METHOD FOR THE DIAGNOSTICS OF ELECTROMECHANICAL SYSTEM BASED ON IMPEDANCE ANALYSIS

• US 20150293177A1
• Filed: 10/08/2013
• Published: 10/15/2015
• Est. Priority Date: 10/26/2012
• Status: Active Grant

• Current Assignee: ABB Schweiz AG (ABB Limited)
• Original Assignee: ABB Technology AG (ABB Limited)
• Inventors: Ottewill, James, Orman, Maciej, Pinto, Cajetan
• Granted Patent: US 10,310,016 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 19/16528 using digital techniques or performing arithmetic operations using digital techniques to measure a voltage or a current, see G01R19/25
• CPC Class Codes: G01R 23/16 Spectrum analysis; Fourier analysis
• CPC Class Codes: G01R 31/343 in operation

Abstract

The present invention is concerned with a method for diagnosing the state of electromechanical systems in which electrical rotating machinery is used on the basis of analysis of impedance estimated from at least two currents and two voltages, measured during an operation of the electromechanical system. The method may be especially useful in the condition monitoring of electric motors and generators. The invention combines the information from both the voltage and current signals measurable at the motor terminals. Specifically, the measurements of voltage and current from two or more phases of a polyphase electrical machine are combined to estimate the impedance of the machine, impedance being the resistance to the flow of current that a circuit exhibits when a voltage is applied to it.

Claims

1. A method for monitoring the condition of an electromechanical system in which electrical rotating machinery is used, comprising the steps of:

measuring at least two phase currents and two phase voltages for the same respective phases supplying the rotating machine,

processing the measured values using a computer processing device adapted to transform the measured values from the time domain to the frequency domain, creating voltage spectrum signals V1_F, V2_F, V3_F, . . . Vn_F and current spectrum signals I1_F, I2_F, I3_F, . . . In_F,

processing the current spectrum signals I1_F, I2_F, I3_F, . . . In_F to obtain the inverted current spectra I1_F,inv, I2_F,inv, I3_F,inv, . . . In_F,inv,

processing the inverted current spectra I1_F,inv, I2_F,inv, I3_F,inv, . . . In_{F, inv} to obtain the impedance spectrum signals Y1_F, Y2_F, Y3_F, . . . Yn_F of the rotating machine,

extracting a vector of amplitudes at frequencies of interest from the impedance spectrum signals which are needed to diagnose the electromechanical system,

calculating the maximum value of the difference between the amplitudes at frequencies of interest extracted from the impedance spectrum signals,

comparing 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, and

indicating an alarm to the user when the limit is exceed.

2. A method according to claim 1, characterized in that the vector of amplitudes at frequency of interest is a third harmonic of the supply frequency.

3. A method according to claim 2, characterized in that the vector of amplitudes at frequency of interest indicate the presence of an eccentricity in the electromechanical system.

6. A computer program product for the method according to claim 1 for monitoring the condition of an electromechanical system in which electrical rotating machinery is used, which said computer program product is loadable into the executable in the computer measuring device.

4. A system for monitoring the condition of an electromechanical system in which electrical rotating machinery is used comprising

means for measuring at least two phase currents and two phase voltages for the same respective phases supplying the rotating machine,

means for processing the measured values and for creating impedance spectrum signals Y1_F, Y2_F, Y3_F, . . . Yn_F of the rotating machine,

means for extracting data of interest from the impedance spectrum signals,

means for indicating an alarm to the user characterized in that it comprises means for calculating the maximum value of the difference between the amplitudes at frequencies of interest extracted from the impedance spectrum signals and for comparing 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.

5. A method according to claim 5 characterized in that the rotating machinery in the electromechanical system is motor or generator.