Spring-Clamp Terminal Blocks in Combined Test Laboratories with up to 5000 A
5 December 2022
Contact-loving at High Current

In combined test labs, devices and systems for high- and medium-voltage technology are extensively and stringently tested: the required electrical specifications must be proven through comprehensive test processes for quality assurance. Security is the top priority in test labs. This applies for all areas and every process – every detail is important. Therefore, Hitachi Energy Germany AG relies on spring clamp terminal blocks instead of screw connections at the new German location of its technology center.

A modern test laboratory for high-voltage and high-current testing has been established in Karlstein am Main. This lab is part of Hitachi Energy’s global technology center. Prior to the final installation or following technical verifications, high-voltage components, which are used in electrical engineering, must be subjected to comprehensive high-voltage tests.
Specifications, like thermal and electrical strength, are tested for circuit breakers or insulators, as well as operating behavior under extreme currents and voltages. Circuit breakers must prove that they are capable of not only maintaining operating voltages, but also that they can cope with surges in case of failures. During so-called temperature-rise tests, the increase in temperature is tested at a nominal load. IDEAS, an engineering consulting company, was commissioned with the new design, installation, and equipping the test lab. IDEAS specializes in the project planning, construction and commissioning of power plants and energy systems, combined heat and power plants, power supply for data centers and drinking and wastewater systems in general.

Save Space and Time

Christian Müller, CEO of IDEAS, summarizes the commission in the following way, “A combined test lab, made from three, previously separate test stations for high-current, high-voltage, and surge voltage testing, was to be built at another location. Therefore, we re-used many of the present components, like transformers. So that the new test lab could reliably satisfy current safety regulations, comprehensive redesigns of the electrical and automation technologies were necessary – within an extremely short timeframe.”

Hitachi Energy’s resource-saving concept also includes sustainable interactions with space as a resource in itself, “More constructed space means more building materials, more sealed surfaces, higher energy expenses, larger CO2 footprints, higher costs, and so on,” states Matthias Schmalz, Head of the Technology Center DE Hitachi Energy. He adds, “We want to deal responsibly with all resources across the entire company.”

The consolidation of the previously-separated test labs necessitated a more compact construction, and there were specific guidelines for efficient use of space. “For example, the control cabinet for the high-voltage test lab could not be larger than 120 × 40 cm,” explains Müller, who then continues, “For cable cross-sections of 95 mm², there’s not much space left. In addition, the safety and calibration guidelines mandated that we had to design many measurement outputs, as well as other inputs and outputs, in the cabinet.”

Maximum Reliability in Minimum Space

Two electrical contactors are used to separate the test circuit from the grid using two independent separating points, and the circuit must then be guided multiple times through the control cabinet. At the specified cabinet dimensions, the designers at IDEAS could conceive of only one possible solution. Müller explains the underlying concept, “A traditional design with screw-type terminal blocks was never even considered; we decided to use high-current terminal blocks from WAGO.” His company has worked for years on many projects using installation, interface, and automation technology from WAGO, and Müller sees confirmation in his selection to meet this challenge, “The easy handling of spring-clamp terminal blocks is simply unparalleled.”

The advantages over conventional screw-type terminal blocks are manifold. The use of cable lugs or ferrules isn’t necessary, even at cable cross-sections of 95 mm². The connection point is opened using an operating tool and locked by pressing the orange locking tab. The conductor can then be inserted, and, by turning the tool quickly to the left, it is optimally clamped. “There is no fumbling, no torque wrench, just an easy, single handed operation – what more could you want? There is no tightening torque to maintain, and unlike screw-connections, the spring-clamp terminal blocks are completely maintenance-free,” a fact that pleases Müller.

There may be up to 5000 A at the output of the test transformer. The WAGO terminal blocks used have a rated current of 232 A and are located at the input side of the transformer, where approximately 150 A is normal. Clamping connections clearly have an advantage, particularly at extreme currents in these types of test stations: because the copper cable can expand during heating and flow phenomena may occur, the contacts in screw connections may gradually loosen during cooling. “This naturally takes years to occur; however, it is one of the reasons that screw connections are considered to be maintenance connections,” explains the CEO and electrical engineer.

Well Thought Out Details

The highest safety and testing requirements are placed on the test station. Therefore, the testing and measurement circuits must be accessible. For these cases, WAGO offers current and voltage taps for the high-current terminal blocks, which can be conveniently inserted into the jumper slot and provide an integrated fuse for downstream energy measuring devices. Otherwise, the high-current terminal blocks also have a voltage tap directly at the power supply. This not only saves space during wiring installation, as additional elements don’t need to be wired in, but also time. At the same time, this combination permits exact measurement results while maintaining accuracy class 0.5 per DIN EN 61869-2, the international series of standards for measuring transducers. “This tap remains accessible, despite the attached contact protections. These details demonstrate how the development engineers at WAGO think about things,” states Maik Hessel.

For even more transparency, all of the high-current terminal blocks can be uniformly marked using WMB markers. The touch panel TP 600 from WAGO, mounted in the control cabinet door, allows for a more transparent operation and an increased level of safety at the same time. Messages, generated by the fieldbus controller, a controller from the I/O System 750 and likewise supplied by WAGO, are output via this touch panel. This supports work safety and efficient workflows: in addition to the electrical engineers, many mechanics also work in the test station, who are not permitted to open the control cabinet when troubleshooting potential errors; therefore, operating states are visualized on the display. Alert messages uniquely indicate the causes of failures. In the future, these can also be expanded to fault elimination through the addition of explicit handling instructions.

“In addition, the maintenance-freedom of the high-current rail-mount terminal blocks is an unbeatable safety aspect,” adds IDEAS CEO Müller. “Poor contact points area a true safety risk, especially at extreme currents and high thermal loads. By using spring-clamp terminal blocks, this risk is controllable without any problems: the contact force is always optimal, because the spring “follows” along.”

Photos: Mathias Leischner Photographie

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