Motor branch circuit health monitoring method

An apparatus, comprising:

• at least one processor;
• at least one memory including computer program code, wherein the computer program code, when executed by operation of the at least one processor, performs an operation comprising:
• calculating, by a three-phase protective device, an expected current unbalance, as a product of a measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for a three-phase load;
• calculating, by the three-phase protective device, an expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the expected current unbalance plus a value of unbalance tolerance/sensitivity;
• determining, by the three-phase protective device, whether a measured current unbalance exceeds at least one of the expected current unbalance or the expected threshold current unbalance;
• performing, by the three-phase protective device, a protection operation relating to a motor protection relay for the three-phase load, based on the determination;
• calculating, by the three-phase protective device, a second expected current unbalance for a three-phase induction motor, as the product of the measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for the three-phase induction motor;
• determining, by the three-phase protective device, that a sum of the measured current unbalance and a product of the measured voltage unbalance times the second expected ratio of current unbalance to voltage unbalance for the three-phase induction motor, exceeds a predetermined fraction of the expected threshold current unbalance;
• and
• providing, by the three-phase protective device, diagnostic information warning of a potential fault condition for the three-phase induction motor.

A computer program product comprising computer executable program code recorded on a computer readable non-transitory storage medium, the computer executable program code comprising:

• code for calculating, by a three-phase protective device, an expected current unbalance, as a product of a measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for a three-phase load;
• code for calculating, by the three-phase protective device, an expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the expected current unbalance plus a value of unbalance tolerance/sensitivity;
• code for determining, by the three-phase protective device, whether a measured current unbalance exceeds at least one of the expected current unbalance or the expected threshold current unbalance;
• code for performing, by the three-phase protective device, a protection operation relating to a motor protection relay for the three-phase load, based on the determination;
• code for calculating, by the three-phase protective device, a second expected current unbalance for a three-phase induction motor, as the product of the measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for the three-phase induction motor;
• code for determining, by the three-phase protective device, that a sum of the measured current unbalance and a product of the measured voltage unbalance times the second expected ratio of current unbalance to voltage unbalance for the three-phase induction motor, exceeds a predetermined fraction of the expected threshold current unbalance;
• and
• code for providing, by the three-phase protective device, diagnostic information warning of a potential fault condition for the three-phase induction motor.

A method, comprising:

• calculating, by a three-phase protective device, an expected current unbalance, as a product of a measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for a three-phase load;
• calculating, by the three-phase protective device, an expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the expected current unbalance plus a value of unbalance tolerance/sensitivity;
• determining, by the three-phase protective device, whether a measured current unbalance exceeds at least one of the expected current unbalance or the expected threshold current unbalance;
• providing, by the three-phase protective device, a protection operation relating to a motor protection relay for the three-phase load, based on the determination;
• calculating, by the three-phase protective device, a second expected current unbalance for a three-phase induction motor, as the product of the measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for the three-phase induction motor, the expected ratio based on whether the three-phase induction motor is in a start state or a run state;
• calculating, by the three-phase protective device, a second expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the second calculated expected current unbalance of the three-phase induction motor plus a value of unbalance tolerance/sensitivity for the three-phase induction motor;
• determining, by the three-phase protective device, that the second measured current unbalance exceeds the second expected threshold current unbalance;
• and
• delaying, by the three-phase protective device, providing protection for the three-phase induction motor, for a duration based on whether the three-phase induction motor is in the start state or the run state.

An apparatus, comprising:

• at least one processor;
• at least one memory including computer program code, wherein the computer program code, when executed by operation of the at least one processor, performs an operation comprising:
• calculating, by a three-phase protective device, an expected current unbalance, as a product of a measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for a three-phase load;
• calculating, by the three-phase protective device, an expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the expected current unbalance plus a value of unbalance tolerance/sensitivity;
• determining, by the three-phase protective device, whether a measured current unbalance exceeds at least one of the expected current unbalance or the expected threshold current unbalance;
• providing, by the three-phase protective device, a protection operation relating to a motor protection relay for the three-phase load, based on the determination;
• calculating, by the three-phase protective device, a second expected current unbalance for a three-phase induction motor, as the product of the measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for the three-phase induction motor, the expected ratio based on whether the three-phase induction motor is in a start state or a run state;
• calculating, by the three-phase protective device, a second expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the second calculated expected current unbalance of the three-phase induction motor plus a value of unbalance tolerance/sensitivity for the three-phase induction motor;
• determining, by the three-phase protective device, that the second measured current unbalance exceeds the second expected threshold current unbalance;
• and
• delaying, by the three-phase protective device, providing protection for the three-phase induction motor, for a duration based on whether the three-phase induction motor is in the start state or the run state.

A computer program product comprising computer executable program code recorded on a computer-readable non-transitory storage medium, the computer executable program code, when executed, configured to perform an operation comprising:

• calculating, by a three-phase protective device, an expected current unbalance, as a product of a measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for a three-phase load;
• calculating, by the three-phase protective device, an expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the expected current unbalance plus a value of unbalance tolerance/sensitivity;
• determining, by the three-phase protective device, whether a measured current unbalance exceeds at least one of the expected current unbalance or the expected threshold current unbalance;
• providing, by the three-phase protective device, a protection operation relating to a motor protection relay for the three-phase load, based on the determination;
• calculating, by the three-phase protective device, a second expected current unbalance for a three-phase induction motor, as the product of the measured voltage unbalance times an expected ratio of current unbalance to voltage unbalance for the three-phase induction motor, the expected ratio based on whether the three-phase induction motor is in a start state or a run state;
• calculating, by the three-phase protective device, a second expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the second calculated expected current unbalance of the three-phase induction motor plus a value of unbalance tolerance/sensitivity for the three-phase induction motor;
• determining, by the three-phase protective device, that the second measured current unbalance exceeds the second expected threshold current unbalance;
• and
• delaying, by the three-phase protective device, providing protection for the three-phase induction motor, for a duration based on whether the three-phase induction motor is in the start state or the run state.