Volume 4 | Issue 5 | Year 2001

The latest news at National Electric Coil (NEC) involves its joint effort with Mechanics Dynamics and Analysis Inc. (MDA). Both leaders in their respective industries, the duo have combined their expertise and technical know-how to create an alliance for the manufacturing, installation and servicing of water-cooled units.

The NEC-MDA alliance offers owners of water-cooled generators a unique and complete range of capabilities and expertise for a wide range of retrofit scenarios. Their joint capabilities include electrical and mechanical design expertise for uprates, upgrades and reverse engineering for both liquid-cooled and conventionally cooled stator windings. Their combined manufacturing capabilities include the production of high-voltage coils and bars with up to class F insulation, a patented two-piece hydraulic/electrical connector and a complete line of rewind components.

National Electric Coil has more than 80 years of experience in the design and manufacture of all types of coil and bar systems. Over this time, NEC has accumulated an extensive database of machine information that is particularly useful in reverse engineering and machine redesign. In more than 15 years as an independent manufacturer, MDA has acquired extensive OEM-related experience in the maintenance and upgrading of turbine and generator system components.

Both NEC and MDA have developed extensive design expertise and practical experience in addressing the elimination of water leaks at various hydraulic connections. Although both had worked independently to solve problems related to water-cooled units, this alliance represents a mutual recognition of each firm’s superior capabilities.

MDA’s patented two-piece hydraulic/electrical connector was designed specifically to address all historic leakage issues for water-cooled stator bars. Its special clip features include machined components to eliminate the risk of casting porosity and leaks; a windowless clip design to eliminate window leaks; the elimination of “blind” brazes, providing full access for critical brazes; and total quality assurance from multiple in-process inspections, flow tests and pressure tests throughout the assembly and brazing process.

Real Cool
NEC uses proven manufacturing technologies and insulation systems. Although the difficulty of manufacturing an inner-cooled bar with transposition is obvious, consistency and “windability” are also key issues. In particular, liquid-cooled winding connections require precise bar shaping during manufacture so that proper positioning can be achieved between the top and bottom bars during installation. During bar fabrication and curing, NEC custom-makes special steel forms and tooling to ensure the conformity of shape and windability at the actual installation.

National Electric Coil also has developed many of the leading techniques for the manufacture and installation of high-voltage windings and revolving field coils for generators and motors. The company builds coils insulated for required voltages and duty cycles, which are engineered to meet standard demands or special ones, and constructed to withstand various operating conditions. NEC has its own wire mills and manufactures all insulating materials to customer requirements.

NEC’s Neccobond® and Neccobond-E® have been designed according to proven component insulating materials. These systems provide reliability for the highest machine voltages in commercial use and allow maximum uprate-ability. The Neccoflex-E® coils are particularly suitable for replacement windings in small-bore machines with slots that cannot accommodate conventional multiturn roebel bars. With Neccoflex-E®, the machine is wound as it would be with conventional diamond-shaped coils. In addition, this coil exceeds the flexibility needed to wind most small-bore machines, resulting in less labor and less downtime.

Neccopak-Z® is a flexible coil side-packing system that reduces the effects of slot discharge and enhances heat transfer to the core. Integral with the coil, Neccopak-Z® eliminates the need for additional side-packing materials. The insight that NEC has gained through numerous upgrades, repairs and rewinds for motors and generators of various types and brands provided the impetus for its design. Neccopack-Z®’s zero-clearance side-packing system is made of flexible conductive silicon rubber with an integral, semiconducting protective exterior surface. Neccopak-Z® closes air gaps at contact surfaces and withstands the higher temperatures at contact points. Its elastic nature ensures the maintenance of tight slots, despite the expansions and contractions of coils during operation. Tests have shown that coils installed with Neccopak-Z® have an improved conductive contact to ground, greater heat dissipation and reduced corona.

Into the Shop
NEC is well equipped to efficiently rebuild any rotor, from incoming inspection up until the rebuilt rotor is lifted from the balancing pit for packing and shipment back to service. NEC’s capabilities include heavy-duty cranes and materials-handling equipment, oversized lathes and metalworking machinery, coil-forming equipment and the testing devices needed to handle rotors weighing up to 100 tons and measuring up to 42 feet long. The company’s Columbus, Ohio, service shop has 400,000 square feet of the latest in equipment, including up to 65-ton cranes, a railroad spur into the shop, two boring mills and an asbestos abatement facility. The shop’s capabilities include cleaning, inspection and testing, troubleshooting and repair, vibration analysis and balancing, bearing spin casting, welding, machining and fabrication.

NEC can build coils of any size and shape, and engineers them to meet standard demands or special ones, such as varied operating conditions. NEC also can custom-design new coils or literally re-engineer an existing design. In more than 80 years of operation, NEC has banked data for more than 250,000 motors and generators. In addition, NEC has an unprecedented ability to serve power producers and heavy industry in the retrofit of generators and motors built by a wide range of OEMs.

Combining a fast, efficient coil manufacturing system, a variety of insulation systems and patented and proprietary installation techniques, the company ensures its customers long, trouble-free operational lives for rewound machines. With its own wire mills, NEC produces all insulating materials to customer specifications as well as its own punched core laminations. Its service shop machines or fabricates any needed replacement parts.

NEC also offers emergency 24-hour service whether the problem is the breakdown of an elevator motor in an office building or a drive motor at a paper mill. Equipment that comes to NEC’s shop for repair is thoroughly inspected to determine the cause of failure, age or time in service, a change in duty cycle or flaws in production. With its engineering know-how and top-quality materials, NEC also can help companies get the most out of their older equipment. Through constant attention to detail and a proven track record in the manufacture of coils, NEC can fulfill any need quickly and efficiently.

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