Method of operating a protection device, associated computer program product, protection device and electrical installation

A non-transitory computer-readable medium encoded with computer-readable instructions that, when executed by a calculator circuit, cause the calculator circuit to perform a method comprising:

• for each phase of a three-phase power source, acquiring over time a corresponding phase current flowing from the power source to at least one electric motor;
• based on the acquired phase currents of the three-phase power source, detecting a current stage of each of the at least one electric motor, among an off stage, an initial stage successive to the off stage, an intermediate stage successive to the initial stage and a steady-state stage successive to the intermediate stage;
• and
• calculating an active threshold value depending on the detected stage of each of the at least one electric motor, the active threshold value during the intermediate stage varying according to a predetermined decreasing function over time,
• wherein the method further includes
• for the at least one electric motor, reading a corresponding nominal current and a corresponding starting current stored in a memory;
• applying a predetermined transformation to the acquired phase currents to obtain a positive sequence component, a negative sequence component and a zero sequence component;
• and
• wherein the detecting comprises detecting that the at least one electric motor is in the initial stage if:
• during a first predetermined time interval, the positive sequence component displays a change in value that is higher than the starting current;
• and
• after the first predetermined time interval, the positive sequence component displays a value that is larger than an offset current value;
• and
• after the first predetermined time interval, each phase current displays a value that is larger than the offset current value;
• and
• during a second predetermined time interval, the negative sequence component displays a transient increase in value, the negative sequence component displaying a value that is larger than a predetermined fraction of the offset current value;
• and
• the positive sequence component is larger than the sum of the negative sequence component and of the zero sequence component.

A protection device configured to be arranged between an electrical three-phase power source and at least one electric motor, comprising:

• an acquisition module configured to acquire over time, for each phase of the three-phase power source, a corresponding phase current flowing from the power source to the at least one electric motor;
• a calculator configured to detect a present stage of each of the at least one electric motor, the current stage being one of an off stage, an initial stage successive to the off stage, an intermediate stage successive to the initial stage and a steady-state stage successive to the intermediate stage, based on the acquired phase currents from the three-phase power source, the calculator being further configured to calculate an active threshold value depending on the detected stage of the at least one electric motor, the active threshold value during the intermediate stage varying according to a predetermined decreasing function over time,
• wherein the calculator is further configured to
• for the at least one electric motor, read a corresponding nominal current and a corresponding starting current stored in a memory,
• apply a predetermined transformation to the acquired phase currents to obtain a positive sequence component, a negative sequence component and a zero sequence component;
• and
• wherein the calculator is configured to detect that the at least one electric motor is in the initial stage if:
• during a first predetermined time interval, the positive sequence component displays a change in value that is higher than the starting current, and
• after the first predetermined time interval, the positive sequence component displays a value that is larger than an offset current value;
• and
• after the first predetermined time interval, each phase current displays a value that is larger than the offset current value;
• and
• during a second predetermined time interval, the negative sequence component displays a transient increase in value, the negative sequence component displaying a value that is larger than a predetermined fraction of the offset current value;
• and
• the positive sequence component is larger than the sum of the negative sequence component and of the zero sequence component.