Programmed overcurrent protection control apparatus and method of operating the same
First Claim
1. Programmed overcurrent protection control apparatus adaptable for use in a power system including a power line to govern the interruption of current through said power line based on a derived overcurrent time-to-trip associated with an overcurrent condition of said power line, said control apparatus comprising:
- a programmed digital signal processor;
memory means, coupled to said programmed processor, for storing a plurality of digitally coded signals representative of predetermined derivation constants;
means for setting a plurality of derivation parameters;
means for measuring the current of said power line and generating a signal representative thereof;
means governed by said programmed processor to sample said current measurement signal at a plurality of first predetermined times during each frequency cycle of the power line current to effect sampled signals and to digitize said sampled signals;
said programmed processor operative over predetermined time intervals to derive for each predetermined time interval a digital signal, representative of a current value Im of a frequency cycle of the current contemporaneous with the corresponding predetermined time interval m, from the sampled signals digitized over the corresponding predetermined time interval;
said programmed processor operative at second predetermined times corresponding to said predetermined time intervals to read said derivation parameter settings;
said programmed processor operative to select certain of said digitally coded derivation constants from said memory means corresponding to said read parameter settings;
said programmed processor operative to detect an overcurrent condition from said derived digital current value signals;
said programmed processor operative, in response to the detection of an overcurrent condition, to derive an overcurrent time-to-trip based on the following relationship;
##EQU20## where m from 1 to N-G·
C2 represent the predetermined time intervals during which said detected overcurrent condition persists;
where G, P, C1, C2 and C3 represent digitally coded derivation constants based on said read parameter settings for each corresponding predetermined time interval m;
where N represents the number of predetermined time intervals which may elapse for the time-to-trip and G·
C2 represents a minimum number of predetermined time intervals for the time-to-trip;
where Im represents the digital current value signal derived for the corresponding predetermined time interval m; and
means for governing the interruption of current through said power line if said overcurrent condition persists for the duration of said time-to-trip derivation.
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Accused Products
Abstract
Programmed overcurrent protection control apparatus with selectable time-overcurrent operation to govern the interruption of current through at least one power line associated with either a ground phase or a power phase of a power system network is disclosed. A programmed processor is included to derive an overcurrent time-to-trip in accordance with sampled measurement current values of the power line and selected derivation constants stored in a memory look-up table. The derivation constants are selected from the look-up table based on derivation parameters which may be set and read by the programmed processor from time to time. The programmed processor utilizes the selected derivation constants to derive the time-to-trip over a number of predetermined time intervals during which the overcurrent condition persists. An alternate overcurrent time-to-trip relationship utilizing different derivation parameters selected from the look-up table may be utilized for the conditions in which overcurrent exists in an initial predetermined range. In some situations, both of the derivation relationships may be used concurrently to derive the overcurrent time-to-trip.
35 Citations
25 Claims
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1. Programmed overcurrent protection control apparatus adaptable for use in a power system including a power line to govern the interruption of current through said power line based on a derived overcurrent time-to-trip associated with an overcurrent condition of said power line, said control apparatus comprising:
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a programmed digital signal processor; memory means, coupled to said programmed processor, for storing a plurality of digitally coded signals representative of predetermined derivation constants; means for setting a plurality of derivation parameters; means for measuring the current of said power line and generating a signal representative thereof; means governed by said programmed processor to sample said current measurement signal at a plurality of first predetermined times during each frequency cycle of the power line current to effect sampled signals and to digitize said sampled signals; said programmed processor operative over predetermined time intervals to derive for each predetermined time interval a digital signal, representative of a current value Im of a frequency cycle of the current contemporaneous with the corresponding predetermined time interval m, from the sampled signals digitized over the corresponding predetermined time interval; said programmed processor operative at second predetermined times corresponding to said predetermined time intervals to read said derivation parameter settings; said programmed processor operative to select certain of said digitally coded derivation constants from said memory means corresponding to said read parameter settings; said programmed processor operative to detect an overcurrent condition from said derived digital current value signals; said programmed processor operative, in response to the detection of an overcurrent condition, to derive an overcurrent time-to-trip based on the following relationship;
##EQU20## where m from 1 to N-G·
