Piecewise estimation of negative sequence voltage for fault detection in electrical systems

An electrical system comprising:

• an input connectable to an AC source;
• an output connectable to terminals of an electrical machine to provide three-phase power thereto, the electrical machine comprising a plurality of stator windings;
• and
• a diagnostic system configured to identify a stator fault in the stator windings of the electrical machine, the diagnostic system comprising a processor that is programmed to:
• receive measurements of three-phase supply voltages and currents provided to the electrical machine, the measurements of the three-phase supply voltages and currents provided from voltage and current sensors connected to the electrical distribution circuit between the input and the output;
• compute positive, negative, and zero sequence components for the supply voltages and currents;
• compensate for noise factors in the negative sequence voltage to isolate a stator fault negative sequence voltage, the noise factors comprising unbalance in the electrical machine resulting from one or more of positive sequence current, negative sequence current, and positive sequence voltage;
• and
• identify a stator fault in the electrical distribution circuit based on the stator fault negative sequence voltage;
• wherein, in compensating for noise factors in the negative sequence voltage, the processor is further programmed to:
• estimate first and second coefficients that are a function of the positive sequence current at a base load value, and with a third coefficient that is a function of the positive sequence current at a zero value;
• calculate, at a plurality of load values, an error between an actual negative sequence voltage and estimated negative sequence voltage using the estimated first and second coefficients and the zero value for the third coefficient;
• and
• estimate the third coefficient by optimizing the error.

A method for identifying an inter-turn stator fault in an electrical machine comprising a plurality of stator windings, the method comprising:

• measuring three-phase voltages and currents provided to terminals of an electrical machine by way of voltage and current sensors;
• causing a diagnostic system to identify an inter-turn stator fault in the stator windings of the electrical machine, wherein causing the diagnostic system to identify the inter-turn stator fault comprises:
• receiving the measured three-phase voltages and currents provided to the terminals of the electrical machine;
• computing a positive, negative, and zero sequence voltage and sequence current from the measured three-phase voltages and currents;
• compensating for noise factors in the negative sequence voltage to isolate a stator fault negative sequence voltage;
• and
• identifying an inter-turn stator fault in the electrical machine based on the stator fault negative sequence voltage;
• wherein compensating for noise factors in the negative sequence voltage comprises performing a modified recursive least square (RLS) estimation to estimate a noise factor contribution to the negative sequence voltage.