Thermal model for electrical apparatus

Claim 2

Apparatus for providing a thermal model of an electric apparatus which has current-carrying conductors and a core material comprising: (a) first and second registers for storing respectively digital values representing conductor temperature and core material temperature; (b) means for deriving, with respect to said conductors, a first digital signal representing current in said conductors and periodically adding said first digital signal to the value in said first register; (c) means for receiving the values stored in said first and second registers to obtain a difference representing the temperature difference between the conductors and the core material and, in response thereto, determining second and third digital signals representing heat transferred from the conductors; (d) means for periodically subtracting said second digital signal from the value in said first register; (e) means for periodically adding said third digital signal to the value in said second register; and, (f) means for receiving the value stored in said second register and determining a fourth digital signal representing heat transferred from said second register.

Claim 3

Apparatus as defined in claim 1 in which said means for receiving the value stored in said second register includes means for comparing the value with a reference value representing temperature of an ambient medium and obtaining a difference representing a temperature difference between said core material and said ambient medium for determining said fourth digital signal.

Claim 4

A thermal model of an electric apparatus, said electric apparatus having current carrying conductors and a core material comprising: (a) means for deriving, with respect to said conductors, a first digital signal representing current in said conductors; (b) a first register for periodically receiving said first digital signal and adding it to the value therein; (c) a second register; (d) means for receiving second and third digital signals from said first and second registers respectively representing the values therein, deriving a difference value, and providing a fourth digital signal related to the difference value and representing heat transferred from the conductors and a fifth digital signal related to the difference and representing heat transferred from the conductors into said core material; (e) means for periodically subtracting the value represented by said fourth digital signal from the value in said first register; (f) means for periodically adding the value represented by said fifth signal to the value in said second register; and (g) means for periodically subtracting from said second register a value representing heat lost by the core material; whereby the value in said first register represents conductor temperature and the value in said second register represents core material temperature.

Claim 5

A thermal model of an electric apparatus, said electric apparatus having current carrying conductors and a core material comprising: (a) means for deriving, with respect to said conductors, a first digital signal representing current in said conductors; (b) a first register for periodically receiving said first digital signal and adding it to the value therein; (c) a second register; (d) means for receiving second and third digital signals from said first and second registers respectively representing the values therein, deriving a difference value, and providing a fourth digital signal related to the difference value and representing heat transferred from the conductors and a fifth digital signal related to the difference and representing heat transferred from the conductors into said core material; (e) means for periodically subtracting the value represented by said fourth digital signal from the value in said first register; (f) means for periodically adding the value represented by said fifth signal to the value in said second register; and (g) means for periodically subtracting from said second register a value representing heat lost by the core material; whereby the value in said first register represents conductor temperature and the value in said second register represents core material temperature.

Claim 6

Apparatus as defined in claim 3 in which said means for deriving said first digital signal comprises a current sensor means and an analog-to-digital converter.

Claim 7

Apparatus for protecting an AC electric motor by interrupting the supply of electrical power to said motor in response to a determination from a thermal model of said motor of unacceptable thermal conditions comprising: (a) means to derive a digital signal represeting current supplied to said motor; (b) first and second registers for storing, respectively, digital values; (c) first adding means connected between said means to derive a digital signal and said first register; (d) a first scale means connected between said first and second registers for receiving the digital values from each register; (e) a first subtracting means connected between said first scale means and said first register; (f) a second adding means connected between said first scale means and said second register; (g) a second scale means connected to said second register for receiving the digital value therefrom; (h) a second subtracting means connected between said second scale means and said second register; (i) said first adding means receiving said digital signal and responsive thereto adding a digital value to said first register representing heating resulting from current flow in the current carrying conductors of said motor; (j) said first scale means receiving a digital value from said first register representing temperature of said conductors and a digital value from said second register representing temperature of the core material of said motor and responsive thereto providing a scaled digital signal to said first subtracting means representing heat transferred from said current carrying conductors and a scaled digital signal to said second adding means representing heat transferred to said core material; (k) said second scale means receiving a digital value from said second register representing temperature of said core material and providing a scaled digital signal to said second subtracting means representing heat transferred from said core material due to ventilation; and (l) a detector means for receiving the digital value in said first register representing conductor temperature and comparing it with a predetermined value representing a critical value, and for providing a trip signal for interrupting said supply when said digital value in said first register exceeds said first predetermined value.

