested a quotation along with the earliest feasible implementation date. To ensure the proper selection of components and to verify the potential electrical energy savings our implementation team, led by Dawid Wróblewski, performed on site measurements and a data analysis, after which we proceeded with the modernisation.

With respect to the question regarding operating efficiency, I would like to highlight two aspects. The first concerns overloads and mechanical stresses that affect system service life and the number of costly downtime events; the second relates to energy efficiency. It should be emphasised that the trolley is one of the key elements of the production line, performing several hundred cycles per day (traveling up and down). Considering this, it is easy to recognise the difference in brake wear and service life before and after the modernisation. To clarify this point, I will use an analogy to automotive braking. Please consider applying the brake at an almost zero speed - there is virtually no brake disc wear, compared with hard braking while traveling, for example, at 50 km/h. In addition, other parts of the system, such as: the gearbox, cables, tensioning wheels, and the overall structure, were continuously exposed to significant stresses and overloads, which reduced service life and, consequently, increased the number of repairs and cost - generating downtime events.

When assessing energy efficiency, several key considerations should be taken into account. First, supplying power directly from the mains creates overload conditions at every commissioning and during each gear change. In such cases, the motor draws an inrush current at commissioning that is several times its rated current, while gear changes produce current spikes resulting from abrupt speed shifts and the need to adapt the drive to new operating conditions. These sudden overloads also adversely affect the operation of other machines and equipment throughout the facility. Second, most motors (as in this case) deliver higher power in the higher, faster gear, which is entirely unjustified under these specific conditions. Although the trolley moves at twice the speed, it does so without a load and, moreover, while traveling downward. As a result, the motor operates significantly underloaded and therefore inefficiently. Third, prior to the upgrade, the trolley was pulled downward by gravity, and maintaining an appropriate speed required electric motor braking - so-called plugging (countercurrent braking). Because no braking control system was in place, the motor received virtually rated current from the line contactor for the entire duration of the trolley’s descent. After installing the variable - frequency drive, we achieved full control over the braking process. During descent, the motor shifts into generator operation, meaning that a very large amount of electrical energy flows back from the motor to the drive. By adding a dedicated regenerative module that enables the recovered energy from the trolley motor to be fed directly into the facility’s electrical grid, we realised substantial electricity savings. Previously, we had to supply a high current to the motor in order to control the trolley’s descent. Now we supply a very low current to the motor, and additionally, during each downward run we generate approximately 4 kW of energy, which is returned to the facility grid and utilised in other production processes.

From my perspective, the greatest challenge each time is confirming that the assumptions we adopted are validated in the final outcome of the modernisation and that we have accounted for every critical factor. The most important stage is always parameter configuration and commissioning, provided, of course, that all components have been properly selected. In this case, I was confident, as we had already performed measurements and analysed the entire application. In various implementations and retrofits, our confidence stems from extensive experience and the knowledge that we provide top-quality products that we trust. The deployment at the concrete plant was, in itself, a challenge, as it served as something of a prototype for us. We had never previously recovered energy in this type of application. In addition, more than twenty years in the industry have taught me that an unforeseen variable can always arise, even due to incomplete information from the client. 

For example, in certain situations during the production process, the client may perform an additional operation; because it occurs only occasionally, it may be considered unimportant and therefore not mentioned. That is why, in addition to measurements, we always ask a number of questions about operation and about scenarios that are infrequent, yet still occur from time to time. In general, the more data we have, the more smoothly the implementation process proceeds. In this specific case, as I previously noted, programming the inverter and optimally configuring all parameters proved essential. During the highly precise parameterisation of the motor-brake control sequence-intended to reduce wear to virtually zero-it became clear that relocating the limit sensors would be necessary. We had to select appropriate acceleration and deceleration times and align them with the proper placement of the sensors on the mechanical structure. 

