US 5,627,717 AGranted

Electronic processing unit, and circuit breaker including such a unit

AssigneePhilips Electronics North America Corporation

InventorsHoward B. Pein, Gregory T. Divincenzo, Paulo Caldiera, Wen-Jian Gu, Stephen L. Wong

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Abstract

Digital processing of current signals allows close matching of arbitrary time delay curves for a circuit breaker. An analog signal proportional to the current is sampled and digitized. Digital samples, with or without further processing, are used to select increment values from a look-up table for accumulation in a counter. The counter is decremented periodically to simulate cooling of the circuit being protected. The values in the look-up table are determined according to the desired time delay curve. Processing of the digital samples may include squaring samples, accumulating the squared values to form a subtotal which is compared with an instantaneous trip threshold, accumulating the subtotals for a time period equal to half a cycle of AC line voltage, taking the square root of the accumulated subtotals, and using that square root as the address for looking up the increment value.

Claims21

Dependent claims

An electronically tripped circuit breaker, comprising:

a first line connection point,
a load connection point,
controllable means for establishing a conductive electrical connection between said first line connection point and said load connection point, and for opening said conductive electrical connection in response to a trip signal,
current sensing means for sensing at least the absolute magnitude of load current flow through said conductive electrical connection, and providing a current signal related to said at least the absolute magnitude of load current, and
an electronic processing unit, responsive to said current sensing means, for providing said trip signal to said controllable means,
characterized in that said electronic processing unit comprises:
sampling means for producing successive digital samples of said current signal at a sampling rate,
first means for determining respective increment values at an incrementing rate, each increment value corresponding to at least one of a sequence of said successive digital samples, each increment value being based on a first predetermined current/time relationship, said first predetermined current/time relationship emulating heating of a thermal mass
a counter for counting and storing a value therein,
means for incrementing the value, stored in said counter, with said respective increment values at said incrementing rate,
second means for determining a succession of respective subtraction values based on the value then stored in said counter, taken at a decrementing rate, each subtraction value being based on a second predetermined current/time relationship, said second predetermined current/time relationship emulating cooling said thermal mass through a thermal resistance
means for reducing said value stored in said counter by successively subtracting the respective subtraction values, at said decrementing rate, and
means for providing said trip signal responsive to said counter value reaching a predetermined value.

10 more elements

An electronically tripped circuit breaker, comprising:

a first line connection point,
a load connection point,
controllable means for establishing a conductive electrical connection between said first line connection point and said load connection point, and for opening said conductive electrical connection in response to a trip signal,
current sensing means for sensing at least the absolute magnitude of load current flow through said conductive electrical connection, and providing a current signal related to said at least the absolute magnitude of load current, and
an electronic processing unit, responsive to said current sensing means, for providing said trip signal to said controllable means,
characterized in that said electronic processing unit comprises:
sampling means for producing successive digital samples of said current signal at a sampling rate,
accumulation means for successively accumulating respective digital values corresponding to respective sequences of said successive digital samples to produce respective accumulated values,
first means for determining respective increment values at an incrementing rate, each increment value corresponding to at least one of said accumulated values, each increment value being based on a first predetermined current/time relationship, said first predetermined current/time relationship emulating heating of a thermal mass
a counter for counting and storing a value therein,
means for incrementing the value, stored in said counter, with said respective increment values at said incrementing rate,
second means for determining a succession of respective subtraction values based on the value then stored in said counter, taken at a decrementing rate, each subtraction value being based on a second predetermined current/time relationship, said second predetermined current/time relationship emulating cooling said thermal mass through a thermal resistance
means for reducing said value stored in said counter by successively subtracting the respective subtraction values, at said decrementing rate, and
means for providing said trip signal responsive to said counter value reaching a predetermined value.

11 more elements

An electronic processing unit for a circuit breaker, for providing a trip signal responsive to an analog current signal meeting at least one predetermined criterion, comprising:

sampling means for producing successive digital samples of said current signal at a sampling rate,
accumulation means for successively accumulating respective digital values corresponding to respective sequences of said successive digital samples to produce respective accumulated values,
first means for determining respective increment values at an incrementing rate, each increment value corresponding to at least one of said accumulated values, each increment value being based on a first predetermined current/time relationship, said first predetermined current/time relationship emulating heating of a thermal mass
a counter for counting and storing a value therein,
means for incrementing the value, stored in said counter, with said respective increment values at said incrementing rate,
second means for determining a succession of respective subtraction values based on the value then stored in said counter, taken at a decrementing rate, each subtraction value being based on a second predetermined current/time relationship, said second predetermined current/time relationship emulating cooling said thermal mass through a thermal resistance
means for reducing said value stored in said counter by successively subtracting the respective subtraction values, at said decrementing rate, and
means for providing said trip signal responsive to said counter value reaching a predetermined value.

5 more elements

Dependencies are inferred from the claim text.