C2 represent the predetermined time intervals during which said detected overcurrent condition persists;where G, P, C1, C2 and C3 represent digitally coded derivation constants based on said read parameter settings for each corresponding predetermined time interval m; where N represents the number of predetermined time intervals which may elapse for the time-to-trip and G·
C2 represents a minimum number of predetermined time intervals for the time-to-trip;where Im represents the digital current value signal derived for the corresponding predetermined time interval m; and means for governing the interruption of current through said power line if said overcurrent condition persists for the duration of said time-to-trip derivation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. Programmed overcurrent protection control apparatus adaptable for use in a three phase power system including three power lines to govern the interruption of current through said power lines based on a derived overcurrent time-to-trip associated with an overcurrent condition of at least one of said power lines, said control apparatus comprising:
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a programmed digital signal processor; memory means, coupled to said programmed processor, for storing a plurality of digitally coded signals representative of predetermined derivation constants; means for setting a plurality of parameters; means for measuring current through said power lines and generating first, second and third signals respectively representative of said currents; means governed by said programmed processor to sample said first, second and third current measurement signals at a plurality of first predetermined times during each frequency cycle of the corresponding power line current and to digitize said sampled first, second and third current measurement signals; said programmed processor operative over predetermined time intervals to derive for each predetermined time interval first, second and third digital signals, each representative of a current value Im of a frequency cycle of its respective current contemporaneous with the corresponding predetermined time interval m, from their respective sampled current measurement signals digitized over the corresponding predetermined time interval; said programmed processor operative at second predetermined times corresponding to said predetermined time intervals to read said parameter settings; said programmed processor operative to select certain of said digitally coded derivation constants from said memory means corresponding to said read parameter settings; said programmed processor operative to detect an overcurrent condition from said derived first, second and third digital current value signals; said programmed processor operative, in response to the detection of an overcurrent condition, to derive an overcurrent time-to-trip based on the following relationship;
##EQU22## where m from 1 to N-G·
C2 represent the predetermined time intervals during which said overcurrent condition exists;where G, P, C1, C2 and C3 represent digitally coded derivation constants based on said read parameter settings for said corresponding predetermined time interval m; where N represents the number of predetermined time intervals which may elapse for the time-to-trip and G C2 represents a minimum number of predetermined time intervals for the time-to-trip; where Im is the detected overcurrent digital current value signal derived for the corresponding predetermined time interval m; and means for governing the interruption of current through said power lines if said overcurrent condition persists for the duration of said time-to-trip derivation. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. Method of governing the interruption of current through a power line of a power system network based on a derived overcurrent time-to-trip associated with an overcurrent condition of said power line, said method comprising the steps of:
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(a) storing a plurality of digitally coded signals representative of predetermined derivation constants in a memory of a digital signal processing system; (b) setting a plurality of derivation parameters; (c) measuring the current of said power line and generating a signal representative thereof; (d) sampling and digitizing said current measurement signal at a plurality of first predetermined times during each frequency cycle of the power line current as governed by a programmed digital signal processor of said processing system; (e) operating said programmed processor over predetermined time intervals to derive for each predetermined time interval a digital signal, representative of a current value Im of a frequency cycle of the power line current contemporaneous with the predetermined time interval m, from the sampled and digitized current measurement signals of said corresponding predetermiend time interval; (f) operating said programmed processor at second predetermined times corresponding to said predetermined time intervals to read said parameter settings; (g) operating said programmed processor to select certain of said digitally coded derivation constants from said memory means corresponding to said read parameter settings; (h) operating said programmed processor to detect an overcurrent condition from said derived digital current value signal Im ; (i) operating said programmed processor in response to the detection of an overcurrent signal to derive an over-current time-to-trip by; (1) accumulating the quantities (Im -C1)p for each predetermined time interval m during the time that the overcurrent condition persists, until the value of said accumulated quantities becomes greater than or equal to G·
K1 '"'"', and(2) delaying for G·
L'"'"' additional predetermined time intervals for which said overcurrent condition persists, where G, P, C1, K1 '"'"' and L'"'"' represent derivation constants based on said read parameter settings for each corresponding predetermined time interval m; and(j) governing the interruption of said current through said power line if said overcurrent condition persists for the duration of said time-to-trip derivation. - View Dependent Claims (22, 23, 24, 25)
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Specification