Water-Cooled Generator

The manufacturing and installation alliance between National Electric Coil-Mechanical Dynamics & Analysis offers owners of water-cooled generators a unique and complete range of capabilities and expertise for a wide range of retrofit scenarios. The NEC-MDA team capabilities include electrical and mechanical design expertise for uprates, upgrades and reverse engineering for both liquid-cooled and conventionally-cooled stator windings. 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, as well as a complete line of rewind components. Both firms have experienced field service crews available to provide emergency and scheduled service for all makes and models of generators anywhere in the world.

The MD&A Two-Piece Clip

MDA's patented two-piece hydraulic/electrical connector was designed specifically to address all historic leakage issues for water-cooled stator bars. Special features of the clip, which can be made to accommodate either leaf or solid bar leads, include:

• Machined components to eliminate the risk of casting porosity and leaks
  
• Window-less clip design to eliminate window leaks
  
• Proven lap-joint technology that results in long-term braze joint reliability
  
• Elimination of "blind" brazes providing full access for critical brazes
  
• Crevice-free brazes to eliminate risk of crevice corrosion
  
• Total quality assurance utilizing multiple in-process inspections, flow tests and pressure tests throughout the assembly and brazing process

National Electric Coil utilizes proven manufacturing technologies and insulation systems. Although the difficulty of manufacturing an inner-cooled bar with transpositions is obvious, consistency and "wind-ability" are also key issues. Liquid-cooled winding connections, in particular, require precise bar shaping during manufacture, so that proper positioning can be achieved between top and bottom bars during installation. During bar fabrication and curing, NEC custom makes special steel forms and tooling in order to ensure conformity of shape and wind-ability at actual installation. Full-scale core models are used to verify the proper alignment of top and bottom bars at various points in the manufacturing process.

A proven insulation is important to extending the life of a new winding. Most water-cooled machines were manufactured with Class B bar insulation systems. NEC water-cooled windings are manufactured with a Class F insulation system as standard, which can help extend winding life under operating conditions. NEC's Class F insulation system has over a 20-year history of reliability. All NEC insulation systems undergo standardized factory tests for thermal cycling, voltage endurance (IEEE 1043), dielectric strength and partial discharge.

In addition, during the manufacturing process, insulation integrity is "proof tested." All bars undergo High Potential (HiPot) Power Factor Tip Up and Dissipation Factor testing.

National Electric Coil, 800 King Avenue P.O. Box 370, Columbus, OH 43216. Tel: 614-488-1151; Fax: 614-488-8892.