S. Lindholm J. Pipkin F. Fu B. Humphries L. Montgomery
Siemens Energy Mülheim, Germany
Siemens Energy Orlando, FL USA
Abstract— Type tests completed in August 2008 have validated all electrical and mechanical design parameters of the 1992 MVA 4-pole, 1500 RPM turbogenerator that Teollisuuden Voima Oy is now installing in the Olkiluoto 3 nuclear power station. Olkiluoto 3 is the first European Pressurized Reactor (EPR) power station. In response to TVO’s requirement that the generator capability be at least 10% above the 1992 MVA nameplate rating, Siemens Energy designed the generator so that its capability is above 2222 MVA (2000 MW, 0.90 power factor). Besides being designed to have this high capability, the generator is also designed to be very efficient (tested generator efficiency is nearly 99% at the 1992 MVA nameplate rating), and it is designed to exhibit very low mechanical vibration levels. In this paper the authors report the following highlights of the electrical and mechanical characteristics that were observed during recent type tests:
• Confirmation of expected steady state MVA capability • Confirmation of expected dynamic stability parameters • Confirmation of expected acceptable mechanical vibration
Index Terms— turbogenerator, nuclear power station,
hydrogen cooling, water cooling, type testing, MVA capability, efficiency, vibration, stability parameters
I. INTRODUCTION
The first EPR turbogenerator with its brushless exciter is shown fully assembled on the test field in Figure 1 at the conclusion of a 3 week type test that was completed in August 2008. A few days after this photograph was taken, the generator was disassembled and shipped to the Olkiluoto 3 power station, where it is now being installed on the turbine deck.
In this paper the authors outline design features that have been previously described in more detail in References 2 and 3, and we also describe the main electrical and mechanical characteristics that were observed during the recent type test.
Successfully completing the type test of this 2000 MW turbogenerator marks a major milestone in a journey that began nearly 40 years ago with the initiation of nuclear turbogenerator designs in this rating class. Some discussions of the work of those earlier days are recorded in Reference 1.
Figure 1 - Olkiluoto 3 turbogenerator with its brushless exciter at the conclusion of the type test
Main performance attributes are summarized in Table 1 below.
TABLE 1 - ATTRIBUTES OF EPR TURBOGENERATOR
Applied Standard
Class of Insulation
IEC 60034
Class 155, with Class 130 temperatures
Apparent Power
Power Factor
Frequency and Speed
Rated Voltage
Rated Current
2222 MVA
0.90
50 Hz, 25 sec-1
27 kV
47.5 kA (50 kA at 95% voltage)
Excitation Brushless Exciter
III. MAIN DESIGN FEATURES
Evolutionary design: As discussed in References 2 and 3, the 2222 MVA EPR turbogenerator design is based on the 1500-1700 MVA Siemens “Konvoi” turbogenerators that have operated with high reliability and availability for decades in nuclear power stations (see Ref 1). To meet requirements specified for the EPR generator, well proven features from other Siemens generators have been incorporated.
Generator Cooling: As illustrated in Figures 2 and 3, this hydrogen-cooled generator is equipped with an all water-cooled stator winding. The rotor winding is axially hydrogen-cooled. The stator core is primarily axially hydrogen-cooled, with radial ducts at each end for supplemental cooling. Hydrogen is circulated with one multi-stage, axial flow blower located at the turbine end of the generator, between two vertical coolers.
Figure 2 - General assembly of EPR turbogenerator
Figure 3 – Axial flow hydrogen-cooled rotor winding and water-cooled
stator winding in EPR turbogenerator
IV. TYPE TEST OVERVIEW
The 3 week type test included the following activities:
• Mechanical runs at rated speed (1500 rpm) Balance and vibration (in air) Ventilation test (in air) Friction and windage losses (in hydrogen)
• Steady-state short circuit tests Short circuit heat runs with collector set Short circuit losses and saturation curve Short circuit heat runs with brushless exciter
• Steady state open circuit tests Open circuit heat runs at 27 kV Open circuit saturation curve and core losses Voltage wave shape analysis
• Rotor moment of inertia (retardation test)
• Sudden short circuit tests (with brushless exciter)
Accomplishing this extensive test program in only 3 weeks was facilitated by the fact that all activities were controlled and monitored by experienced test field personnel working in a state of the art control room overlooking the test field. As shown in Figure 4, throughout the test program key members of the design team joined the test field colleagues in this control room to compare test results with pre-calculated values for key parameters (e.g. temperatures, reactances, vibration levels) as those parameters were being measured.
Figure 5 shows the generator with the test field collector set, and Figure 6 shows the generator with its brushless exciter.
