Modern contact elements combine peak performance with cost-savings, says Oliver Semling
In the power transmission and distribution industry, three characteristics are key for electrical connections: safety, efficiency and durability. The extremely low heat generation, extremely low contact resistance and stable and uniform contact force of louver contacts can ensure excellent electrical connection performance. Here, the technical principles and typical applications of louver contacts are briefly introduced, considering current design requirements and experience.
An electrical connection is a connection between conductors that allows the transmission of electrical energy. The main cause of failure in electrical connections is poor contact, which manifests itself in the form of increased or variable contact resistance. Poor electrical contact may result in abnormal heat generation, exceeding the maximal permitted temperature, which in turn affects the insulating ability of the product and the operational safety of the system. One of the reasons for poor electrical contact can be contamination. It reduces the effective contact area for current transmission compared to the theoretical area created by the mechanical preload of the contact. Layers of pollution on metal surfaces, such as oxide layers, oil films and metal dust, make the effective contact area much smaller than the surface contact area, and the current flow is concentrated on a single contact point, resulting in an increase in contact resistance. In other words: what looks like a current carrying surface-to-surface connection is effectively a high resistance coincidentally point-to-point connection.
Stäubli Electrical Connectors’ two-component Multilam is completely beryllium-free and consists of individual silver-plated copper louvers that are mounted onto a stainless-steel band. Parallel contact points are created between two contact surfaces and provide a certain contact force that can penetrate the pollution layer and achieve an effective electrical contact. Each louver forms an independent elastic current bridge, which significantly reduces the contact resistance between the contact surfaces by connecting several louvers in parallel in one turn. Based on the given contact force, geometry, elastic characteristics and properties of the surface material of each louver, the contact resistance can be calculated accurately. The contact resistance of Multilam corresponds to the resistance of the contact louvers connected in parallel. The geometry of each contact louver is designed to achieve a long lifespan, while the constant elastic pressure of the Multilam keeps the connection between the contact interfaces stable and achieves a constantly low contact resistance.
Ideal For Demanding Applications
Introduced in the early 1960s, the Multilam technology has become an excellent choice for demanding applications: reliable and safe operation in environments with strict requirements for temperature, vibration and shock. Compared with spring contacts, the advantages of the technology are focused primarily on three aspects: high flexibility, low contact resistance and highest reliability. Designed for a high-rated current of up to 240A/cm, ideal for high loads on high-voltage switchgears, short circuit current of 4,400A/cm peak current of 11200A/cm and up to typical 10,000 mating cycles, this contact technology meets all the electrical and mechanical requirements to withstand the service life of a switch, circuit breaker or power transformer. Ease of application and flexibility are enhanced by very high tolerance and misalignment compensation in combination with a simple installation into a cost-effective straight groove.
Current trends in electrical energy supply, such as the miniaturisation of systems to conserve resources while simultaneously the power demand is increasing, the need to replace the climate-damaging SF6 insulating gas as well as increasing requirements due to the expansion of renewable energies force contact technology to adapt to these changes by further evolving towards compactness. The newly introduced ML-CUX contact element features an innovative two-component structure with excellent current-carrying capacity and enables compact connection
solutions with high power density, effectively reducing the total cost of ownership (TCO) of the equipment. Every ML-CUX contact is made to order and to fit the various sizes of medium and high-voltage applications to meet the exact needs of the customer’s diverse requirements.
The application of Multilam as electrical connectors is very sophisticated and widely used in circuit breakers, transformers, switchgear, gas-insulated busbars and other electrical products. The extremely low heat generation, minimal contact resistance and constant contact force ensure exceptional electrical connections, bringing more and longer-term benefits to the power system.
Oliver Semling is with Stäubli Electrical Connectors