Static overcurrent trip device to operate a circuit breaker in response of fault conditions in an alternating current net system
First Claim
1. An electronic trip device for controlling a circuit breaker having separable contacts electrically coupled in the lines of an alternating current system, said trip device comprising:
- current sensing means for measuring the intensity of current flowing in each line of an alternating current system and for generating a signal proportional in magnitude to that line current;
a first time-lag tripping circuit coupled to receive said signal proportional to said line current and provide a first output, said first time-lag tripping circuit including a non-linear function generator which approximates the inverse time tripping characteristics of a circuit breaker and which comprises,an integrating analog circuit constructed as an operational amplifier having inverting and non-inverting inputs and an output,a negative feedback capacitor having a capacitance C electrically connected between the inverting input and output of the operational amplifier,a resistor having a first terminal and a second terminal coupled to said inverting input, said resistor having a resistance R,first means for providing at least one reference signal as a predetermined threshold signal to the first terminal of said resistor, andsecond means for coupling said signal proportional to line current through a selector and peak detector to said non-inverting input of said operational amplifier, said output of said operational amplifier defining the tripping time of the first time-lag tripping circuit wherein the tripping time t is equal to L(b-aI)/(aI-c) where I is the line current, L is the time constant RC, c is a first threshold voltage represented by said reference signal, b is a second threshold voltage and a is a proportionality coefficient set by said selector;
a second instantaneous tripping circuit coupled to receive said signal proportional to line current and provide a second output;
level detector means coupled to receive the outputs of said first and second tripping ciruits for providing a tripping signal when either of said outputs exceed another predetermined threshold voltage;
switching means for providing a switching signal in response to said tripping signal;
a tripping coil coupled to be responsive to said switching signal and operably coupled to cause the opening of the contacts in said circuit breaker in response to said tripping signal.
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Accused Products
Abstract
The analog electronic trip device comprises a time-lag tripping circuit formed by a non-linear function generator likely to elaborate by approximation the tripping characteristic of the circuit breaker.
The device includes an integrating amplifier comprising a negative-feedback capacitor C and two inputs in phase opposition. One of the inputs is submitted to two threshold voltages VR1, VR2 determining the mode of long-time delay or short-time delay operation of the trip device. The second threshold voltage VR2 is set by a resistive switch which determines the short delay tripping threshold.
20 Citations
5 Claims
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1. An electronic trip device for controlling a circuit breaker having separable contacts electrically coupled in the lines of an alternating current system, said trip device comprising:
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current sensing means for measuring the intensity of current flowing in each line of an alternating current system and for generating a signal proportional in magnitude to that line current; a first time-lag tripping circuit coupled to receive said signal proportional to said line current and provide a first output, said first time-lag tripping circuit including a non-linear function generator which approximates the inverse time tripping characteristics of a circuit breaker and which comprises, an integrating analog circuit constructed as an operational amplifier having inverting and non-inverting inputs and an output, a negative feedback capacitor having a capacitance C electrically connected between the inverting input and output of the operational amplifier, a resistor having a first terminal and a second terminal coupled to said inverting input, said resistor having a resistance R, first means for providing at least one reference signal as a predetermined threshold signal to the first terminal of said resistor, and second means for coupling said signal proportional to line current through a selector and peak detector to said non-inverting input of said operational amplifier, said output of said operational amplifier defining the tripping time of the first time-lag tripping circuit wherein the tripping time t is equal to L(b-aI)/(aI-c) where I is the line current, L is the time constant RC, c is a first threshold voltage represented by said reference signal, b is a second threshold voltage and a is a proportionality coefficient set by said selector; a second instantaneous tripping circuit coupled to receive said signal proportional to line current and provide a second output; level detector means coupled to receive the outputs of said first and second tripping ciruits for providing a tripping signal when either of said outputs exceed another predetermined threshold voltage; switching means for providing a switching signal in response to said tripping signal; a tripping coil coupled to be responsive to said switching signal and operably coupled to cause the opening of the contacts in said circuit breaker in response to said tripping signal. - View Dependent Claims (2, 3, 4, 5)
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Specification