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Figure 4 - Control room of test field
Figure 5 - EPR generator and test field collector set on the test field at the
beginning of the test program
Figure 6 - EPR generator and its brushless exciter on the test field at the
end of the test program
V. TEST CONFIRMATION OF THERMAL CAPABILITY
As outlined in Figure 7, tested generator winding temperatures were well below IEC 60034-1 and IEEE C50.13 Class 130 limits. As can also be seen in this figure, tested temperatures closely matched calculated temperatures.
Figure 7 - Summary of test results for steady state thermal capability
Details of the winding temperatures are described in Figures 8 and 9. As shown in Figures 7 and 8, temperatures in the rotor winding are well below IEC and IEEE Class 130 limits.
Figure 8 - Temperatures in rotor winding of EPR turbogenerator
As shown in Figures 7 and 9, stator winding temperatures are well below limits for water-cooled stator windings.
Figure 9 - Stator winding temperatures in EPR turbogenerator
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As shown in Figures 7, 8 and 9, from the point of view of IEC Class 130 thermal limits for the windings, the tested capability exceeds the target maximum apparent power, 2222 MVA, by over 20%.
All additionally measured temperatures (e.g. core, frame, bearing brackets, terminal box) were lower than calculated and lower than any temperatures that would prove injurious to generator components during operation of the generator at the design target maximum apparent power, 2222 MVA.
One of the major design challenges to achieving this 2222 MVA rating is in the design of the terminals. As noted in Figure 7, at this rating, the terminal current approaches 50 kA. Indeed, the numbers recorded in Table 1 in Section II of this paper show that at the lower extreme of the ±5% voltage range specified in IEC and IEEE standards the required terminal current slightly exceeds 50 kA. Designing the terminals needed for so high a current was a major challenge in developing the EPR turbogenerator design. Confirming the proper functioning of these conductors was an important objective of the type test. Results from the short circuit factory tests at 40kA (refer to Figure 7) revealed that temperatures of outlet water leaving the high voltage bushings would be less than 60oC when the generator current reaches 50KA. This temperature is well below the 90oC limit specified by IEC and IEEE standards.
A very important step in validating the design of the 50 kA terminals of the EPR generator was to verify the effectiveness of thermal conduction cooling of the braided copper flexible conductors which are used to electrically connect the 6 water cooled main leads to the 6 water cooled bushings. These connector assemblies, shown in Figures 10 and 11, are used to facilitate connecting the bushings to the main leads during assembly of the terminal box to the generator frame in the power station. They also serve to isolate bushing vibration from main lead vibration. Cooling of these flexible conductors is by thermal conduction to the water-cooled bushings and main leads to which the flexible conductors are bolted.
Figure 10 - Terminals of EPR turbogenerator, showing 6 main leads, 6 flexible connector assemblies and 6 bushings
Figure 11 – Dodecagon flexible connector assemblies between main leads
and bushings
Because each assembly of 12 flexible connectors must carry 50kA, and because cooling is by thermal conduction to adjacent water-cooled components, even distribution of current among the flexible connectors is important. Designing this assembly for even distribution of the connector currents around the circle of conductors shown in Figure 11 included three dimensional electromagnetic finite element analyses. As shown in Figures 10 and 11, the 6 connector assemblies are much larger than a depth of penetration, and the 6 assemblies are close to each other. Consequent electromagnetic coupling induces uneven current distribution. By working with 3D FEA models (and by experimentally confirming these models by favorable comparisons of calculations with tests on a smaller generator with similar flexible connector assemblies) the design team achieved a calculated ±5% variation among the 12 flexible conductors. As reported in Reference 4, observations made with Rogowski coils wrapped around each connector during the type tests showed good agreement between calculations and tests. Comparing calculated distributions of currents in the flexible connectors (the 12 white bars in Figure 12) with results from two separate tests (the blue and red bars.) shows this good agreement and confirms the ±5% variation design goal.
Figure 12 - Comparison of tested and calculated current distributions in
flexible connector assemblies between main leads and bushings
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Validating calculated magnetic saturation and calculated synchronous reactances was an important aspect of the test program. As shown in Figures 13 and 14, the tested saturation curves closely matched the curves calculated by finite element analysis (FEA) of the generator electromagnetic performance.