Claim 8

Apparatus for protecting an AC electric motor by interrupting the supply of electrical power to said motor in response to a determination from a thermal model of said motor of unacceptable thermal conditions comprising: (a) means to derive a digital signal represeting current supplied to said motor; (b) first and second registers for storing, respectively, digital values; (c) first adding means connected between said means to derive a digital signal and said first register; (d) a first scale means connected between said first and second registers for receiving the digital values from each register; (e) a first subtracting means connected between said first scale means and said first register; (f) a second adding means connected between said first scale means and said second register; (g) a second scale means connected to said second register for receiving the digital value therefrom; (h) a second subtracting means connected between said second scale means and said second register; (i) said first adding means receiving said digital signal and responsive thereto adding a digital value to said first register representing heating resulting from current flow in the current carrying conductors of said motor; (j) said first scale means receiving a digital value from said first register representing temperature of said conductors and a digital value from said second register representing temperature of the core material of said motor and responsive thereto providing a scaled digital signal to said first subtracting means representing heat transferred from said current carrying conductors and a scaled digital signal to said second adding means representing heat transferred to said core material; (k) said second scale means receiving a digital value from said second register representing temperature of said core material and providing a scaled digital signal to said second subtracting means representing heat transferred from said core material due to ventilation; and (l) a detector means for receiving the digital value in said first register representing conductor temperature and comparing it with a predetermined value representing a critical value, and for providing a trip signal for interrupting said supply when said digital value in said first register exceeds said first predetermined value.

Claim 9

Apparatus for protecting an AC electric motor as defined in claim 5 and further comprising: (a) a sequencer means connected to said first and second adding means and to said first and second subtracting means for periodically actuating said first and second adding means for adding the respective values therein to said first and second registers respectively and periodically actuating said first and second subtracting means for subtracting the respective values therein from said first and second registers respectively.

Claim 10

Apparatus as defined in claim 5 in which said means to derive a digital signal representing current supplied to said motor comprises a current sensor for deriving an analog value of the current supplied to said motor, and an analog-to-digital converter for converting the peak values of the current into said digital signal.

Claim 11

Apparatus as defined in claim 5 and further comprising a rotation detector means for detecting if the rotor of the motor is rotating or is stationary and for providing a rotation signal representative thereof, said second scale means determining in response to said rotation signal said second scaled signal representing one value of heat transferred from said core material when said rotor is rotating and another value when said rotor is stationary.

Claim 12

Apparatus for protecting an AC electric motor by interrupting the supply of electrical power to said motor in response to a determination from a thermal model of said motor of unacceptable thermal conditions comprising: (a) means to derive a digital signal representing current supplied to said motor; (b) a first register and a second register; (c) first adding means connected between said means to derive a digital signal and said first register; (d) a first scale means connected between said first and second registers for receiving the digital values from each register; (e) a first subtracting means connected between said first scale means and said first register; (f) a second adding means connected between said first scale means and said second register; (g) a second scale means connected to said second register for receiving the digital value therefrom; (h) a second subtracting means connected between said second scale means and said second register; (i) said first adding means receiving said digital signal and responsive thereto adding a digital value to said first register representing heating resulting from current flow in the current carrying conductors of said motor; (j) said first scale means receiving a digital value from said first register representing temperature of said conductors and a digital value from said second register representing temperature of the core material of said motor and responsive thereto providing a scaled digital signal to said first subtracting means representing heat transferred from said current carrying conductors and a scaled digital signal to said second adding means representing heat transferred to said core material; (k) said second scale means receiving a digital value from said second register representing temperature of said core material and providing a scaled digital signal to said second subtracting means representing heat transferred from said core material to ambient; and (l) a detector means for receiving the digital value in said second register representing average temperature in said core material and comparing it with a predetermined value representing a critical value, and for providing a trip signal suitable for interrupting said supply to said motor when said digital value in said second register exceeds said predetermined value.

