Page 275 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

GENERATOR COMPONENTS, AUXILIARIES, AND EXCITATION

13.8 CHAPTER THIRTEEN

FIGURE 13.8 Rotor end ring.

development has proved that austenitic steel containing 18% Mn and 18% Cr is immune to
stress corrosion cracking. New machines use this alloy. It is also used for replacement rings.
This eliminates the need for periodic inspection. It is important to mention that a fracture of an
end ring can result in serious damage to the machine and at least a few months’ outage. It is
highly recommended to replace the traditional material with the new material.
The rings must be heated to 300°C to expand sufficiently for the shrink surface.
Induction heating is preferred to direct heating to prevent possible damage to the rings. The
end ring is insulated from the end winding with a molded-in glass-based liner or a loose
cylinder sleeve. Hydrogen enters the rotor in the clearance between the end winding and
the shaft. The outboard end of the ring is not permitted to contact the shaft, to prevent the
shaft flexure from promoting fatigue and fretting damage at the interfaces. A balancing ring
is also included in the end disk for balancing the rotor.

Wedges and Dampers
Wedges are used to retain the winding slot contents. Wedges are designed to withstand
stresses from the windings while allowing the hydrogen to pass through holes. They must
also be nonmagnetic to minimize the flux leakage around the circumference of the rotor.
They are normally made of aluminum. One continuous wedge is used for each slot.

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