Method and apparatus for motor fault diagnosis

A method of detecting a fault in a motor using a power decomposition technique (PDT), the method comprising the steps of:

• detecting three-phase motor current and generating corresponding signals;
• using the PDT to determine In, Ip, Vsn, and Vsp in response to the signals, wherein In is a negative sequence supply current, Ip is a positive sequence supply current, Vsn is a negative sequence supply voltage and Vsp is a positive sequence supply voltage;
• determining a reactive part (1/Xhn) of a negative sequence impedance based on at least some parameters of a group consisting of In, Ip, Vsn, and Vsp and using the following equation 1 X hn = γ 0 + γ 1 ⁢ ⁢ V sn + γ 2 ⁢ ⁢ sin ⁢ ⁢ ( 2 ⁢ ⁢ φ n ) + γ 3 ⁢ ⁢ cos ⁢ ⁢ ( 2 ⁢ ⁢ φ n )
• wherein φu is an orientation of negative sequence supply voltage Vsn and wherein γ0, γ1, γ2, γ3 are determined using a healthy motor and a parameterization technique;
• determining an expected negative sequence current Isn based on said using step and said determining a reactive part step;
• and
• calculating a fault negative sequence current by subtracting the Isn from the In.

A method detecting an intermittent fault in a motor, the method comprising the steps of:

• sampling, for each cycle of a power supply coupled to the motor, instantaneous signals from the motor;
• deriving sequence components of at least some of the instantaneous signals using a power decomposition technique (PDT), wherein one of the sequence components is a total negative current component;
• calculating an expected negative sequence current based on at least some of the sequence components, wherein one of the sequence components is a reactive part of a negative sequence impedance, (1/Xhn);
• calculating an intrinsic motor negative sequence current based on at least some of the sequence components, and subtracting both the expected negative sequence current and the intrinsic motor negative sequence current from the total negative sequence current to determine a fault negative sequence current;
• and
• wherein the fault negative sequence current is indicative of the fault.

A method of detecting an intermittent fault in a motor, the method comprising the steps of:

• detecting instantaneous three-phase motor current and generating corresponding signals;
• using a PDT to determine In, Ip, Vsn, and Vsp in response to the signals, wherein In is a negative sequence supply current, Ip is a positive sequence supply current, Vsn is a negative sequence supply voltage and Vsp is a positive sequence supply voltage;
• determining a reactive part (1/Xhn) of a negative sequence impedance based on at least some parameters of the group consisting of In, Ip, and Vsn, and using the following equation, 1 X hn = γ 0 + γ 1 ⁢ ⁢ V sn + γ 2 ⁢ ⁢ sin ⁢ ⁢ ( 2 ⁢ ⁢ φ n ) + γ 3 ⁢ ⁢ cos ⁢ ⁢ ( 2 ⁢ ⁢ φ n )
• wherein φu is an orientation of negative sequence supply voltage Vsn, and wherein γ0, γ1, γ2, and γ3 are determined while the motor is healthy and using a parameterization technique;
• determining an expected negative sequence current Isn based on said using step and said determining a reactive part step;
• and
• calculating a fault negative sequence current by subtracting the Isn from the In.

A method of detecting a fault in an induction motor, the method comprising the steps of:

• characterizing the motor using a healthy motor;
• sampling signals from the motor;
• deriving sequence components of at least some of the signals using a power decomposition technique (PDT)), wherein the sequence components comprise at least one of a total negative sequence current component and a reactive part of a negative sequence impedance, (1/Xhn);
• determining a fault negative sequence current based on said characterizing step and the total negative sequence current;
• and
• wherein the fault negative sequence current is indicative of the fault.