NECCOFlex Coils, a VPI Coil for Small Bore Machines
NECCOFlex coils have been designed for small bore, two-pole generators and higher speed hydros to ease the installation of coils at the lap.
NECCOFlex-E™ multi-turn stator coils provide owners with the dielectric advantages of a traditional VPI coil but with a specially-engineered flexibility at the coil knuckles that eases its installation in a small bore machine or one with a tightly lapped winding. Small bore machines typically have slots that cannot always accommodate conventional multi-turn Roebel bars. The NECCOFlex coil exceeds the flexibility needed to properly install the coil cells in the slots. Compared to the alternative of using spliced half coils, a NECCOFlex winding requires only half the number of connections.
In the coil cells, the NECCOFlex multi-turn coil is manufactured with the same insulation and curing processes as NEC's NECCOBond-E VPI coil line. It's in the end turns that The NECCOFlex coil is different. Depending on the physical contraints of the machine and other limitations of its design, NEC offers two NECCOFlex coil designs, each with different ranges of flexilbity. In both cases, the coil design makes the best use of insluation materials and manufacturing processes to achieve the most optimal total dielectric properties for your machine while still maintaining critical flexibility.
Choosing a Coil for
Longevity & Reliability?
High-speed machines (3000/3600 RPM) with bores under 40 inches in diameter can be a challenge to wind. So can salient pole generators or a hydro machines with tight laps. While resin-rich coils can offer limited flexibility in a multiturn coil, the voltage and service profile of a machine may demand the the reliability and longevity of a VPI coil. Some owners might opt for changing the machine's winding to Roebel bars. But if the limitations of the a machine's design preclude converting the winding to bars, then the NECCOFlex™ is the best choice for a multi-turn coil.
The cross sections of the coils shown at the above right illustrate the adaptability of this coil into many different machines: On the left, a three-turn coil is used in a 48 MVA, 13.8 kV, 514 RPM hydro with a 124-inch bore. In the center, a two-turn coil is used in a 24 MVA, 12.5 kV, 3600 RPM two-pole machine with a 32-in bore. On the right, a seven-turn coil with a bricked strand design is used in a 13 MVA, 13.8 kV, 720 RPM hydro with a 69-inch bore.
VPI Coils with End Turn Flexibility
NEC's NECCOFlex™ line of windings offer manufacturing and installation variations to accommodate various machine characteristics.
NECCOFlex is a class F-rated insulation system, available in two winding application types for form-wound, diamond coil stators over 6 kV. As with our VPI'd NECCOBond-E line of windings, every coil is fully tested before shipping.
NECCOFlex I, is a high-flexibilty coil, also known as the SuperFlex™ and has been successfully used in high-voltage machines with bores as small as 25 inches. The photo at the right shows just how flexible this coil is. The NECCOFlex II coil has a more moderate flexibility, but it is still flexible enough to ease what would otherwise be a difficult winding installation due to tight laps or other clearance issues. All coils in the NECCOFlex line are VPI'd and cured only in the cell portions of the coils while in the factory. End turn groundwall insulation is also factory applied, but it is not fully cured until after the coils have been installed in the slots, tied and blocked. Use NEC's proprietary resins and curing processes complete the process.