Digital I.sup.2 T pickup, time bands and timing control circuits for static trip circuit breakers
AssigneeGeneral Electric Company
InventorJohn J. Dougherty
Life of this patent
Estimating the term…
Abstract
Digital implementation of the overcurrent determination and time delay before tripping in a static circuit breaker trip unit allows the trip unit circuit to be manufactured in a single chip configuration. The signal after A/D conversion is compared within a magnitude comparator to determine pickup. A pulse stream proportional to the square of the overcurrent signal is developed by multiplying the outputs of two magnitude comparators which compare the A/D level with a continuous binary count. The time delay determination is obtained by means of 3 cascade connected divide by two counters with their outputs connected to a data selector, or by a rate-limiter circuit which uses a fixed frequency to gate a pulse stream proportional to the overcurrent level squared.
Claims48
A static trip circuit interrupter comprising:
- a pair of electrical contacts;
- current sensing means for sensing current within a protected circuit;
- A/D conversion means for providing a digital output signal representation of said sensed current;
- interrupter means connected with said current sensing means for operating said electrical contacts;
- multiple digital comparison means connected with said interrupter means for providing a control signal to said interrupter means to separate said contacts upon occurrence of a sensed current in excess of first or second predetermined overcurrent values which persist longer than first or second predetermined time delay values;
- and input means connected with said digital comparison means for providing said first and second pre-determined overcurrent and time delay values to said multiple digital comparison means;
- wherein said A/D conversion means comprises a comparator for comparing said sensed current to a reference value, the output of said comparator then being multiplied by a first fixed frequency clock pulse within a first logic gate.
A trip unit for a static trip circuit interrupter comprising:
- a pair of separble contacts connected within an electric circuit;
- separation means connected with said separable contacts for separating said contacts to interrupt circuit current through said electric circuit upon receipt of a trip signal;
- a first counter providing a first fixed clock pulse;
- overcurrent pickup circuit means connecting with a first plurality of input terminals for digitally setting overcurrent pickup values and with an input current signal for outputting a pulse width modulated representation of said input current signal;
- a squaring circuit connecting with said overcurrent pickup circuit and said first counter for providing a pulse width modulated representation of a multiple of said input current signal;
- and
- a long time and short time delay circuit connecting with said squaring circuit and a second plurality of input terminals for providing pre-determined time delay bands received from said second plurality of input terminals to said pulse width modulated representation of said input current signal and said multiple of said input current signal before providing said trip signal to said separation means.
Dependencies are inferred from the claim text.