Using simulation and validation to build trust in new tools

Switch disconnectors are electrical devices suitable for various applications such as electric equipment, machinery and power distribution, to perform quick-make, quick-break operations in low voltage circuits. These devices convert the potential elastic energy stored in the springs into kinetic energy for the mobile contacts in the poles. A quick-make, quick-break operation lasts about 5 milliseconds, so the velocities involved are extremely high.
An optimal design of the switch disconnector control is critical for high performance. In this type of mechanism, performance is identified as the time it takes to switch from ON to OFF during a break maneuver, as well as robustness and durability (over time, the arc generated during ON-OFF operations damages the copper parts).

To understand how LOVATO Electric has changed the way it designs its products, we need to review the original process. In the past, each new product was the result of a rigid multibody analysis, based on experience gained over the years by designers, and from both mechanical and electrical experimental tests. This method was very expensive in terms of time and resources and sometimes, too many iterations were needed to meet the specifications because of the use of inappropriate engineering tools.
Traditional embedded multibody CAD software lacks the threedimensionality of the contact and cannot take into account the flexibility of the parts. These aspects make them unsuitable for applications where the contact surfaces are highly processed (such as in the switch control assembly), and the deformation of the body affects the delay with which the quick-break, quick-make operations are carried out.
LOVATO Electric was looking for a tool that could address all these aspects from the beginning of the design process, helping it to reduce the number of prototypes. That was when RecurDyn came into play with its unique features for detailed contact analysis (GeoSurface) and its proprietary technology for Multi Flexible Body Dynamics (FFlex).

Fig. 2 - Leaf-springs in the pole mechanism

After a period in which LOVATO Electric, shadowed by EnginSoft’s multibody team, tested RecurDyn’s capabilities, it was able to insert RecurDyn correctly into its product design cycle. LOVATO Electric is now able to predict the dynamics with high accuracy, and to identify the optimal configuration, increasing effectiveness and requiring the use of the laboratory for validation purposes only.

The flexibility of certain bodies was fundamental in the switch disconnector that LOVATO Electric decided to analyze to test RecurDyn’s capabilities. In particular, there were two leaf-springs under great deformation in the poles (see Fig. 2). Being subject to large deformations and being in contact with other bodies by means of sliding contacts, these springs show non-linear behavior.
With RecurDyn, LOVATO Electric’s engineers were able to simulate the correct assembly procedure starting from the springs in undeformed shape and loading them to the assembled position by simulating the actual assembly procedure. After the validation of the leaf-spring model against experimental tests (Fig. 3), using the Extract feature, it was possible to create a subassembly of the pole with the leaf-springs already in their loaded configuration, ready to be implemented in the entire switch disconnector model in as many subassemblies as necessary.
The FFlex method allows the stress within the components included in the model to be evaluated (even with non-linear material properties), while considering the effects of the deformation of the body. This aspect is crucial to identify structural problems from the early stages of the design.

Fig. 3 - Validation of leaf-springs subsystem

The switch control assembly is the device required to translate a slow rotation of the handle to a rapid switching of the switch.

At the center of the control unit is a sophisticated cam system involving a central shaft, called the primary shaft, and two other shafts at right angles to it, called secondary shafts.
These three shafts communicate via cam-type surfaces whose shape plays a very important role in performance. This part of the mechanism is impossible to model with a standard joint and it is here that GeoSurface contact was widely used, as it is able to efficiently manage the contacts between complex surfaces characterized by extensive sliding between them.

Fig. 4 - Switch control assembly