Method for the diagnostics of electromechanical system based on impedance analysis

A method for monitoring a condition of an electromechanical system in which an electrical rotating machine is used to measure currents and voltages of more than one phase to be more sensitive to and prevent insensitivity to developing faults, comprising the steps of:

• providing an electrical rotating machine supplied with electrical power by alternating current supply cables;
• connecting a measuring device with an analog to digital convertor to said alternating current supply cables;
• measuring at least two phase currents and two phase voltages for the same respective phases supplying the electrical rotating machine with said analog to digital convertor;
• processing the measured phase currents and phase voltage values using a computer processing device connected to said analog to digital convertor, wherein said computer processing device contains a processor and a processing module which are adapted to transform the measured phase current and phase voltage values from the time domain to the frequency domain, creating voltage spectrum signals V1F, V2F, V3F, . . . VnF and current spectrum signals I1F, I2F, I3F, . . . InF;
• processing in said computer processing device the current spectrum signals I1F, I2F, I3F, . . . InF to obtain an inverted current spectra I1F,inv, I2F,inv, I3F,inv, . . . InF,inv;
• processing in said computer processing device the inverted current spectra I1F,inv, I2F,inv, I3F,inv, . . . InF,inv to obtain impedance spectrum signals Y1F, Y2F, Y3F, . . . YnF of the rotating machine;
• extracting a vector of amplitudes at frequencies of interest from the impedance spectrum signals with an analyzer contained in said computer processing device which are needed to diagnose the electromechanical system;
• calculating a maximum value of a difference between the amplitudes at frequencies of interest extracted from the impedance spectrum signals in said computer processing device;
• comparing a maximum value of the difference between the amplitudes at frequencies of interest extracted from the impedance spectrum signals with a threshold which is given as a limit in said computer processing device so as to reduce the possibility of missed alarms;
• and
• indicating an alarm to the user when the limit is exceeded.