Motor protection system and process

In a method for regulating the operation of a well produced by the operation of a pumping unit including a sucker-rod string and means for reciprocating said sucker-rod string to produce fluid from a subterranean location within said well, the steps comprising:

• a. driving said rod string reciprocating means with an electric motor energized by an electric power supply to said motor under conditions in which the speed of said motor normally varies between maximum values and minimum values occurring during strokes of said rod string;
• b. establishing at least two stall speed set points, the first of said set points corresponding to an upper stall speed for said motor, and the second of said stall points corresponding to a lower stall speed of said motor;
• c. generating a motor speed signal representative of the speed of said motor;
• and
• d. comparing said motor speed signal with said stall speed set points and in response to said motor speed signal having a value corresponding to said first stall speed set point for a first predetermined time period or having a second lower value corresponding to said second stall speed set point for a second time period which is shorter than said first time period, generating a motor control function.

In a system for protecting a motor designed to run under conditions of varying speed against stall conditions, the combination comprising:

• a. means for providing a pulsed motor speed signal which is frequency proportional to said motor speed whereby the period of said signal between pulses increases with decreasing motor speed;
• b. means for establishing at least two stall speed set points, the first of said set points corresponding to an upper stall speed of said motor and comprising a time interval corresponding to the period of said motor signal at said upper stall speed condition, and the second of said set points corresponding to a lower stall speed condition and comprising a time interval which is longer than said first time interval and corresponds to the period of said motor speed signal at said lower stall speed condition;
• c. first and second timers for producing a timeout condition at the conclusion of an elapsed time duration, the elapsed time duration for said first timer being longer than the elapsed time duration for second timer;
• d. means responsive to said motor speed signal for resetting said first timer when the period of said signal between said pulses is within said first set point time interval;
• e. means responsive to said motor speed signal for resetting said second timer when the period of said signal between said pulses is within said second set point time interval;
• and
• f. means responsive to the occurrence of a time out condition for one of said timers for generating a motor control function.

In a system for the protection of a motor having a plurality of operating modes against stall conditions, the combination comprising:

• a. means for providing a pulsed motor speed signal which is frequency proportional to said motor speed whereby the period of said signal between pulses increases with decreasing motor speed;
• b. means establishing at least two stall condition suites corresponding respectively to at least two of said motor modes and having at least two stall speed set points, the first of said set points corresponding to an upper stall speed and the second of said set points corresponding to a lower stall speed;
• c. means for monitoring said motor to determine the existing operational mode of said motor and selecting the stall condition suite corresponding to the existing motor mode;
• and
• d. means for comparing said motor speed signal with the selected stall speed suite and in response to said motor speed signal having a value corresponding to said upper first stall speed set point for a first predetermined time duration or having a second lower value corresponding to said second stall speed set point for a second predetermined time duration which is shorter than said first time duration, generating a motor control function.

In a system for protecting a motor having a plurality of operating modes against stall conditions, the combination comprising:

• a. means for providing a pulsed motor speed signal which is frequency proportional to said motor speed whereby the period of said signal between pulses increases with decreasing motor speed;
• b. means for establishing at least two stall condition suites corresponding respectively to at least two of said motor modes and each having at least two stall speed set points, the first of said set points corresponding to an upper stall speed of said motor and comprising a time interval corresponding to the period of said motor signal at said upper stall speed condition, and the second of said set points corresponding to a lower stall speed condition and comprising a time interval which is longer than said first time interval and corresponds to the period of said motor speed signal at said lower stall speed condition;
• c. means for surveying said motor to determine the existing operational motor mode and selecting the stall condition suite corresponding to the existing motor mode;
• d. first and second timers for producing a time out condition at the conclusion of an elapsed time duration, the elapsed time duration for said first timer being longer than the elapsed time duration for second timer;
• e. means responsive to said motor speed signal for resetting said first timer when the period of said signal between said pulses is within said first set point time interval of said selected stall condition suite;
• f. means responsive to said motor speed signal for resetting said second timer when the period of said signal between said pulses is within said second set point time interval of said selected stall condition suite;
• and
• g. means responsive to the occurrence of a time out condition for one of said timers for generating a motor control function.

In a method of providing stall protection for an electric motor energized by an electric power supply operating under conditions of varying speed the steps comprising:

• a. generating a pulsed motor speed signal which is frequency proportional to the speed of said motor whereby the period of said signal between pulses increases with decreasing motor speed;
• b. establishing at least two stall speed set points, the first of said set points corresponding to an upper stall speed of said motor and comprising a time interval corresponding to the period of said motor signal at said upper stall speed, and the second of said set points corresponding to a lower stall speed and comprising a time interval which is longer than said first set point time interval and corresponds to the period of said motor speed signal at said lower stall speed;
• and
• c. comparing said motor speed signal with said stall speed set points and, in response to the period of said motor speed signal exceeding the time interval of said first stall speed set point for a first time duration or exceeding the longer time interval of said second stall speed set point for a second time duration which is shorter than said first time duration, generating a motor control function.