DIN IEC/TS 60034-32:2016-03 - Draft

AC machines are equipped with multi-strand windings in the stator. The information given in this Technical Specification refers to a design with two-layer winding. The windings are connected to a multiphase voltage system (current system) which builds up a rotating magnetic field in the air gap between the rotor surface and the stator bore. Current and voltage can vary during operation depending on the mechanical load. Electrical machines are usually designed for motor or generator operation. Most AC machines are equipped with symmetrical three-phase windings consisting of three electrically insulated and spatially distributed winding sections designed for normal operation. Large rotating AC electric machines are usually equipped with form-wound windings. The winding head is the part of the stator that protrudes beyond the end of the magnetic core and is usually circularly tapered. Most large AC machines with form-wound coil in the stator winding are provided with a winding head support in the stator. This is intended, among other things, to be able to withstand the high electromagnetic loads to which the machine is subjected in the event of an electrical fault in the electrical supply system. This includes faults in the supply lines of a power system or in an electronic supply device. In most cases the winding head support in the stator is intended to not only increase structural strength, but also to provide the appropriate structural stiffness and inertia to specifically influence the structural dynamics and thus the vibration level during operation. Typical support elements are plates and rings that support the winding head cone as a whole. In addition, the distance between the coils (or rods) of the winding head is determined by spacers and their position is fixed by fastening elements. Support elements, spacers and fastening elements are usually made of composites of fiberglass materials as well as resin-impregnated felts, cords and bandages. Metal parts surrounded by strong electric fields can also cause electrical breakdown and thus affect the permanent dielectric strength. To date, there is no general Technical Specification that can be used to reliably and comparably determine natural frequencies during standstill and the vibration behavior of winding heads in the stator during operation. For the recalculation of large electrical machines the experimental modal analysis of winding heads in the stator for the determination of natural frequencies and natural modes of vibration is a common tool worldwide. The aim is to avoid the operation of a machine where increased vibrations occur at the winding head under the influence of natural frequencies. A commonly used test method is the measurement of transfer functions and determination of structural dynamics properties (for example, natural frequencies, natural modes and other modal parameters) by means of impact testing. This test is used on new machines by the manufacturer and by the operator or supplier as a maintenance tool during the overhaul of large rotating machines. The vibration behavior of winding heads in the stator can be measured periodically by special vibration transducers mounted at selected points on the winding head or as part of permanent online monitoring during operation. Although the measurement of natural frequencies and vibration levels on stator winding heads is a common procedure, the interpretation of the results still requires improvement and further development. For this reason, the first edition is a Technical Specification and not an IEC standard. The responsible committee is DKE/K 311 "Drehende elektrische Maschinen" ("Rotating electrical machines") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.