Resin Rich Coils & Bars Balance Costs & Reliability
For some generators or motors, high-quality resin-rich coils or bars may provide a cost-effective trade-off between winding life & long-term reliability.
The hot-press, resin-rich manufacturing process produces multi-turn coils and Roebel bars that are best suited for industrial applications where product cost will need to be balanced against an acceptable degree of product reliably. Often, this may be the best option for owners of motors and generators that are rated up to 30 MW and operate at voltages up to 11 kv. However, for optimal reliability, care must be exercised in selecting a manufacturer. There are many low-cost producers of these types of windings who have little or no investment in engineering, process management or equipment. NEC has made the investments in its manufacturing equipment, quality management systems and research. For example, tapes must be applied with robot-controlled tension heads, otherwise, the high level of tension and precision needed to achieve the best total dielectric properties is considerably less likely. Because of NEC's long involvement with coil manufacturing, much of this sophisticated manufacturing equipment is in place and in some cases adaptable for both the VPI and resin-rich product lines.
NEC's historic and continuing commitment to the engineering of winding design means that an NEC resin-rich winding will make the best use of the materials and processes to achieve the most optimal total dielectric properties for your machine within an affordable budget. This approach is well-suited for the smaller industrial-type machines because of the lower costs in manufacturing these types of coils. While there are inherent limitations for the resin-rich types of coils, an end of life failure will not result in the same type of catastrophic impacts for this class of machines.
Top Quality Resin Rich Coils & bars require specialized cure presses
Even if the highest quality materials are used in manufacturing processes for resin-rich coils, a marginal product will result, unless pressure- and temperature-controlled cure presses are used, a fact often ignored by some manufacturers. This is because these presses must be able to perform changes in pressure and temperature in concert with the consolidation of the ground wall insulation during the entire cycle of curing. Without the more sophisticated cure presses, the flow of the pre-loaded resins in the tapes cannot be adequately controlled, leading to voids between tape layers. The flow of the resin present in the tape, must be dependent upon to push out all air and moisture out. In addition, special clamping and pressing tooling features are required at the ends of the cure presses to achieve a satisfactory consolidation of the insulation layers and pressing around the cell bends.
Options for Resin Rich Designs: NECCOPress I, II, III for Multi-turn coils
NEC's NECCOPress resin-rich line of windings offer manufacturing and installation variations to accommodate various machine characteristics. NECCOPress is a class F-rated insulation system,
available in three winding application types for form-wound, diamond coil stators up to 11 kV. As with our VPI NECCOBond-E class of windings, every coil is fully tested before shipping.
The coils are hot pressed, then fully cured in a stator dummy core constructed of precision-cut tooling that accurately reflects the mechanical
and electrical clearances during installation. The entire dielectric structure becomes homogeneous with the prescribed degree of
rigidity after the bake cycle.
The coils are hot pressed, then fully cured in a precision stator dummy core reflecting the mechanical and electrical clearances during installation. The application of a fully cured, but flexible mica tape on the coil knuckles and leads allows more flexibility and deflection during installation.
This alternative provides a NECCOPress™ winding with flexible coil ends. Only the cell portions of the coils are hot pressed and factory cured. The thermosetting epoxy loaded tapes on the coil ends are not cured in the factory. After winding the stator, the
thermosetting epoxy-loaded tapes on the coil end-turns and leads must be cured by oven baking, high current or heaters prior to service operation. Because the end turns are not cured until after installation, maximum flexibility is attained for this insulation
system. (NEC also manufactures a VPI coil with flexible end turns, which provides the same flexibility during installation but also the design advantages of a VPI coil. Click for more on NECCOFlex-E coils.)