Customer Application
28 August 2020
Preventing Peak Loads

When industrial firms exceed the power limit guaranteed by their energy supplier, it gets expensive. So, what do you do? Scream “Stop!” and halt the equipment? Of course not. Read here about how manufacturing companies use so-called “peak shaving” to prevent onerous peak loads, reduce their energy costs and establish long-term energy management.

When peak shaving is discussed in electrical engineering, the concern focuses on peak loads, because they can cost companies a pretty penny. Even for smaller mid-sized companies, the costs can add up to 50,000 euros very quickly – and which is then due for the entire year. This has led to strategies to carefully circumvent these loads. Norbert Kordes Kabel, a cable manufacturer from Lower Saxony, shares this opinion, and has worked with WAGO to cap their peak loads.

Norbert Kordes Kabel und Leitungen GmbH u. Co. KG has developed an effective and simultaneously simple solution based on the WAGO PFC200 Controller. In addition, there is now measurement technology installed in the equipment and processing areas, and the data collected there will allow them to achieve long-term improvements in energy efficiency. The controller is programmed using WAGO’s user-friendly e!COCKPIT engineering tool.

Slowing Down at the Right Time – Instead of Hitting the Brakes

“It makes sense to have a close look,” says Andre Wächter, an electrician at the Katlenburg-Lindau facility of Norbert Kordes Kabel. As a maintenance manager, he has set a goal of recording consumption in all parts of production in as much detail as possible, in order to design targeted energy efficiency measures.

Both consumption (kilowatt-hour rates) and peak loads that occur suddenly in the context of demand rates affect the bottom line. It is particularly at demand rates that an unplanned “passing maneuver” can quickly result in costs in the five figure range. Therefore, together with WAGO, Wächter implemented a system that can be compared to a cruise control system that lets up on the gas pedal before costs rise too much.

Exceeding Supply Agreements – a Sample Calculation

A few numbers suffice to give an idea of costly peak loads can be. The regional energy supplier for Kordes Kabel sets the demand price per kilowatt (kW) at around 120 euros for companies with their own medium-voltage supply (which includes Kordes Kabel) and an annual service contract of more than 2,500 hours.

If Kordes Kabel were to exceed the predetermined capacity limit at the end of even just a single 15-minute measurement interval, then each additional kW would increase the demand price by 120 euros. Short-term production increases, which necessitate switching on a medium-sized main drive at 300 kW, would thus cost the company 36,000 euros over the course of the year. Undesired spikes thus have the potential to turn any production calculation into a reductio ad absurdum.

The conclusion is that investments in a system that helps to smooth out peak loads pay off from the very first minute. “However, to do this, we have to know where we can intervene,” explains Wächter. At the cable manufacturer at the foot of the western Harz mountains, the majority of energy is used in the so-called rough draw – the first step in drawing wire. Downstream of this sits a system that reduces the eight-millimeter-thick copper rod to the desired cross-section through the cold-forming method using increasingly narrow drawing plates.

Prior to being processed into sheathed cable (NYM), the copper wire is made pliable through short-circuit current in a resistance annealer. This has an output of 900 kW, and the motor for the drawing system uses 700 kW. There are other elements that also add noticeable loads, including the extrusion lines for insulating wires and compete cables, as well as shrink furnaces in the packaging area. “We have a handful of those with 45 kW outputs. If they all happen to heat up at the same time, then we reach our load limit of 1860 kW very quickly,” explains Andre Wächter.

Gradually Reducing Outputs

If this case occurs, the power consumption can be reduced in four stages without suddenly switching off the whole production area. The programming in the WAGO PFC200 Controller provides a way to reduce the motor output of the rough draw in 70 kW increments. “I can slow down the rough draw, without endangering the process or introducing quality issues in the wire. With extruders, this would not be so easy, since the process is continuous,” explains the maintenance manager. Because the extrusion and wire pulling can be decoupled in production at Kordes Kabel, the peak loads can be taken into consideration in one area while the other takes advantage of interim storage. This method would not be possible for systems in which the entire cable production, from drawing to extrusion, occurs in one pass.

