This invention relates to an electric rotating machine with the features of the preamble of claim 1 and a genset comprising such an electric rotating machine. Electric rotating machine refers to both generators and motors.

It is known that generator rotor windings can overheat because of various generator operation conditions and failure modes. If the temperature gets too high, insulation between the rotor windings can deteriorate leading to electric shortages.

The rotor of the electric rotating machine can be considered of any art such as salient pole, round rotor, squirrel cage, cylindrical, etc.

Prior art concentrates on:

- estimating rotor temperature by measurement of rotor current, and

- controlling the temperature by varying the output load of the generator.

US 8967857 B2 shows a temperature detection device that detects a temperature of a rotor of motor by measuring rotor current.

US 3,358,208 shows a method for controlling temperature rise in rotor windings by varying the output load.

US 2012/0133313 A1 describes a generator provided with a rotor temperature rise estimation device.

US 8482238 B2 describes a system and method for estimating a generator rotor temperature in an electric drive machine. A prime mover is defined as the source of mechanical torque to an electric generator, coming from any source such as a gas turbine, reciprocating engine (diesel or gas), hydro turbine, wind turbine, and all other generation sources. A genset is comprised by an electric generator and a prime mover connected by a shaft to transfer torque. It is an object of the invention to provide an electric rotating machine and a genset where it is possible to control the temperature of the rotor windings more reliably. This object is being accomplished by an electric generator having the features of claim 1 and a genset comprising such an electric generator. Advantageous embodiments of the invention are defined in the dependent claims.

This invention differs from the prior art by:

- measuring directly the rotor windings temperature by using temperature sensors arranged or in the rotor windings

- controlling rotor windings temperature in reaction to the measured temperatures by varying the field current and/or output power It can be provided that the control device is being arranged to reduce the field current carried by the rotor windings and/or power output of the electric generator if the temperature at the location of the at least one sensor reaches or exceeds a given threshold. In this way overheating of the rotor can be avoided. Any one of these measures leads to a decrease in temperature of the rotor windings and thus avoids overheating.

It can be provided that there is a plurality of sensors, the sensors of the plurality being arranged at different positions on or in the rotor windings. The sensors can be placed at so-called hotspots. These are positions where temperature maxima are to be expected.

It can be provided that the at least one sensor is of a passive type, and wherein there is provided an emitter arranged to send a frequency signal, the frequency signal being changed at the position of the at least one sensor depending on the

temperature at the location of the at least one sensor, and wherein the at least sensor is arranged to retransmit the changed frequency signal. No wiring of the sensors is necessary. An example for a sensor of a passive type is a so-called SAW- sensor (surface acoustic wave sensor) which uses and modulates surface acoustic waves to sense physical properties.

It can be provided that the at least one sensor is of an active type (such as

thermocouples, RTDs etc.).

It can be provided that the connection between the control device and the at least sensor comprises slip rings and wires leading from the sensors to the slip rings and from the slip rings to the control unit.

It can be provided that the connection between the control device and the at least sensor comprises at least one passive or active sensor. It can be used together with slip rings, e. g. to transmit the information from the slip rings to the control unit, or without slip rings.

The control unit can be part of an excitation control system of the electric generator. For a genset, it can be part of an electronic control unit of the genset.

Embodiments of the invention are shown in Figures 1 to 3:

Fig. 1 shows schematically an embodiment of an inventive genset 7 having an electric rotating machine 1 in the form of an electric generator and a prime mover 8 (in particular a combustion engine such as a gas or diesel engine having a plurality of pistons arranged movably in combustion cylinders) to drive the electric generator via coupling 10. The electric generator comprises a stator 2 and a rotor 3, the rotor 3 having several rotor windings 4 (two of which are shown in Fig. 1 by way of example). A control unit 5 is arranged to receive information and to send commands as indicated by the dashed lines. In this embodiment the control unit 5 is arranged as an electronic control unit of the complete genset 7.

In this embodiment a plurality of passive sensors 6 (six of which are shown in Fig. 1 by way of example) is arranged on and within the rotor windings 4. There are provided emitter/receiver-units 1 1 (three of which are shown in Fig. 1 by way of example) arranged to send a frequency signal upon a command of the control unit 5, the frequency signal being changed at the position of sensors 6 depending on the temperature at the location of the sensors 6. The sensors 6 retransmit the changed frequency signals which can be received by the emitter/receiver-units 1 1 . No wiring of the sensors 6 is necessary.

If the control unit 5 concludes from the information provided by the sensor 6 via emitter/receiver-units 1 1 that the temperature at one or several of the locations of the sensors 6 reaches or exceeds a given thresholds it can:

- command the prime mover 8 to reduce driving torque of the rotor 3 and/or

- command an excitation control unit 9 to reduce field current carried by the rotor windings 4

Fig. 2 shows an electric generator having a stator 2 and a rotor 3 the rotor 3 being provided with rotor windings 4. The rotor 3 can be driven by a prime mover (not shown, e. g. a combustion engine) via coupling 10. A plurality of sensors 6 located at different positions on and in the rotor windings 4 is shown. Control unit 5 can command a decrease of the field current carried by rotor windings 4 to decrease their temperature and/or to decrease output power of the electric generator.

Fig. 3a to 3d show possible placements for the sensors 6 at the top, bottom, or center of a rotor winding 4 for a rotor 3 of the salient pole type (Figs. 3a, 3b and 3c, Fig. 3b shows a detail of Fig. 3a, here by way of example four poles 14 are shown, Fig. 3d shows a cross section through the rotor 3 of Fig. 3a) and of the non-salient pole type (Figs. 3c).

In Fig. 3d, the outer left plurality of sensors 6 is arranged at a drive end (DE) side, the centre plurality of sensors 6 is arranged at a core pack and the outer right plurality of sensor 6 is arranged at a non drive end (NDE) core. Reference sign 16 denotes a DE section of winding, reference sign 17 shows an NDE section of winding.