Device for condition monitoring and protection of rotating electrical machines, and a method thereof

1. A device for condition monitoring and protection of a rotating electrical machine based on measurements of current signal obtained with a current sensor measuring the current flowing in an electrical line powering the rotating electrical machine, wherein the device is configured to operate a switch to electrically disconnect the rotating electrical machine from the electrical line based on processing of the measured current, the device comprising:

an input interface configured to receive current signal from the current sensor;

a processing unit configured to:

a) extract, using at least one wavelet filter, an approximation coefficient and a frequency band content containing information representative of a condition of a rotor bar from the measured current signal;

b) compare the extracted frequency band content with a threshold value for identifying the condition of the rotor bar in the rotating electrical machine, wherein the condition of the rotor bar includes identifying damage associated with the rotor bar;

c) provide one or more status signals based on the identified condition of the rotor bar; and

an output interface configured to provide a trip signal to the switch based on at least one status signal from the one or more status signals, for electrically disconnecting the rotating electrical machine and protecting the rotating electrical machine based on the identified condition.

2. The device as claimed in claim 1 , wherein the processing unit identifies the condition of the rotor bars including fault conditions for protecting the rotating electrical machine, wherein the fault conditions comprise at least one of rotor bar fault, overcurrent fault and thermal overload fault.

3. The device as claimed in claim 1 , wherein the processing unit extracts the frequency band content containing information representative of the condition of the rotor bar with at least two wavelet filters.

4. The device as claimed in claim 3 , wherein the processing unit uses four consecutive samples of the measured current signals along with outputs from the wavelet filters to provide a real time detection of damage by identifying one or more broken rotor bar conditions.

5. The device as claimed in claim 3 , wherein the at least two wavelet filters comprises a first wavelet filter and a second wavelet filter, and an output of the first wavelet filter is provided to an input of the second wavelet filter.

6. The device as claimed in claim 5 , wherein the output of the first wavelet filter is downsampled and provided as the input of the second wavelet filter.

7. The device as claimed in claim 3 , wherein each wavelet filter of the at least two wavelet filters extracts a corresponding approximation coefficient.

8. The device as claimed in claim 1 , wherein the output interface is configured to provide the one or more status signals to a human machine interface (HMI) associated with the device for displaying the condition of the rotating electrical machine, and wherein the HMI is at least one of a local HMI comprised in the device or a remote monitoring station.

9. The device as claimed in claim 1 , wherein the processing unit provides at least one of an alarm indication from the one or more status signals to indicate an onset of damage in the rotating electrical machine.

10. The device as claimed in claim 1 , wherein at least one status signal from the one or more status signals provides a count of broken rotor bars and wherein the trip signal is generated based on comparison of the count of broken rotor bars with a predefined threshold value.

11. The device as claimed in claim 1 , wherein the processor is further configured to compare the extracted frequency band content and the at least one approximation coefficient with the threshold value for identifying the condition of the rotor bar.

12. A method for monitoring a condition of a rotating electrical machine and protecting the rotating electrical machine using measurements of current signal obtained with a current sensor measuring the current flowing in an electrical machine, the method comprising: receiving current signal from the current sensor;

extracting, using at least one wavelet filter, an approximation coefficient and a frequency band content containing information representative of a condition of a rotor bar from the measured current signal;

comparing the extracted frequency band content with a threshold value for identifying the condition of the rotor bar in the rotating electrical machine, wherein the condition of the rotor bar includes identifying damage associated with the rotor bar;

providing one or more status signals based on the identified condition of the rotor bar; and

generating a trip signal to operate a switch based on at least one status signal from the one or more status signals for electrically disconnecting the rotating electrical machine and protecting the rotating electrical machine.

13. The method as claimed in claim 12 , wherein the step of providing the at least one status signal from the one or more status signals provides for a count of broken rotor bars and wherein the trip signal is generated based on comparison of the count of broken rotor bars with a predefined threshold value.

14. The method as claimed in claim 12 , wherein the step of extracting the frequency band content containing information representative of the condition of the rotor bar is performed using at least two wavelet filters.