rotating rectifier with several diodes per arm in parallel. A pilot exciter machine with permanent pole magnets was chosen as a power supply for the main exciter machine.

Figure 7 - Brushless Exciter for EPR Generator

A four-loop controller was chosen as an automatic voltage regulator (AVR). This four-loop controller was chosen to permit the dynamic behavior of the excitation system to fulfill the client specification. In addition to the generator terminal voltage, controller loops for the generator speed, electrical and mechanical power, and pole angle limiter were included.

The client specification defined several different failure cases and a widely spread grid. One of these required cases was to operate the generator at rated active power and 35% of rated MVAR in the underexcited range. This operation point corresponds to a rotor angle of 90o.

At this operation point, the stator end zones and the stability of the generator at the grid are the main design challenges. The end zones of the EPR generator have been designed to permit this operation point, even at the

required 90% voltage mentioned earlier in this paper. In regard to stability, traditional AVR’s would limit the generator to a significantly smaller MVAR value; the four-loop controller permits this operation point.

One of the more challenging additional requirements was to survive the loss of one of three grid connection lines, each with 80% reactance. With the four-loop controller it is possible to ensure the generator operation within the specified limits and to return the generator to its reference value within 5 seconds.

RAILWAY TRANSPORT OF COMPONENTS

Among the most challenging requirements in the customer specifications was the requirement to design all generator components to accommodate railway shipping constraints imposed by the French railway system, Société Nationale des Chemins de fer Francais (SNCF) and the French railway transport company, Société de Transports Spéciaux Industriels (STSI). Meeting requirements for railway transport on the SNCF railway system with STSI transport cars and tooling required especially careful attention to the size and weight of the wound stator core and fabricated steel frame, the largest and heaviest generator component.

Separate shipment of the section of the frame designed to house the hydrogen coolers and hydrogen compressor (at left end of stator in Figures 1, 2, 4 and 5) allowed the length of the main stator section to be limited to 11 meters, as illustrated in Figure 8. The authors’ Company has used this practice for many years to accommodate shipping size and weight constraints. Also, careful attention to the weights of the wound core and fabricated frame has led to a design that meets the size and weight constraints imposed by SNCF and STSI. Design of these components has been guided by finite element analysis of all loads imposed by railway transport and hydrogen pressurization. As suggested by Figure 8, it is possible to ship the EPR generator stator with STSI transport cars on SNCF railways.

Figure 8 - Railway Transport of EPR Generator Stator

The SNCF railway-loading gauge shown in Figure 9 strongly influenced the frame cross-section design. For example, the flat sides of the frame shown in Figures 1 and 2 were introduced to permit the stator to fit within the 4.15m width limit specified in this loading gauge.

Also, the special narrowed and raised shape of the bottom of the frame near the terminal box adapter was designed to meet loading gauge requirements imposed by clearances to railway station platforms. Those