Current monitoring circuit for static switch of uninterruptable power system

Claim 3

A method in accordance with claim 1 wherein said first reference level is substantially equal to (1.2)×(1.414)×(rated maximum RMS current) and said second reference level is substantially (3)×(rated maximum RMS current).

Claim 4

A method in accordance with claim 2 wherein said selected time interval is substantially two milliseconds.

Claim 5

A method in accordance with claim 1 wherein the effective magnitude of said signal being compared to said second reference level is increased in response to initiation of a transfer for providing a dropout interval.

Claim 6

A current detecting circuit for actuating a switch to initiate the transfer of a load from a first power source to a second power source whenever the r.m.s. load current exceeds the r.m.s. limits of the first power source, the detecting circuit comprising: (a) a signal conversion means linked to said load for providing an output signal representing the instantaneous value of the electrical current from the first power source through said load; (b) a first peak detector circuit means, having its input connected to the output of the signal conversion means and including a first reference level generating circuit, for changing its output state in response to said instantaneous signal exceeding the first reference level; (c) a timing circuit means having an input connected to the output of said first peak detector circuit means for timing the duration that said instantaneous signal uninterruptedly exceeds said first reference level; (d) a timing detector circuit means having its input connected to the output of said timing circuit means and its output connected to the actuating input of said switch for actuating said switch in response to said duration exceeding a selected time interval; and (e) a second peak detector circuit means, having its input connected to the output of said signal conversion means, its output connected to the actuating input of said switch and including a second reference level generating circuit, for changing its ouptut state to actuate said switch in response to said instantaneous signal, which represents the load currents from the first source, exceeding the second reference level.

Claim 7

A current detecting circuit for actuating a switch to initiate the transfer of a load from a first power source to a second power source whenever the r.m.s. load current exceeds the r.m.s. limits of the first power source, the detecting circuit comprising: (a) a signal conversion means linked to said load for providing an output signal representing the instantaneous value of the electrical current from the first power source through said load; (b) a first peak detector circuit means, having its input connected to the output of the signal conversion means and including a first reference level generating circuit, for changing its output state in response to said instantaneous signal exceeding the first reference level; (c) a timing circuit means having an input connected to the output of said first peak detector circuit means for timing the duration that said instantaneous signal uninterruptedly exceeds said first reference level; (d) a timing detector circuit means having its input connected to the output of said timing circuit means and its output connected to the actuating input of said switch for actuating said switch in response to said duration exceeding a selected time interval; and (e) a second peak detector circuit means, having its input connected to the output of said signal conversion means, its output connected to the actuating input of said switch and including a second reference level generating circuit, for changing its ouptut state to actuate said switch in response to said instantaneous signal, which represents the load currents from the first source, exceeding the second reference level.

Claim 8

A circuit in accordance with claim 5 wherein said first and second peak detector circuit means each comprise a different comparator having a reference source connected to one input and said signal connected to the other.

Claim 9

A circuit in accordance with claim 6 wherein said timing circuit means comprises a constant current source connected to a gate and a capacitance to form a current loop for changing the capacitance through the gate, the gate having a control input connected to and which is controlled by the output of said first peak detector circuit means and wherein said timing circuit means comprises a third comparator having one input connected to a reference voltage source for selecting said time duration and the other input of the comparator connected to said capacitor for applying the capacitor voltage to the comparator input.

Claim 10

A circuit in accordance with claim 5 wherein a circuit providing a hysteresis effect is provided comprising a switch means for increasing the amplitude of the signal representing the load current whenever the critical load is connected to the secondary source.