Protection system for an electric motor

A method of controlling and protecting an electric load that is adapted to be connected to a power supply by two or more power lines, said method comprising the steps of:

• (a) coupling to at least one of the lines to sense the level of power current flowing through the line;
• (b) comparing the power current level with an upper limit and a lower limit;
• (c) comparing the length of time it is outside the limits with a preselected time interval when the current level is outside of said limits and determining that a fault condition exists when the level is outside said limits longer than said time interval;
• (d) disconnecting the power from the load when a fault condition exists;
• (e) starting a reset time interval;
• (f) reconnecting the power to the load at the end of said reset time interval;
• (g) comparing the power current level with a low current value when the current level is below said lower limit;
• (h) repeating the foregoing step (2) to form a series of cycles;
• (i) determining whether the power current level was within said limits during a previous cycle;
• and
• (j) disconnecting the power from the load for an off delay interval when the current level was within said limits during a previous cycle but is presently below said lower limit.

A method of controlling and protecting an electric load that is adapted to be connected to a power supply by two or more power lines, the load having a pulse transmitter mounted adjacent it and the transmitter being coupled to at least one power line, the method comprising the steps of:

• (a) coupling to a power line to sense any pulses appearing on said line;
• (b) repeatedly sensing at regular intervals whether pulses appeared on the line during an interval;
• (c) counting successive intervals during which pulses appear on the power line;
• (d) comparing said count with a selected number;
• (e) disconnecting the power from the load when the count equals said number;
• (f) starting a reset time interval;
• (g) reconnecting the power to the load at the end of said reset time interval;
• (h) counting the number of times the load is disconnected;
• and
• (i) vary the length of said reset time interval dependent on the said number of times.

Apparatus for controlling and protecting an electric load that is adapted to be connected to a power supply by two or more power lines, said apparatus comprising:

• (a) means for coupling to at least one of the lines to sense the level of power current flowing through the line and comparing the power current level with an upper limit and a lower limit;
• (b) means for comparing the length of time it is outside the limits with a preselected time interval when the current level is outside of said limits and for determining that a fault condition exists when the level is outside said limits longer than said time interval;
• (c) means for disconnecting the power from the load when a fault condition exists
• (d) means for starting a reset time interval;
• (e) means for reconnecting the power to the load at the end of said reset time interval;
• (f) means for counting the number of faults that occur due to the current level being above the upper limit;
• and
• (g) means for varying the length of said reset time interval dependent on said number of said faults.

Apparatus for controlling and protecting an electric load that is adapted to be connected to a power supply by two or more power lines, said apparatus comprising:

• (a) means for coupling to at least one of the lines to sense the level of power current flowing through the line;
• (b) means for comparing the length of time it is outside the limits with a preselected time interval when the current level is outside of said limits and for determining that a fault condition exists when the level is outside said limits longer than said time interval;
• (c) disconnecting the power from the load when a fault condition exists;
• (d) means for starting a reset time interval;
• (e) means for reconnecting the power to the load at the end of said reset time interval.
• (f) means for comparing the power current level with a low current value when the current level is below said lower limit;
• (g) means for determining whether the power current level was earlier within said limits;
• and
• (h) means for disconnecting the power from the load for an off delay interval when the current level was earlier within said limits but it below said lower limit.

Apparatus for controlling and protecting an electric motor that is adapted to be connected to a power supply by at least two power lines, comprising:

• (a) current sensor means adapted to be connected to at least one line for sensing power current therethrough;
• (b) processing means for comparing said power current with underload and overload current limits, determining whether said power current is outside said limits for a time interval and in such event indicating a fault condition and forming a reset time interval;
• (c) means connected to said processing means for disconnecting power from said motor during said reset time interval,
• (d) header means connected to said processing means for setting said current limits in said processing means;
• (e) pulse sensor means coupled to said power lines for sensing pulses thereon, and said processing means including means responsive to a regular succession of pulses for disconnecting power from said motor;
• (f) said pulse sensor means and said current sensor means comprising a current transformer including a core and separate sensor windings.