CIGRE 2012 A1.2 SCA1 Rotating Electrical Machines http : //www.cigre.org PS1 : Developments in Electrical Machines and experience in Service

TYPE TEST AND TORSIONAL VIBRATION MEASUREMENT OF A GIGATOP 4- POLE GENERATOR FOR AN EPR POWER PLANT

M. LICHTENBERGER / C. PONCOT N. PICHOT / L. DAVID & V. LETELLIER ALSTOM EDF / CNEPE France France [email protected]

The GIGATOP 4-pole turbogenerator is part of the conventional island for the unit 3 of Flamanville Nuclear Power Station. The generator will soon be coupled with the turbine on site. The machine is a new model that will be delivered after a comprehensive type test in the factory, approved by ALSTOM R&D and the customer. The total power increased from 1650 MVA for the N4 reference machines in the actual EDF Nuclear plants, to 1944 MVA for Flamanville unit 3 generator. The required power to accomplish the complete test program followed and rose from 10 MW to 13 MW, thus leading to an enhancement and requalification of the factory test stand.

The investigations allow checking the overall performance of the machine. First heating tests confirm that temperature raises of the generator’s different parts are in compliance with the IEC standard criteria and with predicted values from calculations. A large set of instrumentation has been placed for monitoring temperatures during the tests. It is standard practice to perform three heating tests: 1. No-load and no excitation in field winding 2. Stator winding short-circuited and field winding excited in order to have the nominal current in armature 3. Field winding excited in order to have rated voltage at armature winding. The measured average temperature of stator and rotor windings is checked during the tests and plotted. As the nominal field current can not be reached during the factory running test of the generator, special micro-stickers were placed along the rotor winding and will be used to determine the rotor temperature after a significant duration in operation on site. These heating tests are also used to measure and validate the predicted efficiency, by measuring the power absorbed by drive motor of the test stand.

In addition of the heating tests this paper will include the measurement of short-circuit ratio Kc, key of the generator stability. The maximum reactive power absorption capability is validated. Furthermore, sudden short-circuit tests are performed in order to validate the predicted transient and sub transient reactances and time constants. These tests are performed one with the two terminal boxes short-circuited, and another time with only one terminal box short-

1 circuited. In this case the reactances are lower, confirming the efficiency of such design with two terminal boxes. The neutral and short-circuit bars which connect the terminals of the generator are air-cooled as the current is divided by two with a two terminal boxes configuration. Their temperature is measured with thermal camera during the different tests.

From a mechanical point of view, a special attention is paid to shaft line torsion behaviour. The torsion natural frequencies and responses to sudden and permanent short circuits were calculated to validate the shaft line integrity. During the spin pit testing of the generator rotor the torsion vibration were measured using a telemetry system. The evaluation provides the torsion natural frequencies during balancing runs in the spin pit. In addition two modal analyses were performed in order to assess the influence of drive shaft line. During the type test the torsion natural frequencies and time responses due to short circuit are measured. The vibration responses are transient for the sudden short circuit, and are a harmonic response for the permanent two-phases short circuit. The test conditions are the same as those for electrical short circuits tests. The post-processing delivers vibration amplitude versus time and spectral analysis.

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