All of this required an individualised approach to this application and numerous trials. Another key consideration was maintaining at least the same production throughput that had been achieved prior to the modernisation. Replacing the entire control system extended the overall start-and-stop process. We eliminated all overload conditions; the trolley now starts and stops smoothly, but unfortunately this also affected the resulting production output. We therefore had to increase the trolley’s inbound and outbound travel speeds so that the complete operating cycle would remain within the planned time frame. Certain constraints and issues to be resolved did, of course, arise; however, we addressed each of them successfully. We encountered significantly greater challenges on another at the same customer’s facility, where we modernised a similar transport trolley, but with two electric motors driving a shared shaft. The challenges there were far greater, but that is an entirely separate story.

There is no single, definitive answer to this question, because the energy will flow wherever, at that moment, it has an available path and encounters the least resistance-that is, wherever it can flow most readily. On one occasion it may supply the mixer motor or another drive starting up nearby, and on another it may be used by a different device, such as a fan. The key point is that it is always put to use, rather than being wasted as it was prior to the modernisation.

There are at least several benefits. First and foremost are the most readily apparent ones - financial gains, driven primarily by reduced electricity consumption and fewer downtime events, particularly those caused by unexpected failures. 

However, estimating these benefits for a rollout across all concrete plants within Holcim Polska is quite challenging. For example, how should power consumption be stated when, on one occasion, the trolley transports a relatively dry mix - as is typical on clear days - and, on another, a wet mix that weighs significantly more? In addition, concrete batching plants vary in size. In one location, the system may operate with an 18,5 kW motor, while in another it may be 22 kW or even 37 kW. How should one quantify the savings associated with avoiding failures, given that the same type of fault may cost, for instance, several thousand złoty in one set of circumstances and a multiple of that amount in another? How should the value of improved employee working comfort - and its impact on productivity - be assessed? 

What is the value of the benefits to Holcim’s image: as an employer that enhances working conditions for its teams, and as a modern concrete supplier that, by investing in innovative technological solutions, demonstrates care for the natural environment? From my perspective as an engineer, the very fact of producing a more environmentally responsible concrete while also reducing costs - and therefore generating higher profits - makes this investment an excellent decision.

Unfortunately, no such statistics are currently being collected. I can only refer to measurement results prepared for Holcim before and after the modernisation, under comparable production volumes of the same mixes, which indicated electricity savings of approximately 11 kWh per day - amounting to more than 3 MWh per year for a single trolley. An additional benefit worth noting is the improved work comfort, particularly for employees responsible for maintenance and reliability. As is well known, an equipment failure in itself is not comfortable - let alone working under time pressure when orders have been contracted and the line is down. Following the modernisation, the operator, with the support of FR - software Configurator-2 provides comprehensive monitoring of engine operation along with diagnostic capabilities, enabling maintenance to be scheduled with confidence, including work such as bearing replacement.

With respect to this modernisation, I believe that all key points have already been addressed. I would only add that I am personally very pleased that our team includes engineers and automation specialists who can implement new technological solutions effectively and in an innovative manner. I also take great satisfaction in the fact that, to the best of my knowledge, DWI MOTION is likely the first company in Poland to carry out this type of modernisation. I am not aware of anyone who, before us, modernised a concrete batching plant in this way-using a regenerative module - while achieving even a comparable result. It is also encouraging that companies operating in our country are increasingly adopting the innovative Mitsubishi Electric solutions we offer, thereby realising measurable financial benefits. 

In our view, raising customer awareness and providing education are essential; therefore, both during meetings with clients and throughout the drive-technology trainings we conduct, we place particular emphasis on the advantages of using modern, technologically advanced products. We demonstrate that their use provides a competitive edge and generates additional profit, and that reduced energy consumption also contributes to lowering CO2 emissions into the atmosphere. In this way, we help ensure better living conditions for us, our children, and future generations. Finally, I would like to thank you for the invitation and for the meeting. I hope that this story, as well as my reflections, will be valuable to readers.

Holcim’s experience demonstrates that even seemingly small improvements in drive and automation systems can generate significant business and environmental benefits. With the potential to replicate this solution across additional sites, the opportunity for further energy savings and emissions reductions is substantial, supporting the company’s long-term sustainability ambitions. To learn more about the project and watch a video showcasing the implementation, please visit the link below.