Claim 13

Apparatus for protecting an AC electric motor by interrupting the supply of electrical power to said motor in response to a determination from a thermal model of said motor of unacceptable thermal conditions comprising: (a) means to derive a digital signal representing current supplied to said motor; (b) a first register and a second register; (c) first adding means connected between said means to derive a digital signal and said first register; (d) a first scale means connected between said first and second registers for receiving the digital values from each register; (e) a first subtracting means connected between said first scale means and said first register; (f) a second adding means connected between said first scale means and said second register; (g) a second scale means connected to said second register for receiving the digital value therefrom; (h) a second subtracting means connected between said second scale means and said second register; (i) said first adding means receiving said digital signal and responsive thereto adding a digital value to said first register representing heating resulting from current flow in the current carrying conductors of said motor; (j) said first scale means receiving a digital value from said first register representing temperature of said conductors and a digital value from said second register representing temperature of the core material of said motor and responsive thereto providing a scaled digital signal to said first subtracting means representing heat transferred from said current carrying conductors and a scaled digital signal to said second adding means representing heat transferred to said core material; (k) said second scale means receiving a digital value from said second register representing temperature of said core material and providing a scaled digital signal to said second subtracting means representing heat transferred from said core material to ambient; and (l) a detector means for receiving the digital value in said second register representing average temperature in said core material and comparing it with a predetermined value representing a critical value, and for providing a trip signal suitable for interrupting said supply to said motor when said digital value in said second register exceeds said predetermined value.

Claim 14

Apparatus for protecting an AC electric motor as defined in claim 9 and further comprising: (a) a sequencer means connected to said first and second adding means and to said first and second subtracting means for periodically actuating said first and second adding means for adding the respective values therein to said first and second registers respectively and periodically actuating said first and second subtracting means for subtracting the respective values therein from said first second registers respectively.

Claim 15

Apparatus as defined in claim 9 in which said means to derive a digital signal representing current supplied to said motor comprises a current sensor for deriving an analog value of the current supplied to said motor, and an analog-to-digital converter for converting the peak values of the current into said digital signal.

Claim 16

Apparatus as defined in claim 9 and further comprising a rotation detector means for detecting if the rotor of the motor is rotating or is stationary and for providing a rotation signal representative thereof, said second scale means determining in response to said rotation signal said second scaled signal representing one value of heat transferred from said core material when said rotor is rotating and another value when said rotor is stationary.

Claim 19

The method defined in claim 13 in which the step of determining said fourth digital signal includes comparing the extant digital value in the second store with a reference value representing the temperature of an ambient medium to obtain a difference therebetween.

Claim 20

The method in accordance with claim 13 further including the step of comparing the value in the second store to a predetermined value representing a critical value and for providing in response to a predetermined relationship therebetween, a signal capable of initiating protective action with respect to the electrical apparatus.

Claim 23

The invention in accordance with claim 16 further including the steps: (a) detecting whether the motor is rotating or stationary; and, (b) adjusting the scaling of the value representing the heat lost by the core material as a function of said detecting.

Claim 24

The method in accordance with claim 16 further including the step of comparing the value in the second store to a predetermined value representing a critical value and for providing, in response to a predetermined relationship therebetween, a signal capable of initiating protective action with respect to the electrical apparatus.

Claim 25

The method in accordance with claim 16 further including the steps of: (a) scaling the second digital signal prior to subtracting it from the extant value in first store; (b) scaling the third digital signal prior to adding it to the extant value in the second store; and, (c) scaling the value representing heat lost by the core material prior to subtracting it from the extant value in the second store.

Claim 26

The method in accordance with claim 19 further including the step of comparing the value in the second store to a predetermined value representing a critical value and for providing in response to a predetermined relationship therebetween, a signal capable of initiating protective action with respect to the motor.