Detailed Measurement Values Promote Energy Efficiency

The system implemented with WAGO is sensitive enough to detect and record out-of-control loads early on. “In this case, we switch down at stepped intervals in a targeted way. This way, we avoid slamming on the brakes after 14 minutes and disconnecting the entire system from the mains.” After a short training period with WAGO in how to use the e!COCKPIT engineering software tool, Wächter wrote his own program to determine where the pre-warning signals should occur and to view the current interventions in detail.

The facility in Katlenburg-Lindau collects data from around 100 meters, which measure complete machines and equipment parts. “For example, we consider each extruder individually and split one line according to the subsystems.” This is the only way to see if the efficiency improvements in one area lead to degradations at another point. A superficial consideration of only the entire system would lose most of the detailed changes that affect the sum total.

Incorporating this technology has paid off for us in two ways: We prevent expensive peak loads and also gain insight into the areas where we can most effectively save energy.

Andre Wächter, electrician at Norbert Kordes Kabel und Leitungen GmbH & Co. KG

One System for Peak Management and Energy Efficiency

Consequently, the WAGO system with the PFC200 can be used to evaluate whether measures for improved energy efficiency are working. “Incorporating this technology has paid off for us in two ways. We prevent expensive peak loads, and also gain insight into the areas where we can most effectively save energy,” emphasizes Andre Wächter.

For those tasked with energy efficiency, it is important to find a solution that can be used in the company and is also freely programmable. “We want to decide for ourselves how the measures should look in detail.” The use of ready-made modules in e!COCKPIT facilitates the work without placing limits on functionality. Complete black-box systems are far more rigid. “Most of them sum the loads and then switch off after a limit is reached. Instead of that, we can throttle back, slowly and precisely.”

Raising Awareness about Energy Management

The results are communicated freely among the workforce at Norbert Kordes Kabel und Leitungen GmbH & Co. KG. “I regularly post figures on how much energy we are consuming,” emphasizes Andre Wächter. The data acquisition is so fine-grained that consumption figures can be associated with individual shifts and with the products being manufactured.

Therefore, Andre Wächter plans to send the production data to the PFC200 as well. The evaluation will take place against a tense background, as new requirements are being placed on cables by the Construction Products Directive. As one example among many: According to the experience of Norbert Kordes Kabel und Leitungen GmbH u. Co. KG, the increased incorporation of flame-retardant plastics requires greater energy consumption during processing, and thus will continue to drive up the energy consumption per ton of manufactured cable.

Satisfying ISO 50001

The interest in transparent figures is motivated by both economic factors – in short, manufacturing costs – and by ISO 50001. “We have to be able to prove our savings. Therefore, it is insufficient to simply relate the total quantity to energy consumption, since each product has its own energy profile.”

Summary

The PFC200 Controller, in combination with WAGO’s e!COCKPIT engineering software, makes it easy for users to analyze load distributions during production and to harmonize them with a view toward demand pricing. The openness of the easily-integrated system enables users to implement their own requirements and calculations. The return on investment periods are negligible due to the large savings from avoiding peak loads.

Text: Lukas Dökel | WAGO
Photos: Thorsten Sienk

Product Overview

Item no.: 2759-101/1110-2005

e!COCKPIT ; Multi-User License ; 05 pcs

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Controller PFC200 ; 2 x ETHERNET, RS-232/-485

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Controller PFC200 ; 2nd Generation ; 2 x ETHERNET, RS-232/-485

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Controller PFC200 ; 2nd Generation ; 2 x ETHERNET, RS-232/-485, CAN, CANopen, ...

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Controller PFC200 ; 2nd Generation ; 2 x ETHERNET, RS-232/-485, CAN, CANopen

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Customer Application 28 August 2020 Preventing Peak Loads