Method and system for determining a synchronous machine fault condition

1. A method of determining an electro-mechanical fault condition in a synchronous machine having a stator, a rotor, and an exciter, wherein the exciter is a rotating exciter having an exciter stator, an exciter rotor, and exciter stator windings, wherein the rotating exciter has a DC/AC type of stator-rotor arrangement, wherein the method comprises:

a) obtaining an exciter current signal which is a measurement of an exciter current flowing through the exciter stator windings of the exciter, wherein the exciter current signal is an exciter stator current,

b) transforming the exciter current signal to obtain an exciter current frequency spectrum, and

c) determining that a static eccentricity fault is present in case the harmonic content of the exciter current frequency spectrum comprises a dominant frequency component at the rotation frequency (fr) of the rotor compared to a frequency component at the rotation frequency of the rotor present during healthy conditions, and a direct current, DC, component of the exciter current signal is greater than during healthy conditions.

2. The method as claimed in claim 1 , wherein in case the harmonic content of the exciter current frequency spectrum comprises a dominant frequency component at six times the power supply frequency it is determined in step c) that a rotor short-circuit fault is present.

3. The method as claimed in claim 2 , wherein in case it is determined in step c) that the harmonic content of the exciter current frequency spectrum contains a dominant frequency component at two times the power supply frequency it is concluded that a stator short-circuit fault has occurred at the stator of the synchronous machine.

4. The method as claimed in claim 1 , wherein in case it is determined in step c) that the harmonic content of the exciter current frequency spectrum contains a dominant frequency component at two times the power supply frequency it is concluded that a stator short-circuit fault has occurred at the stator of the synchronous machine.

5. A method of determining an electro-mechanical fault condition in a synchronous machine having a stator, a rotor, and an exciter, wherein the exciter is a rotating exciter having an exciter stator, an exciter rotor, and exciter stator windings, wherein the rotating exciter has an AC/AC type of stator-rotor arrangement, wherein the method comprises:

a) obtaining an exciter current signal which is a measurement of an exciter current flowing through exciter stator winding of the exciter, wherein the exciter current signal is an exciter stator current,

b) transforming the exciter current signal to obtain an exciter current frequency spectrum, and

c) determining that a stator short-circuit fault is present in case the harmonic content of the exciter current frequency spectrum comprises a dominant frequency component at 3fs*(1−2s), where fs is the power supply frequency and s is the rotor slip of the exciter.

6. The method as claimed in claim 5 , wherein in case the harmonic content of the exciter current frequency spectrum comprises a first dominant frequency component at the difference of the power supply frequency and a rotation frequency of the rotor and a second dominant frequency component at the sum of the power supply frequency and the rotation frequency of the rotor, it is determined in step c) that a rotor short-circuit fault is present.

7. A non-transitory computer readable medium having instructions comprising computer-executable components for causing a synchronous machine electro-mechanical fault condition monitoring system to perform the method having the following steps: obtaining an exciter current signal which is a measurement of an exciter current flowing through the exciter stator windings of the exciter, wherein the exciter current signal is an exciter stator current,

a) transforming the exciter current signal to obtain an exciter current frequency spectrum, and

b) determining that a static eccentricity fault is present in case the harmonic content of the exciter current frequency spectrum comprises a dominant frequency component at the rotation frequency (fr) of the rotor compared to a frequency component at the rotation frequency of the rotor present during healthy conditions, and a direct current, DC, component of the exciter current signal is greater than during healthy conditions.

8. A synchronous machine electro-mechanical fault condition monitoring system comprising:

an exciter current sensor arranged to measure an exciter current flowing through stationary windings of an exciter,

processor circuitry arranged to receive an exciter current signal of a measured exciter current, from the exciter current sensor, and

a storage unit storing instructions that, when executed by the processor circuitry causes the synchronous machine electro-mechanical fault condition monitoring system to perform a method, wherein the method includes:

a) obtaining an exciter current signal which is a measurement of an exciter current flowing through the exciter stator windings of the exciter, wherein the exciter current signal is an exciter stator current,

b) transforming the exciter current signal to obtain an exciter current frequency spectrum, and

c) determining that a static eccentricity fault is present in case the harmonic content of the exciter current frequency spectrum comprises a dominant frequency component at the rotation frequency (fr) of the rotor compared to a frequency component at the rotation frequency of the rotor present during healthy conditions, and a direct current, DC, component of the exciter current signal is greater than during healthy conditions.