Stäubli’s MULTILAM technology is designed to perform in harsh conditions.
Stäubli has sponsored this post.
For engineers in many industries, electrical connectors do not seem like something that requires much thought. In many cases, one can simply consult a chart on a supplier order form and order connectors that will fit into the design, with the gauge, materials and service life specs to support the needs of the product. The same largely holds true in many industries, from electronics manufacturers working with USB connectors, all the way to industrial users connecting to a three-phase power supply. But in the high current and high voltage world of power transmission and distribution, connectors are non-trivial, and in many cases require custom engineering to ensure safe and reliable operation.
In large power transmission and distribution systems, the apparent simplicity of electrical contacts is far from reality. Moving high currents under high potentials creates problems unique in electrical engineering. Resistance is key, and connectors must be specially engineered; even small levels of resistance can generate enough heat to destroy the system. In addition, connectors must reliably conduct high current over a service life which may include thousands of mating cycles, potentially damaging contacts through wear and arcing. In the power grid, these connectors are everywhere, and are used in switchgears, circuit breakers, disconnectors, gas insulated lines, transformers and much more.
In addition to the need for a safe and reliable power grid, electrical energy must also be transformed by means of converters. With power electronics, converters and energy storage, electrical energy can then be used sensibly and efficiently—for example, in electric drives, production and logistics processes, for energy storage, or for feeding into the grid.
Stäubli’s electrical connectors for high power transmission are designed to perform in these challenging conditions. Stäubli’s engineers design custom connectors to suit these extreme demands, with solutions including their proprietary MULTILAM technology.
What Is MULTILAM?
MULTILAM is a Stäubli product line of electrical connectors used in electrical distribution switchgear. The key innovation of MULTILAM is in the parallel contact elements creating a redundant and stable connection with low contact resistance. Low contact resistance is especially important in this industry, as contact resistance in the microohms can cause heat in the contacts, annealing the spring and destroying the connector. In addition, power transmission components are frequently installed outdoors, and maintenance intervals can reach 25 years or more.
MULTILAM was originally developed by the Stäubli company Multi-Contact in 1962, when an engineer inspired by heaters with thin fins realized that with heat conduction and electrical conduction so closely related, a fin design could provide an alternative to expensive spring contacts. The product he designed, featuring a louvered design, was the beginning of MULTILAM.
These connectors are characterized by high current-carrying capacity, very low contact resistance, and high reliability and durability under extreme operating conditions at high mating cycle numbers.
Design Challenges for High Power Connectors
Switchgear operates in extreme conditions and is required to perform for long maintenance intervals. In addition, engineers sourcing the right connector for these applications must consider several other factors.
First and foremost is the wear and tear on contacts that occurs after repeated mating cycles. This wear steadily increases the contact resistance until the contact fails. Failure of connector contacts can lead to short circuits and power outages, as well as safety risks.
Most types of electrical connectors use spring force to mate contacts. However, depending on the material, springs are susceptible to fatigue and deformation over time, degrading the effectiveness of the connector.
According to Steve Langston, Business Development Manager at Stäubli, changes in the spring must be anticipated and designed into the product lifecycle.
“We don’t get to skip around the laws of physics, unfortunately,” says Langston. “Springs still have to do what they do.”
However, in many cases spring softening is not the first failure point of the spring. Typically, that is the plating, which wears on the contacts. So, while spring softening must be considered, the design of the MULTILAM contacts helps to reduce this risk of failure.
Lastly, not every connector is created equal. The team at Stäubli approaches each project by considering the specific needs of the application.
“Every system requires its own solution,” says Jason Wright, Head of Power Transmission and Distribution at Stäubli’s North American division. “We need to consider factors of the system. Does this need to be plugged in by humans? Is it done by a tool? Is it being isolated? How heavy are the two parts coming together?”
Custom connectors meet multiple design and performance requirements. A common need is to delicately balance insertion force and contact resistance. High contact spring forces can reduce resistance across the interface, but advanced designs can deliver the benefits of a high insertion force connector while keeping the system user-friendly and error resistant. Forces are highly variable, and are very dependent on the application. For example, the limits for putting a high voltage static bushing into a high voltage circuit breaker are much higher, into the hundreds of pounds of force, than for a rackable power distribution card for a power conditioning device or power supply. Staubli engineers, using various MULTILAM types, can adjust the current rating, contact force and plating for specific solutions to specific problems.
Weight is another key design consideration. On the ground or on a ship, weight is less critical than in aerospace applications, for example. With a ‘roomier’ weight constraint, designing for current and energy specifications is easier. With tighter weight constraints, the design of a connector becomes more challenging. As a result, some connectors are designed to minimize excess material and weight.
Sourcing Custom High-Power Connector Solutions
Engineering.com asked Wright and Langston for their advice for engineers seeking to partner with a supplier like Stäubli for a custom connector. They advised that because the needs and capabilities of electrical connectors vary so widely, it is most important to be honest and direct about the specific challenges of each application, and to provide plenty of time to the supplier to design the solution.
Since the specifications of custom high-power connectors are system dependent, Stäubli engineers design a connector using MULTILAM technology based specifically on the needs of the device. For example, connecting force, current, voltage and IP rating are all considerations that can be provided for. Stäubli can also customize weight, heat dissipation, mass and more, depending on the customer and industry.
“We make connections, everything from half a millimeter in subsea devices, all the way up to feet in diameter for high voltage switch gear and power transmission and distribution, but also very light connections that carry several hundred amps in sub orbital devices that have to survive exit and reentry of the atmosphere. So, we have quite a large portfolio,” says Wright.
For vendors like Stäubli, the most important factor is that customers are open and honest about what their challenges are, and that they initiate the process early—providing all of the electrical, mechanical, environmental needs or expected failure modes of their system so that designers have the information needed to specify a solution within project deadlines.
According to Langston, time is one of the most important gifts you can give your custom electrical connector supplier. As any technology supplier can attest, a lack of information or time inevitably results in higher cost, longer project timelines or design compromises. However, much of this compromise can be reduced by simply considering the connection mechanism earlier on and leaning on Stäubli’s connector expertise to aid in that design process.
For more information about MULTILAM and Stäubli’s high power connectors, check out their website.