# US 11,451,171 B2 · Motor branch circuit health monitoring method

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- Number: US 11,451,171 B2
- Document ID: US11451171B2
- Status: Granted
- Kind: B2
- Application number: 16/446,050
- Filed: 2019-06-19
- Published: 2020-12-24
- Granted: 2022-09-20
- Earliest claimed: 2019-06-19
- Assignees: Schneider Electric USA, Inc.
- Applicants: Schneider Electric USA, Inc.
- Inventors: Kevin M. Jefferies; Benjamin W. Edwards; Alan E. Freeman; Richard K Weiler; Matthew L. White
- Web page: https://patentgrep.com/patent/US11451171B2

## CPC

- H02P 1/26: for starting an individual polyphase induction motor
- H02P 29/024: Detecting a fault condition, e.g. short circuit, locked rotor, open circuit or loss of load
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS

## Abstract

Techniques for monitoring the health of a three-phase induction motor are provided. An expected threshold value is calculated as a function of an expected ratio of current unbalance to voltage unbalance for the three-phase motor. Embodiments determine whether a measured current unbalance exceeds the expected threshold value. Responsive to the measured current unbalance exceeding the expected threshold value, a remedial action may be taken, such as generating diagnostic information or activating one or more protection operations for the three-phase induction motor.

## Claims

### Claim 1

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;
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.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
determining, by the three-phase protective device, that the measured current unbalance exceeds the expected current unbalance; and
providing, by the three-phase protective device, diagnostic information for the three-phase load, based on the determination.

### Claim 3 (depends on 1)

The method of claim 1, wherein performing the protection operation further comprises providing, by the three-phase protective device, protection for the three-phase load, based on the determination.

### Claim 4 (depends on 1)

The method of claim 1, further comprising:
calculating, by the three-phase protective device, the 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 the measured current unbalance exceeds the expected current unbalance; and
providing, by the three-phase protective device, diagnostic information warning of a potential fault condition for the three-phase induction motor.

### Claim 5 (depends on 1)

The method of claim 1, further comprising:
calculating, by the three-phase protective device, the 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;
calculating, by the three-phase protective device, the expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the 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 measured current unbalance exceeds the expected threshold current unbalance; and
providing, by the three-phase protective device, protection for the three-phase load, based on the determination.

### Claim 6 (depends on 1)

The method of claim 1, further comprising:
calculating, by the three-phase protective device, the 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, the expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the 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 that the measured current unbalance exceeds the 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.

### Claim 7

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.

### Claim 8 (depends on 7)

The apparatus of claim 7, further comprising:
the 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 further comprising:
determining, by the three-phase protective device, that the measured current unbalance exceeds the expected current unbalance; and
providing, by the three-phase protective device, diagnostic information for the three-phase load, based on the determination.

### Claim 9 (depends on 7)

The apparatus of claim 7, wherein performing the protection operation further comprises providing, by the three-phase protective device, protection for the three-phase load, based on the determination.

### Claim 10 (depends on 7)

The apparatus of claim 7, further comprising:
the 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 further comprising:
calculating, by the three-phase protective device, the 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 the measured current unbalance exceeds the expected current unbalance; and
providing, by the three-phase protective device, diagnostic information warning of a potential fault condition for the three-phase induction motor.

### Claim 11 (depends on 7)

The apparatus of claim 7, further comprising:
the 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 further comprising:
calculating, by the three-phase protective device, the 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;
calculating, by the three-phase protective device, the expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the 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 measured current unbalance exceeds the expected threshold current unbalance; and
providing, by the three-phase protective device, protection for the three-phase load, based on the determination.

### Claim 12 (depends on 7)

The apparatus of claim 7, further comprising:
the 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 further comprising:
calculating, by the three-phase protective device, the 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, the expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the 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 that the measured current unbalance exceeds the 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.

### Claim 13

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.

### Claim 14 (depends on 13)

The computer program product of claim 13, further comprising:
code for determining, by the three-phase protective device, that the measured current unbalance exceeds the expected current unbalance; and
code for providing, by the three-phase protective device, diagnostic information for the three-phase load, based on the determination.

### Claim 15 (depends on 13)

The computer program product of claim 13, wherein the code for performing the protection operation further comprises code for providing, by the three-phase protective device, protection for the three-phase load, based on the determination.

### Claim 16 (depends on 13)

The computer program product of claim 13, further comprising:
code for calculating, by the three-phase protective device, the 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 the measured current unbalance exceeds the expected 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.

### Claim 17 (depends on 13)

The computer program product of claim 13, further comprising:
code for calculating, by the three-phase protective device, the 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 calculating, by the three-phase protective device, the expected threshold current unbalance indicating a potential fault caused by unbalanced currents, as the calculated expected current unbalance of the three-phase induction motor plus a value of unbalance tolerance/sensitivity for the three-phase induction motor;
code for determining, by the three-phase protective device, that that the measured current unbalance exceeds the expected threshold current unbalance; and
code for providing, by the three-phase protective device, protection for the three-phase load, based on the determination.

### Claim 18

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.

### Claim 19

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.

### Claim 20

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.