H3X | Dossier 25 of H3X’s insulation means that heat from the windings can be dissipated effectively with a liquid cooling jacket at the housing level, without any coolant entering the stator. In addition to their high thermal conductivity, the windings in H3X’s motors can operate safely and continuously at up to 265 C. “That high-temperature performance comes mainly from the careful selection of the polymers, since all polymers’ molecular chains break down and start to carbonise once certain critical temperatures are reached,” Liben explains. “It’s always going to be the polymers that limit your temperature capability, so we haven’t used any traditional polymers or encapsulants. We’ve looked across various industries, from automotive to aerospace, including outer space, in applications not related to e-motor thermal management. But, again, we’re not using anything crazy – our processes are fully scalable and our supply chains can scale with us.” Endurance testing The winding insulation has been tested in H3X’s vacuum chamber to simulate performance at varying air densities and altitudes, including running the windings to their maximum continuous operating temperature and performing surge testing to generate a voltage wavefront of up to 2600 V. H3X reports seeing no partial discharge from the windings to date at any altitude, across all temperatures and voltages, in the normal operating range of the winding. “We’re still in the process of doing thermal endurance testing, cycling and ageing the insulation as much as we can to have a complete picture of how it behaves under every conceivable circumstance over time, but we have already accumulated a good idea of its properties versus conventional materials,” Liben notes. “Our proprietary manufacturing process is also designed to get us to a very high slot-fill factor – about 70% if you count just the copper conductors – whereas state-of-the-art is around 50%, which contributes hugely to our superior current density. There is no dead space in the cross-section of our windings or stator slots. It’s all either copper or insulation, installed at a very deliberate thickness for partial discharge performance.” Choosing stator laminations The development and production of any stator begins with lamination choices. H3X opts for 0.1 mm cobalt iron laminations in its stators, but it has found that buying fully manufactured cobalt iron stacks from several suppliers generally results in some issues. “One critical metric for a stator lamination stack is how accurately it can be made to very tight tolerance specifications; lamination misalignments consume precious space for windings and create a more troublesome surface for heat to travel through. The tight tolerances are also very important for maintaining a small air gap between the stator and rotor,” Liben says. “Mechanical stacking factor is another key metric – how much of your stack is metal versus how much is adhesive? In some stacks we have over 1000 laminations and the adhesive doesn’t contribute anything other than holding your stack together. That’s important for assembling the stator winding, but it is not performancecritical in the end-application.” These metrics would vary between H3X’s previous suppliers, with stacking factors ranging from 87% to 96%, which the company deems insufficient. Higher stacking factors often come with worse tolerancing of metal sheets. In rare instances, a stator would arrive with an excellent stacking factor and tolerancing, but ultimately weak bonds. “To stick our 100 micron-thick laminations together with a high stacking factor, we needed an adhesive that could set at a one- or two-micron thickness between each lamination, but still provide strong adhesion at high temperatures,” Liben says. “In fact, typical high-temperature lamination-bonding adhesives usually can’t hold up beyond 200 C, maybe 220 C, and we’re aiming to run our stator windings with 265 C hotspots. It’s even worse for the rotor and its magnet bonding, but in any case, we developed a specific and proprietary formulation of materials accessible by straightforward supply chains that would maintain adhesion at much higher than usual temperatures, as with our winding insulations.” Simultaneously, H3X developed its own fixtures for stacking the individual laminations supplied externally with tighter tolerances than those of most suppliers. Combined with its in-house adhesive, H3X claims a 98% E-Mobility Engineering | January/February 2024 Although 12s10p e-motors are noisier than 12s8p ones, iron bird testing has confirmed that the e-motors cannot typically be heard over the sound of the propeller
RkJQdWJsaXNoZXIy MjI2Mzk4