SGen5-4000W for Olkiluoto 3 Open Circuit Saturation Curve
0
5
10
15
20
25
30
35
40
0.0 0.5 1.0 1.5 2.0 2.5 3.0
field current normalized by 27 kV open circuit field current
line
to li
ne v
olta
ge [k
V]
Rated VoltageCalculated by FEATest Points
Figure 13 - Calculated and tested open circuit saturation curves
SGen5-4000W for Olkiluoto 3 Short Circuit Saturation Curve
0
5
10
15
20
25
30
35
40
45
50
0.0 0.2 0.4 0.6 0.8 1.0 1.2
field current normalized by 42.6 kA short circuit field current
stat
or p
hase
cur
rent
[kA
]
Rated CurrentCalculatedTest PointsTest Based If(rated current)
Figure 14 - Calculated and tested short circuit saturation curves
VI. CONFIRMATION OF DYNAMIC CHARACTERISTICS
As shown in Figures 15 and 16, all tested reactances were within the calculated min/max range, thus validating grid stability studies completed with reactances calculated during the development of this generator design.
SGen5-4000W Generator Unsaturated Reactances
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
xd x’d x’’d
Rea
ctan
ces
P.U
. at 1
992
MVA
calc unsat maxtest unsatcalc unsat min
Figure 15 – Calculated and tested unsaturated reactances
SGen5-4000W Generator Saturated Reactances
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
xd x’d x’’d
Rea
ctan
ces
P.U
. at 1
992
MVA
calc sat maxtest satcalc sat min
Figure 16 – Calculated and tested saturated reactances
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VII. TEST CONFIRMATION OF ACCEPTABLE VIBRATION
During the type test the stator was extensively instrumented with vibration sensors. These sensors included fiberoptic vibration sensors on the high voltage windings, piezoelectric sensors on the core and frame and bearing brackets, and standard sensors to measure rotor shaft vibration. All sensors were monitored and recorded with computer data acquisition systems that provided both real time output for immediate inspection by the engineers monitoring the test and also orderly storage of the data for post processing. As shown in Figure 17, all tested stator and rotor vibrations were less than specified limits. The Rigi-Flex stator winding vibration levels were quite low, less than 60% of allowable levels. Nearly all vibration levels were less than 80% of specified limits.
Figure 17 - Summary of vibration test results
In regard to the fact shown in Figure 17 that vibration of
the rotor shaft approached its permissible limit, two points are important to note. First, the shaft vibration limit for the Olkiluoto 3 generator rotor was specified to be very low, about 75% of previously acceptable limits. Second, the bearing bracket and rotor shaft vibration levels reflect the nature of the foundation support for the generator in the test field. As can be seen in Figures 1, 5 and 6, in the test field the generator was supported on steel parallels that were nearly 2m tall. Because that support is different from (and less stiff than) the support that is to be provided by the power station foundation, the generator rotor was balanced only to the extent needed to get vibration levels to be acceptable for the type test. When the generator is installed in the power station and connected to the steam turbines, rotor balance can be refined further and the rotor shaft and bearing bracket vibrations can be reduced further below the limits specified for Olkiluoto 3.
All generator vibration levels observed during the test were below specified limits, and it is anticipated that generator vibration levels in the power plant will be less than observed during the factory test.
VIII. CONCLUSIONS
Results from the August 2008 type test of the 2222 MVA, 2000 MW turbogenerator designed and manufactured for the first EPR nuclear power station showed excellent agreement between design values and tested values of the generator parameters. All results met or exceeded requirements set by Siemens and by IEC standards.
Successfully completing the type test of this 2000 MW turbogenerator has marked a major milestone in a journey that began over 40 years ago with the initiation of nuclear turbogenerator designs in the rating class above 1200 MW. All people who conducted and supported this type test, all people who contributed to the previous years of development of the generator design, and all people who contributed to manufacturing the generator have good reason to be pleased with the excellent results after this years-long and very difficult work.
REFERENCES
[1] A. Abolins, H. Achenbach, D. Lambrecht, “Design and performance of large four-pole turbogenerators with semi-conductor excitation for nuclear power stations”, CIGRE Report 11-04, 1972 Session
[2] K. Sedlazeck, W. Adelmann, H. Bailly, I. Gahbler, H. Harders, U.Kainka, U. Schuberth, H. Spiess, R. Chianese, P. Hugh Sam, R. Ward, L. Montgomery, “Influence of customer’s specifications upon design features of the EPR turbogenerator”, CIGRÉ Report 11-106, 2002 Session.
[3] R. Gray, R. Nelson, L. Montgomery, J. Pipkin, S. Joki-Korpella, F. Caguiat, “Designing the world’s most powerful turbogenerator – Olkiluoto Unit 3”, Conference Paper no. 0167, IEEE PES, Montreal, 2006
[4] K. Sedlazeck, L. Montgomery, “Generators > 1200 MW”, Giga-Watt Generation Panel Session, CIGRÉ Group A1 (Rotating Electrical Machines), 2008 Session
